Pub Date : 1900-01-01DOI: 10.1109/THETA.2008.5190977
C. Lasance
This paper discusses the non-trivial issues associated with calculating the heat spreading from a heat source into a thermally conducting body subject to boundary conditions in steady state. It is argued that problems arise with the interpretation of heat spreading effects due to a misconception about the meaning of often-quoted flux limits and especially the physical meaning of thermal resistance. The usefulness of a number of approaches that are generally in use to analyse heat spreading effects is discussed and it is shown that the popular series resistance approach has severe limitations. A number of test cases are covered in detail and the results testify to this assertion.
{"title":"The practical usefulness of various approaches to estimate heat spreading effects","authors":"C. Lasance","doi":"10.1109/THETA.2008.5190977","DOIUrl":"https://doi.org/10.1109/THETA.2008.5190977","url":null,"abstract":"This paper discusses the non-trivial issues associated with calculating the heat spreading from a heat source into a thermally conducting body subject to boundary conditions in steady state. It is argued that problems arise with the interpretation of heat spreading effects due to a misconception about the meaning of often-quoted flux limits and especially the physical meaning of thermal resistance. The usefulness of a number of approaches that are generally in use to analyse heat spreading effects is discussed and it is shown that the popular series resistance approach has severe limitations. A number of test cases are covered in detail and the results testify to this assertion.","PeriodicalId":414963,"journal":{"name":"2008 Second International Conference on Thermal Issues in Emerging Technologies","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130565114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1109/theta.2008.5167174
A. Bontemps, J. Ribeiro, S. Ferrouillat, J. Gruss, O. Soriano, Biran Wang
This paper describes an experimental study on the convective heat transfer of SiO2/water nanofluids inside a circular tube with imposed wall temperature. To our knowledge, very few papers have been published with temperature boundary conditions and none in cooling conditions. The experimental apparatus is described which allows us to measure local wall temperatures as well as fluid inlet/outlet temperatures. The flow regimes range from laminar to turbulent. The Reynolds and Nusselt numbers are deduced by using thermal conductivity and viscosity values measured with the same temperature conditions as those in the tests. The shear rate influence is also taken into account in the viscosity determination.The results indicate that the general trend of standard correlations is respected. However, the heat transfer coefficient values are higher than observed with pure water. An explanation is proposed.
{"title":"Experimental study of convective heat transfer and pressure loss of SiO2/water nanofluids Part 1: Nanofluid characterization - Imposed wall temperature","authors":"A. Bontemps, J. Ribeiro, S. Ferrouillat, J. Gruss, O. Soriano, Biran Wang","doi":"10.1109/theta.2008.5167174","DOIUrl":"https://doi.org/10.1109/theta.2008.5167174","url":null,"abstract":"This paper describes an experimental study on the convective heat transfer of SiO2/water nanofluids inside a circular tube with imposed wall temperature. To our knowledge, very few papers have been published with temperature boundary conditions and none in cooling conditions. The experimental apparatus is described which allows us to measure local wall temperatures as well as fluid inlet/outlet temperatures. The flow regimes range from laminar to turbulent. The Reynolds and Nusselt numbers are deduced by using thermal conductivity and viscosity values measured with the same temperature conditions as those in the tests. The shear rate influence is also taken into account in the viscosity determination.The results indicate that the general trend of standard correlations is respected. However, the heat transfer coefficient values are higher than observed with pure water. An explanation is proposed.","PeriodicalId":414963,"journal":{"name":"2008 Second International Conference on Thermal Issues in Emerging Technologies","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124453093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1109/THETA.2008.5167160
M. Baelmans, F. Rogiers, J. Van Eyndhoven, W. Voets
Thermodynamic efficiencies based on the first and second law of thermodynamics are assessed for their use in the design of recuperators in small-sized gas turbines. It is shown that the first and second law cycle efficiency as well as the Witte-Shamsundar efficiency for heat exchangers show a similar dependency on the heat exchanger pressure drops. This results in design relations for hydraulic diameter ratios and their related number of channels ratio. Further, it is shown that the Witte-Shamsundar efficiency focusing on heat exchanger inlet temperatures only can be used as a good approximation for the overall optimal recuperator design when also pressure drops over the recuperator are accounted for. However the approximation deteriorates with higher heat exchanger mass flow density and lower compressor ratio as well as with decreasing turbine inlet temperature ratio. Deviations from the full cycle efficiency considerations are assessed. It is concluded that the use of the Witte-Shamsundar efficiency for optimization of recuperators in small-sized applications like the 1.5 kW PowerMems gas turbine needs careful assessment.
{"title":"Optimal micro channel recuperators for small-sized gas turbines","authors":"M. Baelmans, F. Rogiers, J. Van Eyndhoven, W. Voets","doi":"10.1109/THETA.2008.5167160","DOIUrl":"https://doi.org/10.1109/THETA.2008.5167160","url":null,"abstract":"Thermodynamic efficiencies based on the first and second law of thermodynamics are assessed for their use in the design of recuperators in small-sized gas turbines. It is shown that the first and second law cycle efficiency as well as the Witte-Shamsundar efficiency for heat exchangers show a similar dependency on the heat exchanger pressure drops. This results in design relations for hydraulic diameter ratios and their related number of channels ratio. Further, it is shown that the Witte-Shamsundar efficiency focusing on heat exchanger inlet temperatures only can be used as a good approximation for the overall optimal recuperator design when also pressure drops over the recuperator are accounted for. However the approximation deteriorates with higher heat exchanger mass flow density and lower compressor ratio as well as with decreasing turbine inlet temperature ratio. Deviations from the full cycle efficiency considerations are assessed. It is concluded that the use of the Witte-Shamsundar efficiency for optimization of recuperators in small-sized applications like the 1.5 kW PowerMems gas turbine needs careful assessment.","PeriodicalId":414963,"journal":{"name":"2008 Second International Conference on Thermal Issues in Emerging Technologies","volume":"376 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116635351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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