本文關(guān)鍵詞：復(fù)雜結(jié)構(gòu)微通道熱沉流動(dòng)可視化及傳熱過程熱力學(xué)分析　出處：《北京工業(yè)大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 微通道熱沉 熱力學(xué) 強(qiáng)化傳熱 Micro-PIV可視化 納米流體

【摘要】：在傳熱學(xué)領(lǐng)域中,存在著許多散熱問題,比如微型設(shè)備的散熱,具有瞬態(tài)熱流密度高及傳熱面積小的特點(diǎn),嚴(yán)重制約著能源動(dòng)力、航天航空、生物化工、軍工核能及微型電子技術(shù)等領(lǐng)域的發(fā)展。隨著大規(guī)模集成電路技術(shù)的迅速發(fā)展,微型電子芯片單位面積的散熱功率不斷升高,甚至高達(dá)107W/m2。為了保持微型電子器件表面溫度的恒定,必須及時(shí)地去除多余熱量。因此,如何解決微型設(shè)備的散熱問題成為亟需解決的關(guān)鍵。隨著微加工工藝的發(fā)展,微通道熱沉由于面體比大、結(jié)構(gòu)緊湊、散熱效率高等優(yōu)點(diǎn)成為解決高熱流密度問題行之有效的方法之一。本文采用實(shí)驗(yàn)、模擬與理論相結(jié)合的方法,針對具有高熱流密度發(fā)熱面微型設(shè)備的冷卻問題,綜合考慮通道結(jié)構(gòu)及工質(zhì)種類兩方面因素,設(shè)計(jì)具有結(jié)構(gòu)緊湊、高散熱性能的復(fù)雜結(jié)構(gòu)微通道熱沉,并建立復(fù)雜結(jié)構(gòu)微通道熱沉強(qiáng)化傳熱過程的熱力學(xué)模型及結(jié)構(gòu)優(yōu)化的數(shù)學(xué)模型,為微通道熱沉強(qiáng)化換熱研究提供理論基礎(chǔ)。主要包括以下幾方面內(nèi)容:首先,為了解決凹穴型微通道在低雷諾數(shù)下散熱不明顯的問題,在此通道的基礎(chǔ)上,在兩個(gè)凹穴之間加入內(nèi)肋,形成結(jié)構(gòu)更為復(fù)雜的凹穴及內(nèi)肋組合的微通道。并且,用數(shù)值模擬的方法研究了不同形狀的凹穴及內(nèi)肋組合的微通道的綜合傳熱性能。模擬結(jié)果表明,在凹穴區(qū),由于面積突擴(kuò)流速減小,容易引起層流分層,形成旋渦,有利于冷熱流體充分混合;而在肋區(qū),由于面積突縮流速增大,流體質(zhì)點(diǎn)能保持相對大的動(dòng)能快速地流過凹穴段,防止形成層流滯止區(qū)�？偟膩碚f,凹穴及內(nèi)肋組合的微通道能明顯增強(qiáng)內(nèi)部擾動(dòng),起到強(qiáng)化傳熱作用。在低雷諾數(shù)時(shí),三角形凹穴及梯形內(nèi)肋組合的微通道的綜合傳熱性能最優(yōu);而在高雷諾數(shù)時(shí),三角形凹穴及三角形內(nèi)肋組合的微通道的綜合傳熱性能最優(yōu)。其次,根據(jù)熱力學(xué)第一及第二定律,推導(dǎo)出復(fù)雜結(jié)構(gòu)微通道流動(dòng)與傳熱過程的熵產(chǎn)模型,并結(jié)合場協(xié)同原理,從熱力學(xué)及傳熱學(xué)角度共同分析影響微通道熱沉強(qiáng)化傳熱的本質(zhì)原因。理論分析表明,降低流體溫度梯度的凈值能起到強(qiáng)化傳熱作用。并指出用強(qiáng)化傳熱因子、場協(xié)同數(shù)、熵產(chǎn)增大數(shù)及熱能傳輸效率這四個(gè)無量綱數(shù)均能評價(jià)通道內(nèi)部的傳熱性能,但由于定義不同,評價(jià)的側(cè)重點(diǎn)也不同。再次,使用先進(jìn)的流動(dòng)可視化手段——Micro-PIV(Micro-Particle Image Velocimetry)系統(tǒng),觀察凹穴及內(nèi)肋組合的微通道熱沉內(nèi)部詳細(xì)的流動(dòng)情況,從流動(dòng)角度分析及驗(yàn)證該類型熱沉的強(qiáng)化傳熱作用。實(shí)驗(yàn)結(jié)果表明,該類型通道的軸向速度呈波峰及波谷相互交替的周期性分布趨勢;在低雷諾數(shù)時(shí),凹穴區(qū)沒有出現(xiàn)旋渦,內(nèi)肋區(qū)的流體具有較大的動(dòng)能帶走凹穴區(qū)的流體,減少流體的滯止時(shí)間,提高了通道的換熱性能;而在高雷諾數(shù)時(shí),凹穴區(qū)容易形成旋渦,二次回流有助于提高通道的換熱性能。接著,使用兩步法制備不同體積分?jǐn)?shù)的Al2O3納米流體,并用實(shí)驗(yàn)手段測量其導(dǎo)熱系數(shù)及動(dòng)力粘度值。并把它作為冷卻工質(zhì),流經(jīng)本課題組前期提出的凹穴型微通道熱沉,目的是對比分析不同種類工質(zhì)對熱沉散熱能力的影響。實(shí)驗(yàn)結(jié)果表明,納米流體的導(dǎo)熱系數(shù)隨著表面活性劑SDS濃度的增大而減小。說明表面活性劑不利于傳熱,其作用是使納米粒子均勻地分散在基液中,因此表面活性劑的添加量要衡量傳熱與均勻性兩方面因素;傳熱實(shí)驗(yàn)結(jié)果與單相模擬結(jié)果不吻合,說明單相模型不再適合用于模擬納米流體流動(dòng)與傳熱的問題;與純水相比,使用納米流體作為工質(zhì)時(shí)熱沉的傳熱性能更優(yōu),并隨雷諾數(shù)及體積分?jǐn)?shù)的增大而增大,但壓降也隨之增大;用性能評價(jià)圖綜合分析熱沉的傳熱性能,表明納米流體的確起到強(qiáng)化傳熱的作用。再接著,設(shè)計(jì)一種新型的復(fù)雜結(jié)構(gòu)雙層微通道熱沉,并建立其熵產(chǎn)模型;然后提出雙層微通道熱沉的整體封裝方式,并分析各種入口流動(dòng)方式對熱沉總性能的影響。結(jié)果表明,當(dāng)體積流量較小時(shí),雙層微通道所產(chǎn)生的不可逆損失較大,不宜采用該類型熱沉對微電子設(shè)備散熱;當(dāng)體積流量較大時(shí),采用逆流布置方式的復(fù)雜結(jié)構(gòu)雙層微通道熱沉進(jìn)行散熱,其底面溫度分布更均勻,能有效地根除熱應(yīng)力作用。而且,下層通道的流體所產(chǎn)生的熵產(chǎn)率是引起總熵產(chǎn)率增大的主要原因。不同的入口布置方式對熱沉整體性能的影響也很明顯。最后,在給定熱沉總尺寸及散熱功率下,由單相流體對流傳熱模型,設(shè)計(jì)滿足要求的微通道熱沉;并以多目標(biāo)遺傳優(yōu)化算法為基礎(chǔ),建立通道結(jié)構(gòu)優(yōu)化的數(shù)學(xué)模型,以熱阻及泵功值兩個(gè)目標(biāo)函數(shù)同時(shí)最小為優(yōu)化目標(biāo),根據(jù)遺傳算法優(yōu)化出傳熱性能優(yōu)良的通道結(jié)構(gòu)。以給定散熱功率100W及散熱面積10mm×10mm為例,根據(jù)要求設(shè)計(jì)出滿足散熱要求的熱沉,并用性能評價(jià)圖分析不同尺寸熱沉的綜合傳熱性能。結(jié)果表明,通道具有中等寬高比αc的熱沉的綜合傳熱性能最好;然后,用遺傳算法優(yōu)化微通道熱沉的結(jié)構(gòu)參數(shù),以熱阻及泵功為優(yōu)化目標(biāo)參數(shù),得到一系列不同泵功下熱阻最優(yōu)的通道結(jié)構(gòu)尺寸。
