放置可移動擾動粒子在一水平加熱銅板上對FC-72池沸騰熱傳增強研究

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國

立

交

通

大

學

機械工程學系

碩士論文

放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

研究生：魏周民

指導老師：林清發教授

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放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

研究生：魏周民 Student：Chou-Min Wei

指導教授：林清發 Advisor：Prof. 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 2013

Hsinchu, Taiwan, Republic of China

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誌謝

轉眼間，三年的研究生生活終於劃下句點，碰到許多事不順意的、不如意的，中途有一度想要放棄的念頭，但在家人與朋友的關心與勸導下，我留了下來，如今在畢業口試後仍留在深深的記憶中。本論文之所以可以順利完成，首先要感謝的是指導老師林清發教授，在受教三年的時光當中，深刻感受到老師獨特的學者涵養、治學嚴謹的態度，在實驗的討論與論文的撰寫潤筆中，不辭辛勞的殷切指導，讓學生受益匪淺，在此由衷致謝。在研究所期間，要特別感謝博士班汪書磊學長在我的求學過程中給予的熱心討論與指導，沒有學長的指導與幫忙下，我今天就沒辦法順利的畢業，也感謝同學葉庭鈞互相砥礪和幫忙，以及帶來歡樂的學弟學妹薛正宏、李貞儀及吳錫寰，感謝一同在研究室生活的大家。誠摯地感謝成功大學機械系何清政教授、中央大學機械系陳志臣博士及清華大學工科系潘欽教授，由於各位老師在口試中提出各項建議，使本論文更趨完整。最後，僅以本文獻給我所關心的人和所有關心我的人。魏周民 2013, 6 於新竹交大

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放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

研究生：魏周民指導老師：林清發教授

國立交通大學機械工程學系

摘要

本論文針對放置可移動擾動粒子於加熱銅板上對 FC-72 池沸騰熱傳增強實驗研究。可移動顆粒放置於加熱銅板表面上並且由一個四方型的壓克力圍牆圍住，來防止可移動顆粒不會因為液體的流動，導致可移動顆粒被沖離了加熱銅板表面。在實驗中探討顆粒種類、顆粒直徑和顆粒的數量。在實驗參數範圍上，熱 通量 q 從 0.1 到 6W/cm2，顆粒直徑有 1.0 和 1.5 mm，顆粒的數量從 100 到 1800(對於直徑為 1.0 mm 的顆粒)和 100 到 800(對於直徑為 1.5 mm 的顆粒)。實驗數據以壁過熱度對應輸入的熱通量及熱傳係數表示，比較對於光滑加熱銅塊下熱傳增強的表現。放置可移動擾動銅粒子相較於光滑表面對於 FC-72 之池沸騰熱傳係數有 430%的增強效果。而對於放置可移動擾動不銹鋼粒子相較於光滑表面，整體的沸騰熱傳係數有 530%的增強效果。甚至當加熱銅板上覆蓋滿顆粒(最多鋪滿兩層)對於整體的散熱效果有明顯的增強。但在高熱通量時，散熱效果有降低的趨勢，特別對於放置直徑 1.5 mm 的顆粒，散熱效果降低的趨勢很明顯。由數據呈現的圖形可得，熱傳增強的表現會因其不同的參數搭配而有不同的增強效果，理想且良好的熱傳增強表現在於適當的顆粒種類、顆粒直徑和顆粒數量的搭配。由數據呈現的結果指出，放置可移動擾動粒子於加熱銅板上後對於整體的散熱效果有增強的效果也有降低的效果。在高熱通量時，散熱效果有明顯降低的現象。

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Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

Student: Chou-Min Wei Advisor: Prof. Tsing-Fa Lin

National Chiao Tung University

ABSTRACT

An experiment is carried out here to investigate how the saturated pool boiling heat transfer of liquid FC-72 over a horizontal heated copper plate of 3×3 𝑐𝑚2_in

surface area is affected by placing metallic particles above the surface, intending to explore the possible pool boiling heat transfer enhancement by the moving particles. Both copper and stainless steel particles are tested. The particles are freely placed above the heated plate with a rectangular fence surrounding the plate so that the particles can be moved by the force induced by the boiling flow without being blown away. In the experiment, the imposed heat flux is varied from 0.1 to 6W/cm2 for the diameter of the particles fixed at 1.0 and 1.5 mm. Besides, the total particle number placed on the plate ranges from 100 to 1800 and from 100 to 800 respectively for the small and large particles. The measured data are presented in terms of boiling curves and boiling heat transfer coefficients for the heating surface with the presence and absence of the particles. The experimental parameters include the imposed heat flux level and the size, material and number of the particles.

The data obtained from the present study for the saturated pool boiling indicate that placing the movable particles can significantly increase the pool boiling heat transfer coefficient of FC-72 at low and medium heat fluxes (wall superheats). For the copper particles the enhancement can be up to 430% over that for a bare surface for a

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certain combination of the experimental parameters. The best enhancement can be as high as 530% for the stainless steel particles. Even when more than one layer of particles are placed on the plate relatively significant boiling heat transfer enhancement can still be obtained. However, the boiling heat transfer enhancement varies nonmonotonically with the particle diameter, number and material and the heat flux applied, reflecting the complex mutual influences of the movable particles and bubble motion near the heated surface. An optimal boiling heat transfer enhancement could be procured by a suitable choice of the experimental parameters. Besides, the wall superheat for the incipient boiling can be substantially reduced by the moving metallic particles. However, at high heat flux (wall superheat) placing the particles on the plate can greatly reduce the boiling heat transfer especially for the large particles.

The results from the visualization of the boiling flow over the copper plate indicate that placing the movable particles above the plate results in two opposite effects of enhancing and retarding the boiling heat transfer. At high heat flux the retarding effect is strong.

