FC-72流量震盪對一可變功率小圓型加熱面之週期性流動沸騰熱傳及氣泡特性研究

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國立交通大學

機械工程學系

碩士論文

FC-72 流量震盪對一可變功率小圓型加熱面之週期性

流動沸騰熱傳及氣泡特性研究

Time periodic flow boiling heat transfer and bubble

characteristics of FC-72 over a small heated circular

plate due to simultaneous refrigerant flow rate and heat

flux oscillations

研究生：陳文慶

指導教授：林清發博士

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FC-72 流量震盪對一可變功率小圓型加熱面之週期性

流動沸騰熱傳及氣泡特性研究

Time periodic flow boiling heat transfer and bubble

characteristics of FC-72 over a small heated circular

plate due to refrigerant flow rate and heat flux oscillation

研究生: 陳文慶

Student: Wun Ching Chen

指導老師 : 林清發

Advisor: Tsing-Fa Lin

國立交通大學

機械工程學系

碩士論文

A Thesis

Submitted to Department of Mechanical Engineering College of Engineering

National Chiao Tung University In partial Fulfillment of the Requirements

For the Degree of Master of Science In Mechanical Engineering

June 2009

Hsinchu, Taiwan, Republic of China

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誌謝

幕然回首兩年前的此時，對於離家到新竹交大求學的我而言，心中真

是充滿了既期待又害怕的複雜心情。來到交大這充滿學術研究氣息的生

活，讓我覺得在此讀書做研究是一種享受。然而，一想到即將要離開這可

愛的校園，不禁令人懷念起在此的點點滴滴。

能獲得碩士學位，首先很榮幸能接受林清發教授的指導，從文獻資料

的蒐集、實驗系統的構思設計到最後物理觀念的闡述分析，都令我受益匪

淺。而老師對我們在研究上嚴謹的要求，更深深地影響到我日後的處事態

度。而能夠順利地完成我的碩士論文，要感謝實驗室博士班文瑞學長以及

建安學長的幫忙及指導使得我的論文能順利完成。同學譯徵、書磊的互相

砥礪幫忙，當然也少不了一群為實驗室注入活力、帶來歡樂的學弟們：游

象麟、許書豪、熊宏嘉及陳俊州的幫忙。得之於人者太多，在此一同向所

有幫助過我的人致謝。

即將踏出交大校門邁向另一求學生涯的我，回首來時路，很慶幸並

沒辜負當初父母對我的期望；在今年能如期獲得碩士學位。我想今天若

我有任何些微的成就，爺爺奶奶和父母對我的教養及支持鼓勵，是我能

一路來的原動力，僅將我的榮耀獻給我摯愛的家人。

陳文慶

2009/6 於風城交大

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FC-72 流量震盪對一可變功率小圓型加熱面之週期性流動沸騰熱傳及氣

泡特性研究

研究生: 陳文慶指導教授: 林清發博士國立交通大學機械工程學系摘要這項研究目的探索 FC-72 在矩形流道中流過一小圓型加熱塊同步時間週期性蓄冷劑震盪和熱通量震盪對沸騰熱傳以及氣泡特徵研究。流量震盪為三角波震盪以及熱通量震盪為正旋波震盪。探討流量以及熱通量同向以及反向震盪研究。實驗參數為流量為 200,300 以及 400 kg/m2 s 震幅為 5%,10%以及 15%,熱通量範圍為 0.1 到 10W/cm2 震幅為 10%,30%以及 50%週期為 10 到 30 秒,次冷度為 0 到 15K,壓力為常壓。實驗結果顯示在單向流中流量和熱通量同向震盪時會有抑制壁溫震盪的效果然而在雙相流中流量和熱通量反向震盪才能有效抑制壁溫的震盪,由於熱通量以及流量對壁溫的反應時間有延遲因此在加以考慮延遲的因素後確實能驗證說單向流中流量和熱通量同向震盪以及雙相流中流量和熱通量反向震盪能有效的防止壁溫的震盪。

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Time periodic flow boiling heat transfer and bubble characteristics of FC-72

over a small heated circular plate due to simultaneous refrigerant flow rate

and heat flux oscillation

Student : Wun Ching Chen Advisor : Prof. Tsing-Fa Lin

Department of Mechanical Engineering National Chiao Tung University

ABSTRACT

This study intends to explore how simultaneously imposed time periodic coolant flow rate and heat flux oscillations affect the temporal flow boiling heat transfer and associated bubble characteristics of FC-72 over a small circular heated copper plate flush mounted on the bottom of a horizontal rectangular channel. The oscillations of the coolant flow rate and heat flux are respectively in the forms of nearly triangular and sinusoidal waves. Both the in-phase and out-of-phase mass flux and heat flux oscillations are investigated. In the experiment the time-average coolant mass flux G is varied from 300 to 400 kg/m2s and the amplitude of the

coolant mass flux oscillation is mainly fixed at 5, 10 and 15% of G. The mean heat flux ranges

from 0.1 to 10W/cm2 with the amplitude of the heat flux oscillation set at 10, 30 and 50% of q for the same period of the heat flux and mass flux oscillations varied from 10 to 30 seconds Besides, the time-average liquid subcooling at the inlet of the test section ranges from 0 to 15K and the system is at slightly subatmospheric pressure.

The transient oscillatory flow boiling heat transfer characteristics are illustrated by presenting the measured time variations of the heated plate temperature and boiling heat transfer coefficient. The experimental results show that the heated surface temperature also oscillates periodically in time at the same frequency as the mass and heat flux oscillations. Besides, the amplitude of the Tw

oscillation is generally smaller in the flow boiling when the out-of-phase G and q oscillations are imposed. But in the single-phase flow the Tw oscillation is normally weaker by imposing in-phase G

and q oscillations. These results indicate that the oscillation in Tw caused by the heat flux oscillation

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can be suppressed by the in-phase G oscillation in the single-phase flow and by the out-of-phase G oscillation in the boiling flow. It is further noted that by imposing the G oscillation at the time instant equal to the difference between the time lags in Tw resulting respectively from the q

oscillation only behind the q oscillation, and G oscillation only behind the q oscillation, the Tw

oscillation can be significantly suppressed and even completely wiped out.

