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Investigation of Thermal Performance of Cylindrical Heatpipes Operated with Nanofluids
KTH, School of Industrial Engineering and Management (ITM).
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanofluids as an innovative class of heat transfer fluids created by dispersing nanometre-sizedmetallic or non-metallic particles in conventional heat transfer fluids displayed the potential toimprove the thermophysical properties of the heat transfer fluids. The main purpose of this study is toinvestigate the influence of the use of nanofluids on two-phase heat transfer, particularly on thethermal performance of the heat pipes. In the first stage, the properties of the nanofluids were studied,then, these nanofluids were used as the working fluids of the heat pipes. The thermal performance ofthe heat pipes when using different nanofluids was investigated under different operating conditionsexperimentally and analytically. The influences of the concentration of the nanofluids, inclinationangles and heat loads on the thermal performance and maximum heat flux of the heat pipes wereinvestigated.This study shows that the thermal performance of the heat pipes depends not only on thermophysicalproperties of the nanofluids but also on the characteristics of the wick structure through forming aporous coated layer on the heated surface. Forming the porous layer on the surface of the wick at theevaporator section increases the wettability and capillarity and also the heat transfer area at theevaporator of the heat pipes.The thermal performance of the heat pipes increases with increasing particle concentration in all cases,except for the heat pipe using 10 wt.% water/Al2O3 nanofluid. For the inclined heat pipe, irrespectiveof the type of the fluid used as the working fluid, the thermal resistance of the inclined heat pipes waslower than that of the heat pipes in a horizontal state, and the best performance was observed at theinclination angle of 60o, which is in agreement with the results reported in the literature. Otheradvantages of the use of nanofluids as the working fluids of the heat pipes which were investigated inthis study were the increase of the maximum heat flux and also the reduction of the entropy generationof the heat pipes when using a nanofluid.These findings revealed the potential for nanofluids to be used instead of conventional fluids as theworking fluid of the heat pipes, but the commercialization of the heat pipes using nanofluids for largescale industrial applications is still a challenging question, as there are many parameters related to thenanofluids which are not well understood.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 103
Series
TRITA-REFR, ISSN 1102-0245 ; 17/01
Keywords [en]
Nanofluid, heat pipe, thermal resistance, heat transfer coefficient, evaporator, condenser, wick, porous layer, heat flux, inclination angle, thermal conductivity, viscosity
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-202566ISBN: 978-91-7729-291-3 (print)OAI: oai:DiVA.org:kth-202566DiVA, id: diva2:1077524
Public defence
2017-03-17, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20170228

Available from: 2017-02-28 Created: 2017-02-28 Last updated: 2017-03-01Bibliographically approved
List of papers
1. Thermal properties and rheological behavior of water based Al2O3 nanofluid as a heat transfer fluid
Open this publication in new window or tab >>Thermal properties and rheological behavior of water based Al2O3 nanofluid as a heat transfer fluid
2014 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 53, p. 227-235Article in journal (Refereed) Published
Abstract [en]

An experimental investigation and theoretical study of thermal conductivity and viscosity of Al2O3/water nanofluids are presented in this article. Various suspensions containing Al2O3 nanoparticles were tested in concentration ranging from 3% to 50% in mass and temperature ranging from 293K to 323K. The results reveal that both the thermal conductivity and viscosity of nanofluids increase with temperature and particle concentration accordingly while the increase in viscosity is much higher than the increase in thermal conductivity. The thermal conductivity and viscosity enhancement are in the range of 1.1-87% and 18.1-300%, respectively. Moreover, the results indicate that the thermal conductivity increases nonlinearly with concentration, but, linearly with the increase in temperature. In addition, the experimental results are compared with some existing correlations from literature and some modifications are suggested. Finally, the average heat transfer coefficient at different basis of comparisons including equal Reynolds number, fluid velocity and pumping power is studied based on the experimental thermal conductivity and viscosity in fully developed laminar and turbulent flow regimes. It is found that equal Reynolds number as a basis of comparison is highly misleading and equal pumping power can be used to study the advantage of using nanofluid instead of the base fluid.