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LIST OF TABLES

Table 2.1 Thermophysical properties of FC-72. 14

Table 2.2 Parameter of particle size and 𝑁_𝑝. 15

Table 3.1 Summary of the results from the uncertainty analysis. --- 26

Table 4.1 Wall superheats at onset of nucleate boiling

for copper particles - - ---39

Table 4.2 Wall superheats at onset of nucleate boiling

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LIST OF FIGURES

Experimental Apparatus

Fig. 2.1 Schematic diagram of the test apparatus. ---16 Fig. 2.2 Schematic diagram of the test heater assembly (not to scale). ---17 Fig. 2.3 Locations of three thermocouples in the copper block and one thermocouple

below the heater (not to scale).---18

Fig. 2.4 Schematic diagram of placing strings on heating plate (not to scale). ---19 Fig. 2.5 Schematic diagram of placing movable particles on heating surface with

acryl rectangular enclosure (not to scale). ---20

Data Reduction

Fig. 3.1 Schematic diagram of six main directions of the heat loss. ---27 Fig. 3.2 Schematic diagram of T'5 and T'6. ---28

Saturated Pool Boiling Heat Transfer

Fig. 4.1 Comparison of the present single-phase natural convection data with the empirical correlation of Radziemska and Lewandowski (2005). ---41 Fig. 4.2 Comparison of the present nucleate boiling heat transfer data on smooth

plate with Rainy and You (2000). ---42 Fig. 4.3 Effects of surface aging on saturated pool boiling curves (a) and boiling

heat transfer coefficients (b) for bare surface. ---43 Fig. 4.4 Effects of copper particle diameter and number on saturated pool boiling

curves (a) and boiling heat transfer coefficients (b) at d𝑝=1.0 mm and

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Fig. 4.5 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁𝑝= 200 . ---45

Fig. 4.6 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁_𝑝= 300 . ---46 Fig. 4.7 Effects of copper particle diameter and number on saturated pool boiling

curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁𝑝= 400 . ---47

Fig. 4.8 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d𝑝=1.0 mm and

𝑁_𝑝= 500 . ---48 Fig. 4.9 Effects of copper particle diameter and number on saturated pool boiling

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Fig. 4.13 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁𝑝= 1000 . ---53

Fig. 4.14 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁_𝑝= 1100 . ---54 Fig. 4.15 Effects of copper particle diameter and number on saturated pool boiling

𝑁_𝑝= 1800 . ---58 Fig. 4.19 Variations of ℎ𝑝⁄ with wall superheat for various copper particle ℎ

numbers at d_𝑝=1.0 mm (solid symbols denote best boiling heat transfer enhancement for various 𝑁𝑝) ---59

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Fig. 4.21 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.5 mm and 𝑁𝑝= 200 .---61

Fig. 4.22 Effects of copper particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.5 mm and 𝑁_𝑝= 300 .---62 Fig. 4.23 Effects of copper particle diameter and number on saturated pool boiling

curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.5 mm and 𝑁𝑝= 400 .---63

𝑁_𝑝= 500 .---64 Fig. 4.25 Effects of copper particle diameter and number on saturated pool boiling

𝑁_𝑝= 700 .---66 Fig. 4.27 Effects of copper particle diameter and number on saturated pool boiling

Fig. 4.28 Variations of ℎ_𝑝⁄ with wall superheat for various copper particle ℎ numbers at d𝑝=1.5 mm (solid symbols denote best boiling heat transfer

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Fig. 4.29 Effects of stainless steel particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁_𝑝 = 200 .---69 Fig. 4.30 Effects of stainless steel particle diameter and number on saturated pool

boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁_𝑝 = 400 .---70 Fig. 4.31 Effects of stainless steel particle diameter and number on saturated pool

boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁𝑝 = 600 .---71

Fig. 4.32 Effects of stainless steel particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d𝑝=1.0 mm

and 𝑁_𝑝 = 800 .---72 Fig. 4.33 Effects of stainless steel particle diameter and number on saturated pool

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Fig. 4.37 Effects of stainless steel particle diameter and number on saturated pool boiling curves (a) and boiling heat transfer coefficients (b) at d_𝑝=1.0 mm and 𝑁_𝑝 = 1800 .---77 Fig. 4.38 Variations of ℎ_𝑝⁄ with wall superheat for various stainless steel particle ℎ

numbers at d_𝑝=1.0 mm (solid symbols denote best boiling heat transfer enhancement for various 𝑁_𝑝) ---78 Fig. 4.39 Effects of stainless steel particle diameter and number on saturated pool

Fig. 4.44 Variations of ℎ_𝑝⁄ with wall superheat for various stainless steel particle ℎ numbers at d𝑝=1.5 mm (solid symbols denote best boiling heat transfer

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Fig. 4.45 Boundaries for boiling heat transfer augmentation and retardation for copper and stainless steel particles with different d_𝑝 and 𝑁_𝑝 based on (a) q vs. 𝑁_𝑝⁄𝑁_𝑝𝑓 and (b) ∆𝑇_𝑠𝑎𝑡 vs. 𝑁_𝑝⁄𝑁_𝑝𝑓. ---85 Fig. 4.46 Photos taken from top view of boiling flow at selected time instants for

q= 0.85 W/ cm2 with copper particles on heated surface at d_𝑝=1.0 mm and 𝑁_𝑝= 600---86 Fig. 4.47 Photos taken from side view of boiling flow at selected time instants for

q= 0.85 W/ cm2 with stainless steel particles on heated surface at

d𝑝=1.0 mm and 𝑁𝑝 = 600---87

Fig. 4.48 Photos taken from side view of boiling flow at selected time instants for q= 1.45 W/ cm2 with stainless steel particles on heated surface at

d_𝑝=1.0 mm and 𝑁_𝑝 = 600---88 Fig. 4.49 Photos taken from side view of boiling flow at selected time instants for

d𝑝=1.0 mm and 𝑁𝑝 = 600---89

Fig. 4.50 Photos taken from side view of boiling flow at selected time instants for q= 3.69 W/ cm2 with stainless steel particles on heated surface at

d_𝑝=1.0 mm and 𝑁_𝑝 = 600---90 Fig. 4.51 Photos taken from side view of boiling flow at selected time instants for

d𝑝=1.0 mm and 𝑁𝑝 = 600---91

Fig. 4.52 Schematic illustration of particle-bubble interactions in boiling flow on heated surface at (a) low flux, (b) medium flux and (c) high flux(∆t ≈ 0.01 sec.)---92 Fig. 4.53 Schematic illustration of retarding bubble growth and departure by

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NOMENCLATURE

A area, mm2 cp specific heat, J/kg∙ dp diameters of particles, mm Np numbers of particles

