Heat Transfer and Pressure Drop in Copper Microchannels

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Title Heat Transfer and Pressure Drop in Microchannels with Different. Inlet Geometries for Laminar and Transitional Flow of Water. Author Darshik Vinay Garach,Student Number 28475705. Supervisors Dr J Dirker and Prof JP Meyer,Degree Master of Engineering Mechanical. Department Mechanical and Aeronautical Engineering. This study consists of an experimental investigation into the fluid flow and heat transfer aspects of. microchannels Rectangular copper microchannels of hydraulic diameters 1 05 mm 0 85 mm and. 0 57 mm were considered Using water as the working fluid heat transfer and pressure drop. characteristics were determined under a constant surface heat flux for different inlet configurations. in the laminar and transitional regimes Three inlet geometries were experimentally investigated a. sudden contraction inlet a bellmouth inlet and a swirl generating inlet The influence of the inlet. conditions on the pressure drop Nusselt number and critical Reynolds number was determined. experimentally Pressure drop results showed good agreement with existing correlations for. adiabatic conditions Diabatic friction factor results for the sudden contraction and bellmouth inlets. were overpredicted when using the friction factor results from literature It is noted that a. relationship between the pressure drop and heat flux existed in the laminar regime where an. increase in the heat input resulted in a decrease in the friction factor The bellmouth inlet condition. showed an enhancement of the heat transfer in the transition regime compared with the sudden. contraction inlet The critical Reynolds number for the onset of transition for the sudden contraction. inlet was found to be approximately 1 950 with a sharp rise to the turbulent regime thereafter The. bellmouth inlet influenced the originating point of the transition regime which commenced at a. Reynolds number of approximately 1 600 A smoother and more gradual increase to the turbulent. regime was observed as an effect of the bellmouth inlet over the sudden contraction inlet The swirl. generating inlet condition produced higher friction factor results in all three flow regimes Transition. occurred at a Reynolds number of approximately 1 500 and the turbulent regime was quickly. reached thereafter The turbulent regime friction factor was found to be significantly higher with the. swirl inlet compared with both the sudden contraction and bellmouth inlets Nusselt numbers. continued to increase until the onset of the transition regime and did not converge to a constant. value as stated in theory Similar enhancement of the transition regime with the bellmouth inlet was. observed for the Nusselt numbers as with the friction factors The initial turbulent regime results. followed the trend of the theory for both the sudden contraction and bellmouth inlet conditions for. most of the data sets with deviation occurring in some of the 0 57 mm test cases The swirl inlet. Nusselt number results were significantly underpredicted by the theory in the early turbulent regime. Keywords microchannel heat transfer pressure drop inlet conditions single phase water. Publications in journals and conferences,Article in related journal. 1 DIRKER J MEYER JP and GARACH DV Inlet flow effects in microchannels in the laminar. transitional and early turbulent flow regimes on single phase heat transfer coefficients and. friction factors Submitted to the International Journal of Heat and Mass Transfer. Reference Number HMT D 13 00415,Conference paper, 1 GARACH DV DIRKER J and MEYER JP Heat transfer and pressure drop in microchannels. with different inlet conditions for water in the laminar and transitional regimes. Proceedings of the 9th International Conference on Heat Transfer Fluid Mechanics and. Thermodynamics HEFAT2012 pp 763 770 16 18 July 2012. Acknowledgements, I would like to thank the following people for their support during my studies.
