自然对流对方腔内相变石蜡熔化蓄热的影响

相对于传统材料，基于潜热储能的相变材料具有更高的储热效率。为了研究方腔内相变材料的蓄热机理，基于Boussinesq假设修正满足于相变过程的动量方程，并建立底边加热下相变材料熔化蓄热的流-固-热三场耦合计算模型。采用有机相变石蜡材料，开展底部恒定温度下的石蜡熔化蓄热试验，验证计算模型的正确性。结果表明，整个相变石蜡熔化过程是由热传导和自然对流传热两者共同主导的。在熔化初期，熔化前缘基本与加热面平行，热量传输主要由热传导提供。当液相层厚度大于2mm后，自然对流传热效应逐渐被激活，加速熔化速率，并形成不规则的融化前缘。根据熔化前缘与液相流动特征，可将整个熔化过程分为热传导、稳定增长、过渡及紊流四个阶段。此外，液相自然对流传热对相变石蜡的熔化蓄热效率提升存在显著的尺寸效应，并随方腔尺寸增加而加剧。当方腔尺寸小于2mm时，自然对流的提升效率不足1%，此时可忽略不计。

Effect of natural convection on melting heat storage of phase change paraffin in a square cavity

Compared with traditional materials, the phase change materials based on latent heat have higher heat storage efficiency. In order to study the heat storage mechanism of phase change materials in a square cavity, the momentum satisfying the phase change was modified based on the Boussinesq hypothesis, and the fluid-solid-thermal coupling calculation model for melting heat storage of phase change materials heated from below was established. Selecting the organic phase change paraffin, the melting experiment of paraffin under bottom constant temperature was carried out to verify the correctness of the calculation model. The results show that the melting process is dominated by conduction and natural convection heat transfer. At the initial stage of melting, the melting front is basically parallel to the heating surface, and the heat transfer is mainly provided by conduction. When the liquid thickness exceeds 2mm, the natural convection heat transfer is gradually activated to accelerate the melting rate, and forms the irregular melting front. According to the characteristics of melting front and liquid flow, the whole melting process can be divided into four stages: conductive regime, stable growth regime, transition regime and turbulent regime. In addition, the natural convective heat transfer in liquid phase has a significant size effect on the improvement of melting heat storage efficiency of phase change paraffin, and intensified with the increase of cavity size. When the square cavity size is less than 2mm, the improvement efficiency of natural convection heat transfer is less than 1% and can be ignored.