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  • 1.
    A Monfared, Behzad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Design and Construction of a Small Ammonia Heat Pump2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In view of the fact that most of the synthetic refrigerants, in case of leakage or release, are harmful to the environment by contributing in global warming or depleting stratospheric ozone layer, many research works have been done recently to find alternative refrigerants posing no or negligible threat to the environment. Among alternative refrigerants, ammonia, a natural refrigerant with zero Global Warming Potential (GWP) and Ozone Depletion Potential (ODP), can be a sensible choice.Although ammonia has been used for many years in large industrial systems, its application in small units is rare. In this project a small heat pump with about 7 kW heating capacity at -5 °C and +40 °C evaporation and condensation temperatures is designed and built to work with ammonia as refrigerant. The heat pump is expected to produce enough heat to keep a single-family house warm in Sweden and to provide tap hot water for the house. After successful completion of this project, it is planned to install the heat pump in a house to test it throughout a heating season to study its performance in real working conditions.Since ammonia is flammable and toxic in high concentrations, the refrigerant charge is tried to be kept low in the heat pump to reduce the risk of fire or poisoning in case of unwanted release of refrigerant to the surroundings. The compact design of the heat pump helps reducing the refrigerant charge. Besides, considering the limited space normally reserved for installation of a heat pump in a house, the compact design of the heat pump is necessary.

  • 2.
    Abacar, Armando
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Optimization of Maputo Power Plant2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Electricidade de Moçambique, E.P. (EDM) is the power utility in Mozambique, responsible to generate, transport and distribute electricity all over the country. The company has three gas turbines installed at Maputo Power Plant. All units burn diesel oil and are used only for back up. Currently only the unit #2 is available for operation.

    The main constraint that EDM faces is the high operation costs due to diesel price. Hence the company is considering converting units #2 and #3 to burn natural gas, resource available locally. The country is currently exporting natural gas to the neighbouring Republic of South Africa.

    This MSc thesis project calculates the power output of all gas turbines when burning natural gas and optimizes the power plant capacity by proposing modifications of the current power turbine cycles to allow sustainable operation

  • 3. Abbas, Ghazanfar
    et al.
    Chaudhry, M. Ashraf
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Singh, Manish
    Liu, Qinghua
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Qin, Haiying
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Study of CuNiZnGdCe-Nanocomposite Anode for Low Temperature SOFC2012In: Nanoscience and Nanotechnology Letters, ISSN 1941-4900, Vol. 4, no 4, 389-393 p.Article in journal (Refereed)
    Abstract [en]

    Composite electrodes of Cu0.16Ni0.27Zn0.37Ce0.16Gd0.04 (CNZGC) oxides have been successfully synthesized by solid state reaction method as anode material for low temperature solid oxide fuel cell (LTSOFC). These electrodes are characterized by XRD followed by sintering at various time periods and temperatures. Particle size of optimized composition was calculated 40-85 nm and sintered at 800 degrees C for 4 hours. Electrical conductivity of 4.14 S/cm was obtained at a temperature of 550 degrees C by the 4-prob DC method. The activation energy was calculated 4 x 10(-2) eV at 550 degrees C. Hydrogen was used as fuel and air as oxidant at anode and cathode sides respectively. I-V/I-P curves were obtained in the temperature range of 400-550 degrees C. The maximum power density was achieved for 570 mW/cm(2) at 550 degrees C.

  • 4.
    Abbas, Ghazanfar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Ashfaq, M.
    Chaudhry, M. Ashraf
    Khan, Ajmal
    Ahmad, Imran
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Electrochemical study of nanostructured electrode for low-temperature solid oxide fuel cell (LTSOFC)2014In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 38, no 4, 518-523 p.Article in journal (Refereed)
    Abstract [en]

    Zn-based nanostructured Ba0.05Cu0.25Fe0.10Zn0.60O (BCFZ) oxide electrode material was synthesized by solid-state reaction for low-temperature solid oxide fuel cell. The cell was fabricated by sandwiching NK-CDC electrolyte between BCFZ electrodes by dry press technique, and its performance was assessed. The maximum power density of 741.87 mW-cm(-2) was achieved at 550 degrees C. The crystal structure and morphology were characterized by X-ray diffractometer (XRD) and SEM. The particle size was calculated to be 25 nm applying Scherer's formula from XRD data. Electronic conductivities were measured with the four-probe DC method under hydrogen and air atmosphere. AC Electrochemical Impedance Spectroscopy of the BCFZ oxide electrode was also measured in hydrogen atmosphere at 450 degrees C.

  • 5. Abbas, Ghazanfar
    et al.
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. COMSATS Institute of Information Technology, Pakistan .
    Chaudhry, M. A.
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Preparation and characterization of nanocomposite calcium doped ceria electrolyte with alkali carbonates (NK-CDC) for SOFC2010In: ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology, FUELCELL 2010, ASME Press, 2010, 427-432 p.Conference paper (Refereed)
    Abstract [en]

    The entire world's challenge is to find out the renewable energy sources due to rapid depletion of fossil fuels because of their high consumption. Solid Oxide Fuel Cells (SOFCs) are believed to be the best alternative source which converts chemical energy into electricity without combustion. Nanostructured study is required to develop highly ionic conductive electrolyte for SOFCs. In this work, the calcium doped ceria (Ce0.8Ca0.2O 1.9) coated with 20% molar ratio of two alkali carbonates (CDC-M: MCO3, where M= Na and K) electrolyte was prepared by co-precipitation method in this study. Ni based electrode was used to fabricate the cell by dry pressing technique. The crystal structure and surface morphology was characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). The particle size was calculated in the range of 10-20nm by Scherrer's formula and compared with SEM and TEM results. The ionic conductivity was measured by using AC Electrochemical Impedance Spectroscopy (EIS) method. The activation energy was also evaluated. The performance of the cell was measured 0.567W/cm2 at temperature 550°C with hydrogen as a fuel.

  • 6.
    Abbas, Ghazanfar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. COMSATS Institute of Information Technology, Pakistan.
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. COMSATS Institute of Information Technology, Pakistan.
    Khan, M. Ajmal
    Ahmad, Imran
    Chaudhry, M. Ashraf
    Sherazi, Tauqir A.
    Mohsin, Munazza
    Ahmad, Mukhtar
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Synthesize and characterization of nanocomposite anodes for low temperature solid oxide fuel cell2015In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 40, no 1, 891-897 p.Article in journal (Refereed)
    Abstract [en]

    Solid oxide fuel cells have much capability to become an economical alternative energy conversion technology having appropriate materials that can be operated at comparatively low temperature in the range of 400-600 degrees C. The nano-scale engineering has been incorporated to improve the catalytic activity of anode materials for solid oxide fuel cells. Nanostructured Al0.10NixZn0.90-xO oxides were prepared by solid state reaction, which were then mixed with the prepared Gadolinium doped Ceria GDC electrolyte. The crystal structure and surface morphology were characterized by XRD and SEM. The particle size was evaluated by XRD data and found in the range of 20-50 nm, which was then ensured by SEM pictures. The pellets of 13 mm diameter were pressed by dry press technique and electrical conductivities (DC and AC) were determined by four probe techniques and the values have been found to be 10.84 and 4.88 S/cm, respectively at hydrogen atmosphere in the temperature range of 300-600 degrees C. The Electrochemical Impedance Spectroscopy (EIS) analysis exhibits the pure electronic behavior at hydrogen atmosphere. The maximum power density of ANZ-GDC composite anode based solid oxide fuel cell has been achieved 705 mW/cm(2) at 550 degrees C.

  • 7.
    Abbassi, Behrang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Hultling, Johannes
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Smarta Elnät – Modell och Marknad2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The Smart Grid technology has during the last decade been established as a way to create a greater flexibility on the electricity grid that will be needed as the development moves towards an increased share of renewable primary energy sources in the electricity production. One part of the Smart Grid technology is the ability to shift loads in time, to adapt to either price or emissions, known as Demand Response. This project, which was conducted at KTH in collaboration with the consulting corporation Capgemini, examines the economic, environmental and social aspects of the Demand Response technology.

     

    In the project, three household products are used in a model that derives the potential savings in costs and emissions of CO2e. The results show that the actual savings measured in SEK are small, but that the savings measured in percent can be as high as 20 percent. Reduction of CO2e emissions is slightly lower. Furthermore, the study shows that the savings increase as more flexibility is given to the model and as the fluctuations of price increases. A scenario that includes more intermittent electricity production, and end users ready to commit to the technology,  is therefore vital for the success of the Demand Response technology. The results also show that an optimization cannot be done in such way that both minimize costs and CO2e emissions simultaneously.