[Abstract]:In the field of heat transfer, there are many problems such as heat dissipation, micro heat dissipation equipment, has the characteristics of high heat flux density and heat transfer area is small, seriously restricting the power, aerospace, chemical, nuclear and military development in the field of micro electronic technology. With the rapid development of large-scale integrated circuit technology, power dissipation miniature electronic chip unit area increasing, even as high as 107W/m2. in order to maintain a constant temperature on the surface of micro electronic devices, must promptly remove excess heat. Therefore, how to solve the problem of heat dissipation of the micro devices become the key to solve. With the development of micro fabrication technology, micro channel heat sink due to surface ratio, compact structure the higher cooling efficiency, has become one of the effective methods to solve the problem of high heat flux. This paper uses the method of simulation and experiment, the combination of theory, aiming at With the cooling of high heat flux heating surface micro devices, considering two aspects of tunnel structure and working fluid type factors, the design has the advantages of compact structure, complex structure and high heat dissipation performance of the micro channel heat sink, and to establish the mathematical model of complex structure of micro channel heat sink thermal strengthening heat transfer model and optimize the structure of micro heat sink enhancement of heat transfer and provide a theoretical basis. It mainly includes the following aspects: first, in order to solve the problems of cavity type micro channel at low Reynolds number the heat is not obvious, based on the channel, between the two recesses in ribs, forming more complex structure and inner cavity the micro channel rib combination. And by using numerical simulation method to study the comprehensive heat transfer of different shapes and internal cavity rib combination of micro channel performance. The simulation results show that in the concave area, because the area expansion velocity decreases, Easy to cause the formation of vortices, stratified, conducive to the hot and cold fluid mixing; and in the costal area, because the area of sudden contraction velocity increases, the fluid particle can maintain a relatively large kinetic energy quickly through the cavity, prevent the formation of laminar flow stagnation zone. In general, the recess and inner rib combined micro channel can enhanced internal disturbance, the heat transfer effect. At low Reynolds number, the optimal heat transfer performance of micro channel combined triangle and trapezoid rib cavity inside; while in the high Reynolds number, the optimal heat transfer performance of micro channel rib combination recess in the triangle and triangle. Secondly, according to the first and the two law entropy model to derive the complex structure of micro channel flow and heat transfer process, and combined with the field synergy principle, from the perspective of thermodynamics and common analysis of the impact of micro channel heat sink nature theoretical analysis shows that the enhancement of heat transfer, To reduce the fluid temperature gradient of the net can play a role. And pointed out that with the enhancement of heat transfer enhancement factor, field synergy number, entropy generation number is increased and heat transfer efficiency of the four dimensionless numbers are the heat transfer performance of the internal evaluation of channel, but because of different definitions, the evaluation focus is also different. Once again, the use of flow visualization method advanced Micro-PIV (Micro-Particle Image Velocimetry) system, observe the notch and inner rib combination of micro channel heat sink with internal flow, and verify the type of heat sink heat transfer enhancement effect from the analysis of flow angle. The experimental results show that the axial velocity of the type of channel with periodically distributed trend peaks and troughs alternating with each other; at low Reynolds number when the recess region does not appear vortex, fluid rib area have more energy to take a recess fluid area, reduce fluid stagnation time, improve the channel The heat transfer performance; while in the high Reynolds