A novel empirical heat transfer model for a solar thermal storage process using phase change materials

Numerical and experimental analyses are often used to evaluate the solar thermal system with latent heat thermal energy storage (LHTES). However, the relationship between the numerical simulation and actual heat transfer process is still unclear. This work compares the simulated average temperature of two different phase change materials (PCMs) with experimental result at different operation conditions for the purpose of developing a temperature correction model. A novel empirical heat transfer model is then established to improve the simulation accuracy of PCM-based solar thermal systems. The contributions of this work include that (1) the system performance could be evaluated by the proposed empirical heat transfer model under sunny and cloudy weather conditions; (2) two PCMs (i.e., PCM1 and PMC2) are used to evaluate the performance of the proposed empirical heat transfer model. The analysis results demonstrate that (a) during solar irradiation variations, the temperature of the latent heat storage tank is much more stable than that of the sensible heat storage tank; (b) the heat transfer power and heat storage amount of PCM1 per unit mass are less than that of the heat transfer oil, while the observations on PCM2 are as opposed to these obtained from PCM1; (c) there is a critical time/temperature for switching the operation mode of the heat storage between different weather conditions; (d) under the conditions of low temperature, low solar radiation intensity and short-time heat storage, LHTES may prefer to perform sensible heat storage rather than latent heat storage, and vice versa. The findings of this paper may provide a theoretical basis to determine the amount of the PCMs and the control strategy of operation model for LHTES.