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  • 51.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Attending remedial class. “Perhaps because I have some AD/HD”2007Conference paper (Refereed)
  • 52.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Barn som far illa och anmälningsplikt2008In: Barn i utsatta livssituationer / [ed] Jane Brodin, Malmö: Gleerups utbildning , 2008Chapter in book (Other (popular science, discussion, etc.))
  • 53.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Child and Youth Science2006Conference paper (Refereed)
  • 54.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Child perspective on before- and after school settings2005Conference paper (Refereed)
  • 55.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Science, Department of Education in Arts and Professions.
    Children’s views on attending a remedial class – because of concentration difficulties2011In: Child Care Health and Development, ISSN 0305-1862, E-ISSN 1365-2214, Vol. 37, no 3, p. 440-445Article in journal (Refereed)
    Abstract [en]

    Background An increasing number of segregating solutions (e.g. remedial classes) can be seen in Swedish schools. The aim of this article is to stress how children describe why they attend a remedial class and what it means to be a pupil in that setting. Methods The data collection consists of semi-structured interviews with 10 pupils between 10 and 12 years old attending 10 different remedial classes because they had been attributed with having concentration difficulties or diagnosed with attention deficit/hyperactivity disorder. The content of the interviews was described and analysed in relation to the classroom context. The socio-cultural perspective is used as a screen to describe and understand the children’s comments about attending remedial class. Results and conclusions All interviews with the children indicate that they are carriers of their schools’ compensatory perspective. This means that they are fully aware of the fact that they are regarded as difficult, with annoying and problematic behaviour, deviating from pupils’ in general. The remedial class creates social difficulties for the children; they see themselves as deviant, they lose old friends and there are limited possibilities of establishing new friendship in remedial classes.

  • 56.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Classroom climate. Changing practices in inclusive schools2009Conference paper (Other academic)
  • 57.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Constructing young masculinity in an after-school centre2011Conference paper (Other academic)
  • 58.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Doing Masculinity in School-Age Child-Care: An Ethnographic Study 2018In: International Journal for Research on Extended Education, ISSN 2196-3673, E-ISSN 2196-7423, Vol. 6, no 1, p. 66-79Article in journal (Refereed)
    Abstract [en]

    This article is based on data from a two-year ethnographic study on children in school-age child-care in Sweden. It describes a boy’s way from positioning himself as a “boy who does not fight” to a “boy who fights”. In Sweden, independence is viewed as paramount. Fostering children to independence can be seen from different perspectives, and the teachers in this particular setting hand over the power to the children. The social climate in the setting was quite tough, and the children – especially the boys – formed a social hierarchy by using their fists. The material was studied with help from analytical tools dealing with gender, position and power.

  • 59.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Ethical dilemmas when interviewing children2006Conference paper (Refereed)
  • 60.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Informal learning at the after school day care - from the children’s perspective2002Conference paper (Refereed)
  • 61.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Interviews with children attending remedial class2007Conference paper (Refereed)
  • 62.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    School-Age Child-Care in Sweden2017Conference paper (Other academic)
  • 63.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    School-Age Educare: Different Ways of Talking as Arenas for Inclusion2012Conference paper (Refereed)
    Abstract [en]

    I present an approach for a proposed study using discourse analysis, with the aim of studying how pupils interact with childcare teachers during school-age childcare and during school hours.

    In Sweden almost 80 % of the child population between six and nine years old attends school-age child-care - mostly integrated in the school. In a Swedish thesis from 1999, Karlsudd, declares that school-age child-care can boast of being like a final integration sanctuary, while the school, unfortunately rarely succeed in their integration efforts (Karlsudd, 1999). Time has changed, in a conference paper 12 years later Karlsudd declares; the final integration sanctuary is probably soon lost (Karlsudd, 2011). In Sweden as in several other countries we can see that medical discourse has been given priority in the educational context (Ljusberg, 2009). Goals in both the Swedish school law and the curricula state that all pupils are to be regarded as equal, to have equal rights to education, and equal circumstances in school. In my thesis (Ljusberg, 2009) I am using different perspectives, a relational perspective and a compensatory perspective (also called the medical psychological perspective (Bailey, 1998), and the individual or categorical perspective (Emanuelsson, Persson & Rosenqvist, 2001). From a compensatory perspective the difficulties are attached to the pupil, from a relational perspective the difficulties are studied as situated social constructions (Hjörne, 2004; Mehan, 1993). In this paper I present my approach for a ethno-methodological study using discourse analysis with the aim to study how pupils interact/are talking with school-age child-care teachers in one hand during school-age child-care and on the other hand during school hours.