Npf maximum particle number forming a single particle layer

h heat transfer coefficient, W/m2∙K

I measured current from DC power supply, A V measured voltage from DC power supply, V k thermal conductivity, W/m∙K L characteristic length, m NuL Nusselt number,  k hL Nu_L 

P system pressure, kPa Q heat transfer rate, W qn net wall heat flux, W/cm2

Ra Rayleigh number T temperature, C t time, sec W plate width, cm Greek Symbols  kinematic viscosity, m2/ s 𝜌_𝑐𝑢 copper density (𝜌_𝑐𝑢=8989.9), kg/m3   liquid density, kg/m3 𝜌𝑝 particle density, kg/m3

𝜌_𝑠𝑠 stainless steel density (𝜌_𝑠𝑠=7984.3), kg/m3

 absolute viscosity, kg/m∙s  coefficient of expansion, /

 surface tension, N/m

 the distance between the thermalcouple tips and the upper surface of the copper plate, m

∆𝑇𝑤 wall superheat, K

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xiv g gravity, 𝑚 𝑠⁄ 2

α Thermal diffusion coefficient, m2

/ s 𝑖𝑙𝑣 Latent heat, kJ/kg

Subscripts Cu copper

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CHAPTER 1 INTRODUCTION

1.1 Motive of the Present Study

Recent significant technological advances in electronics industry have led to a rapid miniaturization of integrated circuits. Consequently, the power dissipation density in various micro processors increases significantly during their normal operation. How to effectively remove the large amount of dissipating heat from the processors poses a great challenge to heat transfer research community. In order to transfer the large quantity of the dissipating heat from the chips with an ultra high microelectronic component density, highly efficient heat transfer methods are required to control their temperatures at allowable level. Although air cooling has been used commonly today over a long period of time, this method has reached its upper performance limit and is unable to solve the cooling problems encountered in the current electronics industry [1]. Therefore, cooling techniques have to be improved and heat transfer systems with better efficiency have to be used. Cooling based on liquid convection and liquid-vapor phase-change heat transfer have been considered. Among these, boiling heat transfer is regarded as one of the most effective methods in electronics cooling comparing with the methods based on single-phase heat transfer because of the exchange of latent heat involved in the boiling processes. Methods to further improve the boiling heat transfer are therefore of great interest.

Over the past decades a number of passive boiling heat transfer enhancement methods have been proposed by modifying geometrical structure of the heated surface such as adding the micro-structures, pin fins and grooves to the surfaces. Significant pool boiling heat transfer enhancement can be obtained. Besides, coating the surfaces with particles and covering the surfaces with screens have been known to be effective. These enhancement methods are based

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on various forms of extended surface fixed firmly onto the surfaces or directly fabricated on the surfaces. Moreover, some active boiling heat transfer enhancement methods such as vibrating and rotating working fluids and/or heated surface by external forces were suggested. These methods are very effective. But they are not welcome because the need to use external force. In the present study, enhancement of FC-72 pool boiling heat transfer by placing a large number of movable small solid particles above a heating plate will be explored. The particles can be moved violently by the vigorous motion of the bubbly flow in the pool boiling on one end. On the other end, the violently moving particles can increase the bubble departing rate from the heated surface and the turbulence level of the boiling flow. These mutual interactions of the particles and bubbly flow can be beneficial in promoting the boiling heat transfer from the heated surface. However, the presence of a large number of the particles can impede the bubble departure from the heated surface and liquid inrush to the surface. This in turn will retard the boiling heat transfer. In the present investigation we intend to delineate the ranges of experimental parameters over which boiling heat transfer can be enhanced by the moving particles.

The working fluid FC-72 is a dielectric fluorocarbon liquid manufactured by the 3M Company and gains popularity in electronics cooling application. It not only has suitable phase-change temperature for thermal control of I.C. components but also owns the quality that does not foul the boiling surface. Importantly, FC-72 has less impact on our environment than alternative liquids like chlorofluorocarbons or organic liquids. Copper has properties of better thermal conductivity than most metals and is often considered to be suitable for heat dissipating elements. Thus the heat transfer enhancement characteristics of pool boiling of the dielectric liquid on a copper plate by placing movable solid particles above the heated surface immersed in FC-72 liquid are explored in the present study. In an earlier study [2] we obtained significant enhancement in pool boiling heat transfer of FC-72 over a small horizontal heated copper plate by placing fine copper strings over the plate with their ends firmly fixed onto the

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plate edges when the string length, size and height are suitably chosen.

1.2 Literature Review

In what follows the literature relevant to the present study is briefly reviewed. Pool boiling heat transfer is a process of vigorous heat transfer resulting from latent heat exchange associated with liquid-to-vapor phase change in a quiescent liquid. Nukiyama [3] conducted a pioneering pool boiling experiment in 1934 and arranged the experimental heat transfer data as a form of the wall superheat versus the heat flux, which is known as the “boiling curve” today. After that, the pool boiling heat transfer research has received considerable attention.

The state of the art cooling technologies for handling heat dissipation in microelectronic equipments have been developed extensively over the past 30 years. Several products were released including Air-Cooled Modules, High Thermal Conduction Modules, and Liquid-Cooled Modules, as discussed by Bar-Cohen [4].

In an early attempt to improve pool boiling heat transfer by using a micro-configured surface, Miller et al. [5] found that vapor retention could be a function of the scale and geometry of the micro-configurations. They pointed out that the relation between the stability of the potential nucleation sites and the micro-configuration size and geometry required further investigation, so that the size and the site density of the cavities could be optimized for boiling heat transfer enhancement.

