Abstract: The condensation process of the propane outside the tube in the condenser unit of the Intermediate Fluid Vaporizer （IFV） which is suitable for LNG cold energy generating device was examined. By establishing the corresponding numerical model, the VOF model was used to trace the gas-liquid phase interface, and the LEE model was used as the phase change heat and mass transfer model. The transient two-dimensional CFD simulation was carried out on the liquid-film flow and condensation heat transfer of gaseous propane outside the tube. The flow and condensation heat transfer characteristics of the liquid film outside the propane of the condenser under different tube bundle arrangements were analyzed, and the simulated value of the average heat transfer coefficient outside the tube was calculated. In addition, the effect of wall subcooling on the phase transition of propane condensation was also analyzed. It was found that gas backflow occurs in the bottom discharge pipe of both the straight discharge and the fork discharge structure at a large wall supercooling degree, resulting in the first drop in the bottom discharge pipe.