Optimum orthogonally structured fins in charging enhancement of phase change materials (PCMs): PCMs? thermophysical properties effects

Ameliorating energy storage and utilization efficiency is significant to achieving the goal of carbon peak and carbon neutralization. The orthogonal fins have been applied to enhance the average charging rate of specific phase change material (PCM) such as paraffin wax, the optimum structure dimension has been obtained. In practical applications, there are many kinds of PCMs and their thermophysical properties are different. There-fore, systematic investigations about influences of PCMs' thermophysical properties on optimum dimensions of orthogonal fins are significant. In this work, thermophysical property effects of PCMs are numerically discussed. The mechanism is illustrated semi-quantitatively and the corresponding prediction correlations between opti-mum dimension of orthogonal fins and thermophysical properties of PCMs are regressed by the results. Compared to non-optimum orthogonal fins, average charging rate can be further enhanced by 20% after opti-mization. Thermophysical properties of PCMs significantly influence the optimum dimension of orthogonally structured fins. Higher thermal expansion coefficient, thermal conductivity, density and heat of fusion induce smaller optimum dimension, while higher viscosity and specific heat capacity induce larger optimum dimension. Meanwhile, power correlations between optimum dimension of orthogonal fins and thermal expansion coeffi-cient, thermal conductivity, viscosity, specific heat capacity and heat of fusion are regressed. An exponential correlation between optimum dimension and density is obtained. The correlations between the optimum relative distance and the dimensionless numbers (include Stefan, Prandtl and Rayleigh numbers) are regressed from the simulations. The reliabilities of the correlations are also verified. The results supply useful information to choose and design optimum orthogonal fins to enhance average charging rate of PCMs-based LHTES unit with various thermophysical properties.