In this study, the heat and mass transfer processes in direct contact membrane distillation (DCMD) are compared with the heat transfer process in the traditional surface-type heat exchanger. A hollow fiber membrane heat exchanger is proposed for the heat transfer on the basis of the principle of DCMD. Unlike in DCMD, both the heat conduction and the latent heat transfer across the membrane wall are beneficial to the membrane heat exchanger. The heat conduction across the membrane wall is the basic heat transfer mode, while the transfer of latent heat of water vapor across the membrane is a new mode of heat transfer enhancement. A mathematical model of the heat and mass transfer processes is established for the hollow fiber membrane heat exchanger by using the distributed parameter method. The membrane heat exchanger is more compact and has a lower volume capacity than the traditional surface-type heat exchanger. Further, because of its large heat transfer contact area and the latent heat transfer enhancement mode, the membrane heat exchanger is more suitable for working conditions wherein the flow rate and the temperature difference between the hot and cold feeds in a heat transfer process are small.