發(fā)布時(shí)間：2018-05-04 17:19

  本文選題：Lattice + Boltzmann��； 參考：《中國科學(xué)院研究生院(工程熱物理研究所)》2015年碩士論文

【摘要】：微通道冷卻技術(shù)在微電子及激光器件冷卻領(lǐng)域已得到廣泛用,但隨著電子器件熱流密度的不斷攀升,常規(guī)微通道熱沉的冷卻能力面臨巨大挑戰(zhàn),而利用水力空化對(duì)傳熱的強(qiáng)化作用可顯著提升微通道熱沉的冷卻能力,對(duì)微通道的空化流動(dòng)特性及其對(duì)傳熱的影響進(jìn)行研究具有重要科學(xué)意義與實(shí)用價(jià)值,相關(guān)研究已成為國內(nèi)外學(xué)者關(guān)注的熱點(diǎn)。本文針對(duì)傳統(tǒng)CFD方法在模擬空化流動(dòng)傳熱現(xiàn)象時(shí)存在的問題,以內(nèi)置空化結(jié)構(gòu)的微通道為研究對(duì)象,首次將耦合偽勢(shì)模型的格子Boltzmann方法用于微通道的空化流動(dòng)傳熱研究,以期從數(shù)值角度探明微通道內(nèi)空化現(xiàn)象發(fā)生的條件,空化泡形成、生長和潰滅過程的動(dòng)力學(xué)特性及其對(duì)傳熱的影響。論文首先對(duì)格子Boltzmann方法的基本理論進(jìn)行了簡單回顧,分析了偽勢(shì)模型中粒子間相互作用力的計(jì)算形式及其處理方式。在此基礎(chǔ)上,作者選用加權(quán)方式的粒子間相互作用力計(jì)算形式和精確差分形式的粒子間相互作用力處理方式,構(gòu)建了單組份多相格子Boltzmann模型。為了實(shí)現(xiàn)對(duì)水-水蒸氣氣液兩相系統(tǒng)的準(zhǔn)確描述,將P-R狀態(tài)方程引入到單組份多相格子Boltzmann模型中,并從表面張力與靜態(tài)接觸角的角度對(duì)模型的可靠性進(jìn)行了驗(yàn)證。驗(yàn)證結(jié)果表明：隨著溫度的升高,表面張力呈現(xiàn)線性遞減趨勢(shì),而接觸角的大小與液固粒子間相互作用力強(qiáng)度系數(shù)gs成線性關(guān)系,表明P-R狀態(tài)方程能夠用于氣液兩相系統(tǒng)的模擬�；谀Ｐ偷目煽啃�,建立了內(nèi)置空化結(jié)構(gòu)的二維微通道模型,并采用單組份多相格子Boltzmann模型對(duì)其內(nèi)部空化流動(dòng)進(jìn)行了數(shù)值模擬。本文模擬得到的空化流型與文獻(xiàn)實(shí)驗(yàn)結(jié)果符合較好,進(jìn)一步證明了模型可靠性。模擬結(jié)果表明：空化泡最先于空化結(jié)構(gòu)出口處兩側(cè)對(duì)稱的低壓區(qū)域內(nèi)產(chǎn)生,符合壓力的實(shí)際分布情況；基于偽勢(shì)模型的格子Boltzmann模型可以成功預(yù)測出空化泡與壁面之間的液膜,在此基礎(chǔ)上作者分析了近壁面薄膜形成的原因及其影響因素,揭示出流體與固體壁面的相互作用力是形成近壁面液膜的關(guān)鍵因素。在分別固定壓力梯度和壓差的條件下,作者進(jìn)一步研究了微通道內(nèi)影響空化現(xiàn)象產(chǎn)生的因素,結(jié)果表明：在固定壓力梯度條件下,空化誘發(fā)結(jié)構(gòu)的喉部寬度存在一個(gè)最佳值,喉部寬度在此最佳值附近時(shí)空化現(xiàn)象易于發(fā)生,而偏離最佳值程度較大時(shí)將難以產(chǎn)生空化現(xiàn)象；在固定進(jìn)出口壓差條件下,空化結(jié)構(gòu)下游微通道的出口段長度存在最佳值,在此最佳值附近時(shí)空化現(xiàn)象易發(fā)生,而偏離最佳值較遠(yuǎn)時(shí)難以產(chǎn)生空化現(xiàn)象�；趩谓M份多相格子Boltzmann模型,作者引入能量方程對(duì)微通道內(nèi)空化泡的動(dòng)力學(xué)特性及其對(duì)傳熱的影響展開了初步研究,成功實(shí)現(xiàn)了氣泡生長和潰滅過程的模擬,捕捉到了氣泡在潰滅時(shí)的回彈現(xiàn)象,獲得了氣泡生長和潰滅過程中溫度、壓力等參數(shù)的變化規(guī)律。在此基礎(chǔ)上,作者首先對(duì)靜止?fàn)顟B(tài)下微通道中兩個(gè)氣泡之間的融合過程進(jìn)行了模擬,結(jié)果發(fā)現(xiàn),氣泡的融合受微通道上下壁面的影響較大。緊接著對(duì)氣泡在微通道中的流動(dòng)與傳熱展開了研究,揭示了空化泡的流動(dòng)規(guī)律及其對(duì)傳熱的影響,模擬結(jié)果發(fā)現(xiàn),氣泡在高壓段的流動(dòng)過程中,氣泡后部存在著高溫的尾跡區(qū)域,引起了氣泡后側(cè)流體溫度的升高；同時(shí)也得到了兩個(gè)氣泡在不同條件下發(fā)生相互作用而變形的動(dòng)態(tài)過程。
[Abstract]:Microchannel cooling technology has been widely used in the field of microelectronics and laser device cooling. However, with the increasing heat flux of the electronic devices, the cooling capacity of conventional microchannel heat sink is facing great challenges. The enhancement of the heat transfer by hydraulic cavitation can significantly improve the cooling capacity of the microchannel heat sink and the cavitation flow of the microchannel. The study of dynamic characteristics and its effect on heat transfer is of great scientific and practical value. The related research has become a hot topic of attention of scholars at home and abroad. This paper aims at the problem of the traditional CFD method in simulating the heat transfer in the cavitation flow. The microchannel with the built-in cavitation structure is the research object, and the lattice of the coupled pseudo potential model is first used. The sub Boltzmann method is used to study the heat transfer of the cavitation flow in microchannels in order to find out the conditions of cavitation in the microchannel, the formation of cavitation bubbles, the dynamic characteristics of the process of growth and collapse and the influence on the heat transfer from a numerical point of view. The paper first briefly reviews the basic theory of the lattice Boltzmann method and analyzes the pseudo potential model. On this basis, the