Keywords
Al2O3 nanoparticle, Heat transfer, Nanofluid, Thermal conductivity, Viscosity
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-142818 (URN)10.1016/j.expthermflusci.2013.12.013 (DOI)000331422700025 ()2-s2.0-84892546097 (Scopus ID)
Note

QC 20140312

Available from: 2014-03-12 Created: 2014-03-12 Last updated: 2017-12-05Bibliographically approved
2. Experimental investigation on thermo-physical properties of copper/diethylene glycol nanofluids fabricated via microwave-assisted route
Open this publication in new window or tab >>Experimental investigation on thermo-physical properties of copper/diethylene glycol nanofluids fabricated via microwave-assisted route
Show others...
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 65, no 1-2, p. 158-165Article in journal (Refereed) Published
Abstract [en]

This study investigates the fabrication, thermal conductivity and rheological characteristics evaluation of nanofluids consisting of copper nanoparticles in diethylene glycol base liquid. The fabricated Cu nanofluids displayed enhanced thermal conductivity over the base liquid. Copper nanoparticles were directly formed in diethylene glycol using microwave-assisted heating, which provides uniform heating of reagents and solvent, accelerating the nucleation of metal clusters, resulting in monodispersed nanostructures. Copper nanoparticles displayed an average primary particle size of 75 ± 25 nm from SEM micrographs, yet aggregated to form large spherical particles of about 300 nm. The physicochemical properties including thermal conductivity and viscosity of nanofluids were measured for the nanofluids with nanoparticle concentration between 0.4 wt% and 1.6 in the temperature range of 20-50 C. Proper theoretical correlations/models were applied to compare the experimental results with the estimated values for thermal conductivity and viscosity of nanofluids. For all cases, thermal conductivity enhancement was higher than the increase in viscosity showing the potential of nanofluids to be utilized as coolant in heat transfer applications. A thermal conductivity enhancement of ∼7.2% was obtained for nanofluids with 1.6 wt% nanoparticles while maximum increase in viscosity of ∼5.2% was observed for the same nanofluid.

Keywords
Copper nanoparticles, Microwave synthesis, Nanofluids, Thermal conductivity, Viscosity
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-142326 (URN)10.1016/j.applthermaleng.2014.01.003 (DOI)000335099100017 ()2-s2.0-84893161468 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 228882
Note

QC 20140305

Available from: 2014-03-05 Created: 2014-02-28 Last updated: 2017-12-05Bibliographically approved
3. Thermal and rheological properties of micro- and nanofluids of copper in diethylene glycol: as heat exchange liquid
Open this publication in new window or tab >>Thermal and rheological properties of micro- and nanofluids of copper in diethylene glycol: as heat exchange liquid
Show others...
2013 (English)In: Nanoscale Thermoelectric Materials: Thermal and Electrical Transport, and Applications to Solid-state Cooling and Power Generation, Cambridge: Cambridge Scholars Publishing, 2013, , p. 6p. 165-170Conference paper, Published paper (Refereed)
Abstract [en]

This study reports on the fabrication of nanofluids/microfluids (NFs/MFs) with experimental and theoretical investigation of thermal conductivity (TC) and viscosity of diethylene glycol (DEO) base NFs/MFs containing copper nanoparticles (Cu NPs) and copper microparticles (Cu MPs). For this purpose, Cu NPs (20-40 nm) and Cu MPs (0.5-1.5 urn) were dispersed in DEG with particle loading between 1 wt% and 3 wt%. Ultrasonic agitation was used for dispersion and preparation of stable NFs/MFs, and thus the use of surfactants was avoided. The objectives were investigation of impact of size of Cu particle and concentration on TC and viscosity of NFs/MFs on DEG as the model base liquid. The physicochemical properties of all particles and fluids were characterized by using various techniques including Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) techniques. Fourier Transform Infrared Spectroscopy (FTIR) analysis was performed to study particles' surfaces. NFs and MFs exhibited a higher TC than the base liquid, while NFs outperformed MFs showing a potential for their use in heat exchange applications. The TC and viscosity of NFs and MFs were presented, along with a comparison with values from predictive models. While Maxwell model was good at predicting the TC of MFs, it underestimated the TC of NFs, revealing that the model is not directly applicable to the NF systems.

