Abstract In this paper, a nano-PCM filled enclosure, which is a representative geometry of a thermal energy storage (TES) system, is investigated using scale analysis, numerical simulation, and experimental analysis. The enclosure is assumed to be square in shape. It is also assumed that one vertical wall of the enclosure is actively participating in absorbing energy from a source while the remaining walls are insulated. The thermal boundary condition at the active wall is treated as ‘constant heat flux boundary condition’ in this paper. The energy absorbing material, i.e., the nano-PCM, is CuO nanoparticles dispersed in coconut oil PCM. The influence of the volume fraction of nanoparticles ( 0 ≤ φ ≤ 5 % ) is investigated on the flow and thermal fields, heat transfer rate, energy stored and liquid fraction during the melting process of nano-PCM at different values of Rayleigh number based on base PCM ( 10 4 ≤ R a φ = 0 % ≤ 10 8 ). The Rayleigh number is adjusted by adjusting the size of the enclosure (i.e., higher R a represents the larger enclosure). In addition to the isothermal lines and velocity vectors, heatlines are utilized to exhibit the energy flow patterns inside the enclosure during the melting process. Besides the numerical calculations, scale analysis is presented to demonstrate the different stages of melting process of nano-PCM. The detailed scale analysis assists to identify relationship of Nusselt number and solid-liquid interface location as a function of well established dimensionless numbers: Stefan number ( S t e ), Fourier number ( F o ), and Rayleigh number ( R a φ = 0 % ). Finally, an experimental setup is developed to visualize the melting process of nano-PCM inside a prototype enclosure. Experiments are conducted to illustrate the impact of adding nanoparticles into PCM on the melting process. The numerical and experimental results show the significant improvement of the melting process by adding nanoparticles to PCM.

中文翻译：

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用于太阳能热应用的纳米 PCM 填充储能系统

摘要 在本文中，纳米 PCM 填充外壳是热能存储 (TES) 系统的代表性几何形状，使用比例分析、数值模拟和实验分析进行了研究。外壳假定为方形。还假设外壳的一个垂直壁积极参与从源吸收能量，而其余壁是绝缘的。在本文中，活动壁处的热边界条件被视为“恒定热通量边界条件”。能量吸收材料，即纳米PCM，是分散在椰子油PCM中的CuO纳米颗粒。研究了纳米颗粒的体积分数 (0 ≤ φ ≤ 5 % ) 对流动和热场、传热速率、基于基本 PCM ( 10 4 ≤ R a φ = 0 % ≤ 10 8 ) 的不同瑞利数值下纳米 PCM 熔化过程中储存的能量和液体分数。瑞利数是通过调整外壳的大小来调整的（即，较高的 R a 表示较大的外壳）。除了等温线和速度矢量外，热线还用于展示熔化过程中外壳内部的能量流动模式。除了数值计算外，还提出了比例分析，以展示纳米 PCM 熔化过程的不同阶段。详细的尺度分析有助于确定 Nusselt 数和固-液界面位置之间的关系，作为已建立的无量纲数的函数：Stefan 数 (Ste)、Fourier 数 (Fo) 和 Rayleigh 数 (R a φ = 0 %) ）。最后，开发了一种实验装置来可视化原型外壳内纳米 PCM 的熔化过程。进行实验以说明将纳米粒子添加到 PCM 中对熔化过程的影响。数值和实验结果表明，通过将纳米颗粒添加到 PCM 中，熔化过程得到了显着改善。