微通道内空化流动传热的Lattice Boltzmann模拟

发布时间：2018-05-04 17:19

本文选题：Lattice + Boltzmann　；参考：《中国科学院研究生院(工程热物理研究所)》2015年硕士论文

【摘要】：微通道冷却技术在微电子及激光器件冷却领域已得到广泛用,但随着电子器件热流密度的不断攀升,常规微通道热沉的冷却能力面临巨大挑战,而利用水力空化对传热的强化作用可显著提升微通道热沉的冷却能力,对微通道的空化流动特性及其对传热的影响进行研究具有重要科学意义与实用价值,相关研究已成为国内外学者关注的热点。本文针对传统CFD方法在模拟空化流动传热现象时存在的问题,以内置空化结构的微通道为研究对象,首次将耦合伪势模型的格子Boltzmann方法用于微通道的空化流动传热研究,以期从数值角度探明微通道内空化现象发生的条件,空化泡形成、生长和溃灭过程的动力学特性及其对传热的影响。论文首先对格子Boltzmann方法的基本理论进行了简单回顾,分析了伪势模型中粒子间相互作用力的计算形式及其处理方式。在此基础上,作者选用加权方式的粒子间相互作用力计算形式和精确差分形式的粒子间相互作用力处理方式,构建了单组份多相格子Boltzmann模型。为了实现对水-水蒸气气液两相系统的准确描述,将P-R状态方程引入到单组份多相格子Boltzmann模型中,并从表面张力与静态接触角的角度对模型的可靠性进行了验证。验证结果表明：随着温度的升高,表面张力呈现线性递减趋势,而接触角的大小与液固粒子间相互作用力强度系数gs成线性关系,表明P-R状态方程能够用于气液两相系统的模拟。基于模型的可靠性,建立了内置空化结构的二维微通道模型,并采用单组份多相格子Boltzmann模型对其内部空化流动进行了数值模拟。本文模拟得到的空化流型与文献实验结果符合较好,进一步证明了模型可靠性。模拟结果表明：空化泡最先于空化结构出口处两侧对称的低压区域内产生,符合压力的实际分布情况；基于伪势模型的格子Boltzmann模型可以成功预测出空化泡与壁面之间的液膜,在此基础上作者分析了近壁面薄膜形成的原因及其影响因素,揭示出流体与固体壁面的相互作用力是形成近壁面液膜的关键因素。在分别固定压力梯度和压差的条件下,作者进一步研究了微通道内影响空化现象产生的因素,结果表明：在固定压力梯度条件下,空化诱发结构的喉部宽度存在一个最佳值,喉部宽度在此最佳值附近时空化现象易于发生,而偏离最佳值程度较大时将难以产生空化现象；在固定进出口压差条件下,空化结构下游微通道的出口段长度存在最佳值,在此最佳值附近时空化现象易发生,而偏离最佳值较远时难以产生空化现象。基于单组份多相格子Boltzmann模型,作者引入能量方程对微通道内空化泡的动力学特性及其对传热的影响展开了初步研究,成功实现了气泡生长和溃灭过程的模拟,捕捉到了气泡在溃灭时的回弹现象,获得了气泡生长和溃灭过程中温度、压力等参数的变化规律。在此基础上,作者首先对静止状态下微通道中两个气泡之间的融合过程进行了模拟,结果发现,气泡的融合受微通道上下壁面的影响较大。紧接着对气泡在微通道中的流动与传热展开了研究,揭示了空化泡的流动规律及其对传热的影响,模拟结果发现,气泡在高压段的流动过程中,气泡后部存在着高温的尾迹区域,引起了气泡后侧流体温度的升高；同时也得到了两个气泡在不同条件下发生相互作用而变形的动态过程。
[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.

【学位授予单位】：中国科学院研究生院(工程热物理研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN601

【参考文献】