Enhancing the Thermal Performance of a Three-Pass Solar Air Heater Using Latent Heat Storage Materials: A Comprehensive Review

Abstract

with latent heat storage materials (Phase Change Materials, PCMs) are reviewed to improve the thermal conductivity. The principle behind this integration is based on the high energy-storage density of PCMs, whose heat absorption and heat release occur at nearly constant temperatures, that enhances the system efficiency and smooths the convergence of the outlet air temperature. The enhancement of the air residence time and heat transfer rate is achieved by the three-pass flow pattern although more pressure drop and design complexity are introduced. A review of literature reveals that the use of PCMs brings about considerable improvement in the total thermal performance as compared to the conventional systems more so by way of prolonging the heating duration beyond the retardation of solar radiation. Proper PCM melting temperature and high thermal conductivity of PCM are important for efficient charging/discharging processes Major obstacles are the low thermal conductivity of typical PCMs which generally needs to be enhanced by means of fins, metal matrices or by encapsulation methods. The core technical difficulties are the very low thermal conductivity of the ordinary PCMs, which usually needs to be enhanced by fin, metal matrices, or encapsulation methods. Leakage during melting and long-term material stability are also importantly design issues. Moreover, the hydrodinam¬ics of the three-pass configurations becomes increasingly intricate., thus rendering the airflow distribution and pressure drops as the dominant system optimization parameters. The literature on PCM incorporated three-pass heaters is still scarce, as the most of the works related to that of single- or double-pass collectors. There are important gaps in dynamic modeling of multi-pass systems with PCM, long-term cycling studies, and cost – benefit analyses. The review emphasizes the requirement of development of advanced numerical models, superior PCM composites with enhanced conductivity and system level integrated designs that can include reasonably complexity in thermo-technical performances. To sum up, the incorporation of latent heat storage materials into three-pass solar air heaters offers an attractive way to enhance the heat transfer performance, meanwhile, further work is required to solve the material, design and economic issues for large scale implementation.