An effective thermal conductivity correlation for three high-temperature chloride salts melting in a spherical thermal storage capsule

Chloride salts are viable phase change materials (PCMs) for packed-bed thermal energy storage for third-generation concentrating solar power (CSP) systems. In the study, a two-dimensional, axisymmetric and transient model is developed to simulate the constrained melting process of three chloride salts (NaCl-CaCl₂, LiCl and MgCl₂) in a spherical capsule while considering the natural convection of the salt. The simulation results lead to the proposal of an effective thermal conductivity correlation for the liquid part of these three PCMs’ melting process in a sphere, represented as λ_eff/λ_l = 0.38Ra^0.26(δ/R_i)^0.25. Additionally, a simplified conduction-controlled numerical model has been developed for predicting the melting process of chloride salts in a spherical capsule with improved accuracy and efficiency. The proposed correlation improves the conduction-controlled model’s accuracy in predicting the melting process compared to other correlations previously reported in literature. The proposed correlation comprehensively reflects the conduction and natural convection of the chloride salts during the constrained melting process in a sphere.