Thermal performance analysis of arc-shaped fins of horizontal latent heat thermal energy storage system

Aiming at the generally low thermal conductivity of PCM in the LHTES (latent heat thermal energy storage) system, this study proposes a new kind of fin structure by adding arc-shaped fractal fins on the longitudinal straight fins for the improvement of the melting efficiency within the horizontal double-tube LHTES system. Numerical simulations were performed to analyze the effects of the curvature direction of arc-shaped fins, curvature size, and distance between fractal fins on the thermal characteristics. The results indicate that negative curvature fins have better melting performance. With the influence of natural convection, the temperature response speed of the PCM near the outer pipe wall at the higher half of the system is faster than that in the central region; versus conventional straight fins, a 90° fractal fin has the best melting characteristics versus a traditional straight fin, and reducing the PCM complete melting time by 34.27 %. The fractal fin spacing change affects the internal PCM’s phase transition process. The PCM melts the fastest when the fractal fin spacing decreases uniformly from lateral to medial. This results in a 2.5 % reduction in total melt time and a 2.57 % improvement in energy storage rate over a system with uniformly distributed fins. Finally, the minimum complete melting time, together with the fastest energy storage rate of the PCM, are taken as the optimization objectives. Response surface methodology is used to optimize fin radian angle and spacing. The results indicate that the system has optimal melting characteristics when the fin radian angle θ = 98.81°, the fin spacing tolerance d = 0.20 mm, and the total melting rate of the PCM are enhanced by 35.297 %. The energy storage rate is improved by 52.16 %.