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LIST OF TABLES

Table 1.1 Thermodynamic properties for FC-72 12

Table 1.2 Some single-phase convection heat transfer correlations for electronic cooling 13

Table 2.1Experimental parameters 18

Table 2.2Thermodynamic and transport properties of the dielectric refrigerant FC-72 list 19

Table 3.1 Summary of the uncertainty analysis 32

Table 4.1 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q_at Δq/q= 30%,ΔG G/ =10% and tp=20sec. for G=200 kg/m2s. 40

Table 4.2 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30,50%,ΔG G/ =5% and tp=20sec. for G=300kg/m2s. 41

Table 4.3 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30, 50%,ΔG G/ =10% and tp=20sec. for G=300kg/m2s. 42

Table 4.4 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 30%,ΔG G/ =15% and tp=20sec. for G=300kg/m2s. 43

Table 4.5 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 30%,ΔG G/ =10% and tp=20sec. for G=400kg/m2s. 43

Table 4.6 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30,50%,ΔG G/ =5% and tp=30sec. for G=300kg/m2s. 44

Table 4.7 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,20%,ΔG G/ =15% and tp=20sec. for G=300kg/m2s. 45

Table 4.8 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,15%,ΔG G/ =20% and tp=30sec. for G=300 kg/m2s. 45

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Table 5.1 Amplitudes of Tw oscillation and relative time lags in transient oscillatory subcooled flow

boiling for various q for Δq/q=30%,ΔG G/ =10% and tp=20sec. at G=300kg/m2s and

sub

T

Δ =5K. 106 Table 5.2 Amplitudes of Tw oscillation and relative time lags in transient oscillatory subcooled flow

boiling for various q_for Δq/q=30%,ΔG G/ =10% and tp=20sec. at G=200kg/m2s and

sub

T

sub

T

sub

T

boiling for various q_for Δq/q=10,30,50%,ΔG G/ =10% and tp=20sec at G=300kg/m2s

and ΔTsub=10K. 108

boiling for various q_for Δq/q=30%,ΔG G/ =10% and tp=20sec at G=400kg/m2s and

sub

T

boiling for various q for Δq/q=30%,ΔG G/ =10% and tp=20sec at G=300kg/m2s and

sub

T

boiling for various q_for Δq/q=30%,ΔG G/ =10% and tp=30sec at G=300kg/m2s and

sub

T

boiling for various q_for Δq/q=5,10,23%,ΔG G/ =5% and tp=20sec at G=300kg/m2s and

sub

T

boiling for various q_for Δq/q=8,30,32,45%,ΔG G/ =10% and tp=20sec at G=300kg/m2s

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boiling for various q_for Δq/q=15,35,50%,ΔG G/ =15% and tp=20sec at G=300kg/m2s

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LIST OF FIGURES

Experiment Apparatus

Fig. 2.1 Schematic diagram of experimental apparatus 23

Fig. 2.2 Three-dimensional plots of test section along with inlet and outlet sections 24

Fig. 2.3 Three-dimensional plots illustrating the test section in the rectangular flow channel 25

Fig. 2.4 Three-dimensional pictures showing (a) hollow cylindrical Teflon block and (b) cylindrical Teflon bolt 26

Fig. 2.5 Locations of thermocouples 27

Fig. 2.6 Schematics of the copper plate module 28

Fig. 2.7 Locations of the thermocouples inside the cylindrical-hollow Teflon block 29

Fig. 2.8 Schematic diagram of heat flux oscillation control loop 30

Saturated Flow Boiling Fig. 4.1 Comparison of the present steady single-phase liquid convection heat transfer data with the correlation of Gersey and Mudawar (1992) for (a)h₁_φ vs. G and (b)Nu_L vs. Re_L. 46

Fig. 4.2 Time variations of the copper plate temperature in stable saturated flow boiling for various imposed heat fluxes at (a)G=300kg/ m2s (b) G=400kg/m2s 47

Fig. 4.3 Fig. 4.2 (a) Stable saturated flow boiling curve (b) Stable saturated flow boiling heat transfer coefficients. 48

Fig.4.4 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₂₀₀ _/ 2 G= kg m s and +G G/ =10%for+q q/ =30%and t_p =20sec. 49

Fig.4.5 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₃₀₀ _/ 2 G= kg m s and +G G/ =5%for+q q/ =10%and tp =20sec. 50

Fig.4.6 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₃₀₀ _/ 2 G= kg m s and +G G/ =5%for+q q/ =30%and 20sect_p = . 51 Fig.4.7 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat

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flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations

at ₃₀₀ _/ 2

G= kg m s and +G G/ =5%for+q q/ =50%and 20sect_p = . 52 Fig.4.8 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations

at ₃₀₀ _/ 2

G= kg m s and +G G/ =10%for+q q/ =10%and 20sectp = . 53

Fig.4.9 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations

at ₃₀₀ _/ 2

at ₄₀₀ _/ 2

at ₃₀₀ _/ 2

G= kg m s and +G G/ =5%for+q q/ =30%and t_p =30sec. 59 Fig.4.15 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations

at ₃₀₀ _/ 2

G= kg m s and +G G/ =5%for+q q/ =50%and t_p =30sec. 60 Fig.4.16 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only, and (c) in-phase or out-of-phase G

and q oscillations at ₃₀₀ _/ 2

G= kg m s and +G G/ =15%for various q at t_p =20sec. 61 Fig.4.17 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only, and (c) in-phase or out-of-phase G

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G= kg m s and +G G/ =20%for various q at tp =30sec. 62

Fig. 4.18 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₂₀₀ _/ 2

G= kg m s and

/ 10%

G G=

+ for+q q/ =30%and 20sect_p = . 63 Fig. 4.19 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b)

in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₃₀₀ _/ 2

G= kg m s and

/ 5

G G=

+ %for+q q/ =10%and 20sect_p = . 64 Fig. 4.20 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b)

G= kg m s

and +G G/ =5%for+q q/ =30%and 20sect_p = . 65 Fig. 4.21 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b)

G= kg m s and

/ 5

G G=

+ %for+q q/ =50%and 20sectp = . 66

Fig. 4.22 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₃₀₀ _/ 2

G= kg m s and

/ 10%

G G=

G= kg m s and

/ 10%

G G=

G= kg m s and

/ 10%

G G=

G= kg m s and

/ 15%

G G=

+ for+q q/ =30%and 20sectp = . 70

Fig. 4.26 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₄₀₀ _/ 2

G= kg m s and

/ 10%

G G=

(15)