     

    A discussion on the strategic opportunities for Capgemini shows that focus should be on collecting, interpreting and compiling the large amounts of data that the technology will result in. There are also possibilities in peripheral services tied together with the Smart Grid technology, such as the development of a charging infrastructure for electric cars.

  • 8.
    Abd Alrahman, Chadi
    Dalarna University, School of Technology and Business Studies, Electrical Engineering.
    Evaluation of a PVT Air Collector2015Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Hybrid Photovoltaic Thermal (PVT) collectors are an emerging technology that

    combines PV and solar thermal systems in a single solar collector producing heat and

    electricity simultaneously. The focus of this thesis work is to evaluate the performance of

    unglazed open loop PVT air system integrated on a garage roof in Borlänge. As it is

    thought to have a significant potential for preheating ventilation of the building and

    improving the PV modules electrical efficiency. The performance evaluation is important

    to optimize the cooling strategy of the collector in order to enhance its electrical efficiency

    and maximize the production of thermal energy. The evaluation process involves

    monitoring the electrical and thermal energies for a certain period of time and investigating

    the cooling effect on the performance through controlling the air mass flow provided by a

    variable speed fan connected to the collector by an air distribution duct. The distribution

    duct transfers the heated outlet air from the collector to inside the building.

    The PVT air collector consists of 34 Solibro CIGS type PV modules (115 Wp for each

    module) which are roof integrated and have replaced the traditional roof material. The

    collector is oriented toward the south-west with a tilt of 29 ᵒ. The collector consists of 17

    parallel air ducts formed between the PV modules and the insulated roof surface. Each air

    duct has a depth of 0.05 m, length of 2.38 m and width of 2.38 m. The air ducts are

    connected to each other through holes. The monitoring system is based on using T-type

    thermocouples to measure the relevant temperatures, air sensor to measure the air mass

    flow. These parameters are needed to calculate the thermal energy. The monitoring system

    contains also voltage dividers to measure the PV modules voltage and shunt resistance to

    measure the PV current, and AC energy meters which are needed to calculate the

    produced electrical energy. All signals recorded from the thermocouples, voltage dividers

    and shunt resistances are connected to data loggers. The strategy of cooling in this work

    was based on switching the fan on, only when the difference between the air duct

    temperature (under the middle of top of PV column) and the room temperature becomes

    higher than 5 °C. This strategy was effective in term of avoiding high electrical

    consumption by the fan, and it is recommended for further development. The temperature

    difference of 5 °C is the minimum value to compensate the heat losses in the collecting

    duct and distribution duct.

    The PVT air collector has an area of (Ac=32 m2), and air mass flow of 0.002 kg/s m2.

    The nominal output power of the collector is 4 kWppv (34 CIGS modules with 115

    Wppvfor each module). The collector produces thermal output energy of 6.88 kWth/day

    (0.21 kWth/m2 day) and an electrical output energy of 13.46 kWhel/day (0.42 kWhel/m2

    day) with cooling case. The PVT air collector has a daily thermal energy yield of 1.72

    kWhth/kWppv, and a daily PV electrical energy yield of 3.36 kWhel /kWppv. The fan energy

    requirement in this case was 0.18 kWh/day which is very small compared to the electrical

    energy generated by the PV collector. The obtained thermal efficiency was 8 % which is

    small compared to the results reported in literature for PVT air collectors. The small

    thermal efficiency was due to small operating air mass flow. Therefore, the study suggests

    increasing the air mass flow by a factor of 25. The electrical efficiency was fluctuating

    around 14 %, which is higher than the theoretical efficiency of the PV modules, and this

    discrepancy was due to the poor method of recording the solar irradiance in the location.

    Due to shading effect, it was better to use more than one pyranometer.

  • 9.
    Abdi, Amir
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Analysis of heat recovery in supermarket refrigeration system using carbon dioxide as refrigerant2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this study is to investigate the heat recovery potential in supermarket refrigeration systems using CO2 as refrigerants. The theoretical control strategy to recover heating demand from refrigeration system is explained thoroughly and the heat recovery process from two existing supermarket using CO2 booster units is analyzed and evaluated. The measured data of refrigeration systems is obtained through Iwmac interface, processed using Excel and Refprop. The aim is to see what control strategy is used in these systems and weather it matches the theoretical one and at what level heat is recovered from the system.

    Besides, a simulation model is made by EES to investigate the potential of higher rate of heat recovery in the supermarkets. The simulation results are compared with field measurement and validated by measured values. Then, the ability of refrigeration system to do heat recovery at quite high rates for covering the total heating demand without using parallel heating system is evaluated and efficiency of the system is calculated. At the next step the heat recovery potential at other refrigeration solutions such as R404A conventional and CO2-ammonia cascade systems are studied and the results are compared to booster units. Finally, the potential for selling heat from the refrigeration system in supermarket to district heating network is investigated. Two different scenarios are made for such purpose and the results are evaluated.

    The heat recovery control strategy of existing supermarkets does not match the theoretical strategy and regarding the capacity of the system, heat is recovered to low extent. Simulation shows that heat can be recovered to higher extent at quite high heating COP of 3-5. Additionally the other heat recovery solutions for R404A conventional and CO2-ammonia cascade systems are found to be competitive to CO2 booster system.  The analysis of selling heat to district heating network shows that CO2 booster system is capable of covering the demand at reasonable heating COP as the first priority and selling the rest to district heating network at heating COP of 2 as second priority.  

  • 10.
    Abdul Hayee, Muhammad
    KTH, School of Chemical Science and Engineering (CHE).
    Characterization and utilization of agroforestryresidues as energy source in Brazil2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Brazil is very much rich in agriculture and forestry. The agro industry occupies an area of 28840726 ha. The more important crops are sugarcane (7080920 ha), rice (289030 ha), wheat (1853220 ha), coconut (283205 ha), cassava (1894460 ha), corn (13767400 ha) and grass (140000 ha). These crops generated 597 million tons of residues. Forest plantations in Brazil supplied 102.9 million m3 of industrial roundwood, of which nearly half is for renewable fuelwood and charcoal. Part of this plantation output is destined for the pulp and paper industry:

    The renewable sources are fulfilling 46.4% of the total Brazilian energy demands.

    Energy forestation in Brazil includes mainly Eucalyptus and Bracatingas.

    In this study three biomasses abundant in the Brazil are studied:  i.e. Eucalyptus, Garapeira/Peroba (wood dust) and Sewage Sludge.

    The wood samples (Eucalyptus and Peroba/Garapeira) have higher heating value than the sewage sludge because the wood samples have higher amounts of carbon and hydrogen than the sewage sludge. The sewage sludge has higher ash content and lower amount of volatiles and fixed carbon than the wood samples resulting in a lower heating value.

    The pyrolysis of eucalyptus, garapeira/peroba and sewage sludge has been studied in a thermobalance over a wide range of degradation temperatures. Between 225 °C - 375 °C (for eucalyptus) and 225 °C - 425 °C (for garapeira), the thermal decomposition of the biomass leads to significant weight loss.

    The weight loss for Eucalyptus between 265°C and 350°C is 0.48 % / °C and taking into account a heating rate of 10°C/min, the weight loss is 4.8 % /min. Garapeira has a similar behaviour than eucalyptus. The weight loss for garapeira between 265°C and 365°C is 0.4 % / °C and taking into account a heating rate of 10°C/min, the weight loss is 4 % /min.

    The behaviour of the sewage sludge to the increase of temperature from 25°C to 700 °C in an inert atmosphere do not show such different zones as the behaviour of the woody biomass. Between 150 °C and 235°C the weight loss of the sewage sludge was 0.07 %/°C (0.7 %/min). The highest weight loss takes place between 300 °C and 390 °C (0.15 %/°C or 1.5 %/min). In the third zone, between 500 °C and 600°C, the weight loss was 0.03 %/°C (0.3 %/min).

    The pyrolysis is assumed to be a first order decomposition. The activation energy (E) and the pre exponential factor (A) are calculated for the studied samples.

    The proximate analysis shows differences between the woody biomass and the sewage sludge. The sewage sludge has higher ash content and lower fixed carbon and volatiles. Eucalyptus has lower carbon fixed and higher volatiles than peroba-garapeira.

  • 11.
    Abeywardana, Asela Janaka
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Solar - Biomass hybrid system for process heat supply in medium scale hotels in Sri Lanka2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study aimed at evaluating and demonstrating the feasibility of using Concentrated Solar Thermal technology combined with biomass energy technology as a hybrid renewable energy system to supply the process heat requirements in small scale industries in Sri Lanka. Particularly, the focus was to apply the concept to the expanding hotel industry, for covering the thermal energy demand of a medium scale hotel.

