Numerical heat transfer enhancement study on phase change thermal energy storage exchanger with perforated fins

Addition of fins is one of effective methods for heat transfer enhancement in heat exchangers. However, adding fins inside the heat exchanger also impedes fluid flow, which in turn affects natural convection heat transfer, especially for phase change heat storage exchangers. This study involves perforating the internal fins of the phase change thermal storage heat exchanger to reduce the obstruction of fins to the natural convection of phase change materials. The computations, carried out using the melting and solidification model for three-dimensional unsteady simulations. In the numerical simulation study on heat transfer enhancement, eight longitudinal perforated fins are imbedded uniformly and non-uniformly in a tubular phase change heat exchanger and their heat transfer enhancement performance are carefully examined and compared. The perforation diameter and hole distributions are evaluated by analyzing liquid phase ratio of the phase change material and the total melting time, thereby maximizing the combined enhancement effect of fin conduction and natural convection heat transfer in the liquid. The results indicate that fin perforation can effectively balance the thermal conductivity of the fins with the natural convection of the phase change materials when combined with full-scale fins. The optimal heat transfer enhancement occurs when the distance between the two holes and the inner tube is 6 mm and 15 mm, respectively, with an axial hole spacing of less than 10 mm and a hole diameter of 0.86 mm. On this basis, the use of perforated non-uniform fins significantly reduced the total melting time of the phase change material by 45.3 % compared to fins without perforating, thereby improving the efficiency of the phase change heat exchanger.