G= kg m s and

/ 5

G G=

+ %for+q q/ =10%and 30sectp = . 72

G= kg m s and

/ 5

G G=

G= kg m s and

/ 5

G G=

imposed mass flux oscillation only and (c) out-of-phase G and q oscillations at

2

300 /

G= kg m s and +G G/ =15%for+q q/ =10, 20%and 20sect_p = . 75 Fig. 4.31 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only and (c) out-of-phase G and q oscillations at

2

300 /

G= kg m s and +G G/ =20%for+q q/ =10,15%and 20sect_p = . 76 Fig. 4.32 Photos of stable saturated flow boiling at certain time instants in statistical state for various imposed heat fluxes for (a)G = 200kg/m2s, (b)G = 300kg/m2s and (c)G = 400kg/m2s. 77 Fig. 4.33 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for an imposed constant mass flux at q =4.03W/cm2, △q/ q =30%, G = 200kg/m2s and tp = 20sec. 78

Fig. 4.34 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for imposed in-phase G & q oscillations at G=200kg/m2s, △G/G=10%, q =4.03W/cm2 and △q/ q =30% with tp = 20sec. 79

Fig. 4.35 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for imposed out-of-phase G & q oscillations at G=200kg/m2s, △G/G=10%, q =4.03W/cm2 and △q/ q =30% with tp = 20sec. 80

Fig. 4.36 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for an imposed constant mass flux at q =4.03W/cm2_{, △q/ q =30%, G = 300kg/m}2_{s and t}

p = 20sec. 81

Fig. 4.38 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for

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imposed out-of-phase G & q oscillations at G=300kg/m2s, △G/G=10%, q =4.03W/cm2 and △q/ q =30%with tp = 20sec. 83

Fig. 4.40 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for imposed out-of-phase G & q oscillations at G=300kg/m2_{s, △G/}_G_{=15%, q =4.03W/cm}2_and

△q/ q =30% with tp = 20sec. 85

Fig. 4.41 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for an imposed constant mass flux at q =4.03W/cm2, △q/ q =50%, G = 300kg/m2s and tp = 20sec. 86

Fig. 4.44 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for an imposed constant mass flux at q =4.03W/cm2, △q/ q =30%, G = 300kg/m2s and tp = 30sec. 89

Fig. 4.45 Photos of saturated flow boiling at certain time instants in a typical time periodic cycle for imposed in-phase G & q oscillations at G=300kg/m2_{s, △G/}_G_{=10%, q =4.03W/cm}2_and

△q/ q =30% with tp = 30sec. 90

Fig. 4.47 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for an

imposed constant mass flux at q =4.01W/cm2, △q/ q =15%, G = 300kg/m2s with tp = 20sec. 92

Fig. 4.48 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for an imposed constant heat flux at q =4.01W/cm2, G = 300kg/m2s, △G/G=10%with tp = 20sec. 93

Fig. 4.49 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for imposed out-of-phase G & q oscillations at G=300kg/m2s, △G/G=10%, q =4.01W/cm2 and △q/ q =15% with tp = 20sec. 94

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Fig. 4.50 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for an imposed constant mass flux at q =4.01W/cm2, △q/q =20%, G = 300kg/m2s with tp = 20sec. 95

Fig. 4.51 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for an imposed constant heat flux at q =4.01W/cm2, G = 300kg/m2s, △G/G=15%with tp = 20sec. 96

Fig. 4.52 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for imposed out-of-phase G & q oscillations at G=300kg/m2s, △G/G=15%, q =4.01W/cm2 and △q/q =20% with tp = 20sec. 97

Fig. 4.53 Time period oscillatory saturated flow boiling of FC-72 with

q= 4.03W/cm2,Δq q/ = 30%,G=300kg/m2s, ΔG G/ =10% and tp=20sec. for the time variations

of bubble characteristics: (a) bubble departure diameter (b) bubble departure frequency (c) active nucleation site density. 98 Fig. 4.54 Time period oscillatory saturated flow boiling of FC-72 with

q= 4.03W/cm2,Δq q/ = 30%,G=300kg/m2s, ΔG G/ =15% and tp=20sec. for the time variations

of bubble characteristics: (a) bubble departure diameter (b) bubble departure frequency (c)

active nucleation site density. 99

Subcooled Flow Boiling

Fig. 5.1 Time variations of the copper plate temperature in stable sibcooled flow boiling for various imposed heat fluxes at (a)G=300kg/m2s and (b) G=400kg/m2s 112 Fig. 5.2 (a) Stable subcooled flow boiling curve and (b) stable subcooled flow boiling heat transfer coefficient. 113 Fig. 5.3 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at ₃₀₀ _/ 2

G= kg m s and +G G/ =10%for+q q/ =30%and 20sect_p = . for ΔTsub=5K. 114

Fig. 5.4 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations

at ₂₀₀ _/ 2

at ₃₀₀ _/ 2

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at ₃₀₀ _/ 2

G= kg m s and +G G/ =10%for+q q/ =10%and 20sectp = . for ΔTsub=10K. 117

at ₃₀₀ _/ 2

G= kg m s and +G/G=15%for+q/q=30%and 20sect_p = . for ΔTsub= 120

Time variations of the measured instantaneous heated surface temperature for (a) imposed heat 10K.

Fig. 5.10

at ₄₀₀ _/ 2

G= kg m s and +G G/ =10%for+q q/ =30%and 20sect_p = . for ΔTsub=10K. 121

Tim the mea neou face t ed heat

Fig. 5.11 e variations of sured instanta s heated sur emperature for (a) impos

at ₃₀₀ _/ 2

Time variations of the measured instantaneous heated surface temperature for (a) imposed heat

flux , (b) in- G and q llations

at Fig. 5.12

oscillation only phase G and q oscillations and (c) out-of-phase osci

2

300 /

Fig. 5.13 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only, and (c) in-phase or out-of-phase G

q

/ 5

G G=

+

G= kg m s and %for various at t_p =20sec. for

sub

T

Δ =10K. 124 Fig. 5.14 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only, and (c) in-phase or out-of-phase G

G= kg m s and +G G/ =10%for various at q t_p =20sec. for

sub

T

Δ =10K. 125 Fig. 5.15 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only, and (c) in-phase or out-of-phase G