Slightly later a few studies have been carried out to examine the influences of the surface fabricated microstructures on the pool boiling heat transfer. These include boiling of FC-72 on micro-porous surfaces with particle coating tested by Chang and You [6] and by Vemuri and Kim[7], adding micro-porous pin-fins and in the meantime coating particles to the surface investigated by Rainey and You [8,9], and fabricating micro-pin-fins and submicron-scale roughness on the surfaces by Honda et al. [10] and Wei et al. [11]. The study of Rainey and You [8, 9] concluded that the microporous coating can significantly enhance the boiling heat

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transfer performance over the pin-finned surfaces. In examining the pool boiling on the micro-pin-fin surfaces, Honda et al. [10] and Wei et al. [11] noted that the boiling curves were characterized by that a very small increase in the wall superheat could cause a large increase in the heat flux. And increasing the fin height was found to provide better heat transfer in the nucleate boiling regime and result in a higher critical heat flux. Nucleation site interaction in pool boiling on an artificial surface was investigated by Zhang and Shoji [12] and by Yu et al. [13]. The hydrodynamic interaction can be also influenced by some factors, such as the liquid properties, subcooling, system pressure. The study of Yu et al. [13] concluded that the critical heat flux was dependent on the cavity density. The evaporation/boiling heat transfer regimes in the capillary wicking structures were identified and discussed by Li et al.[14] and Li and Peterson[15]. Anderson and Mudawar [16] reported that microstructures in the forms of fins, studs, grooves and vapor-trapping cavities on the boiling surface significantly shifted the boiling curve toward lower superheats while increasing the incipience excursion. Their results also suggest that the maximum boiling heat flux is a function of surface geometry and orientation but independent of the initial conditions, surface roughness, or the presence of large artificial cavities. Intending to augment boiling heat transfer, O’Connor and You [17] painted silver flakes on the boiling surface. Their experimental data show that the incipience boiling superheats are 70-85% lower and the nucleate boiling superheats are 70-80% lower than the bare surface. Besides, the critical heat flux is increased by 109%. O’Connor et al. [18] then compared two methods of generating surface microstructures, “spraying” and “painting”, for pool boiling heat transfer enhancement. They noted that the incipient boiling superheat showed 33-55% reduction for the sprayed alumina and 63-85% reduction for the painted diamond. The enhancement in the critical heat flux can be up to 47% for the sprayed alumina and 103% for the painted diamond microstructures. Chang and You [19] further studied the effects of coating different sizes of the diamond particles on the pool boiling heat transfer performances. They classified the coating thickness into two groups. For coatings thinner than

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100 μm, increasing the coating thickness would generate a higher active nucleation density. But for coatings thicker than 100 μm, a further increase in the coating thickness does not always enhance the pool boiling heat transfer. They attributed this result to higher impedance for liquid-vapor exchange channels and higher thermal resistance for the thicker coating. Jung and Kwak [20] investigated the effects of submicron-scale roughness on the subcooled boiling heat transfer over a boiling surface anodized in DMF (dimethylforamide) and HF (hydrofluoric acid). Both surface treatments were found to increase the effective boiling area and served for increasing the nucleation sites and hence showed considerable enhancement in the boiling heat transfer. The critical heat flux also increases linearly. Honda and Wei [21] reviewed recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids through the use of surface microstructures and concluded that most of the surface microstructures were effective in decreasing the wall superheat at the boiling incipience. The nucleate boiling heat transfer also can be improved and the critical heat flux is raised. Rainey and You [22] and Rainey et al. [23] respectively studied the effects of the orientation and pressure on the pool boiling heat transfer from microporous surface. Their data show that nucleate boiling performance increases slightly for the surface inclined from 0(horizontal) to 45 and then decreases for the inclination angle ranging from 90 to 180. Moreover, for the plain and microporous surfaces increases in boiling performance and critical heat flux and decrease in the incipience wall superheat were noted as the pressure increased.

Chou et al. [24] arranged several grooved patterns on surfaces intending to enhance boiling heat transfer of distilled water. Their experimental data reveal that the radial grooved pattern has the best enhanced boiling heat transfer performance and the spiral or concentric grooved pattern has poorer boiling heat transfer coefficient. The worst performance is noted for the grid or the spotted grooved pattern. All grooved patterns they investigated have better heat transfer performance than the plain surface and the denser groove is better than the sparser one for the same patterns.

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Hasegawa et al. [25] covered a heat pipe with a woven screen to investigate the associated boiling characteristics and burnout phenomena. Their results disclose that the additional screen produces two opposite effects of inhibiting and enhancing the boiling heat transfer. Tsay et al. [26] explored pool boiling heat transfer enhancement by covering the boiling surface with a screen in distilled water. They found that the screen coverage could raise bubble generation frequency and enhance the boiling heat transfer. But the screen can also cover some nucleation sites and hence may retard the boiling heat transfer. They also noted that the boiling heat transfer became poorer at lowering the liquid level. They concluded that covering the heated surface with a screen could augment the pool boiling heat transfer if the mesh size was comparable with the bubble departure diameter. In boiling of methanol and HFE-7100, Liu et al. [27] pointed out that placing a fine mesh layer on the boiling surface enhanced nucleate boiling heat transfer at low wall superheat (∆T_𝑠𝑎𝑡<10K) but an opposite trend resulted at a high superheat (∆T𝑠𝑎𝑡>10K). They also reported that the heat transfer in

nucleate boiling always became worse with a coarse mesh on the boiling surface when compared with that on a smooth surface. Moreover, Franco et al. [28] used dielectric refrigerant R141b to investigate enhancement in the boiling heat transfer performance by covering the heated surface with wire meshes. The boiling heat transfer coefficient was noted to increase significantly, especially at relatively low heat fluxes. They also found that the wire mesh coverage on the heating surface resulted in slower transition to steady film boiling. In studying the effects of the wall superheat and the mesh layer covering on boiling heat transfer, Kurihara and Myers [29] tested several working fluids including water, acetone, n-hexane, carbon tetrachloride, and carbon disulfide. They found that active nucleation sites on the heating plate increased due to the mesh covering and the boiling heat transfer coefficient was proportional to the one-third power of the bubble column numbers at high numbers.

Shi et al. [30] investigated pool boiling heat transfer in liquid saturated particle bed and fluidized bed of distilled water. The tests were conducted for glass beads, steel ball, find sand

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and 𝐴𝑙₂𝑂₃ particles. They showed that boiling heat transfer could be enhanced greatly by adding the solid particles into the liquid whether in fixed particle bed or in fluidized particle bed. The boiling heat transfer enhancement is closely related to the particle size (𝑑𝑝=0.5, 1.0

and 2.0 mm), initial bed depth (𝐻_𝑝=3.0, 6.5, 9.5 and 13.4 mm) and heat flux applied. The best heat transfer enhancement is 120% for the particles diameter 𝑑_𝑝=1.0 mm and bed height 𝐻_𝑝=9.5 mm. A similar study was conducted by Matijevic et al. [31] using lead spheres to cover a heating surface. The spheres were packed as closely as possible into a single layer. They noted that boiling heat transfer from the heating surface to water could be enhanced substantially by the metallic spheres (d=3.0, 3.5, 3.6, 4.0 and 4.5 mm), and the smaller spheres resulted in a better enhancement of boiling heat transfer.