    Solar modules utilize the rooftop area of the building to a valuable application. Linear Fresnel type of solar concentrator is selected considering the requirement of the application and the simplicity of fabrication and installation compared to other technologies. Subsequently, a wood-fired boiler is deployed as the steam generator as well as the balancing power source to recover the effects due to the seasonal variations in solar energy. Bioenergy, so far being the largest primary energy supply in the country, has a good potential for further growth in industrial applications like small hotels. 

    When a hotel with about 200-guests capacity and annual average occupancy of 65% is considered, the total annual CO2 saving is accounted as 207 tons compared with an entirely fossil fuel (diesel) fired boiler system. The annual operational cost saving is around $ 40,000 and the simple payback period is within 3-4 years. The proposed hybrid system can generate additional 26 employment opportunities in the proximity of the site location area.  

    This solar-biomass hybrid concept mitigates the weaknesses associated with these renewable technologies when employed separately. The system has been designed in such a way that the total heat demand of hot water and process steam supply is managed by renewable energy alone. It is thus a self-sustainable, non-conventional, renewable energy system. This concept can be stretched to other critical medium temperature applications like for example absorption refrigeration. The system is applicable to many other industries in the country where space requirement is available, solar irradiance is rich and a solid biomass supply is assured.    

  • 12.
    Abeywardana, Asela M.A.J.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Solar-Biomass hybrid system for process heat supply in medium scale hotels in Sri Lanka2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study aimed at evaluating and demonstrating the feasibility of using Concentrated Solar Thermal technology combined with biomass energy technology as a hybrid renewable energy system to supply the process heat requirements in small scale industries in Sri Lanka. Particularly, the focus was to apply the concept to the expanding hotel industry, for covering the thermal energy demand of a medium scale hotel.

    Solar modules utilize the rooftop area of the building to a valuable application. Linear Fresnel type of solar concentrator is selected considering the requirement of the application and the simplicity of fabrication and installation compared to other technologies. Subsequently, a wood-fired boiler is deployed as the steam generator as well as the balancing power source to recover the effects due to the seasonal variations in solar energy. Bioenergy, so far being the largest primary energy supply in the country, has a good potential for further growth in industrial applications like small hotels. 

    When a hotel with about 200-guests capacity and annual average occupancy of 65% is considered, the total annual CO2 saving is accounted as 207 tons compared with an entirely fossil fuel (diesel) fired boiler system. The annual operational cost saving is around $ 40,000 and the simple payback period is within 3-4 years. The proposed hybrid system can generate additional 26 employment opportunities in the proximity of the site location area.  

    This solar-biomass hybrid concept mitigates the weaknesses associated with these renewable technologies when employed separately. The system has been designed in such a way that the total heat demand of hot water and process steam supply is managed by renewable energy alone. It is thus a self-sustainable, non-conventional, renewable energy system. This concept can be stretched to other critical medium temperature applications like for example absorption refrigeration. The system is applicable to many other industries in the country where space requirement is available, solar irradiance is rich and a solid biomass supply is assured.

  • 13. Abeyweera, Ruchira
    et al.
    Senanayake, Nihal S.
    Senaratne, Chamindie
    Jayasuriya, Jeevan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. EIT InnoEnergy, Sweden.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. EIT InnoEnergy, Sweden.
    Capacity Building Through a Web Based Master Degree Programme in Sustainable Energy Engineering2017In: PROCEEDINGS OF 2017 IEEE GLOBAL ENGINEERING EDUCATION CONFERENCE (EDUCON2017), IEEE, 2017, 800-805 p.Conference paper (Refereed)
    Abstract [en]

    Open Distance Learning is gaining popularity as a successful alternative for on-campus higher education especially with the emergence of web based platforms which enable the online delivery of courses worldwide. This emerging educational pedagogy can successfully be employed as means of capacity building of the people living in the less fortunate parts of the world where higher education especially at master level are scarce. This paper presents a two-year collaborative master study programme in sustainable energy engineering offered in synchronous with an on-campus study programme conducted by the KTH Royal Institute of Technology of Sweden, to students of Sri Lanka, which was facilitated by the Open University of Sri Lanka. The paper describes the need of such a programme, the format of course delivery and assessment thereof, plus the benefits gained. This programme has produced 72 post graduates in Sri Lanka alone and more than 200 distant postgraduates worldwide in the field of sustainable energy engineering during last 10 years period. In terms of capacity building in the energy sector in Sri Lanka this is considered a great achievement. The experience gained by the local staff in the role of local facilitators who engaged in some of the academic related activities such as evaluation of students' presentation and co-supervision of thesis projects have been greatly appreciated as being additional benefits to the staff in terms of their own academic development and capacity building. Finally, conclusions are made on how remote programmes of study could successfully be delivered to places where such know-how is scarce by adapting appropriate technologies in training personnel at postgraduate level to meet the needs of the industry.

  • 14.
    Abolhassani Monfared, Behzad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Optimization of layered regenerator of a magnetic refrigeration device2015In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 57, 103-111 p.Article in journal (Refereed)
    Abstract [en]

    Magnetic refrigeration, as an alternative to vapor-compression technology, has been the subject of many recent investigations. A technique to enhance the performance of magnetic refrigerators is using layers of different materials in the regenerator of such devices. In this study the choice of magnetocaloric materials in a multi-layered packed bed regenerator is investigated in order to optimize the performance. A numerical model has been developed to simulate the packed bed in this study. Optimized packed bed designs to get maximum temperature span or maximum efficiency are different. The results indicate that maximum temperature span can be achieved by choosing the materials with the highest magnetocaloric effect in the working temperature range, while maximum Carnot efficiency is achieved by choosing materials with Curie temperatures above the average layer temperature.

    The full text will be freely available from 2017-10-01 00:01
  • 15.
    Abou Jaoudeh, Elie
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Developement of Optimization Method/A Tool for RE applications in Intermittent Grids with focus on Lebanon2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Renewable energy applications require sound design and optimization of life cycle costs because they need upfront investments and as long as possible operating lifetimes are expected. Using modern tools for optimizing designs of grid-tied and autonomous plants allows investors to deploy these technologies while keeping risks within acceptable limits.

    Nevertheless in Lebanon, the grid is intermittent and the most adapted solutions are dual-mode plants that can operate autonomously and with grid-tie. There are no existent simulation models particularly adapted to optimize these applications for such a situation. The objective of this research is to suggest and test a model adapted from commercially available software that can simulate the particular conditions of Lebanon. The studied solution has a PV generator associated with a PV charge controller, lead acid battery, a dual mode inverter, and transfer switchgear and protections. The research successfully met the objective of finding a setup in HOMER 2.68beta for simulating and optimizing a PV-Battery AC plant for an intermittent grid with scheduled blackouts.

    The setup and adaptation in HOMER is made to replicate an existing reference PV-Battery plant at a public school. The measured data from this public school is used to validate the results obtained from the adapted HOMER simulation. The grid is supplied for an average of 12 hours per day at the reference site with a tariff of USD 0.1/kWh.

    After the validation process, a sensitivity analysis is performed to simulate this plant under

    1. Different grid supply hours, 12 and 18 hours of supply daily
    2. Different grid electricity prices, USD 0.1 and 0.1375 /kWh
    3. Simulation of PV plants to meet other load profiles typical of community and municipality building centers

    All the simulations cross matched 20 different PV generator sizes to 7 different battery sizes for 5 different total setups.

    The levelized cost of electricity, COE, is the main parameter used to find the optimum setups, whereas options that shortened the battery life to less than 12 years or couldn’t meet at least 90% of the required yearly load were filtered out. The COE is calculated manually since several corrections related to grid and net-metering limitations are not obtained directly from HOMER.

    The simulated results can serve as a good indicator on how the systems would perform for typical public institutions in Lebanon, given the current conditions, and knowing that the range of this study is limited to small scale institutions with consumption levels less than 30 kWh/day. Storage capacity should also be limited to 100 kWh/day of useful storage, since batteries are not the best option to use for storage capacities higher than the mentioned limit.

    The setup has a great potential for advancement and acts as a first step for Lebanon to have a specialized tool for simulating the performance of PV-battery AC plants optimized for the conditions existing in the country. Future steps could be made to improve and diversify the software to include:

    • irradiation data that come from actual data logging data from other PV sites which are installed around the whole country, almost a 100
    • financial analysis for offsetting private generation with fossil fueled gensets, which is the main backup for electricity blackouts
    • wind turbine simulations, several installations are provisioned to be completed by the end of 2012, and it would be possible to carry out a similar validation process for small wind turbines
    • pollution and other environmental costs
    • value of lost load, “VOLL”, to compare different options in parallel with COE.