G= kg m s and +G G/ =15%for various at q t_p =20sec. for

sub

T

Δ =10K. 126

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G= kg m s and sub T Δ / q q= + 20sec / 10% G G=

+ for 30% and tp = . for =5

Fig. 5.17 Time

K. 127 variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b)

2

200 /

G= kg m s and

in-phase G and q oscillations and (c) out-of-phase G and q oscillations at

sub / 30% q q= + and 20sect / 10% G G= + for = . for ΔT =10K. 128

nt for posed heat flux oscillation only, (b)

p

Fig. 5.18 Time variations of the heat transfer coefficie (a) im

2

300 /

G= kg m s and

sub

/ 5%

G G=

+ for+q q/ =30%and 20sect = . for ΔT =10K. 129

p

2

300 /

G= kg m s and

ient for imposed heat flux oscillation only, (b)

p

Fig. 5.20 Time variations of the heat transfer coeffic (a)

2

300 /

G= kg m s and

p

2

300 /

G= kg m s and

sub

/ 10%

G G=

p

2

300 /

G= kg m s and

p

2

400 /

G= kg m s and

p

2

300 /

G= kg m s and

sub

/ 10%

G G=

p

2

400 /

G= kg m s and

(20)

/ 10%

G G=

+ for+q q/ =30%and 30sectp = . for ΔTsub=10K. 136

nt for posed heat flux oscillation only, (b) Fig. 5.26 Time variations of the heat transfer coefficie (a) im

imposed mass flux oscillation only and (c) out-of-phase G and q oscillations at

/ 5%

G G=

+ for+q q/ =5,10, 23%and 20sectp = . ΔTsub=

2

300 /

G= kg m s and for 10K

. 137 nt for posed heat flux oscillation only, (b) imposed mass flux oscillation only and (c) out-of-phase G and q oscillations at

2 _/ _10%

G G=

+ for ΔTsub=10K.

138

300 /

G= kg m s and +q q/ =8,30,32, 45%and 20sectp = . for

Fig. 5.28 Time variations of the heat transfer coefficient for (a) imposed heat flux oscillation only, (b) imposed mass flux oscillation only and (c) out-of-phase G and q oscillations at

2

300 /

G= kg m s and +G G/ =15%for+q q/ =15,35,50%and 20sect_p = . for ΔTsub=10K.

139 Fig. 5.29 Photos of stable subcooled flow boiling at certain time instants in statistical state for various imposed heat fluxes for (a)G = 200kg/m2_{s ,(b)G = 300kg/m}2_{s and (c)G = 400kg/m}2_{s at}

sub

T

Δ =10K. 140

Fig. 5.30 Photos of subcooled f at ce in time instants in a typical time period l

constant imposed mass flux at

low boiling rta ic cyc e for a

=4.01W/cm2, △q/q =30% and G = 200kg/m2s with tp = 20 q sec. sub T Δ =10K. 141 and

Fig. 5.31 Photos of subcooled flow boiling at certain time instants in a typical time periodic cycle for imposed in-phase G & q oscillations at G=200kg/m s, △G/2 _G_{=10%, q =4.01W/cm and}

△q/

2

q =30% with tp = 20sec. and ΔTsub=10K. 142

Phot subcooled flow boiling at certain time instants in a typical time periodic cycle for

Fig. 5.32 os of

G=200kg/m2s, △G/G=10%,

imposed out-of-phase G & q oscillations at q =4.01W/cm2 and

△q/q =30% with tp = 20sec. and ΔTsub=10 . 143

Photo of subcooled flow boiling a ain time instants in a typical time periodic cycle for a K

Fig. 5.33 s t cert

constant imposed mass flux at q =4.01W/cm , △q/2 _{q =30% and G = 300kg/m s with t}

p = 20sec. and 2 sub T Δ =10K. 144 time instants in a typical time periodic cycle for Fig. 5.34 Photos of subcooled flow boiling at certain

imposed in-phase G & q oscillations at G=300kg/m s, △G/2 _G_{=10%, q =4.01W/cm and}

△q/

2

q =30% with tp = 20sec. and ΔTsub=10K. 145

Fig. 5.35 os of

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G=300kg/m2s, △G/

imposed out-of-phase G & q oscillations at G=10%, q =4.01W/cm2 and

Photos of subcooled flow boiling rtain time instants in a typical time periodic cycle for K

Fig. 5.36 at ce

imposed in-phase G & q oscillations at G=300kg/m2_{s, △G/}_G_{=15%, q =4.01W/cm}2_and

△q/q =30% with tp = 20sec. and ΔTsub=10K 147

Photos of subcooled flow boiling rtain time instants in a typical time periodic cycle for .

Fig. 5.37 at ce

G=300kg/m2s, △G/G=15%,

Photo of subcooled flow boiling a ain time instants in a typical time periodic cycle for a K

Fig. 5.38 s t cert

constant imposed mass flux at q =4.01W/cm2, △q/q =50% at G = 300kg/m2s with tp = 20sec.

Photos of subcooled flow boiling rtain time instants in a typical time periodic cycle for

Fig. 5.39 at ce

imposed in-phase G & q oscillations at G=300kg/m2s, △G/G=10%, q =4.01W/cm2 and △q/q =50% with a tp = 20sec. and ΔTsub=10K. 150

Fig. 5.40 os of

G=300kg/m2s, △G/G=10%,

△q/q =50% with a tp = 20sec. and ΔTsub=10K. 151

Photo of subcooled flow boiling at in time instants in a typical time periodic cycle for a

Fig. 5.41 s certa

Photos of subcooled flow boiling a ain time instants in a typical time periodic cycle for

Fig. 5.42 t cert

G=300kg/m2s, △G/G=10%,

imposed in-phase G & q oscillations at q =4.01W/cm2 and

△q/q =30% with tp = 30sec. and ΔTsub=10K. 153

Fig. 5.43 os of

G=300kg/m2_{s, △G/}_G_=10%,

imposed out-of-phase G & q oscillations at q =4.01W/cm2 _and

△q/q =30% with tp = 30sec. and ΔTsub=10K 154

Photo of subcooled flow boiling a ain time instants in a typical time periodic cycle for a .