Heat transfer enhancement by employing nanofluids has become very popular recently. In nanofluids a very large number of nano particles (diameters smaller than 100 nm) are added into a working fluid which is considered to significantly increase thermal conductivity of the fluid. Wen and Ding [32] reported an enhancement of boiling heat transfer coefficient for about 40% with alumina water based nanofluids. On the other hand, by using the same nanoparticles in the same fluid, Bang and Chang [33] found that the boiling heat transfer coefficient deteriorated for about 20% when the nanoparticles are added.

Some active techniques to enhance boiling heat transfer were also proposed in the literature. Jeong and Kwon [36] found that the CHF augmentation in pool boiling of water due to ultrasonic vibration was closely related to its effects on the process of bubble generation and its departure. They noted that the rate of increase in CHF for downward facing surface ranged from 87~126% as the water subcooling varied from 5 to 40℃. Cipriani et al. [37] imposed electric field on pool boiling of FC-72 over a heated platinum wire (d=0.1 and 0.2 mm)and found that the boiling heat transfer was strongly influenced by the presence of the electric field at a low wire superheat. An increase of the boiling heat transfer coefficient up to 400% was encountered with the maximum applied voltage. But it is almost unaffected by electrical force

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8

at high wire superheat. Through heated surface vibration, Navruzov et al. [38] demonstrated that boiling heat transfer of ethanol could be substantially enhanced at low imposed heat flux. The amplitude of the surface vibration is found to be a governing parameter for heat transfer enhancement at low-frequency vibrations. Besides, the vibration of the heat transfer surface significantly alters the heat transfer process both in subcooled boiling and in free convection. The single-phase heat transfer curves are 70-80% above the basic curve at increasing heat loads.

1.3 Objective of Present Study

The above literature review clearly reveals that considerable works have been carried out in the past to investigate the enhancement in the pool boiling heat transfer over a surface by passive methods through fabricating surface microstructures such as roughness and micro-pin-fins and by covering the surface with mesh screens and particle coating. All these microstructures are fixed firmly onto the boiling surface. Besides, some effective active heat transfer augmentation methods such as vibrating or rotating heating surface and/or fluid and applying electric field to vibrate a heating surface have been suggested. In this study, an experimental study is conducted to explore the possible enhancement in the FC-72 pool boiling heat transfer by placing movable metallic particles on the boiling surface. The violent motion of the bubbles in the boiling flow can significantly move the particles. The particles, in turn, can greatly affect the bubble dynamics near the surface. Thus we expect the boiling heat transfer from the surface can be enhanced by the particles. The method proposed here is passive in nature. However, it behaves like an active heat transfer enhancement method.

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9

CHAPTER 2 EXPERIMENTAL APPARATUS AND PROCEDURES

A schematic arrangement of the experimental apparatus for the present investigation of the pool boiling heat transfer enhancement by movable metallic particles driven by the boiling flow is similar to that employed in the previous study [2] and is shown in Fig. 2.1. The experimental system includes a main test chamber, a test heater assembly, and other auxiliary parts such as a D.C. power supply, a data acquisition unit and a high-speed photographic unit. The working fluid, FC-72, is a highly wetting dielectric fluorocarbon liquid produced by 3M Industrial Chemical Products Division, which has been considered as a good candidate fluid for liquid immersion cooling applications. It is chemically stable, dielectric, and has a relatively low boiling point (Tsat=56C at atmospheric pressure). Some thermophysical

properties of FC-72 are given in Table 2.1.

2.1 Main Test Chamber

The main test chamber is a hermetic stainless steel pressure vessel of 205 mm in height and 216 mm in diameter. An internal water condenser is installed inside the chamber and connects with a thermostat (LAUDA RK20) to maintain the bulk temperature of the working fluid in the chamber at the preset level. The maximum cooling power of the thermostat is 180W (at 20C). We further use an external temperature controller (FENWAL MYSPEC Digital Temperature Controller) to control the bulk temperature of FC-72 in the test chamber with an accuracy of  0.1C. Besides, a cartridge heater is located near the bottom of the test chamber to provide additional heating during the degassing process. In order to prevent the heat

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10

loss from the vessel to the ambient, a superlon layer of 10-mm thick is wrapped around the chamber. Moreover, a pressure transducer with an operating range of 0-200 kPa is located at the gate valve to measure the pressure of the work fluid. Meanwhile, the working fluid temperature is measured by two resistance temperature detectors (RTDs) located at the gate valve and at a selected location 5 cm above the bottom surface of the chamber with a calibrated accuracy of 0.1C. An auxiliary tank of 10-liter liquid FC-72 is placed right above the test vessel and it is only used for subcooled pool boiling experiment to prevent regassing of the working fluid after degassing. A pressure transducer and a RTD are placed in the auxiliary tank to measure the internal gas pressure and liquid temperature. In addition, a test heater assembly is mounted to a stainless steel shelf to fix the PEEK substrate. The working fluid is maintained at approximately 80 mm above the heated surface in the experiment.

2.2 Test Heater Assembly

A schematic of the test heater assembly is shown in Fig. 2.2. The assembly consists mainly of a film heater and it is adhered to the lower surface of a square copper plate by epoxy Omegabond 200. The plate is 10 mm thick with 30x30 𝑚𝑚2 in surface area. The heater supplies the required power input to the copper plate. The copper plate is flush mounted onto a much larger PEEK (Polyether Ether Ketone) block. Liquid FC-72 boils on the upper surface of the copper plate. More specifically, the copper plate is heated by D.C. current delivered from a D.C. power supply to the film heater. Besides, three calibrated copper-constantan thermocouples (T-type) with a calibrated accuracy of 0.2C are installed at selected locations in the copper plate right below the boiling surface. They are used for the control and determination of the

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11

boiling surface temperature. The detailed locations of the thermocouples installed in the copper plate are shown in Fig. 2.3. Note that the whole copper plate is inserted into a PEEK block which serves as a heat insulator (k_T 0.25W/mK), intending to reduce the heat loss from the lateral and bottom surfaces of the plate to the ambient. Besides, the locations of thermocouples in the PEEK block are shown in Fig. 2.4.

