Effects of non-uniform fin arrangement and size on the thermal response of a vertical latent heat triple-tube heat exchanger

The aim of this study is to explore the impact of incorporating annular fins with nonuniform distribution on the thermal response of phase change material in a vertical triple-tube heat exchanger involving two counter-current flow streams of the heat-transfer fluid. The phase change material is accommodated in the middle tube, with one stream of the heat transfer fluid flowing in an outer tube in the direction of gravity and another stream flowing contrary to gravity in an inner tube. The main contribution of this study is detecting the best locations and sizes of the fins to achieve the highest storage performance of the unit by simulating five annular fins each on both the inner and outer tubes. Considering the constant relative volume occupied by the fins in all cases studied, the results show significant uniformity of the melting rate and temperature field can be achieved with the optimization of fin distribution between the inner and outer tubes of the heat exchanger. The fin distribution and size are optimized based on the melting process, and the best case is then investigated during solidification compared with the no-fin case considering different Reynolds numbers and inlet temperatures of the fluid. The best usage of five fins shows -29% saving in the melting time and -37% in the charging rate compared with the uniform fins distribution during the melting process considering the identical volume of the fins. The results based on the optimized fin arrangement show that the melting and solidification times can be reduced by -53% and -9%, respectively, compared with the no-fin case.