Fig. 5.44 s t cert

Photos of subcooled flow boiling rtain time instants in a typical time periodic cycle for

Fig. 5.45 at ce

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imposed in-phase G & q oscillations at G=300kg/m2s, △G/G=10%, q =5.03W/cm2 and △q/q =30% with tp = 20sec. and ΔTsub=15K. 156

Fig. 5.46 os of

G=300kg/m2_{s, △G/}_G_=10%,

imposed out-of-phase G & q oscillations at q =5.03W/cm2_and

q/q =30% with t = 20sec. and ΔTsub

△ p =15 157

Photo of subcooled flow boiling a ain time instants in a typical time periodic cycle for a K.

Fig. 5.47 s t cert

Photo of subcooled flow boiling a ain time instants in a typical time periodic cycle for a

Fig. 5.48 s t cert

constant imposed heat flux at q =4.01W/cm2 at G = 300kg/m2s, △G/G=5%with tp = 20sec.

Fig. 5.49 os of

G=300kg/m2s, △G/G=5%,

subcooled flow boiling at certain time instants in a typical time periodic cycle for a Fig. 5.50 Photos of

Fig. 5.51 s t cert

constant imposed heat flux at q =4.01W/cm2 at G = 300kg/m2s, △G/G=10%with tp = 20sec.

Fig. 5.52 os of

G=300kg/m2s, △G/G=10%,

subcooled flow boiling at certain time instants in a typical time periodic cycle for a Fig. 5.53 Photos of

Fig. 5.54 s t cert

constant imposed heat flux at q =4.01W/cm2_{at G = 300kg/m}2_{s, △G/}_G_{=15%with t}

p = 20sec.

Fig. 5.55 os of

(23)

G=300kg/m2s, △G/

imposed out-of-phase G & q oscillations at G=15%, q =4.01W/cm2 and

Time d oscillatory subcooled flow boiling of FC-72 with

Fig. 5.50 perio

q= 4.01W/cm2_, _/

q q

Δ = 30%,G=300kg/m2_s, _/

G G

Δ =10% and tp=20sec. for the time variations

of bubble characteristics: (a) bubble departure ameter (b) bubble departure frequency (c)

active nucleation site density. 167

di

Fig.5.51 Time period oscillatory subcooled flow boiling of FC-72 with q = 4.01W/cm2_, _/

q q

Δ = 30%,G=300kg/m2_s, _/

G G

Δ =15% and t =20sec. for the time

bubbl

168

p

variations of e characteristics: (a) bubble departure diameter (b) bubble departure

frequency (c) active nucleation site density.

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NOMENCLATURE

area, m2 B element height, m A p c specific heat, J/kg℃ ter of rectangular-channel, m g avity, m/s2 H height, m D hydraulic diame G mass flux, kg/m2s acceleration due to gr 2 W/m K⋅

h heat transfer coefficient,

I measured current from DC power supply, A

tion, J/kg K⋅

lv

i enthalpy of vaporiza

k thermal conductivity, W/m K⋅

L length, mm

l ocouple tips with the copper surface

mass flow rate, kg/s

vertical distance between the therm m sub ΔT , l pl sub v lv ρ C ΔT Ja' = ρ i ⋅ ⋅ ⋅

Ja' Jacob number based on , dimensionless

Nu Nusselt number, Nu = h L

k ⋅

, dimensionless

Nac nsity 2

Nconf Confinement number,

Active nucleation site de , n/m

(

)

0.5 conf h D g N = σ ⋅ Δρ , dimensionless

P system pressure, kPa

Pr Prandtl number, _Pr=μ Cp

k ⋅

, dimensionless

Q heat transfer rate, W

x, W/cm2

q average imposed heat flu

Re Reynolds number, Re=G D⋅ , dimensionle

μ ss

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tl time lag, sec

tp heating period, sec

V coolant FC-72 flow velocity, m/s

age from DC power supply, V T temperature,℃ V measured volt W width, m Greek Symbols ΔT temperature difference, ℃ μ dynam specific volume, m /kg density, kg/m3

ε relative heat loss, dimensionless

Subscripts

ave average

c,h oper surface

cross-section of rectangular-channel

f the test section f the test section

of the test section phase

e mixture or between the inlet and exit

2 ic viscosity, _{N s/m}_⋅ 2

3

ν

ρ

from heater surface to co cu copper cs d diameter e effective g gas h hydraulic i at the inlet o in at the inlet o

i,o at inlet and exit

lv liquid phase to vapor

m average value for the two phas

M mica

n net power input to the coolant FC-7

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o at the outlet of the test section 2 ve heat transfer FC-72 p preheater r coolant FC-72 s surface

sat saturated state for coolant FC-7

sp single-phase convecti

sub subcooled state for coolant

T teflon t total

tp two-phase boiling heat transfer

v vapor w wall w water 1φ single-phase 2φ two-phase xxii

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CHAPTER 1 INTRODUCTION

1.1 Motive of the Present Study

With recent fast progress in the IC(Integrated Circuit) technology, the IC chips are currently designed to be relatively light, thin, short and small to enhance their performance. As the microelectronic systems become miniaturized, the density of the power dissipation in them increases significantly. It is also well known that the IC junction temperature must be kept under 85℃ to avoid being damaged and to maintain its normal operation[1]. The heat removal method based on the gas cooling is usually not sufficiently effective for the high generation components. Besides, the use of the direct liquid cooling can greatly increase the heat removal rate. But it is still not higher enough for high power density in advanced CPUs. Moreover, the method utilizing the boiling of liquid is most effective because of the latent heat transfer involved in the process. Furthermore, the power dissipation in IC chips are often time dependent in practical operation. Therefore heat removal rate must be varied in time to meet the required time varying cooling load. To accommodate the time varying heat removal rate, the coolant flow rate is controlled instantly at the required level. Specifically, the coolant flow rate is often set to increase with the heat removal rate and vice versa. In stable flow boiling in which the coolant mass flux and heat flux are kept at constant levels, however, the boiling curves are known to be only slightly affected by the mass flux. How the flow boiling heat transfer characteristics are influenced by the simultaneous time varying imposed heat flux and mass flux remains largely unexplored.

In employing the liquid boiling in the electronics cooling the coolants must be chemically stable, inert and dielectric. The coolant FC-72, a fluorocarbon liquid manufactured by the 3M Company, meets the above requirements and is appropriate for the electronics cooling. However, our understanding of time dependent flow boiling due to time varying heating and coolant flow rate is poor. In the present study an initial attempt is made to unravel how the characteristics of FC-72

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flow boiling heat transfer and bubble motion over a flush mounted small heated surface in a rectangular channel are affected by the simultaneous time periodic refrigerant flow rate and imposed heat flux. Some thermophysical properties for FC-72 are given in Table 1.1

1.2 Literature Review

In what follows the literature relevant to the present study is reviewed, especially on the use of boiling of dielectric liquids for cooling of electronic equipments including the single-phase and boiling heat transfer.