2.3 Confinement of Particles and Experimental Parameters

Solid particles of the same material and uniform size are placed freely on the upper surface of the copper plate, as schematically shown in Fig. 2.5. In order to insure that the particles would not be blown away by the vigorous motion of the bubbles, we install an acryl fence of 2-cm high and 1-cm thick around the edges of the heating copper plate. In the present study tests will be conducted for copper and stainless steel (type304) particles. The densities of copper and stainless steel are measured before the experiment with 𝜌_𝑐𝑢 = 8990 𝑘𝑔 𝑚⁄ 3 and 𝜌_𝑠𝑠 = 7984 𝑘𝑔 𝑚⁄ 3. These two kinds of metallic particles are chosen here because the copper and stainless steel have much higher densities than liquid FC-72. Besides, the chosen particles should not be too small so that they float in the liquid above the plate and do not contact the heating surface. Moreover, they should not be too large and cannot be moved by the boiling flow. Here, the particle diameter is selected to be 1.0 and 1.5 mm. The chosen particle size and number for the cases tested here are summarized in Table 2.2. The measured data expressed in terms of boiling curves and boiling heat transfer coefficients will be compared with that of a bare heating surface.

2.4 DC Power Supply

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by a programmable D.C. power supply (Gpc 3030D). It offers a maximum D.C. power of 180W for an output voltage of 60V and an output current of 3A. The power input to the copper block is transmitted through a GPIB interface to a personal computer. In order to measure the D.C. current, a precision ammeter (KYORITSU A.C./D.C. DIGITAL CLAMP METER) is arranged in series connection with the electric circuit. Besides, a YOKOGAWA data recorder is used to measure the voltage drop across the test heater assembly. All the voltage, current and power measurement devices are calibrated by a YOKOGAWA WT200 power meter according to the Center of Measurement Standards in Industrial Technology Research Institute of Taiwan.

2.5 Data Acquisition

A 20-channel YOKOGAWA data recorder (MX-100) combined with a personal computer is used to acquire and process the data from various transducers. All signals detected from the T-type thermocouples, RTDs, pressure transducer, ammeter, data recorders and power meter are all collected and converted by the internal calibration equations in the computer during the data acquisition.

2.6 Optical Measurement Technique

A high-speed camera along with a microscope is installed in front of the observation window to observe the boiling activity in the flow. The photographic apparatus consists mainly of a high speed digital video camera (IDT High-speed CMOS Camera), a micro-lens (Optem Zoom 16), and a three-dimensional positioning mechanism. The high-speed motion analyzer can take photographs up to 143,307 frames/sec. In the present experiment the recording rate is 1000 frames/sec. After the

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13

experimental system reaches a statistical state, we start capturing the images of the particles and bubbles in the boiling flow. Besides, we store and display the images in the personal computer through an image-capturing software.

2.7 Experimental Procedures

The boiling surface is polished by fine sand paper (Number 3000, 2000 and 1000) and cleaned by ethyl alcohol before each experimental run. In each test, we place the chosen metallic particles on the heated plate. Besides, we remove non-condensable gases existing in the empty test chamber by running a vacuum pump for about 15 minutes and then fill the FC-72 liquid into the chamber until the liquid level is higher than the heating plate for about 8 cm. Next, the FC-72 liquid in the test chamber is heated to the saturation state which is detected and maintained by a digital temperature controller. Moreover, the FC-72 liquid is boiled vigorously for 1 hour to further remove the dissolved non-condensable gases in it. After the working fluid pressure and temperature stabilize to one atmosphere and at the saturation state, we turn on the test heater. The imposed heat flux on the boiling surface is adjusted by controlling the electric current delivered to the heater from the D.C. power supply. Upon reaching the statistical state, we begin collecting the required heat transfer data and visualizing the boiling activity. Effects of the particle material, size and number density on the possible heat transfer enhancement are investigated in the experiment.

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14

Table 2.1 Thermophysical properties of FC-72.

Properties at 25C FC-72

Appearance Clear, colorless

Average Molecular Weight 338

Boiling Point (1atm) 56C

Pour Point (1atm) -90C

Estimated Critical Temperature 449K

Estimated Critical Pressure 1.83 × 106 Pa

Vapor Pressure 3.09 × 104 Pa

Latent Heat of Vaporization hfg

(at normal boiling point)

88 J/g

Liquid Density _ 1680 kg/m3

Absolute Viscosity  6.4× 10-3 poises ; 6.4× 10-4 kg/m∙s Kinematic Viscosity  3.8 × 10-3 stokes ; 3.8 × 10-7 m2/ s

Liquid Specific Heat cp 1100 J/kg∙C

Liquid Thermal Conductivity k 0.057 W/m∙C

Coefficient of Expansion  0.00156 /C

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Table 2.2 Cases covered in present study

Particle 𝑁𝑝 Particle 𝑁𝑝 Copper (d𝑝=1.0 mm) 100 Stainless steel (d_𝑝=1.0 mm) 200 200 400 300 600 400 800 500 1000 600 1200 700 1400 800 1600 900 1800 1000 Particle 𝑁𝑝 1100 Stainless steel (d_𝑝=1.5 mm) 200 1200 400 1400 600 1600 700 1800 800 Copper (d_𝑝=1.5 mm) 100 200 300 400 500 600 700

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16 800

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17

Fig. 2.1 Schematic diagram of the test apparatus. Liquid

Level

P

Condenser Coil

Observation Window

To Degassing Tank and Drain

Computer GPIB MX100 Data Acquisition Heater Boiling Surface FC-72 Digital Temperature Controller Shelf RTD Condenser Test Heater Assembly Observation Window Electric Cord Signal Cord Programmable D.C. Power Supply Liquid Level

P

Condenser Coil Observation Window

To Degassing Tank and Drain

Computer GPIB MX100 Data Acquisition Heater Boiling Surface FC-72 Digital Temperature Controller Shelf RTD Condenser Test Heater Assembly Test Heater Assembly Observation Window Electric Cord Signal Cord Programmable D.C. Power Supply

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Fig. 2.2 Schematic diagram of the test heater assembly (not to scale).

30

30 7

100

Embedded Copper Plate

Electric Film Heater

Perspective view

Front view

Top view

PEEK substrate

(unit:mm)

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19

Fig. 2.3 Locations of three thermocouples in the copper plate and one thermocouple below the heater (not to scale).