  • 16.
    Abrahamsson, Cajsa
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Miljöpåverkan, hälsopåverkan och LCC för direktdrivna kontra växellådsdrivna vindkraftverk med avseende på deras innehåll av jordartsmetaller2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    Vindkraftverk med olika magnetiseringsmetoder (elektromagneter eller permanentmagneter) och maskindriftstyper (direktdrift eller växellådsdrift) undersöks i denna rapport, gällande användningen av jordartsmetaller i dessa. I första delen av rapporten studeras miljö- och hälsopåverkan från jordartsmetallindustrin i den kinesiska provinsen Baotou. Detta då Baotou står för en stor del av försörjningen av jordartsmetaller till vindkraftverksindustrin. I den andra delen av rapporten undersöks skillnaderna i livscykelkostnader mellan vindkraftverk med olika generator- och maskindriftsystem. Rapporten innehåller informationssökningar om olika aspekter som berör dessa teman såsom exempelvis olika typer av vindkraftverksgeneratorer på marknaden, miljöpåverkan från olika ämnen i jordartsmineraler, återvinning av jordartsmetaller och processen från jordartsmineral till permanent-magnet. Informationen är främst inhämtad från vindkraftverkstillverkare, tekniska rapporter och artiklar.

    I miljö- och hälsoanalysen blev slutsatsen att den negativa påverkan från jordartsmetallindustrin i Kina var för omfattande för att användningen av jordartsmetaller skulle rättfärdigas ur ett etiskt och miljömässigt perspektiv. Gruvdriften och bearbetningen av jordartsmetaller har lett till stora utsläpp av skadliga ämnen, såsom exempelvis tungmetaller och radioaktivt avfall, i provinsen Baotou. Dessa har gett allvarliga negativa konsekvenser för djur, människor och växtlighet.

    Livscykelkostnaderna för vindkraftverk med olika generatorsystem beräknades med hjälp av LCC-metoden. Slutsatsen blev att det i dagsläget inte skiljde så mycket kostnadsmässigt i valet av maskindrifttyp eller magnetiseringsmetod. Enligt beräkningar ledde användningen av permanent-magneter inte till några ekonomiska fördelar. Istället var det kostnadsförhandlingar och osäkerhet i indata som gav de största kostnadsskillnaderna. Drift och underhållskostnaderna stod för de definitivt största utgifterna och investeringskostnaderna till generatorsystemen för de näststörsta utgifterna.

  • 17.
    Abrahamsson, Erik
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Värmeöverföring från smälta till vattenkyld tapputrustning2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis work is done on behalf of Boliden Mineral AB at Rönnskärsverken.

    Kopparhyttan is an electric copper furnace for melting of copper concentrates and secondary materials in the form of ashes, metal scrap, crushed matte, slag and sludge.

    Depending on how the input material varies, the chemical composition of the melt will vary as well. Variations in the chemical composition of the melt also imply that the physical properties of the melt vary and the heat transfer between melt and tap block.

    A high heat load on the tap block during tapping of matte, results in increased wear and severe erosion of the tap channel and therefore the need of an understanding of the underlying causes to prevent and if possible avoid the high heat load.

    The completed analysis shows that a high heat load on the tap equipment mainly is associated with the copper content. A lower copper content leads to the melting point is lowered and also reduces the viscosity, leading to an increased mass flow. The increased heat load thus indicate an increased mass flow in combination with a reduced melting point, which means that the freezing of an erosion protective coating of matte on the inside of tapping channel walls becomes more difficult and thus increases the erosion on the tap equipment. Sulphur deficit, which is calculated from a chemical analysis of matte, showed no correlation to a high heat load and no connection between the sulfur deficit and the erosion of the tap equipment were successfully concluded.

    Measures proposed to reduce the wear on the tap equipment are increasing the flow of cooling water and a possible reduction of the tap channel diameter.

  • 18.
    Abrahamsson, Erika
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Gröna tak - potentialen för dagvattenreglering i Karlstad: Simuleringar i Mike Urban2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As urban areas become more populated and denser, stormwater management becomes an important matter. Since natural areas are becoming exploited and green areas in cities are removed the stormwater flow increases due to the conversion of impermeable surfaces into hard surface areas. The increase in stormwater flow can cause flooding if the pipeline system is insufficient.

    Change in climate caused by anthropogenic emissions will expose our communities to difficult challenges. Urban flooding from sewers is one of them, and may become more frequent in parts of the world where precipitation is predicted to increase in the future. In order to develop our cities in a sustainable manner and create resilience, the urban drainage system has to be a part of this development. Many of the techniques related to sustainable urban drainage systems, like storage reservoirs and open channels, require access to land space. However, about 40-50 % of the impermeable surfaces in cities consist of roof. Consequently, an interesting alternative to decrease stormwater flow is green roof due to its ability to reduce and attenuate the flow.

    The aim of this thesis is to demonstrate the benefits of green roof’s stormwater management through simulations in Mike Urban. The simulations are made over two neighborhoods in Karlstad with future climate changes. The simulations indicated that green roof in these neighborhoods show good potential to lower the risk of flooding and the numbers of flooded wells by a 10- and 2-year rain is decreased by 42 and 58 %.

  • 19.
    Abrahamsson, Jonas
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Lindqvist, Jakob
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Nedsmutsade värmesystems påverkan på energisystemet: Effektivisering vid användning av rengöringsmetoder2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Contamination of the heating system is not a well-known problem that can have major economic consequences. Due to minerals and low pH in the system arises limescale and corrosion that can clog the system and can damage components. This will result in increased energy consumption for users and a higher energy input from the district heating company. The purpose of this work is to study different cleaning methods for heating systems and if it is viable with cleaning of heating systems. The cleaning effect on the district heating demand and how it affects greenhouse gas emissions and primary energy use. And examine whether the maintenance of the heating system provides less energy than remodeling the building envelope. Previous studies in this area were examined and relevant data were collected after talks with interesting companies working with cleaning of heating systems. Cleaning the heating system was compared with various packages such as remodeling of the building envelope and heat recovery ventilation. Cleaning the heating systems with an efficiency of 10 % resulting in a reduced heating need at 1,63 GWh per year and a reduction in emissions of 177 tonnes CO2e per year. The reduced heating demand resulted in a reduction in primary energy consumption by 113 750 kWh per year. Installation of the cleaning systems can result in a saving for Tunabyggen of 759 200 SEK per year. The conclusion of this work is that the cleaning prolongs the lifetime of heating systems, but can’t replace remodeling of the building envelope in terms of reduced energy consumption.

  • 20.
    Abuasbeh, Mohammad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fault Detection and Diagnosis for Brine to Water Heat Pump Systems2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The overall objective of this thesis is to develop methods for fault detection and diagnosis for ground source heat pumps that can be used by servicemen to assist them to accurately detect and diagnose faults during the operation of the heat pump. The aim of this thesis is focused to develop two fault detection and diagnosis methods, sensitivity ratio and data-driven using principle component analysis.

    For the sensitivity ratio method model, two semi-empirical models for heat pump unit were built to simulate fault free and faulty conditions in the heat pump. Both models have been cross-validated by fault free experimental data. The fault free model is used as a reference. Then, fault trend analysis is performed in order to select a pair of uniquely sensitive and insensitive parameters to calculate the sensitivity ratio for each fault. When a sensitivity ratio value for a certain fault drops below a predefined value, that fault is diagnosed and an alarm message with that fault appears. The simulated faults data is used to test the model and the model successfully detected and diagnosed the faults types that were tested for different operation conditions.

    In the second method, principle component analysis is used to drive linear correlations of the original variables and calculate the principle components to reduce the dimensionality of the system. Then simple clustering technique is used for operation conditions classification and fault detection and diagnosis process. Each fault is represented by four clusters connected with three lines where each cluster represents different fault intensity level. The fault detection is performed by measuring the shortest orthogonal distance between the test point and the lines connecting the faults’ clusters. Simulated fault free and faulty data are used to train the model. Then, a new set of simulated faults data is used to test the model and the model successfully detected and diagnosed all faults type and intensity level of the tested faults for different operation conditions.

    Both models used simple seven temperature measurements, two pressure measurements (from which the condensation and evaporation temperatures are calculated) and the electrical power, as an input to the fault detection and diagnosis model. This is to reduce the cost and make it more convenient to implement. Finally, for each models, a user friendly graphical user interface is built to facilitate the model operation by the serviceman.

