Numerical investigation of PCM melting process in sleeve tube with internal fins

•The melting process of PCM in a sleeve-tube unit was numerically investigated.•Effect of fin-ratio, thickness and angle on the optimum geometry were studied.•The conductivity of outer tube had great effect on the melting process.•The natural convection was found to have great effect on the melting process. Due to the poor thermal conductivity of the Phase Change Materials (PCMs), heat transfer performance of Latent Thermal Energy Storage (LTES) systems is usually unsatisfactory. In this work, a detailed numerical study is carried out to analyze the impact of fin geometry (including fin-length, fin-ratio and the angle between neighbor fins) and outer tube conductivity on PCM melting process; the influence of the natural convection in the horizontal sleeve-tube unit within the longitudinal fins is further examined. Results shows that small fin-ratio can reduce melting time, but not remarkably; the angle between neighbor fins has little impact on melting process, however, there is an optimization of the angle between neighbor fins to reduce melting time in the full-scale unit. The outer tube conductivity has great impact on melting process whether considering the natural convection or not.