Place, publisher, year, edition, pages
Cambridge: Cambridge Scholars Publishing, 2013. p. 6
Series
Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1543
Keywords
Copper, Nanofluid, diethylene glycol, Thermal conductivity, Viscosity
National Category
Nano Technology
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-124180 (URN)10.1557/opl.2013.675 (DOI)2-s2.0-84893372647 (Scopus ID)9781605115207 (ISBN)
Conference
2013 MRS Spring Meeting; San Francisco, CA; United States; 1 April 2013 through 5 April 2013
Projects
NanoHex
Funder
EU, FP7, Seventh Framework Programme
Note

QC 20140225

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-03-02Bibliographically approved
4. Thermal performance of screen mesh heat pipe with Al2O3 nanofluid
Open this publication in new window or tab >>Thermal performance of screen mesh heat pipe with Al2O3 nanofluid
Show others...
2015 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 66, p. 213-220Article in journal (Refereed) Published
Abstract [en]

This study presents the effect of Al2O3 nanofluid (NF) on thermal performance of screen mesh heat pipe in cooling applications. Three cylindrical copper heat pipes of 200 mm length and 6.35 mm outer diameter containing two layers of screen mesh were fabricated and tested with distilled water and water based Al2O3 NF with mass concentrations of 5% and 10% as working fluids. To study the effect of NF on the heat pipes thermal performance, the heat input is increased and then decreased consecutively and the heat pipes surface temperatures are measured at steady state conditions. Results show that using 5 wt.% of Al2O3 NF improves the thermal performance of the heat pipe for increasing and decreasing heat fluxes compared with distilled water, while utilizing 10 wt.% of Al2O3 NF deteriorates the heat pipe thermal performance. For heat pipe with 5 wt.% Al2O3 NF the reduction in thermal resistance of the heat pipe is found to be between 6% and 24% for increasing and between 20% and 55% for decreasing heat fluxes, while the thermal resistance increased between 187% and 206% for increasing and between 155% and 175% for decreasing steps in heat pipe with 10 wt.% of Al2O3 NF.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
nanofluid, alumina nanoparticle, thermal conductivity, heat pipe
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-166178 (URN)10.1016/j.expthermflusci.2015.03.024 (DOI)000356129000021 ()2-s2.0-84928125292 (Scopus ID)
Note

Qc 20150507

Available from: 2015-05-04 Created: 2015-05-04 Last updated: 2017-12-04Bibliographically approved
5. Thermal performance of inclined screen mesh heat pipes using silver nanofluids
Open this publication in new window or tab >>Thermal performance of inclined screen mesh heat pipes using silver nanofluids
2015 (English)In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 67, p. 14-20Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-202527 (URN)10.1016/j.icheatmasstransfer.2015.06.009 (DOI)000362143700003 ()
Note

QC 20170228

Available from: 2017-02-25 Created: 2017-02-25 Last updated: 2017-11-29Bibliographically approved
6. Improvement of heat transfer characteristics of cylindrical heat pipe by using SiC nanofluids
Open this publication in new window or tab >>Improvement of heat transfer characteristics of cylindrical heat pipe by using SiC nanofluids
2015 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 90, p. 127-135Article in journal (Refereed) Published
Abstract [en]

