Numerical Simulation of the Effect of Tube Shape on the Triplex-Tube Heat Exchanger and Exergy Efficiency using Phase Change Material

Different inner tube shapes of the triplex tube heat exchanger with phase change material has been investigated numerically. Water is used as the working fluid in the inner and outer tubes, and the middle tube is filled with RT35 as a phase change material (PCM). The PCM effectiveness among the inner tube shapes such as straight, indented, and sinusoidal in a triplex tube heat exchanger were studied. Energy and exergy efficiencies, and the effect of mass flow rate on the melting process of PCM have been sought. Enthalpy-porosity method has been applied for the simulation. Results demonstrate that the best melting time in triplex tube heat exchanger has been observed in the sinusoidal tube, and by increasing the number of pitches, the melting time decreases. In addition, sinusoidal and indented tube heat exchangers effectiveness are better than straight tube. Melting time is reduced by maximum of 2.6% by increasing the flow rate of a laminar flow from 0.006 kg/s to 0.012 kg/s. Moreover, the melting time is reduced by a maximum of 13.5% for the turbulent condition with flow rate of 0.024 kg/s. In the analysis of energy and exergy, the indented tube shows higher and preferable efficiency in comparison to the sinusoidal and straight type.