number, the recess is easy to form a vortex, two backflow helps to improve the heat transfer performance of the channel. Then, the Al2O3 nanoparticles prepared with different volume fraction using the two step method, and measured the thermal conductivity and viscosity values. And take it as the coolant flows through, ourgroup proposed cavity type micro channel heat sink, to comparative analysis of effects of different kinds of refrigerant on the heat sink capacity. Experimental results show that the thermal conductivity of nanofluids decreases with increasing surfactant concentration of SDS. It shows that the surfactant is not conducive to the heat transfer. The effect is to make the nanoparticles are uniformly dispersed in the liquid medium, the addition of surfactants to measure two aspects of heat transfer and uniformity factor; the experimental results and the simulation results of single-phase heat transfer does not match, that model is no longer suitable for single-phase mode The flow and heat transfer of nanofluids; compared with water, the use of nano fluid as the heat transfer performance of refrigerant heat sink is more excellent, and increases with the increase of Reynolds number and volume fraction, but the pressure drop increases; the heat transfer performance evaluation chart comprehensive analysis of heat sink performance shows that the nano fluid plays the effect of heat transfer enhancement. Then, the design of the complex structure of a new double microchannel heat sink, and to establish the entropy model; and then put forward the overall package of double microchannel heat sink, and analyze all kinds of entrance flow can affect the total precipitation of heat. The results show that when the volume flow rate is low double micro channel generated by the larger irreversible loss, should not use this type of heat sink of microelectronic device cooling; when volume is larger, the layout of the complex structure of the dual countercurrent micro channel heat sink for cooling, the bottom surface The temperature distribution is more uniform, can effectively eliminate the effect of thermal stress. Moreover, the entropy production fluid produced by the lower channel is mainly caused by the increase of the total entropy generation rate. The influence of different ways of entrance layout of heat sink performance is also very obvious. Finally, the total power dissipation in the sink size and given heat. The single-phase convective heat transfer model, micro channel heat sink design to meet the requirements; and the multi-objective genetic algorithm as the foundation, established the mathematical model for the optimization of channel structure, two objective functions at the same time as the optimizing goal and pump power on the thermal resistance value, according to the genetic algorithm to optimize channel structure. With excellent heat transfer performance given 100W cooling power and cooling area of 10mm * 10mm for example, according to the design meet the cooling requirements of the heat sink, and performance evaluation analysis of heat transfer performance of different size heat sink. The results show that the channel has The comprehensive heat transfer performance of the heat sink with a medium height to width ratio of alpha C is the best. Then, the genetic algorithm is used to optimize the structural parameters of the microchannel heat sink, and the thermal resistance and pump power are taken as the optimization target parameters, and a series of optimal channel structure sizes of different pump power are obtained.

【學(xué)位授予單位】：北京工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TK124

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相關(guān)期刊論文 前1條

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本文編號：1408937