  • 21.
    Acuna, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fossa, Marco
    University of Genova.
    Monzó, Patricia
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Numerically generated g-functions for ground coupled heat pump applications2012In: Proceedings of the COMSOL Conference in Milan, 2012Conference paper (Refereed)
    Abstract [en]

    In most ground-coupled heat pump systems, Borehole Heat Exchangers (BHE) represent the typical engineering solution for utilizing renewable energy from the ground. The design of a complex BHE field is a challenging task, due the inherent transient nature of the thermal interaction between the heat exchangers and the surrounding soil. A computation effective method for solving the 3D transient conduction equation describing the ground response to a variable heat load profile is the temporal superposition of pre-calculated temperature response factors or g-functions. In this study Comsol heat conduction models have been developed to calculate g-function values for a borehole field with 64 boreholes. The aim of the investigation is to get an insight on the numerical generation of temperature transfer functions and to some extent provide new information on the Finite Line Source method for analytically generated g-functions as well as on those existing behind existing design software such as EED. The results generally showed a good agreement in lower time ranges. Further in time, the Comsol model revealed to be influenced either by the domain dimensions or the simulation end time.

  • 22.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Characterization and Temperature Measurement Techniques of Energy Wells for Heat Pumps2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Ground source heat pumps are a widely used approach to efficiently heat single family houses. In addition to using the ground as a heat source during the winter, it can be used as heat sink and as a free cooling source during the summer. The most common way to carry out the heat exchange with the ground is with the help of energy collectors (borehole heat exchangers) in vertical wells. The quality of the heat exchange depends on the type of collector and on the flow conditions of the circulating fluid. For a complete understanding of the heat transfer performance, it is necessary to carry out careful temperature measurements at research installations and to do a preliminary characterization of the boreholes. These activities might represent a significant cost saving since the system can be optimized based on their outcome. The characterization consists of determining the type of rock and its thermal properties, the groundwater flow at different depths, and the borehole deviation according to the expected position. A comprehensive study about these characterization actions as well as temperature measurement techniques in boreholes using thermocouples and fiber optic technology are described in this report. Study cases from real installations are also presented to exemplify the characterization and measurement methods.

  • 23.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Effektivare Utnyttjande av Energibrunnar för Värmepumpar Undersöks på KTH2010In: KYLA Värmepumpar, Vol. 6Article in journal (Other (popular science, discussion, etc.))
  • 24.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Framtidens värmesystem med borrhålsvärmeväxlare2011In: Energi&Miljö, ISSN 1101-0568, no 2Article in journal (Other (popular science, discussion, etc.))
  • 25.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bergvärmepumpar Kan Göras Ännu Mer Effektiva2008In: Enegi&Miljö, ISSN 1101-0568, no 3Article in journal (Other (popular science, discussion, etc.))
  • 26.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Forskningsprojekt Ska Ge Effektivare Bergvärme2009In: VVS Forum, ISSN 0346-4644, no 1Article in journal (Other (popular science, discussion, etc.))
  • 27.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Slang intill bergväggen ger effektivare värmeväxling2009In: HUSBYGGAREN, ISSN 0018-7968, no 6Article in journal (Other (popular science, discussion, etc.))
  • 28.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Optimera med Rätt Kollektorval2010In: Borrsvängen, ISSN 1103-7938, no 2Article in journal (Other (popular science, discussion, etc.))
  • 29.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed thermal response tests: New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.

    Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.

    A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.

    The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO2 as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO2 may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.

    Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.

    Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.

    At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.

    Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.

    Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N2, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.

  • 30.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Palne
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Thermal Response Tests on a Multi-pipe Coaxial Borehole Heat Exchanger2011In: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 17, no 6, 1012-1029 p.Article in journal (Refereed)
    Abstract [en]

    In a distributed thermal response test, distributed temperature measurements are taken along a borehole heat exchanger during thermal response tests, allowing the determination of local ground thermal conductivities and borehole thermal resistances. In this article, the first results from six heat injection distributed thermal response tests carried out on a new, thermally insulated leg type, multi-pipe coaxial borehole heat exchanger are presented. The borehole heat exchanger consists of 1 insulated central and 12 peripheral pipes. Temperature measurements are carried out using fiber-optic cables placed inside the borehole heat exchanger pipes. Unique temperature and thermal power profiles along the borehole depth as a function of the flow rate and the total thermal power injected into the borehole are presented. A line source model is used for simulating the borehole heat exchanger thermal response and determining local variations of the ground thermal conductivity and borehole thermal resistance. The flow regime in the peripheral pipes is laminar during all distributed thermal response tests and average thermal resistances remain relatively constant, independently of the volumetric flow rate, being lower than those corresponding to U-pipe borehole heat exchangers. The thermal insulation of the central pipe significantly reduces the thermal shunt to the peripheral pipes even at low volumetric flow rates.

  • 31.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Palne
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Evaluation of a coaxial borehole heat exchanger prototype2010In: Proceedings of the 14th ASME International Heat Transfer Conference, ASME Press, 2010Conference paper (Refereed)
    Abstract [en]

    Different borehole heat exchanger designs have been discussed for many years. However, the U-pipe design has dominated the market, and the introduction of new designs has been practically lacking. The interest for innovation within this field is rapidly increasing and other designs are being introduced on the market. This paper presents a general state of the art summary of the borehole heat exchanger research in the last years. A first study of a prototype coaxial borehole heat exchanger consisting of one central pipe and five external channels is also presented. The particular geometry of the heat exchanger is analyzed thermally in 2-D with a FEM software. An experimental evaluation consisting of two in situ thermal response tests and measurements of the pressure drop at different flow rates is also presented. The latter tests are carried out at two different flow directions with an extra temperature measurement point at the borehole bottom that shows the different heat flow distribution along the heat exchanger for the two flow cases. The borehole thermal resistance of the coaxial design is calculated both based on experimental data and theoretically.

  • 32.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Preben
    Palne Mogensen AB.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Thermal Response Test on a U-Pipe Borehole Heat Exchanger2009In: Proc. Effstock 2009, 11th International Conference on Thermal Energy Storage, Stockholm, Sweden: Academic Conferences Publishing, 2009Conference paper (Refereed)
    Abstract [en]

    In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and boreholethermal resistance are determined at many instances along the borehole. Here, such a testis carried out at a 260 m deep water filled energy well, equipped with a U-pipe borehole heatexchanger, containing an aqueous solution of ethanol as working fluid. Distributed temperaturemeasurements are carried out using fiber optic cables placed inside the U-pipe, duringfour test phases: undisturbed ground conditions, fluid pre-circulation, constant heat injection,and borehole recovery. A line source model is used for simulating the borehole thermal response.Fluid temperature profiles during the test are presented. The results show local variationsof the ground thermal conductivity and borehole thermal resistance along the boreholedepth, as well as a deviation of the latter as compared to the one resulting from a standardthermal response test.

  • 33.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    First Experiences with Coaxial Borehole Heat Exchangers2011In: Proceedings of the IIR Conference on Sources/Sinks alternative to the outside Air for HPs and AC techniques, International Institute of Refrigeration, 2011Conference paper (Refereed)
    Abstract [en]

    Some experiences with coaxial borehole heat exchanger prototypes are discussed here. Four different designs are described as they have been part of a research project at KTH: two pipe-inpipe annular designs, one multi-pipe and one multi-chamber design. A special focus is given to two of the prototypes, a pipe-in-pipe design with the external flow channel consisting of an annular cross section and partly insulated central pipe, and a multi-pipe design with twelve parallel peripheral pipes and an insulated central channel. The secondary fluid temperature profiles at low volumetric flow rates are presented for these two prototypes, measured with fiber optic cables during thermal response tests and allowing a detailed visualization of what happens along the heat exchanger depth. It is the first time this is carried out in these types of borehole heat exchangers. The measurements indicate good thermal performance and point at potential uses for these heat exchangers in different ground coupled applications.

  • 34.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Temperature Measurements on a Multi-pipe Coaxial Borehole Heat Exchanger2011In: IEA Heat Pump Conference, International Energy Agency , 2011, 4.19- p.Conference paper (Refereed)
    Abstract [en]

    The first experiences with a multi-pipe borehole heat exchanger prototype consisting of an insulated central pipe and twelve parallel peripheral pipes are described. Secondary fluid distributed temperature measurements along the borehole depth, being the only ones of its kind in this type of heat exchanger, are presented and discussed. The measurements are carried out with fiber optic cables during heat injection into the ground, giving a detailed visualization of what happens both along the central and peripheral flow channels. The heat exchange with the ground mainly occurs along the peripheral channels and an indication of almost no thermal short circuiting, even while having large temperature differences between the down and upwards channels, is observed.

