Melting behavior in a finned PCM solar thermal receiver/storage unit: A numerical study of heat load and orientation effects

Phase change materials (PCMs) are advantageous for solar thermal applications due to their high energy density, but their performance is often limited by low thermal conductivity. Improving the charging rate of latent heat thermal energy storage (LHTES) units under varying operational conditions is therefore a critical challenge. This study numerically investigates how incident heat flux and inclination angle interact to govern the charging performance of a finned latent heat thermal energy storage unit. (Methods) A computational model was developed to simulate the melting of n-docosane Phase Change Material in a rectangular enclosure subjected to four heat flux levels (1000–2500 W/m²) and four tilt angles (0°–90°). Results show that a vertical (90°) orientation significantly enhances melting rates via natural convection, reducing the total charging time by over 30 % compared to a horizontal orientation for a given heat flux. Crucially, higher inclination angles also resulted in lower maximum absorber plate temperatures, demonstrating a dual benefit of both improving system performance and ensuring better thermal management. • Increasing incident heat flux and inclination angle both accelerate PCM melting. • Natural convection, enhanced by tilting, plays a crucial role in heat transfer. • Melting rate is maximized at a vertical (90°) orientation of the storage unit. • Higher tilt angles notably reduce the maximum temperature of the absorber plate.