Numerical simulation of the melting and solidification processes of stearic acid/carbon fiber composite phase change material for solar water heating applications

Abstract

Phase Change Materials (PCMs) are one of the most promising materials for storing thermal energy and supplying stored energy for Domestic Hot Water (DHW) applications. This paper presents a detailed numerical analysis to describe transient heat transfer in a phase-change composite thermal energy-storage system. The composite was composed of 92.5 % stearic acid, 7.5 % carbon fiber, and a heat transfer fluid (ethylene cellulose). Numerics were implemented using ‘The Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics’. The results were validated using experimental data and demonstrated acceptable agreement and an accurate representation of this specific transient heat transfer problem. The difference between the simulation and experimental results was so small that we considered the simulation results reliable. When the phase change heat storage process is about 800 s, the heat is transferred to the entire phase change heat storage tank, and when the phase change heat storage process is about 10800s, the temperature of all composite phase change materials reaches the phase change temperature. When the phase change heat storage process is about 8 h, the temperature of the composite phase change material in the whole phase change heat storage tank reaches 90 ℃. The temperature tends to be stable after the phase transition heat release process for about 500 s, and there is no large fluctuation in temperature with the passage of time. When the phase change heat release process reaches 7200 s, the cold-water inlet temperature is 15 ℃, 20 ℃ and 25 ℃, and the outlet temperature is 25.8 ℃, 30.8 ℃ and 35.7 ℃, respectively, indicating that the application of composite phase change materials in phase change heat storage water tank has a good effect.