臺灣博碩士論文加值系統

As cost-effective and manufacturing advantages, plane plate heat sink has been widely used for electronic-cooling industry. However, it is not an easy task to develop a proper heat sink perfectly fitting into electronic system. Not only rating problem, but also sizing problem is an essential part of system packaging, and definitely worth to be addressed within integration of multi-disciplines.

Analyses have been performed to predict pressure drop and heat transfer behaviors in plane plate heat sink. It takes into account of many design variables, including heat sink geometry, material property, heat source size and location, environment condition, and coolant pumping constraint…etc. The utilization of existing correlations for friction factor and Nusselt number was investigated. The study indicated that novel all-in-one asymptotic solutions provided by present author can predict pressure drop and heat transfer performance of fin array within acceptable accuracy over laminar, transition and turbulent flow, saying Re<5000. The model assumes heat source in contact with heat sink base that cooled by equivalent convective heat transfer coefficient specified over opposite side, and adiabatic for the rest surfaces. Method of separation of variables was used to obtain exact solution in form of infinite series.

Compared to experimental data, pressure drop predicted by present model is within -14% to +9%. Prediction discrepancy of overall thermal resistance between present model and Flotherm model is within -3% to 5%.

By the aid of self-development numerical program, the influences of design variables and performance limitation of heat sink have been systematically examined. The results illustrated that specifying operation point of heat sink for pressure drop and airflow rate is an essential part of optimization for heat sink performance. The minimal achievable overall thermal resistance is limited by given pressure drop and airflow rate while heat sink is subjected to specified frontal area, heat source size/location, environmental conditions and variation range of design variables. There exists critical pressure drop and airflow rate to achieve target heat transfer performance. It is bare possible to achieve design goal if either specified pressure drop or airflow rate is less than those critical value.

Compensation factor has been defined for quantitatively evaluating the location effect of heat source with variations in base thickness, effective heat transfer coefficient and heat source size. The study of compensation factor indicated that, increasing heat transfer coefficient and reducing heat source size alleviates the location effect of heat source, or obtains a lower compensation factor. On the other hand, as increase of base thickness, compensation curve rise up when base is thin, then fall down and reach a valley when dimensionless thickness is over than 0.6~0.7.

ABSTRACT I
ACKNOWLEDGEMENT II
誌謝 II
CONTENTS III
FIGURE LIST V
TABLE LIST IX
NOMENCLATURE X
1. INTRODUCTION 1
1.1 Background 1
1.2 Literature review 2
1.3 Objective of this work 13
2. THERMAL PERFORMANCE AND PRESSURE DROP MODELLING 14
2.1 Basic concepts for modelling 14
2.2 Major assumptions 14
2.3 Transition flow 15
2.4 Pressure drop analysis 16
2.4.1 Friction factor 17
2.4.2 Loss coefficients 23
2.5 Convective heat transfer analysis 25
2.6 Temperature dependent fluid properties 32
2.7 Fin efficiency and effective heat transfer coefficients 33
2.8 Base heat spreading model 34
2.9 Constant pressure drop as constraint 39
2.10 Flow chart of numerical programs 40
3. EXPERIMENT AND NUMERICAL ANALYSIS 43
3.1 Objective 43
3.2 Experimental plan 43
3.3 Experimental set-up & data reduction 45
3.4 Numerical analysis 46
4. RESULTS AND DISCUSSION 47
4.1 Confidence comparison 47
4.1.1 Pressure drop comparison among different models and Kays & London data 47
4.1.2 Comparison of pressure drop prediction and experimental data 51
4.1.3 Comparison of convective heat transfer prediction and Kays & London data 61
4.1.4 Comparison of heat transfer predictions between present model and Flotherm 67
4.2 Behaviour of design parameters 72
4.2.1 Effects of heat sink geometric variables and environmental parameters 72
4.2.2 Effects of heat source 83
4.3 Performance limitation under given frontal area 90
4.3.1 Pressure head is a constraint 90
4.3.2 Constant airflow rate is a constraint 94
4.3.3 Critical pressure drop and airflow in order to obtain desired thermal resistance 97
5. CONCLUSION 98
REFERENCES 100
APPENDIX A: CORRELATION OF AIR PROPERTIES 103
APPENDIX B: EXPERIMENTAL DATA OF PRESSURE DROP AND AIRFLOW RATE FOR TEST UNITS 104
APPENDIX C: COMPARISON OF FRICTION FACTOR AMONG MODELS & EXPERIMENTAL DATA 106
APPENDIX D: COMPARISON OF NUSSELT NUMBER AMONG MODELS & EXPERIMENTAL DATA 109

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