逆向流动边界下窄方腔内相变材料融化传热数值研究

Numerical Investigation on Melting Heat Transfer of PCM in a Narrow Square Cavity with Reverse Flow Boundary

为分析复杂流动边界条件对相变材料融化进程的影响,采用计算流体动力学方法进行数值模拟,研究了窄方腔内月桂酸在逆向流动边界中的融化传热特性。建立了填充有相变材料的窄方腔两侧流过参数相同但逆向的传热流体的物理模型。通过数值模拟得到了相变材料融化形态变化以及相对应的液体分数、温度、速度矢量分布等瞬态传热特性,从中总结出了腔体中相变融化机制和传热机理。选取雷诺数1×10^(4),3×10^(4),5×10^(4),7×10^(4)和瑞利数3×10^(6),4×10^(6),5×10^(6),6×10^(6)的7种工况,分析了不同边界条件对传热过程的影响。结果表明:腔内自然对流的产生大大增加了传热强度,导致顶部相变材料率先完全融化;融化阶段的传热方式依次为导热、导热与对流混合、对流主导传热;在两侧流体的共同传热作用下腔内外换热效果明显增强;雷诺数和瑞利数都对融化过程有积极的影响,但融化前期雷诺数影响较大,后期瑞利数逐渐起主导作用。

To analyze the influence of complex flow boundary condition on the melting process of phase change material(PCM),the computational fluid dynamics method was used for numerical simulation,and the melting heat transfer characteristics of lauric acid in a narrow square cavity with reverse flow boundary were studied.The physical and numerical models were established,and the same but reverse heat transfer fluids(HTFs)flowed through two sides of the cavity filled with PCM.After the simulation,the melting morphology variation of PCM and the corresponding transient heat transfer characteristics such as liquid fractions,temperatures and velocity vector distributions were obtained,from which the phase change melting and heat transfer mechanisms were summarized.The effects of different boundary conditions on the heat transfer process were analyzed by selecting Reynolds number in the range of 1×10^(4),3×10^(4),5×10^(4),7×10^(4) and Rayleigh number in the range of 3×10^(6),4×10^(6),5×10^(6),6×10^(6).The results show that the generation of natural convection in the cavity greatly increases the heat transfer intensity,resulting in the first complete melting of the PCM at the top;the heat transfer modes in the whole melting stage are heat conduction,mixed heat conduction and convection,and convection dominated heat transfer in turn;the heat transfer effects inside and outside the cavity are significantly enhanced under the joint action of HTFs on two sides;Reynolds number and Rayleigh number both have positive effects on the whole melting process,but Reynolds number has a great influence in the early stage,and Rayleigh number gradually plays a leading role in the later stage.