Abstract Nanoencapsulated phase change materials (nePCMs) – which are composed of a core with a phase change material and of a shell that envelopes the core – are currently under research for heat storage applications. Mechanically, one problem encountered in the synthesis of nePCMs is the failure of the shell due to thermal stresses during heating/cooling cycles. Thus, a compromise between shell and core volumes must be found to guarantee both mechanical reliability and heat storage capacity. At present, this compromise is commonly achieved by trial and error experiments or by using simple analytical solutions. On this ground, the current work presents a thermodynamically consistent and three-dimensional finite element (FE) formulation considering both solid and liquid phases to study thermal stresses in nePCMs. Despite the fact that there are several phase change FE formulations in the literature, the main novelty of the present work is its monolithic coupling – no staggered approaches are required – between thermal and mechanical fields. Then, the FE formulation is implemented in a computational code and it is validated against one-dimensional analytical solutions. Finally, the FE model is used to perform a thermal stress analysis for different nePCM geometries and materials to predict their mechanical failure by using Rankine’s criterion.

中文翻译：

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用于研究用于储能的纳米封装相变材料中的热应力的有限元公式

摘要纳米封装相变材料 (nePCMs) - 由具有相变材料的核和包裹该核的壳组成 - 目前正在研究用于储热应用。在机械上，nePCMs 的合成中遇到的一个问题是由于加热/冷却循环过程中的热应力导致外壳失效。因此，必须找到壳和芯体积之间的折衷以保证机械可靠性和储热容量。目前，这种折衷通常是通过反复试验或使用简单的分析解决方案来实现的。在此基础上，当前的工作提出了一种热力学一致的三维有限元 (FE) 公式，同时考虑了固相和液相，以研究 nePCM 中的热应力。尽管文献中有几种相变有限元公式，但目前工作的主要新颖之处在于其在热场和机械场之间的整体耦合——不需要交错的方法。然后，有限元公式在计算代码中实现，并针对一维解析解进行验证。最后，使用有限元模型对不同的 nePCM 几何形状和材料进行热应力分析，以使用 Rankine 准则预测其机械故障。有限元公式在计算代码中实现，并针对一维解析解进行验证。最后，使用有限元模型对不同的 nePCM 几何形状和材料进行热应力分析，以使用 Rankine 准则预测其机械故障。有限元公式在计算代码中实现，并针对一维解析解进行验证。最后，使用有限元模型对不同的 nePCM 几何形状和材料进行热应力分析，以使用 Rankine 准则预测其机械故障。