     

  • 64.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Self-conception in children attending remedial classes in state primary schools in Sweden2005Conference paper (Refereed)
  • 65.
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Science, Department of Education in Arts and Professions.
    The structured classroom2011In: International Journal of Inclusive Education, ISSN 1360-3116, E-ISSN 1464-5173, Vol. 15, no 2, p. 195-210Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to highlight the organisation of the remedial classroom. The data were collected from observations and semi-structured interviews with 10 teachers in remedial classes for children seen and treated as having concentration deficits. The teachers use primarily compensatory language that places the deficits in the pupils. Something appearing both in the interviews and in the organisation of the classroom is the structured classroom. In the remedial class it can be expresse by dividing the pupils’ working place areas with screens or turning the pupils’ desks toward a bare wall, and strongly structuring the teaching. By pointing out the problem as pupils’ social deficits, the schools reduce their agency. The goal of remedial classes is that the pupils will return to the ordinary class. This article suggests that what pupils in remedial classes learn primarily is to be a pupil in a remedial class.

  • 66.
    Ljusberg, Anna-Lena
    Stockholm University, The Stockholm Institute of Education.
    Two different disciplines are working together2005Conference paper (Refereed)
  • 67.
    Ljusberg, Anna-Lena
    Stockholm University.
    Two different disciplines working together2005In: EuroRehab, Vol. 3-4, p. 85-90Article in journal (Refereed)
  • 68.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Brodin, Jane
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    IRIS Improvement Through Research in Inclusive Schools: EU-project2008In: Ensuring a Society for ALL: 21st International Congress of Rehabilitation International, 2008Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    A presentation of the IRIS project which is a cooperation with six countries and seven partners involved. The overall aim is to promote a school for all children.

  • 69.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Brodin, Jane
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Self-concept in children with attention deficits2007In: International Journal of Rehabilitation Research, ISSN 0342-5282, E-ISSN 1473-5660, Vol. 30, no 3, p. 195-201Article in journal (Refereed)
  • 70.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Brodin, Jane
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Lindstrand, Peg
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Ethical issues when interviewing children in remedial classes2007In: International Journal of Rehabilitation Research, ISSN 0342-5282, E-ISSN 1473-5660, Vol. 30, no 3, p. 203-207Article in journal (Refereed)
  • 71.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Brodin, Jane
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Lindstrand, Peg
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Interviewing children in remedial classes2007In: International Journal of Rehabilitation Research, ISSN 0342-5282, E-ISSN 1473-5660, Vol. 30, no 3, p. 203-207Article in journal (Refereed)
    Abstract [en]

    This study concerns the ethical issues related to interviews with children. In a sub study of the Basic Skills, Social Interaction and Training of the Working Memory (BASTA) project, 10 children between 10 and 12 years of age were interviewed. Interviews involving children have to address many more ethical issues than interviews with adults. Children constitute an overexposed group because they are under age, and because they stand in a dependent relationship with adults. One ethical dilemma for the researcher in interviews with children might be the conflict between professional secrecy and the obligation to report, as stated in the Swedish Social Services Act. According to this Act and to ethical research principles, researchers are bound to maintain professional secrecy.

  • 72.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Gottzén, Lucas
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    The image of the child in school-age childcare education textbooks2016Conference paper (Refereed)
  • 73.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Hippinen Ahlgren, Anneli
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Child perspectives in a School-Age Educare setting2015In: : Barcelona, Catalunya, Spain7th - 10th September 2015, 2015Conference paper (Other academic)
    Abstract [en]

    The aim is to study children’s meaningmaking about learning in school age educare. The university trained school age educare teachers’ competence differs to some degree from a classroom teacher due to the pedagogy that focuses more on child perspectives, identity making, care and learning through practical and aesthetical methods (Hansen, 1999; Carlander, 1999; Haglund, 2004). From a child´s perspective this can mean that school age educare teachers can offer different tools that will help them in their subject’s orientated learning process and in lifelong learning (Evaldsson, 1993; Hippinen-Ahlgren, fortcoming; Johansson & Ljusberg, 2004; Kjaer, 2005; Pálsdóttir, 2010)

    The theoretical perspective used is socio-cultural. Pupils are constructed by and also construct themselves in interaction with various discourses they encounter. Discourses are built in and around artifacts (Vygotskij 1999; Bakhtin 1986; Säljö 1999, 2000). Learning and sense making is seen from this perspective as participation in communication/interaction.

