PCM melting characteristics in a sidewall-heated rectangular cavity with non-uniform longitudinal fins near the bottom

This paper employs three-dimensional numerical simulations to investigate the influences of adding non-uniform longitudinal fins near the bottom of a rectangular enclosure with a heated sidewall on the melting process of RT42. The focus is on enhancing natural convection, especially in the final melting stage. Using the longitudinal rectangular fins on the sidewall as a baseline case, we investigate the effects of the heights at the left (Ll) and right (Lr) sides of the fin, fin thicknesses (0.2, 0.25, and 0.3 mm), and the number of fins (1 or 2) on the heat storage characteristics. The results indicate that adding fins in the lower region of the container significantly improves energy storage efficiency. A greater right-side fin height demonstrates relatively superior melting performance. When fin thickness is 0.2 mm, the optimal non-uniform fin configuration (Case 8: Ll = 3 mm and Lr = 7 mm) reduces the melting time by 27.5 %, increases the energy storage rate by 37.3 %, and enhances the average Nusselt number by 28.5 % compared to the baseline case. Additionally, while double fins decrease the melting rate, they improve the uniformity of temperature distribution and enhance natural convection. Compared to the baseline case, the heat storage rate and the maximum average velocity increase by 56.3 % and 18.6 %, respectively.