PCM液桥固液相变与热毛细对流耦合机理研究

Study on the Coupling Mechanism of Solid-liquid Phase Transition and Thermocapillary Convection in PCM Liquid Bridge

为了揭示空间微重力下相变材料(PCM)液桥相变过程中固液相变与热毛细对流耦合机理,本文建立了两维轴对称PCM液桥数理模型,系统研究了固液界面拓扑结构演化规律、热毛细对流流动特征及相变强化机理。结果表明,小温差作用下,PCM液桥在自由表面附近率先出现单胞热毛细对流结构,并逐渐增大最终向液桥内部扩展,固液相变界面表现为平滑过渡结构。大温差作用下,PCM液桥相变过程中出现热流体波不稳定性,其对流涡胞数量先增大后减小;热毛细对流流场振幅和频率随相变过程发生动态变化,相变固液界面出现波型结构。随着PCM液桥温差增大,相变时间缩短且热毛细强化因子逐渐增强,热毛细对流的转捩、演化或湮灭是存在于固液相变过程的瞬时动力学行为。

In order to reveal the coupling mechanism of solid-liquid phase change and thermocapillary convection in the process of phase change material(PCM)liquid bridge phase change under microgravity,a two-dimensional axisymmetric PCM liquid bridge mathematical model was established in this paper.The evolution law of the topological structure of the solid-liquid interface,the characteristics of thermal capillary convection fow and the phase change enhancement mechanism were systematically studied.The results show that under the action of small temperature difference,the PCM liquid bridge takes the lead in the single cell thermal capillary convection structure near the free surface,and gradually increases and finally expands to the inside of the liquid bridge.The phase change solid-liquid interface shows a smooth transition structure.Under the action of large temperature difference,the hydrothermal wave instability occurs during the phase transition of PCM liquid bridge,and the number of convective vortex cells first increases and then decreases;the amplitude and frequency of the thermal capillary convection flow field change dynamically with the phase change process,and the wave structure appears at the solid-liquid interface of the phase change.With the increase of PCM liquid bridge temperature difference,the phase transition time is shortened and the thermocapillary enhancement factor is gradually enhanced.The transition,evolution or annihilation of thermocapillary convection are transient dynamic behaviors existing in the solid-liquid phase transition process.