1.2.1 Steady single-phase and stable flow boiling heat transfer

Incropera et al. [2] investigated single-phase convective heat transfer of water and FC-77 from single array and four-row arrays of 12 flush-mounted heat sources in a horizontal rectangular channel for the channel Reynolds numbers ranging from 1,000 to 14,000. They developed a model to predict the relation between the Reynolds number and Nusselt number for the turbulent flow

regime with 5,000< ReD <14,000. Unfortunately, the measured data were significantly

under-predicted in the laminar flow regime. Investigation of single-phase and subcooled flow boiling heat transfer from a small heated patch with R-113 and FC-72 was carried out by Samant and Simon [3]. They combined the experimental data for R-113 and FC-72 to develop an empirical correlation. In addition, they observed large temperature excursions at the onset of nucleate boiling and a boiling hysteresis near the onset of nucleate boiling in the subcooled boiling. Garimella and Eibeck [4] analyzed the heat transfer characteristics of an six-row array of 30 heat sources in single-phase forced convection of water for the channel Reynolds number ranging from 150 to 5,150. They reported that the heat transfer coefficient decreased with decreasing Reynolds number and the Nusselt number decreased with increasing ratio of the channel height to protruding element height. Gersey and Mudawar [5] studied the orientation effect on the single-phase forced convection and subcooled flow boining of FC-72 over a nine in-line microelectronic chips. They proposed an empirically generalized equation based on their experimental data. Heindel et al. [6,7] examined single-phase liquid convection and flow boiling of water and FC-72 over a 1 x 10 array of flush

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mounted discrete heat sources in a horizontal rectangular channel. In investigating the critical heat flux of FC-72 for four in-line simulated electronic chips in vertical channel flow boiling experiments, Tso et al. [8] found that temperature of the chip surface decreased with the increases in the flow velocity and liquid subcooling in the partial boiling region and this result was opposed to that of Willingham and Mudawar [9] . The fluid velocity and subcooling temperature have smaller effect on the surface temperature in the fully-developed boiling region. They observed that increases in the fluid velocity and liquid subcooling resulted in a delay in the incipience of nucleate boiling and in an increase in the critical heat flux.

The single-phase heat transfer correlations proposed in some of the above studies are listed in Table 1.2.

1.2.2 Transient pool boiling heat transfer

Hohl et al. [10] conducted pool boiling of FC-72 subject to an increasing heating rate and found that CHF increased with the heating rate. Besides, the transient CHF is higher than the steady state CHF. Sakurai and Shiotsu [11] investigated transient pool boiling of water over a platinum wire of 1.2 mm in diameter and 97.9 mm in length to simulate a step input of reactivity in a nuclear reactor in which the reactor power rised exponentially with time. The incipient boiling heat flux was found to increase exponentially with time for the exponential period ranging from 5 ms to 10s. Besides, the wire surface temperature at first increases with the heat input. Moreover, the heat transfer coefficient and heat flux at the incipient boiling point are higher for a shorter heating period. Okuyama et al. [12] conducted pool boiling of R-113 at large stepwise power generation in a 7-μm thick copper foil focusing on the transient critical heat flux above which the effective heat removal in transient nucleate boiling could not be expected. They noted that the transient critical heat flux was lower than the critical heat flux in the steady state under a low system pressure. In the case of the low system pressure, the bubble near the transient critical heat flux has a peculiar shape like a “straw hat” which was considered to be due to the consumption of the nucleate boiling liquid layer. In the case of high system pressure, no more vapor bubble appears in transient nucleate boiling and

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transition occurs due to filling of the fine initial bubbles on the heat transfer surface. Besides, at low heat generation rate the wall superheat drops for a moment after boiling incipience. But at high heat generation rate this becomes hard to see, because the duration of nucleate boiling becomes extremely short. Later Okuyama and Iida [13] moved further to investigate liquid nitrogen pool boiling over a platinum wire with a stepwise heat generation. In the case of a low heat generation rate, boiling transition was observed to occur due to the coalescence of nucleate boiling bubbles. While in the case of a high heat generation rate, a vapor sheath grows along the test wire since the excess superheat energy is stored in the liquid layer at boiling incipience. Besides, in the case of an extremely high heat generation rate, a lot of fine initial bubbles grow rapidly and simultaneously. Boiling transition occurs due to the filling of the bubbles on the heater.

Transient nucleate boiling of several highly wetting fluids on a thick flat sample and a wire also with a stepwise heat generation was experimentally studied by Duluc et al. [14]. They observed that for the cases with high thermal inertia, fewer transient pool boiling was developed owing to the large heat capacity of the heater. Besides for the transient experiments subject to very fast heating, the wall superheat at boiling onset may be higher than the steady condition. Auracher and Marquardt et al. [15] investigated transient pool boiling from a thick copper with FC-72. They observed a hysteresis between the heating and cooling transient conditions. Under steady boiling conditions and with a clean heater surface, no hysteresis was observed.

1.2.3 Transient single-phase forced convection heat transfer

Girault and Petit [16] investigated transient single-phase forced convection in a horizontal plane channel with different time varying imposed heat fluxes on the channel walls. On the bottom plate the imposed heat flux varies like a sinusoidal wave. While on the top plate the imposed heat flux is like a rectangular wave. During the power-on period both the top and bottom plate temperatures were found to vary smoothly. There is a small wall temperature oscillation for the power-off situation. This is considered to result from the existence of internal energy in the channel walls even when the power is turned off. Bhowmik and Tou [17, 18] performed an experiment to

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study transient FC-72 forced convection heat transfer from a four-in-line chip module that is flush-mounted onto one wall of a vertical rectangular channel. The Reynolds number based on the heat source length ranges from 800 to 2,625 for the heat flux varying from 1 to 7 W/cm2. Their data suggest that the transient characteristics of the overall heat transfer coefficient are both of importance in the thermal systems during the power-on and power-off periods. Besides, the hear transfer coefficient was noted to be affected strongly by the number of chips. In a similar experiment [19] they investigated the transient heat transfer characteristics from an array of 4 x 1 flush mounted simulated electronic chips using water as the working fluid during the power-off periods. The Reynolds number based on the heat source length ranges from 1,050 to 2,625. The transient heat transfer regime in the period of 75s after the heater power is cut-off is examined. They observed that the Nusselt numbers of the four chips at the beginning of power-off were close but then they diverged with time. However, the Nusselt number increases with time, due to the chip wall temperature decrease with time. When compared with water, an overall increase of 70% in the Nusselt number is obtained by using FC-72.