  • 35.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Comprehensive Summary of Borehole Heat Exchanger Research at KTH2010In: IIR/Eurotherm Sustainable Refrigeration and Heat Pump Technology Conference, Stockholm: KTH Royal Institute of Technology, 2010, 69- p.Conference paper (Refereed)
    Abstract [en]

    A research project that aims at presenting recommendations for improving the COP of ground source heat pump systems by 10-20% through better design of Borehole Heat Exchangers (BHE) is described in this paper. Experiments are carried out with temperature measurements taken in different BHE types during heat pump operation conditions as well as during the thermal response tests. It is also expected to point out methods for having natural fluid circulation in the BHE, i.e. demonstrating that the heat carrier fluid can naturally circulate thanks to temperature induced density differences along the borehole depth, and thereby avoiding the use of electricity consuming pumps. A brief background presenting the most relevant work regarding BHE research around the world is first presented, followed by a comprehensive description of the current research at KTH. Some new measurements and obtained results are presented as an estimation of to what extent the project results have been achieved is discussed. An analysis on how the project results could allow reducing the borehole depth keeping today’s Coefficient of Performance is presented.

  • 36.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental Comparison of Four Borehole Heat Exchangers2008In: Refrigeration Science and Technology Proceedings, Copenhagen: International Institute of Refrigeration, 2008, SEC09-W1-09 p.Conference paper (Refereed)
    Abstract [en]

    The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports the heat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with the ground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluid and its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcohol with 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet. The collectors are compared based on their borehole thermal resistance and pressure drop at different flow rates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute to better heat transfer, and inner micro fins in the pipes improve the performance of the collectors.

  • 37.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A novel coaxial BHE: Description and first Distributed Thermal Response Test Measurements2010In: Proceedings World Geothermal Congress 2010, 2010, paper 2953- p.Conference paper (Refereed)
    Abstract [en]

    The thermal performance of a Borehole Heat Exchanger plays a significant role when defining the quality of heat exchange with the ground in Ground Source Heat Pumps. Different designs have been discussed and increased interest on innovation within this field has taken place during the last years. This paper presents the first measurement results from a 189 meters deep novel coaxial Borehole Heat Exchanger, consisting of an inner central pipe and an annular channel in direct contact with the surrounding bedrock. The measurements were taken during a distributed thermal response test using fiber optic cables installed in the energy well. Fluid temperature every ten meters along the borehole depth are presented and compared with similar measurements from a common U-pipe heat exchanger. A unique measurement of the borehole wall temperature in the coaxial collector illustrates how effective the heat transfer performance is through the annular channel.

  • 38.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hill, Peter
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Characterization of Boreholes: Results from a U-pipe Borehole Heat Exchanger Installation2008In: Proceedings 9th IEA Heat Pump Conference 2008: Conference Proceedings, Zurich, Switzerland: International Energy Agency , 2008, 4-19 p.Conference paper (Refereed)
    Abstract [en]

    Heat exchange with the bedrock for ground source heat pumps is commonly done with the help of U-pipe energy collectors in vertical boreholes. At the moment, there exist many uncertainties about how efficient the heat transfer between the rock and the collector is. For a complete performance analysis of these systems, a 260 m deep water filled borehole is characterized, by measuring the borehole deviation, the ground water flow and the undisturbed ground temperature. Significant attention is devoted to detailed temperature measurements along the borehole depth during operation providing a complete description of the temperature variations in time both for the secondary working fluid and for the ground water. The results show a deviated borehole from the vertical direction without any relevant ground water flow. The undisturbed ground temperature gradient varies from negative to positive at approximately half of the borehole depth. The transient response of the borehole during the heat pump start up is illustrated and it is observed that there does not exist any thermal short circuiting between the down and up-going pipes when the system is in operation.

  • 39.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmat
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Weber, Kenneth
    Distributed Temperature Measurements on a U-pipe Thermosyphon Borehole Heat Exchanger With CO22010In: Refrigeration Science and Technology Proceedings, Sydney, Australia: International Institute of Refrigeration, 2010Conference paper (Refereed)
    Abstract [en]

    In thermosyphon Borehole Heat Exchangers, a heat carrier fluid circulates while exchanging heat with the ground without the need of a circulation pump, representing an attractive alternative when compared to other more conventional systems. Normally, the fluid is at liquid-vapor saturation conditions and circulation is maintained by density differences between the two phases as the fluid absorbs energy from the ground. This paper presents some experimental experiences from a 65 meter deep thermosyphon borehole heat exchanger loop using Carbon Dioxide as heat carrier fluid, instrumented with a fiber optic cable for distributed temperature measurements along the borehole depth. The heat exchanger consists of an insulated copper tube through which the liquid CO2 flows downwards, and a copper tube acting as a riser. The results show temperatures every two meters along the riser, illustrating the heat transfer process in the loop during several heat pump cycles.

  • 40.
    Adam, Stenlund
    et al.
    Linnaeus University, Faculty of Technology, Kalmar Maritime Academy.
    John, Barnekow
    Linnaeus University, Faculty of Technology, Kalmar Maritime Academy.
    Energieffektivisering av Ronneby is-arena samt vädrets termodynamiska påverkan2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract

    Today Sweden has 341 ice hockey arenas, around 140 outdoor ice hockey rinks, 60 ice fields for bandy and about 35 curling arenas. In addition, the numbers of indoor bandy arenas are increasing. The cooling systems installed today should be able to lower its energy consumption with 10-30%.In this thesis, Ronneby ice-arena has been researched. This artificial cooling facility was inaugurated 2011 and is one of the newest in Sweden. This is an outdoor ice field for bandy and therefor has no roof or walls to cover the field. Ronneby ice-arena has problems with uneven cooling distribution of the ice field. This results in cracks and uneven ice quality. These problems also result in higher energy consumption than necessary.To find a solution for the uneven cooling of the ice field flow measurements were carried out in the brine circuit. To get a better understanding of the cooling distribution, temperature measurements were carried out on the brine feeding lines. A calculation has been performed on what energy savings a speed control of the brine circulation pumps depending on the outdoor temperature could generate. Another calculation was made to see the possible savings with a windshield around the field. In this thesis the benefits of a heat recovery system on the cooling compressors refrigerant has been investigated. The heat recovery system could heat the locker rooms, the clubhouse, the showers and the hot water for the Zambonis.In order to perform the necessary calculation for this thesis, Fredriksbergs BK and Ronneby municipality provided operating data.The actions proposed to Ronneby ice-arena to solve the uneven cooling of the ice field is to change the location of the brine feeding line connection point. At the same time this work is carried out it’s suggested that the brine feed and return lines get insulated. When the uneven cooling problems have been solved, a speed control system should be installed to control the brine circulation pumps, in order to lower the electricity consumption. Ronneby ice-arena has the possibility to install a heat recovery system. Therefore it is suggested to install a heat exchanger on each cooling compressor refrigerant. This installation is to be used to heat the clubhouse, the showers and the hot water for the Zambonis. The system to cool the condensers with seawater and currently the heat pump are not optimal designed. The installed heat pump does not work when the seawater temperature is below 5°C, therefore the system should be redesigned.

  • 41.
    Adamsson, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    An investigation of cross-section geometry effects on the deposition rate in annular two-phase flows with a Lagrangian model2007In: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12, 2007Conference paper (Refereed)
    Abstract [en]

    The motion of liquid drops in annular two-phase flow in pipes, annuli and subchannels has been investigated with a model based on Lagrangian particle tracking. The results confirm that large drops may deposit by direct impaction. It is also demonstrated that the deposition rate does not differ significantly between pipes and subchannels except for very large drops, which deposit slower in subchannels. Furthermore the Saffman lift force is shown to have a large impact on the results but it is questionable of the standard formulation is applicable to the drops considered here. Finally it is concluded that accurate modeling of high pressure steam-water flows requires a model for drop-drop collisions.

  • 42.
    Adamsson, Carl
    et al.
    KTH, Superseded Departments, Physics.
    Anglart, Henryk
    KTH, Superseded Departments, Physics.
    Dryout predictions in bwr fuel assemblies with spacers2004In: Proceedings of the Sixth International Conference on Nuclear Thermal-Hydraulics, Operation and Safety, 2004Conference paper (Refereed)
    Abstract [en]

    A new spacer model has been implemented into the subchannel code Mona-3 and validated against dryout experiments in various rod bundles with different number of spacers and different spacer designs. The spacer-induced deposition enhancement is captured by proper modeling of the turbulence intensity downstream of a spacer.