    The study is based on semi structural interviews with children attending school age educare.

    Places and individuals are made anonymous in field notes and in the processing of the material. The audio recordings are kept locked in filing cabinets at Stockholm University. In the written informed consent directed to teachers, students and their guardians it is clear who is responsible for the project with contact information. Observational studies and interviews carried out only where participants (and guardians) gave their consent.

    How can we understand children’s meaningmaking about learning in school age educare?

    How can we understand and develop the practice from children’s perspective?

  • 74.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Holmberg, Linnéa
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Lärare, barn och lärande i kurslitteratur – ideologiska dilemman i talet om fritidshem2019In: Educare - Vetenskapliga skrifter, ISSN 1653-1868, no 3, p. 17-33Article in journal (Refereed)
    Abstract [en]

    In recent years, the number of different course books focused on school-age educare available for undergraduates in teacher education programs for primary school has increased. Thus studying what particular version of school-age educare is legitimized in this discursive practice and how this is done rhetorically becomes pertinent. This article examines and illuminates how this course literature – used at several universities in Sweden – stages a certain way of speaking about school-age educare and thereby may ascribe teachers and children specific subject positions. The study shows how recurrent ideological dilemmas are used as linguistic resources to manage some constantly present contradictions: school-age educare is supposed to be both democratic and child centered, as well as professionally planned and lead. The findings illuminate a homogenous depiction of how school-age educare is distinguished from traditional and formal schooling and thereby promoted as a unique but also necessary form of education. As a consequence, an ideal teacher is someone who is specialized in being actively passive and passively active, and an expert on children’s learning while children are considered expertson themselves and in the activities as well. That is, teacher’s professionalism in educare is tied to the skill of not being formal and school-like, but still being educational in a way that promotes politically-approved learning and development.

  • 75.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Holmberg, Linnéa
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Teachers' Professionalism in Educare2019Conference paper (Refereed)
    Abstract [en]

    In Sweden there has in recent years there been an increase in literature focused on school-age educare available for undergraduates in teacher education program for primary school, specializing in school-age educare. With this, it seems pertinent to study which particular version of school-age educare that is legitimized in this discursive practice, and how this is done rhetorically. Thus, this article examines and highlight how this literature – used at several universities in Sweden – stage a certain way of speaking about this phenomenon and thereby ascribes teachers and children specific subject positions. The study shows how recurrent ideological dilemmas are used as linguistic resources in order to manage some constantly present contradictions; school-age educare is supposed to be both democratic and child centered, as well as professionally planned and lead. The findings illustrate a homogenous depiction of how school-age educare should be distinguished from traditional and formal schooling and thereby be viewed as a unique but also necessary form of education. As a consequence, an ideal teacher is positioned as someone who is specialized in being actively passive and passively active, and as an expert on children´s learning while children are to be considered as experts in the activities as well. That is, teacher’s professionalism in educare lies in the skills of not being formal and school-like but still being educational in a way that promotes politically approved learning and development.

  • 76.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Kane, Eva
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Adults presence in children’s play in school age childcare2013Conference paper (Other academic)
  • 77.
    Ljusberg, Anna-Lena
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Philgren, Ann
    Stockholm University, Faculty of Social Sciences, Department of Education.
    Rohlin, Malin
    Stockholm University, Faculty of Social Sciences, Department of Special Education.
    Schön, Gudrun
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Hippinen, Anneli
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Education in School-Age Childcare and Learning Studies2011Conference paper (Other academic)
  • 78.
    Lucchese, Riccardo
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Olsson, Jesper
    Luleå University of Technology.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Garcia-Gabin, Winston
    ABB Corporate Research, Västerås.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Energy savings in data centers: A framework for modelling and control of servers’ cooling2017In: IFAC-PapersOnLine, ISSN 1045-0823, E-ISSN 1797-318X, Vol. 50, no 1, p. 9050-9057Article in journal (Refereed)
    Abstract [en]

    Aiming at improving the energy efficiency of air cooled servers in data centers, we devise a novel control oriented, nonlinear, thermal model of the servers that accounts explicitly for both direct and recirculating convective air flows. Instrumental to the optimal co-design of both geometries and cooling policies, we propose an identification methodology based on Computational Fluid Dynamics (CFD) for a generic thermal network of m fans and n electronic components. The performance of the proposed modelling framework is validated against CFD measurements with promising results. We formalize the minimum cooling cost control problem as a polynomially constrained Receding Horizon Control (RHC) and show, in-silico, that the resulting policy is able to efficiently modulate the cooling resources in spite of the unknown future computational and electrical power loads.