My parents for their unconditional love and support through the good times and the bad. Your love and guidance have inspired me to do my utmost best and overcome the obstacles. in front of me To my brother and sister whose influence guides me to be a better person I. love you both more than you can imagine, My friends who have supported assisted and guided me throughout my life Thank you for. your support your guidance and your friendship, My colleagues at the University of Pretoria whose company help and guidance I know to be. the reason why I have learnt so much during my studies Thanks for making this part of my. life unforgettable Special thanks to Louw Coetzee for his tremendous partnership during. our collaboration together and to Mduduzi Ntuli for all the assistance and friendship gained. both on and off campus You are good scholars but friends there are no better. My supervisors Dr Jaco Dirker and Prof Josua Meyer whose continuous guidance. assistance enthusiasm and faith in my work have inspired me to do my utmost best. Mr Danie Gouws whose input and help have been crucial in all my experimental work you. are truly an asset to the department and the students Mr Koos Mthombeni for his. continuous assistance and inspiring personality Mr Neels Smith whose guidance and. instruction in the workshop ensured the success of this project. I would like to thank the following people and institutions for their assistance in this study. The funding obtained from the NRF TESP University of Stellenbosch University of Pretoria. SANERI SANEDI CSIR EEDSM Hub and NAC is acknowledged and duly appreciated. Mr Joe de Oliveira of Executive Mould Services Thank you for the manufacturing of the. microchannels used in this study Your assistance over the period of my work has shed a new. light on manufacturing techniques and processes, Dr Suretha Potgieter of the CSIR Manufacturing and Materials division whose assistance. with laser microscopy has been beneficial in the validation of the surface roughness of the. microchannels Thank you for your assistance and your patience. Mr Tony Wynne of the TUT Centre for Advanced Manufacturing for the laser manufacturing. of the micro holes in the test section Thank you for your assistance and input with regard to. my studies,Abstract i,Publications in journals and conferences iii. Acknowledgements iv,List of appendices vii,List of figures vii.
List of tables ix,Nomenclature xi,1 Introduction 1. 1 1 Background 1,1 2 Previous work 2,1 3 The effect of axial heat conduction 13. 1 4 Inlet Conditions 14,1 5 Purpose of the study 15. 1 6 Scope of study 15,1 7 Overview of the thesis 15. 2 Experimental facility 16,2 1 Introduction 16,2 2 Test facility design 16.
2 3 Test section design 20,2 3 1 Microchannel design and construction 21. 2 3 2 Inlet section design and construction 26,2 3 3 System interface components 30. 2 3 4 Microchannel test section assembly 32,2 4 Summary 35. 3 Experimental procedure calibration and data reduction 36. 3 1 Introduction 36,3 2 Experimental procedure 36,3 3 Logging of measurement data 38. 3 4 Equipment calibration and uncertainty 38,3 4 1 Mass flow meter calibration 39.
3 4 2 Thermocouple calibration 39,3 4 3 Pressure transducer calibration 39. 3 4 4 Measurement equipment uncertainties 40,3 5 Data reduction 41. 3 5 1 Friction factor data reduction 41,3 5 2 Heat transfer data reduction 42. 3 5 3 Colburn j factor 44,3 6 Uncertainty analysis of data reduction 44. 3 7 Summary 45,4 Results Friction factor and Nusselt number 46.
4 1 Introduction 46,4 2 Adiabatic results 46,4 3 Diabatic results 52. 4 3 1 Sudden contraction inlet section results 52,4 3 2 Bellmouth inlet section results 58. 4 3 3 Swirl inlet section results 63,4 4 Summary of results 66. 5 Results Analysis and comparison 67,5 1 Introduction 67. 5 2 Friction factor analysis 67,5 3 Nusselt number comparison 71.
5 4 The Colburn j factor 75, 5 4 1 Comparison of j factor of the different inlet conditions 76. 5 4 2 Relationship between the friction factor and the j factor 78. 5 5 Summary of result analysis and comparison 93,6 Summary conclusions and future work 95. 6 1 Summary 95,6 2 Conclusions 96,6 3 Future work 98. 7 References 99,List of appendices, Calculation of the thermophysical properties of water for use in data analysis A. Calibration of thermocouples B, Calibration of the pressure transducer diaphragms C.
Uncertainty analysis D,List of figures, Figure 1 Comparison of semi empirical friction factor correlations for water flowing through a. microchannel of hydraulic diameter 1 mm and an aspect ratio of 1 evaluated at a temperature of. Figure 2 Comparison of semi empirical Nusselt number correlations for the flow of water in a. microchannel of hydraulic diameter 1 mm aspect ratio 1 and a Prandtl number of 7 11. Figure 3 Schematic diagram of microchannel test facility 16. Figure 4 Microchannel base as seen from the top 22. Figure 5 Microchannel lid as seen from below 22, Figure 6 a Pressure port position in test section top left b Inlet pressure port top right c. Exit pressure port bottom right 23, Figure 7 The effect of axial heat conduction on the three test section hydraulic diameters 24. Figure 8 Thermal and hydrodynamic entrance lengths for the 1 05 mm microchannel at different. Reynolds numbers 25, Figure 9 Sudden contraction inlet condition design 27. Figure 10 Bellmouth inlet condition design 28,Figure 11 Swirl inlet condition design 29.