1.2.4 Transient flow boiling heat transfer

Kataoka et al. [20] investigated transient flow boiling of water over a platinum wire subject to an exponentially increasing heat input. The wire diameter and length respectively vary from 0.8 to 1.5 mm and from 3.93 to 10.4 cm. Two types of transient boiling were observed. In A-type (heating period is 20ms, 50ms, or 10s) boiling, the transient maximum critical heat flux increases with decreasing period at constant flow velocity. Whereas, in the B-type (heating period is 5ms, 10ms, or 14ms) boiling, the transient maximum heat flux decreases first with the period and then increases. Two-phase flow and heat transfer in a small tube of 1 mm internal diameter using R-141b as the working fluid were studied by Lin et al. [21]. At a low heat flux input, a relatively constant wall temperature was obtained. Besides, forced convection evaporation occurs towards the outlet end of the tube and the fluctuations in the wall temperature are small. With a high heat flux input, however, significant fluctuation in the wall temperature can be observed. This is caused by a

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combination of time varying heat transfer coefficient and time varying local pressure and fluid saturation temperature.

Two-phase flow instability in the flow boiling of various liquids in a long heated channel has been recognized for several decades [22, 23]. On a certain operating condition significant temporal oscillations in pressure, temperature, mass flux and boiling onset occur. Recently, some detailed characteristics associated with these instabilities were investigated through experimental measurement and theoretical modeling. Specifically in flow boiling of refrigerant R-11 in a vertical channel, the pressure-drop and thermal oscillations were observed by Kakac et al. [24]. Two-phase homogeneous model along with the thermodynamic equilibrium assumption was used to predict the condition leading to the thermal oscillation. And their predicted periods and amplitudes of the oscillations were in a good agreement with their measured data. Kakac and his colleagues [25] further noted the presence of the density wave oscillation superimposed on the pressure-drop oscillations. Moreover, the dirft flux model was employed in their numerical perdiction. In a continuing study for R-11 in a horizontal tube of 106 cm long, Ding et al. [26] examined the dependence of the oscillation amplitude and period on the system parameters and located the boundary of various types of oscillations on the steady-state pressure-drop versus mass flux characteristic curves. A similar experimental study was carried out by Comakli et al. [27] for a 319.5 cm long tube. They showed that the channel length has an important effect on the two-phase flow dynamic instabilities.

The dynamic behavior for a horizontal boiling channel connected with a surge tank for liquid supply has also received some attention. Mawasha and Gross [28] used a constitutive model containing a cubic nonlinearity combined with a homogeneous two-phase flow model to simulate the pressure-drop oscillstion. Their prediction is matched with the measured data. Later, the channel wall capacity effects was included [29] to allow the wall temperature and heat transfer coefficient to vary with time.

Wang et al. [30] noted that the boiling onset in a upward flow of subcooled water in a vertical

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tube of 7.8-m long connected with a liquid surge tank could cause substantial flow pressure and density-wave oscillations. These boiling onset oscillations were attributed to a sudden increase of pressure-drop across the channel and a large fluctuation in the water flow rate at the onset of nucleate boiling. This in turn results from the feedback of the pressure-drop and flow rate by the system, causing the location of the boiling onset to move in and out of the channel.

Brutin et al. [31] reported the pressure-drop oscillations of n-pentane liquid in a vertical small rectangular channel (Dh=0.889mm, L=50mm & 200mm). A non-stationary state of two-phase flow

was observed. The effects of the inlet flow condition on the boiling instabilities were found to be relatively significant [32]. A similar study for subcooled flow boiling of deionized water was conducted by Shuai et al. [33] and the pressure-drop oscillations were also noted.

1.2.5 Bubble Characteristics

Literature relevant to the bubble characteristics in boiling flow is briefly reviewed. A recent experiment conducted by Chang et al. [34] focused on the behavior of near-wall bubbles in subcooled flow boiling of water. The population of the near-wall bubbles was found to increase with the increase in the heat flux and in the superheated liquid layer very small bubbles were noted to attach to the heated wall. In addition, the coalesced bubbles are smaller for a higher mass flux of the flow. Cornwell and Kew [35] examined various flow regimes for boiling of refrigerant R-113 in a vertical rectangular multi-channel with Dh = 1.03 and 1.64 mm. Based on visualization of the flow

and measurement of the heat transfer, three flow regimes have been suggested, namely, the isolated bubble, confined bubble and annular-slug bubble flows. In the isolated bubble regime, heat transfer coefficient depends on the heat flux and hydraulic diameter. In the confined bubble regime, heat transfer coefficient depends on the heat flux, mass flux, vapor quality and hydraulic diameter. While in the annular-slug bubble regime, heat transfer coefficient depends on the mass flux, vapor quality and hydraulic diameter. Lie and Lin [36, 37] examined flow boiling heat transfer and associated bubble characteristics of R-134a in a narrow annular duct (Dh=4, 2 mm). They concluded that the

bubbles are suppressed to become smaller and less dense by raising the refrigerant mass flux and

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inlet subcooling. The mean bubble departure frequency increases with the increasing refrigerant mass flux and saturated temperature and with the decreasing duct size. Moreover, the active nucleation site density is much higher at a lower refrigerant mass flux particularly at a high imposed heat flux. Bang et al. [38] examined boiling of R-134a in a vertical rectangular channel focusing on the characteristic structures in the near-wall region. They noted the presence of the vapor remnants below the discrete bubbles and coalesced bubbles and the presence of an interleaved liquid layer between the vapor remnants and bubbles. Besides, the bubble layer was divided into two types, a near-wall bubble layer dominated by small bubbles and a following bubble layer prevailed by large coalesced bubbles. Kandlikar [39] examined the subcooled flow boiling of water in a rectangular horizontal channel. They concluded that the bubble growth was slow at high subcooling and the departure diameter decreased as the flow rate increased.

