臺灣博碩士論文加值系統

在本研究中，已成功地發展出一套新修正暫態液晶量測方法來探討矩型渠道中不加裝與加裝散熱座之熱流特性。同時，也針對此類問題的局部及平均有效熱流特性做一系列參數研究，這些影響參數與情況包括渠道入口之空氣預熱溫度，流速及散熱座種類。
從熱傳方面考量，渠道入口之空氣預熱溫度對於散熱座之有效局部和平均熱傳係數沒有顯著的影響；而有效局部及平均熱傳係數則隨著流速增加或矩形渠道之孔隙率降低而遞增。在特定入口流速下，完全限制和無限制之散熱座分別具有最大及最小的有效平均熱傳係數；在不同流速下，本研究針對各類型被限制散熱座提出一條新的平均有效熱傳係數經驗公式。另外，亦針對散熱座被限制空間而產生之熱傳增益，提出了兩個校正係數K1和K2。對於局部熱傳特性，在研究中發現：無限制散熱座之局部熱傳係數沿著流向而遞減，其最大熱傳出現在散熱座入口區域；而部分與完全限制散熱座之局部熱傳係數首先從散熱座入口處遞增到 X=0.1-0.15處，然後再沿著流向而遞減，其最大局部熱傳通常出現於X=0.1-0.15區間。
從流阻方面考量，整個渠道壓降則隨著流速增加或渠道之孔隙率降低而遞增；在特定入口流速下，完全限制和無限制之散熱座分別具有最大及最小的壓降。
最後，本實驗更進一步引入了一個熱傳增益量j/f 的觀念。根據實驗數據發現：對於特定的散熱座，j/f值幾乎與雷諾數無關；對於各類型的散熱座，完全限制與無限制之散熱座分別具有最大及最小的j/f值，其比值分別為0.0603及0.0124。

A series of experimental investigations with a new modified transient liquid crystal method on the studies related to the fluid flow and heat transfer characteristics in a channel installed without and with a heat sink have been successfully performed. The parametric studies on the local and average effective heat transfer characteristics for confined heat sinks have been explored. The influencing parameters and conditions include air preheating temperature at channel inlet(ΔT), flow velocity (V) and heat sink types.
From the thermal aspect, the effect of the air preheating temperature on local and average effective heat transfer coefficients of confined heat sinks is not significant. The local and average effective heat transfer coefficients increase with increasing flow velocity. The average effective heat transfer coefficient increases with decreasing channel porosity; the highest and lowest average effective heat transfer coefficients can be found for fully-confined and unconfined heat sinks at a specific channel inlet velocity, respectively. A new empirical correlation of average effective heat transfer coefficient for confined heat sinks with various flow velocities is proposed. In addition, two correction factors of K1 and K2 representing average heat transfer enhancement due the confinement effect of confined heat sinks are proposed. The local heat transfer coefficient gradually decreases along the streamwise direction for unconfined heat sinks; and the maximum heat transfer is generally existed around the entrance region of unconfined heat sinks; while, for partially-confined and fully-confined heat sinks, the heat transfer coefficient increases from the entrance region of the confined heat sink to X=0.1-0.15 and then gradually decreases along the streamwise direction. A maximum heat transfer is generally existed around X=0.10-0.15 for confined cases.
From the frictional aspect, the overall channel pressure drop increases with increasing flow velocity or decreasing channel porosity; the highest and lowest pressure drops can be found for fully-confined and unconfined heat sinks at a specific channel inlet velocity, respectively.
Finally, a concept of the amount of enhanced heat transfer (AEHT) is introduced and defined as the ratio of j/f. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink. The maximum and minimum j/f ratios are 0.0603 and 0.0124 for fully-confined and unconfined heat sinks, respectively.

ABSTRACT i
ACKNOWLEDGMENTS iii
TABLE OF CONTENTS iv
LIST OF TABLES viii
LIST OF FIGURES ix
NOMENCLATURE xv
CHAPTER 1 INTRODUCTION 1
1.1 RATIONALE 1
1.2 LITERATURE SURVEY 2
1.2.1 Heat Sink 2
1.2.2 Transient Liquid Crystal Method 4
1.3 RESEARCH OBJECTIVES 7
1.4 THESIS ORGANIZATION 8
CHAPTER 2 THE EXPERIMENTS 10
2.1 DESCRIPTION OF EXPERIMENTAL FACILITIES 10
2.1.1 Air Supply Facilities 10
2.1.2 Test Section 11
2.1.3 Heat Sinks 12
2.1.4 Image Capture System 12
2.1.5 Apparatus and Instrumentation 13
2.2 DATA ACQUISITION AND CONTROL 14
2.3 EXPERIMENTAL PROCEDURE 15
(A) Starting Procedure 15
(B) Shutdown Procedure 16
2.4 METHOD OF DATA REDUCTION 17
2.4.1 Evaluation of Heat Transfer Coefficient of HeatSink with Traditional TransientLiquidCrystalTechnique 17
2.4.2 Evaluation of Heat Transfer Coefficient of Heat Sink
with a Modified Transient Liquid Crystal Technique 20
(A) Model (I) 20
(B) Model (II) 21
(C) Model (III) 21
(D) Model (IV) 21
2.5 TEST MATRIX 24
2.6 UNCERTAINTY ANALYSIS 24
CHAPTER 3 RESULTS AND DISCUSSION 57
3.1 HEAT TRANSFER IN A RECTANGULAR HOLLOW CHANNEL 57
3.1.1 DEFINITION OF HEAT TRANSFER PARAMETERS 58
TABLE OF CONTENTS (cont'd)
Page
3.1.2 TRANSIENT VARIATION OF AIR TEMPERATURE AT CHANNEL
IMLET 58
3.1.3 LOVCAL HEAT TRANSFER CHARACTERISTICS 59
3.1.4 AVERAGE HEAT TRANSFER CHARACTERISTICS 60
3.2 HEAT TRANSFER IN A CHANNEL INSTALLED WITH HEAT SINKS 61 3.2.1 DEFINITION OF HEAT TRANSFER PARAMETERS 62 3.2.2 TRANSIENT VARIATION OF AIR TEMPERATURE AT CHANNEL
INLET 62
3.2.3 AVERAGE HEAT TRANSFER CHARACTERISTICS 63
(A) Parametric Studies 63
(a) Effect of Air Preheating Temperature 64
(b) Effect of Flow Velocity 64
(c) Effect of Heat Sink Type 66
(B) New Correction Factors for Confined Heat Sinks 69
3.2.4 LOCAL HEAT TRANSFER CHARACTERISTICS 70
(A) Distribution of Local Heat Transfer Parameters 71
(B) Parametric Studies 72
(a) Effect of Air Preheating Temperature 72
(b) Effect of Flow Velocity 73
(c) Effect of Heat Sink Type 73
3.2.5 OVERALL CHANNEL PRESSURE DROP 74
(A) Parametric Studies 74
(B) Correlations of the Amount of Enhanced Heat Transfer 75
CHAPTER 4 CONCLUSIONS AND RECOMMENDATIONS 137
4.1 CONCLUSIONS 137
4.2 RECOMMENDATIONS 140
REFERENCES 141
APPENDIX A COLOR CALIBRATION OF LIQUID CRYSTALS WITH
TEMPERATURE 144
APPENDIX B EMPIRICAL CORRELATIONS FOR AIR PROPERTIES 146
APPENDIX C DETERMINTION OF THERMAL CONDUCTIVITY OF CHANNEL
WALL MATERIAL 150
APPENDIX D UNCERTAINTIES OF EXPERIMENTAL DATA 154

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