  • 79.
    Lundström, T. Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Rahkola, Mattias Brynjell
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Green, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Evaluation of Guiding Device for Downstream Fish Migration with In-field Particle Tracking Velocimetry and CFD2015In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 8, no 3, p. 579-589Article in journal (Refereed)
    Abstract [en]

    The performance of a fish guiding device located just upstream a hydropower plant is scrutinized. The device is designed to redirect surface orientated down-stream migrating fish (smolts) away from the turbines towards a spillway that act as a relatively safe fishway. Particles are added up-stream the device and the fraction particles going to the spillway is measured. A two-frame Particle Tracking Velocimetry algorithm is used to derive the velocity field of the water. The experimental results are compared to simulations with CFD. If the smolts move passively as the particles used in the study the guiding device works very well and some modifications may optimize its performance. In-field Particle Tracking Velocimetry is a suitable technique for the current case and the results compare well with numerical simulations.

  • 80.
    Pavasson, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Johansson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Challenges and opportunities within simulation-driven functional product development and operation: Special Session: Product Development for Through-Life Engineering Services2014In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 22, p. 169-174Article in journal (Refereed)
    Abstract [en]

    The product development process at industrial companies has traditionally focused on hardware-oriented solutions. Business strategies strive towards more service-oriented solutions e.g., functional product business models. In this paper two case studies are developed and the objective is to highlight important challenges and opportunities by implementing a simulation-driven strategy in functional product development and operation. It can be concluded that challenges and opportunities within simulation-driven functional product development and operation are related to both quality and management of the simulations. With the proposed strategies for validation and coupling of the simulations, some of the challenges within functional product development can be overcome.

  • 81.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Xiong, Damiano
    Sveriges Lantbruksuniversitet.
    Nilsson, Michael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Distance- Spanning Technology.
    A modelling methodology for assessing use of datacenter waste heat in greenhouses2017Conference paper (Refereed)
    Abstract [en]

    In Sweden, the number of datacenters establishments are steadily increasing thanks to green, stable and affordable electricity, free air cooling, advantageous energy taxes and well-developed Internet fiber infrastructures. Even though datacenters use a lot of energy, the waste heat that they create is seldom reused. A possible cause is that this waste heat is often low grade and airborne: it is therefore hard to directly inject it into a district heating system without upgrades, which require additional energy and equipment that generate extra costs. One option for reusing this heat without needs for upgrades is to employ it for heating up greenhouses. But assessing the feasibility of this approach by building physical prototypes can be costly, therefore using computer models to simulate real world conditions is an opportunity. However, there is a lack of computer modelling methodologies that can assess the possibility of using waste heat from datacenters in greenhouses in cold climates.

    The objective of this paper is therefore to propose such a methodology and discuss its benefits and drawbacks in comparison with other research studies. This methodology combines computational fluid dynamics, process modelling and control engineering principles into a computer model that constitutes a decision support system to study different waste heat and greenhouse or mushroom house scenarios.

    The paper validates the strategy through a case study in northern Sweden, where we assess the amount of produced waste heat by collecting temperature, relative humidity, and fan speed data for the air discharged from the datacenter.

    The resulting methodology, composed by conducting measurements and computer models, calculations can then be used for other datacenter operators or greenhouse developers to judge whether it is possible or not to build greenhouses using datacenter waste heat.

