Latent heat thermal energy storage (LHTES) systems have gained significant attention recently owing to their high energy-storage-density per unit volume and nearly isothermal behavior during the phase-change process. This study numerically investigates the melting performance of a phase-change material (PCM: Ba(OH)(2).8H(2)O) in a triplex tube heat exchanger (TTHX). First, the physical and mathematical models of the TTHX are established. Then, the governing equations are discretized by the finite volume method (FVM). Finally, numerical calculations are carried out by implementing the developed numerical algorithm in FORTRAN computer code. The results reveal that the inlet temperature and flow state of the heat transfer fluid (HTF) significantly influences the PCM melting performance and exergy efficiency ratio of the investigated TTHX. A higher inlet temperature and turbulent state of the HTF can accelerate the phase-change process. However, increasing the mass flow rate of the HTF decreases the exergy efficiency ratio of the investigated TTHX. In conclusion, considering both the melting time and exergy efficiency ratio, increasing the HTF inlet temperature to a certain extent and reducing the mass flow rate of the HTF in the turbulent state can improve the thermal performance of the investigated TTHX. (C) 2019 Elsevier Ltd. All rights reserved.