Silicon as high-temperature phase change medium for latent heat storage: A thermo-hydraulic study

Abstract

Latent heat storage (LHS) using high-temperature phase change medium (PCM) can provide cost-competitive solutions for dispatchable solar power and accumulate surplus Photo-voltaic (PV) and wind power. Moreover, at a sufficiently high temperature, the round trip efficiency of LHS system may approach that of electrochemical storage system. A conceptual LHS system utilizing high-temperature silicon as the phase change medium (PCM) is presented in the article. Silicon is chosen due to its high melting point (1414 °C), latent heat (1.8 × 106 J/kg), and thermal conductivity (25–50 W/mK). The thermo-hydraulic behavior during melting of silicon is modeled using a combined numerical methodology in COMSOL Multiphysics. The thermal performance of proposed system is compared against high-temperature salt-based system for different aspect ratios (AR). Results indicate that silicon systems are significantly superior to high-temperature salts under the same operating conditions. The anomalous behavior of silicon melting is established by demonstrating natural convection pattern in molten silicon. A generalized correlation is developed to predict the melting fraction as a function of Rayleigh number, Stefan number, and Fourier number for various domain sizes.