A computational model is presented for the prediction of the heat transfer between a heat transfer fluid (HTF) and a phase change material (PCM) of a latent heat storage unit. Two models of flow, hydrodynamically fully developed flow and developing flow, of the HTF were proposed in this study. A two-dimensional enthalpy method was used for the computation of the phase change heat transfer in the PCM. A fully implicit finite difference scheme was utilized for the calculation of convective heat transfer in the HTF. The unknown time dependent boundary condition between the HTF and the PCM was found iteratively. The predictions are substantiated by their excellent agreement with experimental data. Factors which affect the heat transfer rates between the HTF and the PCM were studied numerically for both hydrodynamically fully developed flow and developing flow. It is found that the Nusselt number is significantly increased by the developing temperature profiles. The developing velocity profiles also will increase the Nusselt number. However, the influence on Nusselt number due to the developing temperature profiles. Other factors which affect the Nusselt number are discussed. The heat transfer of this latent heat storage unit was also studied experimentally. The experimental results were compared with the numerical results for P116, a sun wax.