By using optical measurement techniques, Maurus et al. [40,41] examined the bubble size distribution and local void fraction in subcooling flow boiling of water at atmospheric pressure. They reported that the bubble size increased with an increase in the heat flux but reduced with an increase in the mass flux. The total bubble life time, the remaining lifetime after the detachment process and the waiting time between two bubble cycles decreased significantly as the mass flux increased. In a recent study Maurus and Sattelmayer [42] further defined the bubbly flow region by the ratio of the averaged phase boundary velocity to the averaged fluid velocity. On the other hand, an experimental analysis was carried out by Thorncroft et al. [43] to investigate the vapor bubble growth and departure in vertical upflow and downflow boiling of FC-87. They found that the bubble growth rate and bubble departure diameter increased with the Jacob number (increasing

△Tsat) and decreased at increasing mass flux in both upflow and downflow. Bubble rise

characteristics after the bubble departure from a nucleation site in vertical upflow tube boiling were investigated by Okawa et al. [44-46]. They noted that the flow inertia had a significant influence on the onset of detachment but the influence was gradually reduced with time. They also observed three different bubble rise paths after the departure from nucleation sites. Specifically, some bubbles slide upward along the vertical wall, some bubbles detach from the wall after sliding, and

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other bubbles remain close to the wall and reattach to the wall. Forced convection boiling experiments conducted by Situ et al. [47,48] for water in a vertical annular channel revealed that the bubble departure frequency increased as the heat flux increased. Moreover, the experimental results indicate that bubble lift-off diameter increases at increasing inlet temperature and heat flux. In addition, Yin et al. [49] examined the subcooled flow boiling of R-134a in a horizontal annular duct and noted that both the bubble departure size and frequency reduced at increasing liquid subcooling. They found that only the liquid subcooling showed a large effect on the bubble size.

1.3 Objective of This Study

The above literature review clearly indicates that detailed characteristics of the time dependent flow boiling of liquids resulting from imposed time varying heat input and/or coolant flow rate are still poorly understood. In this study, an experiment will be carried out to investigate how simultaneously imposed time periodic heat flux and mass flux oscillations in the form of sinusoidal-like waves affect the temporal flow boiling heat transfer and associated bubble characteristics of FC-72 flow over a small heated circular plate flush mounted on the bottom of a horizontal rectangular channel. The imposed heat flux and mass flux oscillate at the same frequency. The use of this heated surface intends to simulate the power dissipating chip in an electronic system. In the experiment both the time periodic saturated and subcooled flow boiling will be examined. Effects of the mean level, period and amplitude of the imposed heat flux and mass flux oscillations on the boiling characteristics will be inspected in detail for FC-72. Besides, the effects of in-phase and out-of phase of the heat flux and mass flux oscillations on the flow boiling characteristics will be explored.

FC-72流量震盪對一可變功率小圓型加熱面之週期性流動沸騰熱傳及氣泡特性研究

國 立 交 通 大 學

機 械 工 程 學 系

碩 士 論 文

FC-72 流量震盪對一可變功率小圓型加熱面之週期性

流動沸騰熱傳及氣泡特性研究

Time periodic flow boiling heat transfer and bubble

characteristics of FC-72 over a small heated circular

plate due to simultaneous refrigerant flow rate and heat

flux oscillations

研 究 生：陳 文 慶

指 導 教 授：林 清 發 博士

FC-72 流量震盪對一可變功率小圓型加熱面之週期性

流動沸騰熱傳及氣泡特性研究

Time periodic flow boiling heat transfer and bubble

characteristics of FC-72 over a small heated circular

plate due to refrigerant flow rate and heat flux oscillation

研 究 生: 陳文慶

Student: Wun Ching Chen

指 導 老 師 : 林清發

Advisor: Tsing-Fa Lin

國 立 交 通 大 學

機械工程學系

碩士論文

誌謝

幕然回首兩年前的此時，對於離家到新竹交大求學的我而言，心中真

是充滿了既期待又害怕的複雜心情。來到交大這充滿學術研究氣息的生

活，讓我覺得在此讀書做研究是一種享受。然而，一想到即將要離開這可

愛的校園，不禁令人懷念起在此的點點滴滴。

能獲得碩士學位，首先很榮幸能接受林清發教授的指導，從文獻資料

的蒐集、實驗系統的構思設計到最後物理觀念的闡述分析，都令我受益匪

淺。而老師對我們在研究上嚴謹的要求，更深深地影響到我日後的處事態

度。而能夠順利地完成我的碩士論文，要感謝實驗室博士班文瑞學長以及

建安學長的幫忙及指導使得我的論文能順利完成。同學譯徵、書磊的互相

砥礪幫忙，當然也少不了一群為實驗室注入活力、帶來歡樂的學弟們：游

象麟、許書豪、熊宏嘉及陳俊州的幫忙。得之於人者太多，在此一同向所

有幫助過我的人致謝。

即將踏出交大校門邁向另一求學生涯的我，回首來時路，很慶幸並

沒辜負當初父母對我的期望；在今年能如期獲得碩士學位。我想今天若

我有任何些微的成就，爺爺奶奶和父母對我的教養及支持鼓勵，是我能

一路來的原動力，僅將我的榮耀獻給我摯愛的家人。

陳文慶

2009/6 於風城交大

FC-72 流量震盪對一可變功率小圓型加熱面之週期性流動沸騰熱傳及氣

泡特性研究

Time periodic flow boiling heat transfer and bubble characteristics of FC-72

over a small heated circular plate due to simultaneous refrigerant flow rate

and heat flux oscillation

Student : Wun Ching Chen Advisor : Prof. Tsing-Fa Lin

ABSTRACT

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

NOMENCLATURE

(

)

CHAPTER 1

INTRODUCTION

1.1 Motive of the Present Study

1.2 Literature Review

1.2.1 Steady single-phase and stable flow boiling heat transfer

1.2.2 Transient pool boiling heat transfer

1.2.3 Transient single-phase forced convection heat transfer

1.2.4 Transient flow boiling heat transfer

1.2.5 Bubble Characteristics

1.3 Objective of This Study

國立交通大學

機械工程學系

碩士論文

研究生：陳文慶

指導教授：林清發博士

研究生: 陳文慶

指導老師 : 林清發

國立交通大學