Front view

Top view

(unit:mm)

Perspective view

              #3,5 #3 #3 #1,8 #1,8 #1 #4 #2 #5 #2,4 #8 #5 #4 #2 1 5 5 30 30

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20

Fig. 2.4 Locations of two thermocouples in the PEEK (not to scale).

(unit:mm)

Perspective view

PEEK

substrate

  #7 #6

Front view

 3.5 #6  #7 12

Top view

Copper Surface

  #7 #6

Copper Plate

31

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Fig. 2.5 Schematic diagram of placing movable particles on heating surface with acryl rectangular enclosure (not to scale).

Perspective view

Top view

PEEK substrate PEEK Surface

(unit:mm)

Right view

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21

CHAPTER 3 DATA REDUCTION

3.1 Boiling Heat Transfer Coefficient

The space-average natural convection and boiling heat transfer coefficients over the upper surface of the heated square copper plate when the flow is at a statistical state are both defined as

h = 𝑞𝑛

∆𝑇𝑤

⁄ (3.1)

where qn is the net heat flux imposed on the upper surface andΔTsat is the wall

superheat defined as the difference between the average surface temperature and the saturated temperature of FC-72. The average heated surface temperature 𝑇_𝑤 is estimated from the measured average temperature from the thermocouples installed at different locations near the upper surface of the copper plate according to the steady-state one-dimensional conduction heat transfer. Specifically,

         Cu n Cu w k δ q T T (3.2) where

TCu = the average measured temperature from the thermocouples (C)

kCu = the thermal conductivity of copper (W/m∙K)

= the vertical distance between the thermocouple tips and the upper surface of the copper plate (m)

The total power input Qt to the copper plate can be obtained from the

measured voltage drop across the film heater in the test heater assembly and the current passing through it,

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22 V

I

Q_t   (3.3) where

Qt = total power input to the upper surface of the copper plate (W)

I = electric current passing through the film heater (Amp.) V = voltage drop across the film heater (Volts)

The substrate of the test section is made from PEEK, which have a much lower thermal conductivity (k_T 0.25W/mK) than the copper (_k₃₈₆_W/m_K). In evaluating total heat loss from the heater assembly, we focus on heat transfer from the heater and copper plate surface to the PEEK. Figures 2.3 and 2.4 are the schematic diagrams of the thermocouples buried in the copper plate and PEEK. The heat dissipation model used to estimate the heat loss is shown in Fig. 3.1, and the total heat loss can be estimated as follows:

Q

_loss

= k

_p

∙

(T8−T7) L1

∙ A

1

+ 4 ∙ k

p

∙

(TCu−T6) L2

∙ A

2

+

2π∙kp∙L3∙(TCu−T6) ln( r6 rCu,2)

+

+k

_p

∙

(TCu−T′5) L5

∙ A

5

+k

p

∙

(TCu−T′6) L6

∙ A

6 where

T6 , T7 , T8 : the average measured temperatures at the measured locations inside the

PEEK insulator, as schematically shown in Figs. 2.3 & 2.4

𝐿 1, 𝐿2 , 𝐿 3 , 𝐿 4 , 𝐿 5 , 𝐿 6: shortest distances between locations No.1~No.6 and the

film heater or copper plate (m)

A1 , A2, A3, A4, A5, A6 : bottom and lateral surface areas of the copper plate

T'5 , T'6 : these two temperatures are calculated by using interpolation method based

on 𝑇₆, as schematically shown in Fig. 3.2

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Finally, the net imposed input heat flux to the upper surface of copper plate can be evaluated from the relation

Cu loss t n A Q Q q   (3.5) where ACu_{is the area of the upper surface of the copper plate.}

3.2 Uncertainty Analysis

An uncertainty analysis is carried out here to estimate the uncertainty levels in the experiment. Kline and McClintock [34] proposed a formula for evaluating the uncertainty in the result F as a function of independent variables, X1, X2, X3∙∙∙∙∙∙∙∙∙∙∙∙Xn,

F=F (X1 ,X2, X3∙∙∙∙∙∙∙∙∙∙∙∙Xn) (3.6)

The absolute uncertainty of F is expressed as

2 1 2 2 3 3 2 2 2 2 1 1                                                                      _n n X X F X X F X X F X X F F       (3.7)

and the relative uncertainty of F is

2 1 2 2 3 3 3 2 2 2 2 2 1 1 1                                                                                              n n n X X nX nF X X nX nF X X nX nF X X nX nF F F               (3.8) If 1 2 3... c b a X X X

F  , then the relative uncertainty is

2 1 2 3 3 2 2 2 2 1 1                                                  X X c X X b X X a F F     (3.9) where i X F  

and X_i are, respectively, the sensitivity coefficient and uncertainty

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24

obtained by a root-mean-square combination of the precision uncertainty of the instruments and the unsteadiness uncertainty, as recommended by Moffat [35]. The choice of the variableX to be included in the calculation of the total uncertainty _i level of the result F depends on the purpose of the analysis.

The uncertainties of the parameters in the present study are calculated as follows: (1) Uncertainty of temperature difference, Tw=Tw-Tsat









2 1 2 2 2 1 2 2 2 1 2 2 ) ( ) (                                                                                                                               sat w sat sat w w sat sat sat w sat w w sat w w sat sat sat sat w w w w sat w sat w sat w T T T T T T T T T T T T T T T T T T nT T T n T T nT T T n T T T T            (3.10) (2) Uncertainty of total power input, Qt

V I Q_t   (3.3) and 2 1 2 2                       V V I I Q Q t t    (3.11)

(3) Uncertainty of net wall heat flux, 𝑞_𝑛

Cu loss t n A Q Q q   (3.5) and

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25 2 1 2 2 2 2 1 2 2 2 2 1 2 2 2 1                                                                                                                                                                     loss t loss loss t t Cu Cu loss loss loss t loss t t loss t t Cu Cu loss loss loss n t t t n Cu Cu Cu n n n Q Q Q Q Q Q A A Q Q Q Q Q Q Q Q Q Q A A Q Q nQ nq Q Q nQ nq A A nA nq q q                 (3.12) Where

Q

_loss

= k

_p

∙

(T8−T7) L1

∙ A

1

+ 4 ∙ k

p

∙

(TCu−T6) L2

∙ A

2

+

+k

_p

∙

(TCu−T′5) L5

∙ A

5

+k

p

∙

(TCu−T′6) L6

∙ A

6 (3.4) (4) Uncertainty of space-average heat transfer coefficient, h

sat n T q h _Δ (3.1) and









2 1 2 2 2 1 2 2 2 1 2 2 1 1                                                                                                                    sat w sat w n n sat w sat w n n sat w sat w sat w n n n T T T T q q T T T T q q T T T T T T n nh q q nq nh h h           

A summary of the results from the present uncertaintly analysis is given in Table 3.1.