author constructs a single component multiphase lattice Boltzmann model in order to realize the water vapor two-phase system in order to realize the water vapor two-phase system. Accurate description, the P-R equation of state is introduced into a single component multiphase lattice Boltzmann model, and the reliability of the model is verified from the angle of the surface tension and the static contact angle. The results show that the surface tension decreases linearly with the increase of temperature, and the contact angle is strong and the interaction force between the liquid and solid particles is strong. The degree coefficient GS is linear. It shows that the P-R state equation can be used to simulate the gas-liquid two phase system. Based on the reliability of the model, a two-dimensional microchannel model with a built-in cavitation structure is established. The numerical simulation of the internal cavitation flow is carried out by using the single component multiphase lattice Boltzmann model. The cavitation flow pattern and the literature obtained in this paper are simulated in this paper. The experimental results agree well with the model reliability. The simulation results show that the cavitation bubble is most advanced in the symmetrical low pressure region at the exit of the cavitation structure, which is in line with the actual distribution of the pressure. The lattice Boltzmann model based on the pseudo potential model can successfully predict the liquid film between the cavitation bubble and the wall. The author analyses the reasons for the formation of the near wall film and its influencing factors, and reveals that the interaction force between the fluid and the solid wall is the key factor for the formation of the near wall liquid film. Under the conditions of the pressure gradient and pressure difference fixed, the author further studies the factors that affect the cavitation in the microchannel. Under the constant pressure gradient, the throat width of the cavitation induced structure has an optimal value, and the space-time phenomenon of the throat width near the best value is easy to occur, and the cavitation phenomenon will be difficult to produce when the deviation from the best value is large. The spatiotemporal phenomenon near the best value is easy to occur, but it is difficult to produce cavitation phenomenon when the deviation from the best value is far away. Based on the single component multiphase lattice Boltzmann model, the author introduces the energy equation to the kinetic characteristics of the cavitation bubble in the microchannel and the influence on the heat transfer. On the basis of the simulation, the fusion process between two bubbles in the microchannel under static state is simulated. The results show that the bubble fusion is influenced by the upper and lower surface of the microchannel. The flow and heat transfer of the bubble in the microchannel were studied, and the flow law of the cavitation bubble and its influence on the heat transfer were revealed. The simulation results showed that there was a high temperature wake region in the rear of the bubble during the flow process of the high pressure section, which resulted in the increase of the fluid temperature in the rear side of the bubble; at the same time, two of the bubbles were obtained. The dynamic process of deformation of bubbles under different conditions.

【學(xué)位授予單位】：中國科學(xué)院研究生院(工程熱物理研究所)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TN601

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本文編號(hào)：1843895