    The Mona-3 code with the new spacer model captures spacer effects in a correct manner. Both the effect of the number of spacers and the effect of the spacer design are predicted correctly. In particular, the critical power difference between 24-rod bundles with 6 and with 7 spacers is measured to be larger than the difference between 25-rod bundles with 6 and with 7 spacers. This experimental finding is well captured with the Mona-3 code with the present spacer model.

  • 43.
    Adolphe, Cyril
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Commissioning the Heating and Cooling Systems on an FPSO (Floating Production Storage and Offloading facility)2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The project under discussion is the FPSO Ichthys. The FPSO is a ship comprising the offshore production facility for an oil&gas field, financed by INPEX/Total. An oil platform extracts the product received via the flexible risers and separates it into gas and condensate. The condensate is transferred to the FPSO, which processes it, and separates it between natural gas and oil. The oil is stored in the FPSO and then exported via a tanker. The gas is transferred via a pipeline.

    An FPSO is a complex installation in many respects. It is a condensate treatment factory, installed on a 450-metre-long ship. It should have the capacity to store one week’s condensate production. The FPSO is self-sufficient in terms of energy production (electricity, heating and cooling). Owing to the proximity of the hazardous production area to the living quarters, strict safety regulations are applied. For instance, all equipment has to be designed with redundancy (2x50% or 3x33% for critical equipment); the heating and cooling systems are managed with the help of emergency logic diagrams. These enable vital functions to be maintained even in cases of extreme failure.

    Despite its complexity, the FPSO has to be constructed within a short period of time. However, safety issues are important, and maintenance of defective equipment is expensive since the ship will be located 300km away from the coast. This is the reason why the constructor contracted Actemium, a part of VINCI Energies. Actemium commissions the FPSO. The commissioning mission has to prove that the systems function in accordance with the designs. Commissioning occurs right after the pre-commissioning (de-energized verifications). Commissioning is divided into three main activities: functional tests (which prove that individual pieces of equipment work in accordance with the designs); operational tests (which prove that all subsystems work in accordance with the designs of different modes); and piping and vessels pressurization (which prove that there is no leak).

    This master thesis describes the requirements of such projects and focuses on the operational tests. A description of the installation is detailed. Secondly, the subcontractor for the commissioning of the project, Actemium, and the method used for the commissioning are presented thereafter. Finally, the operational test procedures of the cooling and heating systems are examined in detail.

  • 44. Adomavicius, A.
    et al.
    Belousov, A.
    Gylys, J.
    Jasiulevicius, Audrius
    KTH, Superseded Departments, Energy Technology.
    Kubarev, Andrej
    KTH, Superseded Departments, Energy Technology.
    Ognerubov, V.
    Ziedelis, S.
    The studies of RBMK-1500 reactor core behavior during abnormal operation transients2004In: Proceedings of the PHYSOR 2004: The Physics of Fuel Cycles and Advanced Nuclear Systems - Global Developments, 2004, 1035-1047 p.Conference paper (Refereed)
    Abstract [en]

    This paper describes series of RBMK-1500 reactor transient investigations, performed with CORETRAN code. Aspects of the reactor core neutronic and thermal hydraulic behavior during postulated core transients were analyzed, hi particular, RBMK-1500 transients leading to changes in reactor power and core reactivity were considered. Three reactivity-initiated accident cases were addressed: a) spontaneous control rod bank withdrawal in the central part of the core; b) spontaneous control rod bank withdrawal in core periphery and c) release of one Shortened Absorber Rod from the reactor core. Reactor nominal power operation was used as the reference core state. Analysis was performed using data, obtained from the actual plant database recorded for Ignalina Nuclear Power Plant Unit 2 on 27th January 2001. The CORETRAN calculations were benchmarked against STEPAN code results.

  • 45. Aebischer, B.
    et al.
    Hilty, Lorenz
    KTH, School of Computer Science and Communication (CSC), Centres, School of Architecture and the Built Environment (ABE), Centres, Centre for Sustainable Communications, CESC. University of Zurich, Switzerland .
    The energy demand of ICT: A historical perspective and current methodological challenges2015In: ICT Innovations for Sustainability, Springer, 2015, 71-103 p.Chapter in book (Refereed)
    Abstract [en]

    This chapter provides an overview of energy demand issues in the field of ICT with a focus on the history of measuring, modelling and regulating ICT electricity consumption and the resulting methodological challenges. While the energy efficiency of ICT hardware has been dramatically improving and will continue to improve for some decades, the overall energy used for ICT is still increasing. The growing demand for ICT devices and services outpaces the efficiency gains of individual devices. Worldwide per capita ICT electricity consumption exceeded 100 kWh/year in 2007 (a value which roughly doubles if entertainment equipment is included) and is further increasing. Methodological challenges include issues of data collection and modelling ICT devices and services, assessing the entire life cycle of ICT devices and infrastructures, accounting for embedded ICT, and assessing the effect of software on ICT energy consumption.

  • 46.
    af Burén, Claës
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Piska eller morot?: En studie av möjligheter och hinder samt förslag på åtgärder till förändringar inom den svenska industrin i syfte att öka energieffektiviseringsarbetet.2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Our nation is dependent on secure energy supply at competitive prices. Even though energy efficiency tools are available Sweden hasn’t achieved its full potential. The Swedish industry and its energy efficiency is affected by a number of instruments concerning climate and energy, such as energy- and carbon taxes, the European emission trading system (EU ETS) and the Swedish program for energy efficiency (PFE). 

    Optional or obligatory, today there is a difference of opinion concerning the design of energy efficiency instruments. This paper focus on the research of energy efficiency instruments in the industry and to identify potential opportunities, obstacles and give recommendations of actions to improve the energy efficiency. This paper is a part of a project,”Ett energieffektivt samhälle”,   initiated by the Royal Swedish Academy of Engineering Sciences (IVA).  The research is based on interviews with industry related representatives of companies, associations, government agencies and other independent operators.

    PFE, EKC, the environmental code, ErP, energy- and carbon taxes, ETS and the Swedish system of electricity certificates, influences the energy efficiency work. None of these instruments have an overall impact on the industry. PFE and ErP are popular instruments but EKC has to improve to be an incentive for the industry.  The environmental code is criticized for its interpretation and enforcement. Competitiveness is adversely affected by taxes and ETS in contrary to PFE and EKC. Continuously energy work is only required by PFE and the environmental code.

    Both authorities and companies have to provide clear guidelines, follow-ups and the gains to be obtained of the energy efficiency work. Authorities have to support critical investments and to avoid interfering with the competition on the market. Long-term planning, cost-effectiveness, technology neutrality and being a legitimate stakeholder is of vital importance. Companies have to provide the financial structure suited for energy efficiency work. They also have to apply a continuous and long-term efficiency work, for example by highlighting new ratios and to encourage employees to participate in the development process. Collaboration in the form of co-production between different universities, institutes, lobby-associations and companies have to be encouraged to improve knowledge exchange and reduced costs.

    The question is if energy efficiency instruments should be based on “the stick or carrot approach”? Research about energy efficiency shows, that a combination of voluntary, mandatory and economical instruments is absolutely necessary for a favourable development.  Parts with different interests and qualifications demands a number of arrangements that both is a “stick and a carrot approach” to a necessary energy efficiency work.  Many of the participants in the study underline the importance to address the heterogeneity of the parts otherwise it will disfavour the energy efficiency work when the industry moves abroad. Actually the following conclusion could be made, that the initial question about the “stick or carrot approach” must be put in a different way. About an effective energy efficiency work it’s absolutely necessary to create a combination of both “the stick and the carrot” approach and the wider look on the concept energy efficiency. It’s most important to have a very well done combination and harmonization of the instruments to support the energy efficiency work, the industry and the society at large.

  • 47.
    Afzal, Mohammad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Numerical modelling and analysis of friction contact for turbine blades2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    High cycle fatigue failure of turbine and compressor blades due to resonance in the operating frequency range is one of the main problems in the design of gas turbine engines. To suppress excessive vibrations in the blades and prevent high cycle fatigue, dry friction dampers are used by the engine manufacturers. However, due to the nonlinear nature of friction contact, analysis of such systems becomes complicated.

    This work focuses on the numerical modelling of friction contact and a 3D friction contact model is developed. To reduce the computation time in the Newton-iteration steps, a method to compute the Jacobian matrix in parallel to the contact forces is proposed. The developed numerical scheme is successfully applied on turbine blades with shroud contact having an arbitrary 3D relative displacement. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of the cyclic symmetry boundary condition for a periodic structure.

    The developed 3D coupled numerical contact model is compared with a 3D contact model having uncoupled tangential motion and drawback of the uncoupled contact model is discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different harmonic indices (nodal diameters) of the bladed disk are systematically presented. Moreover, due to the quasi-analytical computation of the Jacobian matrix, the developed scheme is proved to be effective in solving the equations of motion and significant reduction in time is achieved without loss of accuracy.