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26

Table 3.1 Summary of the results from the uncertainty analysis.

Parameter Uncertainty

Geometry Length & thickness (%)

Area (%) Particle diameter (%) Particle density(%) 0.167% 0.334% 10% 13.4% Parameter measurement Temperature, T (C) Temperature difference, ∆𝑇𝑠𝑎𝑡 (C)

System pressure, P (kPa)

0.2

0.36

0.5

Boiling heat transfer on the copper flat plate Total power input, Qt (%)

Imposed net heat flux, qn (%)

Heat transfer coefficient, h(%)

5.9%

8.3%

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27

Fig. 3.1 Schematic diagram of six main directions of the heat loss. 2 3 4 5 6 1 Copper block

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28

Fig. 3.2 Schematic diagram of T'5 and T'6

Film heater

Copper block

T′5 T′6

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29

CHAPTER 4 POSSIBLE POOL BOILING HEAT TRANSFER ENHANCEMENT OF

FC-72 OVER HEATED COPPER SURFACE

The experimental results to illustrate possible enhancement of saturated pool boiling heat transfer of FC-72 by placing movable particles on the heating surface obtained in the present study are examined in this chapter. The present experiments are carried out for the copper and stainless steel particles with the diameter of the particles d_𝑝 fixed at 1.0 and 1.5 mm, and the total number of particles 𝑁_𝑝 varied from 100 to 1800 for the particles with the diameter 1.0 mm or from 100 to 800 for the particles with the diameter 1.5 mm. The FC-72 liquid in the test chamber is maintained at saturated liquid state corresponding to the atmospheric pressure. Note that the maximum number of particles forming a single closely packed particle layer over the boiling surface 𝑁𝑝𝑓 is 900 and 400 respectively for the particles with the

diameter of 1.0 mm and 1.5 mm when each particle contact directly with neighboring particles. In the experiment tests are also conducted for the particle number well exceeds 𝑁_𝑝𝑓 and many particles are on top of the other particles. The measured data are presented in terms of the boiling curves and boiling heat transfer coefficients for various diameters and numbers of the copper and stainless steel particles and for a bare heating surface. Effects of the experimental parameters on the possible boiling heat transfer enhancement will be examined in detail. Selected data are presented in the following to illustrate the possible pool boiling heat transfer enhancement by the boiling flow driven metallic particles.

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4.1 Single-phase Natural Convection Heat Transfer

Before conducting the pool boiling experiment, we first measure steady natural convection heat transfer of FC-72 liquid over the heated copper surface without the presence of any particles which prevails at low imposed heat flux, intending to verify the present experimental setup. The measured data for the natural convection heat transfer coefficient are compared with the empirical correlation of Radziemska and Lewandowski [39] in Fig. 4.1. Their correlation is

NuL=(2.1e-48W+1.2)RaL0.2 (4.1)

where w is the width of the heating plate (m). The correlation given in Eq.(4.1) is based on the data for a small horizontal plate heated from below for 105<RaL<108.

Note that the characteristic length L used in defining the dimensionless groups in the above equation is chosen to be the ratio of the heated surface area and its perimeter, and the Nusselt and Rayleigh numbers are respectively defined as

(4.2) and

(4.3) The results in Fig. 4.1 indicate that our natural convection data are in good agreement with that calculated from Eq. (4.1). Thus the experimental system established here is considered to be suitable for the present study.

4.2 Saturated Pool Boiling on Bare Copper Surface

To further verify the suitability of the present experimental system, the measured boiling curve for saturated pool boiling of liquid FC-72 on the bare heated copper plate is obtained next. These data are compared with that from Rainey and You [22] in Fig. 4.2 for pool boiling of FC-72 on a square copper plate of 5 × 5 cm2 in

 k hL NuL    3 L )L ( Ra  g Tsat

放置可移動擾動粒子在一水平加熱銅板上對FC-72池沸騰熱傳增強研究

國

立

交

通

大

學

機 械 工 程 學 系

碩 士 論 文

放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

研 究 生：魏 周 民

指 導 老 師：林 清 發 教授

放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

研 究 生 ： 魏 周 民 Student：Chou-Min Wei

指導教授 ： 林 清 發 Advisor：Prof. Tsing-Fa Lin

國立交通大學

機械工程學系

碩士論文

誌謝

放置可移動擾動粒子在一水平加熱銅板上

對 FC-72 池沸騰熱傳增強研究

研 究 生：魏 周 民 指 導 老 師：林 清 發 教授

摘要

Enhancement of FC-72 Pool Boiling Heat Transfer by

Movable Particles on a Horizontal Plate

Student: Chou-Min Wei Advisor: Prof. Tsing-Fa Lin

National Chiao Tung University

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

1.3 Objective of Present Study

CHAPTER 2

EXPERIMENTAL APPARATUS AND PROCEDURES

2.1 Main Test Chamber

2.2 Test Heater Assembly

2.3 Confinement of Particles and Experimental Parameters

2.4 DC Power Supply

2.5 Data Acquisition

2.6 Optical Measurement Technique

2.7 Experimental Procedures

P

P

Embedded Copper Plate

Electric Film Heater

Perspective view

Front view

Top view

PEEK substrate

(unit:mm)

Front view

Top view

(unit:mm)

Perspective view

(unit:mm)

Perspective view

PEEK

substrate

Front view

Top view

Copper Surface

Copper Plate

Copper Plate

Perspective view

Top view

(unit:mm)

Right view

CHAPTER 3

DATA REDUCTION

機械工程學系

碩士論文

研究生：魏周民

指導老師：林清發教授

研究生：魏周民 Student：Chou-Min Wei

指導教授：林清發 Advisor：Prof. Tsing-Fa Lin

研究生：魏周民指導老師：林清發教授