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首页> 外文期刊>Journal of Heat Transfer >Solidification of Phase Change Materials Infiltrated in Porous Media in Presence of Voids
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Solidification of Phase Change Materials Infiltrated in Porous Media in Presence of Voids

机译：有空洞时渗透到多孔介质中的相变材料的凝固

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Infiltration of phase change materials (PCM) into highly conductive porous structures effectively enhances the thermal conductivity and phase change (solidification and melting) characteristics of the resulting thermal energy storage (TES) composites. However, the infiltration process contributes to formation of voids as micron-size air bubbles within the pores of the porous structure. The presence of voids negatively affects the thermal and phase change performance of TES composites due to the thermophysical properties of air in comparison with PCM and porous structure. This paper investigates the effect of voids on solidification of PCM, infiltrated into the pores of graphite foam as a highly conductive porous medium with interconnected pores. A combination of the volume-of-fluid (VOF) and enthalpy-porosity methods was employed for numerical investigation of solidification. The proposed method takes into account the variation of density with temperature during phase change and is able to predict the volume shrinkage (volume contraction) during the solidification of liquids. Furthermore, the presence of void and the temperature gradient along the liquid-gas interface (the interface between void and PCM) can trigger thermocapillary effects. Thus, Marangoni convection was included during the solidification process and its importance was elucidated by comparing the results among cases with and without thermocapillary effects. The results indicated that the presence of voids within the pores causes a noticeable increase in solidification time, with a sharper increase for cases without thermocapillary convection. For verification purposes, the amount of volume shrinkage during the solidification obtained from numerical simulations was compared against the theoretical volume change due to the variation of density for several liquids with contraction and expansion during the freezing process. The two sets of results exhibited good agreement.
机译：相变材料（PCM）渗透到高导电性多孔结构中可有效增强所得热能存储（TES）复合材料的导热性和相变（凝固和熔化）特性。然而，渗透过程有助于在多孔结构的孔内形成微米级气泡的空隙。与PCM和多孔结构相比，由于空气的热物理特性，空隙的存在会对TES复合材料的热和相变性能产生负面影响。本文研究了孔隙对PCM固化的影响，这些PCM渗入石墨泡沫的孔中，作为具有相互连接的孔的高导电性多孔介质。流体体积（VOF）和焓-孔隙率方法的组合用于凝固的数值研究。所提出的方法考虑了相变过程中密度随温度的变化，并且能够预测液体凝固过程中的体积收缩（体积收缩）。此外，空隙的存在和沿液-气界面（空隙与PCM之间的界面）的温度梯度会触发热毛细管效应。因此，在固化过程中包括了Marangoni对流，并且通过比较有无热毛细管效应的情况下的结果来阐明其重要性。结果表明，孔中孔隙的存在导致凝固时间的显着增加，对于没有热毛细对流的情况，则急剧增加。为了进行验证，将在数值模拟中获得的凝固过程中的体积收缩量与理论体积变化进行了比较，这是由于几种液体的密度在冷冻过程中随收缩和膨胀而变化所致。两组结果显示出良好的一致性。

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