An experimental study was performed to investigate the thermal performance of heat pipes using SiC/water nanofluid as the working fluid. Four cylindrical copper heat pipes containing two layers of screen mesh were fabricated and tested with water and water based SiC nanofluids with nanoparticle mass concentrations of 0.35%, 0.7% and 1.0% as working fluids. SiC nanofluids properties and characteristics are evaluated and its effects on thermal performance improvement of screen mesh heat pipes at different concentrations and inclination angles are investigated. Experimental results show that nanofluid improves the performance of the heat pipes and the thermal resistance of the heat pipe with SiC nanofluid decreases with increasing nanoparticle concentration. Thermal resistance reduction of heat pipes by 11%, 21% and 30% was observed with SiC nanofluids containing 0.35 wt.%, 0.7 wt.% and 1.0 wt.% SiC nanoparticles as compared with water. In addition, it is revealed that the inclination angle has remarkable influence on the thermal performance of the heat pipes and the lowest thermal resistance belongs to the inclination angle of 60 in all concentrations. The present investigation indicates that the maximum heat removal capacity of the heat pipe increases by 29% with SiC nanofluids at nanoparticle mass concentration of 1.0 wt.%.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Heat pipe, Nanofluid, Thermal resistance, Inclination, Screen mesh
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-177937 (URN)10.1016/j.applthermaleng.2015.07.004 (DOI)000364246500014 ()2-s2.0-84937441415 (Scopus ID)
Note

QC 20151202

Available from: 2015-12-02 Created: 2015-11-30 Last updated: 2017-12-01Bibliographically approved
7. An investigation of thermal performance improvement of a cylindrical heat pipe using Al2O3 nanofluid
Open this publication in new window or tab >>An investigation of thermal performance improvement of a cylindrical heat pipe using Al2O3 nanofluid
2016 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, p. 1-11Article in journal (Refereed) Published
Abstract [en]

In this study, effect of Al2O3 nanofluid on thermal performance of cylindrical heat pipe is investigated. An analytical model is employed to study the thermal performance of the heat pipe utilizing nanofluid and the predicted results are compared with the experimental results. A substantial change in the heat pipe thermal resistance, effective thermal conductivity and entropy generation of the heat pipe is observed when using Al2O3 nanofluid as a working fluid. It is found that entropy generation in the heat pipe system decreases when using a nanofluid due to the lower thermal resistance of the heat pipe which results in an improved thermal performance. It is shown that the proposed model is in reasonably good agreement with the experimental results and can be used as a fast technique to explore various features of thermal characteristics of the nanofluid based heat pipe.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Aluminum, Entropy, Heat resistance, Nanofluidics, Thermal conductivity, Effective thermal conductivity, Entropy generation, Fast techniques, Nanofluids, Pipe system, Thermal characteristics, Thermal Performance, Working fluid, Heat pipes
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-197123 (URN)10.1007/s00231-016-1871-9 (DOI)2-s2.0-84979240852 (Scopus ID)
Note

QC 20161214

Available from: 2016-12-14 Created: 2016-11-30 Last updated: 2017-11-29Bibliographically approved
8. Entropy generation analysis of cylindrical heat pipe using nanofluid
Open this publication in new window or tab >>Entropy generation analysis of cylindrical heat pipe using nanofluid
2015 (English)In: Thermochimica Acta, ISSN 0040-6031, E-ISSN 1872-762X, Vol. 610, p. 37-46Article in journal (Refereed) Published
Abstract [en]

Thermal performance of cylindrical heat pipe with nanofluid is studied based on the laws of thermodynamics. The objective of the present work is to investigate nanofluids effect on different sources of entropy generation in heat pipe caused by heat transfer between hot and cold reservoirs and also frictional losses and pressure drop in the liquid and vapor flow along heat pipe. An analytical study was performed to formulate all sources of entropy generation and the predicted results are compared with experimental ones. Cylindrical miniature grooved heat pipes of 250 mm length and 6.35 mm outer diameter were fabricated and tested with distilled water and water based TiO2 and Al2O3 nanofluids at different concentrations as working fluids. Analytical and experimental results revealed that the entropy generation in heat pipes decreases when nanofluids are used as working fluids instead of basefluid which results in improved thermal performance of the heat pipes with nanofluids.

Keywords
Heat pipe, Nanofluid, Thermodynamics, Entropy generation, Thermal resistance
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-169951 (URN)10.1016/j.tca.2015.04.028 (DOI)000355707700006 ()2-s2.0-84929461189 (Scopus ID)
Note

QC 20150626

Available from: 2015-06-26 Created: 2015-06-25 Last updated: 2017-12-04Bibliographically approved

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