Figure 12 System interface components at the inlet 30. Figure 13 Calming sections to reduce flow inconsistencies perspex calmer left and copper calmer. Figure 14 System interface components at the outlet 31. Figure 15 Flow mixer used at the exit of the microchannel to allow for more accurate temperature. measurements 32, Figure 16 Attachment of thermocouples to the base of the test section 32. Figure 17 Placement of PTFE tape above the base a First layer left b Completion right 33. Figure 18 Securing of lid to the base by means of hexagon screws 33. Figure 19 Assembly diagram of a test section 34, Figure 20 Complete test section ready for experimentation 35. Figure 21 Adiabatic results for the 1 05 mm test section with a sudden contraction inlet 47. Figure 22 Adiabatic results for the 1 05 mm test section with a bellmouth inlet 48. Figure 23 Comparison of the 1 05 mm sudden contraction and bellmouth adiabatic friction factor. results for the transition regime 49, Figure 24 Adiabatic results for the 0 57 mm test section with a sudden contraction inlet 50. Figure 25 Comparison of the 1 05 mm and 0 57 mm sudden contraction adiabatic results 51. Figure 26 Diabatic friction factor results for the 1 05 mm microchannel with a sudden contraction. Figure 27 Nusselt number results for the 1 05 mm microchannel with a sudden contraction inlet 53. Figure 28 Diabatic friction factor results for the 0 85 mm microchannel with a sudden contraction. Figure 29 Nusselt number results for the 0 85 mm microchannel with a sudden contraction inlet 54. Figure 30 Diabatic friction factor results for the 0 57 mm microchannel with a sudden contraction. Figure 31 Nusselt number results for the 0 57 mm microchannel with a sudden contraction inlet 55. Figure 32 Diabatic friction factor results for the 1 05 mm microchannel with a bellmouth inlet 58. Figure 33 Nusselt number results for the 1 05 mm microchannel with a bellmouth inlet 58. Figure 34 Diabatic friction factor results for the 0 85 mm microchannel with a bellmouth inlet 59. Figure 35 Nusselt number results for the 0 85 mm microchannel with a bellmouth inlet 59. Figure 36 Diabatic friction factor results for the 0 57 mm microchannel with a bellmouth inlet 60. Figure 37 Nusselt number results for the 0 57 mm microchannel with a bellmouth inlet 60. Figure 38 Diabatic friction factor results for the 1 05 mm microchannel with a swirl inlet 63. Figure 39 Nusselt number results for the 1 05 mm microchannel with a swirl inlet 63. Figure 40 Diabatic friction factor results for the 1 05 mm microchannel for all three inlet conditions. and heat fluxes 68, Figure 41 Magnified view of transition regime in 1 05 mm microchannel for all three inlet. conditions and heat fluxes Legends of Figure 40 to be used The T symbols indicates the beginning. of transition 68, Figure 42 Diabatic friction factor results for the 0 85 mm microchannel for two inlet conditions and.
three heat fluxes 69, Figure 43 Diabatic friction factor results for the 0 57 mm microchannel for two inlet conditions and. three heat fluxes 70, Figure 44 Nusselt number results for the 1 05 mm microchannel for all three inlet conditions and. heat fluxes The T symbol indicates transition 72, Figure 45 Nusselt number results for the 0 85 mm microchannel for the two inlet conditions and. three heat fluxes 73, Figure 46 Nusselt number results for the 0 57 mm microchannel for the two inlet conditions and. three heat fluxes 74, Figure 47 Colburn j factor results for the 1 05 mm microchannel for the three inlet conditions and.
heat fluxes 76, Figure 48 Colburn j factor results for the 0 85 mm microchannel for the two inlet conditions and. three heat fluxes 77, Figure 49 Colburn j factor results for the 0 57 mm microchannel for the two inlet conditions and. three heat fluxes 77, Figure 50 Comparison of 1 05 mm sudden contraction inlet friction factor and Colburn j factor. Heat Transfer and Pressure Drop in Microchannels with Different Inlet Geometries for Laminar and Transitional Flow of Water by D V Garach Submitted in the full fulfilment of the requirements of the degree

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