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  • 82. Wendelborg, Christian
    et al.
    Caspersen, Joakim
    Mordal, Siri
    Ljusberg, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Valenta, Marko
    Bunar, Nihad
    Stockholm University, Faculty of Social Sciences, Department of Child and Youth Studies.
    Lek, læring og ikke-pedagogikk for alle: Nasjonal evaluering av skolefritidsordningen i Norge2018Report (Other academic)
  • 83.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    CFD Simulations Comparing Hard Floor and Raised Floor Configurations in an Air Cooled Data Center2016In: 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malaga, Spain, 11-13 July 2016, s. 450-455, 2016Conference paper (Refereed)
    Abstract [en]

    An increasing number of companies and organisations have started to outsource their data storage. Although the potential of future investments in data centers is prosperous, sustainability is an increasingly important factor. It is important to make sure that the server racks in data centers are sufficiently cooled whereas too much forced cooling leads to economical losses and a waste of energy. Computational Fluid Dynamics (CFD) is an excellent tool to analyze the flow field in data centers. This work aims to examine the performance of the cooling system in a data center using ANSYS CFX. A hard floor configuration is compared to a raised floor configuration. When a raised floor configuration is used, the cold air is supplied into an under-floor space and enters the room through perforated tiles in the floor, located in front of the server racks. The flow inside the main components and the under-floor space is not included in the simulations. Boundary conditions are applied to the sides where the flow goes out of or into the components. The cooling system is evaluated based on a combination of two different performance metrics. Results show that the performance of the cooling system is significantly improved when the hard floor configuration is replaced by a raised floor configuration. The flow field of the air differs in the two cases. It is considered to be improved when the raised floor configuration is used as a result of reduced hot air recirculation around the server racks.

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  • 84.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Comparing Performance Metrics of Partial Aisle Containments in Hard Floor and Raised Floor Data Centers Using CFD2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 8, article id 1473Article in journal (Refereed)
    Abstract [en]

    In data centers, efficient cooling systems are required to both keep the energy consumption as low as possible and to fulfill the temperature requirements. The aim of this work is to numerically investigate the effects of using partial aisle containment between the server racks for hard and raised floor configurations. The computational fluid dynamics (CFD) software ANSYS CFX was used together with the Reynolds stress turbulence model to perform the simulations. Velocity measurements in a server room were used for validation. Boundary conditions and the load of each rack were also retrieved from the experimental facility, implying an uneven load between the racks. A combination of the performance metrics Rack Cooling Index (RCI), Return Temperature Index (RTI) and Capture Index (CI) were used to evaluate the performance of the cooling systems for two supply flow rates at a 100% and 50% of operating condition. Based on the combination of performance metrics, the airflow management was improved in the raised floor configurations. With the supply flow rate set to operating conditions, the RCI was 100% for both raised floor and hard floor setups. The top- or side-cover fully prevented recirculation for the raised floor configuration, while it reduced the recirculation for the hard floor configuration. However, the RTI was low, close to 40% in the hard floor case, indicating poor energy efficiency. With the supply flow rate decreasing with 50%, the RTI increased to above 80%. Recirculation of hot air was indicated for all the containments when the supply rate was 50%, but the values of RCI still indicated an acceptable performance of the cooling system

  • 85.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Comparison of hard floor and raised floor cooling of servers with regards to local effects2018In: IECON 2018: 44th Annual Conference of the IEEE Industrial Electronics Society, 2018Conference paper (Refereed)
  • 86.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Comparison of turbulence models when modeling the airflow in a data center2016Conference paper (Refereed)
  • 87.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 3, article id 644Article in journal (Refereed)
    Abstract [en]

    The worldwide demand on data storage continues to increase and both the number and the size of data centers are expanding rapidly. Energy efficiency is an important factor to consider in data centers since the total energy consumption is huge. The servers must be cooled and the performance of the cooling system depends on the flow field of the air. Computational Fluid Dynamics (CFD) can provide detailed information about the airflow in both existing data centers and proposed data center configurations before they are built. However, the simulations must be carried out with quality and trust. The k–ɛ model is the most common choice to model the turbulent airflow in data centers. The aim of this study is to examine the performance of more advanced turbulence models, not previously investigated for CFD modeling of data centers. The considered turbulence models are the k–ɛ model, the Reynolds Stress Model (RSM) and Detached Eddy Simulations (DES). The commercial code ANSYS CFX 16.0 is used to perform the simulations and experimental values are used for validation. It is clarified that the flow field for the different turbulence models deviate at locations that are not in the close proximity of the main components in the data center. The k–ɛ model fails to predict low velocity regions. RSM and DES produce very similar results and, based on the solution times, it is recommended to use RSM to model the turbulent airflow data centers.

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