This study presents a numerical and experimental analysis of the forced convective heat transfer of paraffin, which is intended for use in environmental control systems (ECSs). The research concentrates on the heat transfer characteristics of paraffin in laminar flow. The results of the simulation present the relationship between the convective heat transfer coefficient (CHTC) and the tube length in the flow direction. It is determined that the CHTC of the paraffin undergoes a slight increase throughout its phase change stage (the corresponding material temperatures ranged from 291.15 K to 288.15 K). Compared with water, the value of the CHTC of paraffin is 9.8–10.7 times larger, depending on the flow rate of the fluid. For given values of the parameters tube length and inner diameter, there is an optimal flow velocity of the paraffin for heat flux enhancement. In the present work, the optimum flow velocity is 0.020 m/s. The maximal heat flux, in the meantime, reaches 465.1 W, which accounts for 58.2% of the total heat capacity of paraffin. The approach of using flowing paraffin in ECSs for thermal energy storage/transfer may be technically viable. In addition, the assumption that the flowing paraffin has been thermally fully developed in the heat transfer tube cannot be used for solving the energy equations.