     

     

     

  • 48.
    Afzal, Mohammad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH.
    On efficient and adaptive modelling of friction damping in bladed disks2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work focuses on efficient modelling and adaptive control of friction damping in bladed disks. To efficiently simulate the friction contact, a full-3D time-discrete contact model is reformulated and an analytical expression for the Jacobian matrix is derived that reduces the computation time drastically with respect to the classical finite difference method. The developed numerical solver is applied on bladed disks with shroud contact and the advantage of full-3D contact model compared to a quasi-3D contact model is presented. The developed numerical solver is also applied on bladed disks with strip damper and multiple friction contacts and obtained results are discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different nodal diameters of the bladed disk are systematically presented. The main parameters that influence the effectiveness of friction damping in bladed disks are engine excitation order,  contact stiffnesses,  friction coefficient, relative motion at the friction interface and the normal contact load. Due to variation in these parameters during operation, the obtained friction damping in practice may differ from the optimum value. Therefore, to control the normal load adaptively that will lead to an optimum damping in the system despite these variations, use of magnetostrictive actuator is proposed. The magnetostrictive material that develops an internal strain under the influence of an external magnetic field is employed to increase and decrease the normal contact load. A linearized model of the magnetostrictive actuator is used to characterize the magnetoelastic behavior of the actuator.  A nonlinear static contact analysis of the bladed disk reveals that a change of normal load more than 700 N can be achieved using a reasonable size of the actuator. This will give a very good control on friction damping once applied in practice.

  • 49.
    Aghaali, Habib
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Exhaust Heat Utilisation and Losses in Internal Combustion Engines with Focus on the Gas Exchange System2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Exhaust gas energy recovery should be considered in improving fuel economy of internal combustion engines. A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocharger and turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the efficiency and mass flow of the turbine(s) as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity. The exhaust gas pressure is the principal parameter which is required for the turbine energy recovery, but higher exhaust back-pressures on the engines create higher pumping losses. This is in addition to the heat losses in the turbochargers what makes any measurement and simulation of the engines more complex.

    This thesis consists of two major parts. First of all, the importance of heat losses in turbochargers has been shown theoretically and experimentally with the aim of including heat transfer of the turbochargers in engine simulations. Secondly, different concepts have been examined to extract exhaust heat energy including turbocompounding and divided exhaust period (DEP) with the aim of improved exhaust heat utilisation and reduced pumping losses.

    In the study of heat transfer in turbochargers, the turbocharged engine simulation was improved by including heat transfer of the turbocharger in the simulation. Next, the heat transfer modelling of the turbochargers was improved by introducing a new method for convection heat transfer calculation with the support of on-engine turbocharger measurements under different heat transfer conditions. Then, two different turbocharger performance maps were assessed concerning the heat transfer conditions in the engine simulation. Finally, the temperatures of turbocharger’s surfaces were predicted according to the measurements under different heat transfer conditions and their effects are studied on the turbocharger performance. The present study shows that the heat transfer in the turbochargers is very crucial to take into account in the engine simulations, especially in transient operations.

    In the study of exhaust heat utilisation, important parameters concerning turbine and gas exchange system that can influence the waste heat recovery were discussed. In addition to exhaust back-pressure, turbine speed and turbine efficiency, the role of the air-fuel equivalence ratio was demonstrated in details, because lower air-fuel equivalence ratio in a Diesel engine can provide higher exhaust gas temperature. The results of this study indicate that turbocompound engine efficiency is relatively insensitive to the air-fuel equivalence ratio.

    To decrease the influence of the increased exhaust back-pressure of a turbocompound engine, a new architecture was developed by combining the turbocompound engine with DEP. The aim of this study was to utilise the earlier phase (blowdown) of the exhaust stroke in the turbine(s) and let the later phase (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow was divided between two different exhaust manifolds with different valve timing.

    According to this study, this combination improves the fuel consumption in low engine speeds and deteriorates it at high engine speeds. This is mainly due to long duration of choked flow in the exhaust valves because this approach is using only one of the two exhaust valves on each cylinder at a time.

    Therefore, the effects of enlarged effective flow areas of the exhaust valves were studied. Two methods were used to enlarge the effective flow area i.e. increasing the diameters of the blowdown and scavenging valves by 4 mm; and modifying the valve lift curves of the exhaust valves to fast opening and closing. Both methods improved BSFC in the same order even though they were different in nature. Fast opening and closing of the exhaust valves required shorter blowdown duration and longer scavenging duration. The modified lift curves provided less pumping losses, less available energy into the turbine and larger amplitude of the pulsating flow through the turbine.

    In order for defining a set of important parameters that should be examined in experimental studies, a sensitivity analysis was performed on the turbocompound DEP engine in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency.

    Finally, to overcome the restriction in the effective flow areas of the exhaust valves, DEP was implemented externally on the exhaust manifold instead of engine exhaust valves, which is called externally DEP (ExDEP). This innovative engine architecture, which benefits from supercharging, turbocharging and turbocompounding, has a great fuel-saving potential in almost all load points up to 4%.

  • 50.
    Aghaali, Habib
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    On-Engine Turbocharger Performance Considering Heat Transfer2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Heat transfer plays an important role in affecting an on-engine turbocharger performance. However, it is normally not taken into account for turbocharged engine simulations.

    Generally, an engine simulation based on one-dimensional gas dynamics uses turbocharger performance maps which are measured without quantifying and qualifying the heat transfer, regardless of the fact that they are measured on the hot-flow or cold-flow gas-stand. Since heat transfer situations vary for on-engine turbochargers, the maps have to be shifted and corrected in the 1-D engine simulation, which mass and efficiency multipliers usually do for both the turbine and the compressor. The multipliers change the maps and are often different for every load point. Particularly, the efficiency multiplier is different for every heat transfer situation on the turbocharger. The heat transfer leads to a deviation from turbocharger performance maps, and increased complexity of the turbocharged engine simulation. Turbochargers operate under different heat transfer situations while they are installed on the engines.

    The main objectives of this thesis are:

    • heat transfer modeling of a turbocharger to quantify and qualify heat transfer mechanisms,
    • improving turbocharged engine simulation by including heat transfer in the turbocharger,
    • assessing the use of two different turbocharger performance maps concerning the heat transfer situation (cold-measured and hot-measured turbocharger performance maps) in the simulation of a measured turbocharged engine,
    • prediction of turbocharger walls’ temperatures and their effects on the turbocharger performance on different heat transfer situations.

    Experimental investigation has been performed on a water-oil-cooled turbocharger, which was installed on a 2-liter GDI engine for different load points of the engine and different heat transfer situations on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. In addition, several thermocouples have been used on accessible surfaces of the turbocharger to calculate external heat transfers.

    Based on the heat transfer analysis of the turbocharger, the internal heat transfer from the bearing housing to the compressor significantly affects the compressor. However, the internal heat transfer from the turbine to the bearing housing and the external heat transfer of the turbine housing mainly influence the turbine. The external heat transfers of the compressor housing and the bearing housing, and the frictional power do not play an important role in the heat transfer analysis of the turbocharger.

    The effect of the extra cooling fan on the energy balance of the turbocharger is significant. However, the effect of the water is more significant on the external heat transfer of the bearing housing and the internal heat transfer from the bearing housing to the compressor. It seems the radiation shield between the turbine and the compressor has no significant effect on the energy balance of the turbocharger.

    The present study shows that the heat transfer in the turbocharger is very crucial to take into account in the engine simulations. This improves simulation predictability in terms of getting the compressor efficiency multiplier equal to one and turbine efficiency multiplier closer to one, and achieving turbine outlet temperature close to the measurement. Moreover, the compressor outlet temperature becomes equal to the measurement without correcting the map.

    The heat transfer situation during the measurement of the turbocharger performance influences the amount of simulated heat flow to the compressor. The heat transfer situation may be defined by the turbine inlet temperature, oil heat flux and water heat flux. However, the heat transfer situation on the turbine makes a difference on the required turbine efficiency multiplier, rather than the amount of turbine heat flow. It seems the turbine heat flow is a stronger function of available energy into the turbine. Of great interest is the fact that different heat situations on the turbocharger do not considerably influence the pressure ratio of the compressor. The turbine and compressor efficiencies are the most important parameters that are affected by that.

    The component temperatures of the turbocharger influence the working fluid temperatures. Additionally, the turbocharger wall temperatures are predictable from the experiment. This prediction enables increased precision in engine simulations for future works in transient operations.

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