高气液密度比的传热相变复合模型

为研究两相流动中热量传递机制，基于格子Boltzmann热模型及大密度比模型，将相变源项引入到控制两相密度分布函数中，来描述温度场对气液相变的影响，提出了一个可以描述气液密度比达到2778的传热相变复合模型。通过对压力速度分布函数的回归修正克服了气液密度比过大造成的数值不稳定问题。模拟了溴化锂水溶液中双气泡的上升运动过程及周围的温度场分布，研究发现：双气泡上升时，碰撞前上方气泡温度高于下方气泡，碰撞时，两气泡间液桥打开，发生热量传递，气泡内部温度变得均匀；双气泡体积先减小再增大，碰撞时体积达到最大值，在融合成一个气泡后体积逐渐缩小，最终趋于稳定；初始气泡的体积越大，气泡上升过程中的速度越大。

Composite model of heat transfer and phase transition with high gas and liquid density ratio

Based on lattice Boltzmann thermal model and large density ratio model, a phase transition source term was introduced into two-phase density distribution control function to describe effect of temperature field on gas-liquid phase transition. A composite lattice Boltzmann thermal model, which can describe heat transfer and phase transition at gas-liquid ratio up to 2778, was proposed to study two-phase heat transfer mechanism. Numerical instability caused by extremely large gas-liquid density ratio was resolved by regress correction of pressure velocity distribution function. Double bubble rising movement and the surrounding temperature field distribution in lithium bromide solution was simulated using the model. Upper bubble temperature was higher than that of lower bubble prior to collision during moving up. Upon coalescence, liquid bridge between the two bubbles was open, heat transfer started and temperature inside the bubble became uniform. The volume of the double bubbles decreased first and then increased with maximum at time of two bubbles collision. After bubble coalescence, the volume gradually decreased and eventually stabilized to certain value. The larger the initial bubble volume is, the greater the velocity of the bubble rises.