||Investigation of Silver Nano-fluid Heat Pipe Thermal Performance
||Department of Mechanical and Electro-Mechanical Engineering
||The purpose of this thesis is to study the effects of silver nano-fluids on grooved heat pipe and sintered heat pipe thermal performance. The nano-fluid used in this study is an aqueous solution of 10 nm and 35nm diameter silver nanoparticles. The experiment was performed to measure the temperature distribution and compare the heat pipe thermal resistance using nano-fluid and DI-water. The experimental result of grooved heat pipe showed that thermal resistance decreased 10%~80% compared to DI-water at an input power of 30~60W. And the measured results also show that the thermal resistances of the heat pipe decrease as the silver nanoparticle size and concentration increase. The experimental result of sintered heat pipe, the nano-fluids filled heat pipe temperature distribution demonstrated that the temperature difference decreased 0.56~0.65℃ compared to DI-water at an input power of 30~50W. And the nano-fluid as working medium in heat pipe can up to 70W and is higher than pure water about 20W.
In addition, the characteristics of silver nano-fluid concentrations and sizes on copper plate surface wettability were investigated. The experimental results presented that the surface wettability changed with the nano-fluid concentrations and particle sizes. The most significant finding was that the nanoparticle composition percentage, nano-porous layer distribution and particle concentration were influenced mainly by the contact angle.
The fundamental mechanisms (effective thermal conductivity, surface wettability and convective heat transfer) of enhanced heat transfer for heat pipes have taken the first step to investigate. The results showed that surface wettability enhancement can be mainly mechanism in improved the heat pipe thermal performance. Due to a significant increase in wettability, thus leading to the capillary force, critical heat flux and condensation enhancement.
|| Table of Content
Abstract (Chinese) II
Abstract (English) IV
Table of Content VI
List of Figure IX
List of Table XII
Chapter 1 Introduction 1
1.1 Motivation and Background 1
1.2 Literature Review 2
1.2.1 Review of Heat Pipes 2
220.127.116.11 Basic Concepts of Heat Pipes 2
18.104.22.168 Literature Review of Heat Pipes 4
1.2.2 Review of Nano-fluids 7
22.214.171.124 Basic Concepts 7
126.96.36.199 Effective Thermal Conductivity 8
188.8.131.52 Convective Heat Transfer 17
184.108.40.206 Critical Heat Flux and Surface Wettability 20
1.3 Nano-fluid Application in Heat Pipes 24
1.3.1 Heat Pipes 24
1.3.2 Thermosyphon 26
1.3.3 Oscillating Heat Pipe 29
Chapter 2 Heat Pipe Thermal Performance 32
2.1 Experimental Setup and Procedure 32
2.1.1 Experimental Setup 32
2.1.2 Test Procedure 35
2.2 Experimental Results 36
2.2.1 Grooved Heat Pipe 36
220.127.116.11 Effect of Nanoparticle Concentration 36
18.104.22.168 Effect of Nanoparticle Size 39
22.214.171.124 Preliminary Summary 42
2.2.2 Sintered Heat Pipe 43
126.96.36.199 Effect of Nanoparticle Concentration 43
188.8.131.52 Effect of Nanoparticle Size 48
184.108.40.206 Preliminary Summary 50
Chapter 3 Surface Wettability 51
3.1 Experimental Setup and Procedure 51
3.2 Experimental Results 52
3.3 Preliminary Summary 58
Enhanced Mechanisms of Heat Transfer in Nano-fluid Heat Pipe 59
4.1 Effective Thermal Conductivity 59
4.2 Surface Wettability 63
4.2.1 Capillary Phenomena 63
4.2.2 Critical Heat Flux 63
4.2.3 Condensation 67
4.3 Convective Heat Transfer 69
4.4 Preliminary Summary 70
Chapter 5 Summary and Conclusions 72
5.1 Summary 72
5.2 Conclusions 72
Appendix I Experimental data of groved heat pipe 86
Appendix II Experimental data of sintered heat pipe 93
Appendix III Experimental uncertainty analysis 97
Publication List 111
List of Figure
Fig.1 Heat pipe working principle 2
Fig.2 Equivalent thermal resistance of a heat pipe 4
Fig.3 Comparision of experiemntal data on thermal conductivity of nanofluids 16
Fig.4 Measured values of the thermal resistance of heat pipe with nano-fluids 25
Fig.5 Boiling heat transfer of nano-fluids under 7.4kPa on grooved surfaces 25
Fig.6 Effect of the mass concentration of nanoparticles on the heat resistance 26
Fig.7 Thermal resistance of the thermosyphons at different heat flow rates 27
Fig.8 Total heat resistances of thermosyphon using water and nano-fluid 28
Fig.9 hermal resistance of the thermosyphon with different nanofluids as compared to pure water 28
Fig.10 Effect of nano-fluid on the heat transport capability in OHP 29
Fig.11 Thermal resistance at various heat loads and operating temperatures 30
Fig.12 Thermal performance of silver nano-fluid filled OHP and pure water filled OHP at various heat load……………………….…………..31
Fig.13 TEM micrograph of 10 nm (Left) and 35 nm (Right) Ag nanoparticles 32
Fig.14 (a) Schematic of the experimental setup and (b) Thermocouple distributions on the tested heat pipe 34
Fig.15 Average temperature of heat pipe distribution in different heat load and concentration (10 nm) 38
Fig.16 Average temperature of heat pipe distribution in different heat load and concentration (35 nm) 39
Fig.17 Measured value of thermal resistance of heat pipe with nano-fluid prepared under different conditions 42
Fig.18 Average temperature of heat pipe distribution in different heat load and concentration (10 nm) 45
Fig.19 Average temperature of heat pipe distribution in different heat load and concentration (35 nm) 47
Fig.20 Effect of particle concentration on the temperature difference of heat pipe under various input power 48
Fig.21 Effect of particle size on the temperature difference of heat pipe under different input power 50
Fig.22 Effect of silver nanoparticle concentration on contact angle 53
Fig.23 The OM image of evaporated droplet(Pure Water and 10nm) 55
Fig.24 The OM image of evaporated droplet (35nm) 55
Fig.25 The SEM image of outside (a) and inside(b) on evaporated droplet (35nm) 56
Fig.26 Comparison of thermal resistance between experimental and theatrical 62
Fig.27 Illustrations on high power density apply to the evaporator section of the heat pipe 64
Fig.28 Liquid layer concept of CHF phenomena 65
Fig.29 Illustrations the effect of porous layer on capillarity 66
Fig.30 Illustrations the effect of wettability and liquid film thickness on condensation 68
List of Table
Table 1 Measured Effective Thermal Conductivity(keff) of Nanofluids 99
Table 2 Experimental Investigation on Convective Heat transfer Coefficient of Nanofluids (hnf) 104
Table 3 Experimental Investigation on Critical Heat Flux of Nanofluids (CHF)nf and Pool Boiling Performance (PBP) nf 106
Table 4 Experimental Investigations on Nanofluids Filled in Heat Pipes 109
Table 5 Results of the compositions of rim on droplet, analyzed by FE-SEM EDS 57
Table 6 Thermal conductivity of working fluid 60
Table 7 The specification of grooved heat pipe 60
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