Fluid flow and heat transfer in PCM panels arranged vertically and horizontally for application in heating systems
Fluid flow and heat transfer in PCM panels arranged vertically and horizontally for application in heating systems
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DOI：
10.1016/j.renene.2016.05.089
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发表时间：
2016-11
期刊：
影响因子：
8.7
通讯作者：
M. Prieto;B. González
中科院分区：
文献类型：
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作者：
M. Prieto;B. González
矩形面板属于相变材料 (PCM) 中最常见的几何形状。然而，对于排列（垂直或水平）和厚度如何影响热通量和相变持续时间缺乏了解。这些知识对于 PCM 热交换器的设计非常有帮助。本文研究了 RT60 石蜡的行为，Pr ≈ 330，相变温度在 53 至 61 °C 之间；脂肪酸棕榈酸，Pr ≈ 110，相变温度为 65 °C。进行参数研究，分析以下因素的影响：壁的温度 (5 × 105<Ra≤ 2 × 106)、相变过程（熔化和凝固）、面板位置和 PCM 厚度（纵横比 1/20 和 3/20）。使用速度图和体积液体分数等值线分析随时间变化的流动行为。描述了贝纳德细胞的形成及其进化。讨论了无量纲弦函数和瑞利数的自由对流依赖性。水平板熔化过程中的自由对流变得非常重要，与垂直板相比，平均热通量增加至两倍。然而，对于凝固来说，传导变得更加重要。通过计算传热率凸显了这两种机制的重要性。
The rectangular panel is within the most common geometries in phase change materials (PCM). Nevertheless, there is a lack of knowledge regarding how the arrangement (vertical or horizontal) and thickness affect heat flux and phase change duration. Such knowledge would be very helpful both in the design of PCM heat exchangers. This paper studies the behavior of the RT60 paraffin, Pr ≈ 330, phase change temperature between 53 and 61 °C; and the fatty acid Palmitic Acid, Pr ≈ 110, phase change temperature of 65 °C. Parametric studies analyzing the influence of: temperature of the walls (5 × 105<Ra≤ 2 × 106), phase change processes (melting and solidification), panel position and PCM thickness (aspect ratio1/20 and 3/20) are performed. The flow behavior is analyzed over time using velocity plots and volumetric liquid fraction contours. The formation of Bénard cells and their evolution is described. Free convection dependence of dimensionless string function and Rayleigh number is discussed. Free convection during melting for horizontal panels becomes very important and the mean heat fluxes increase up to twofold compared to vertical panels. For solidification, however, conduction becomes more relevant. The importance of both mechanisms is highlighted by calculating heat transfer rates.