A non-isothermal, non-isobaric water and thermal management model with phase change has been developed to simulate the mass and energy (sensible heat, latent heat, chemical reaction energy, electrical energy) transfer processes inside a PEM fuel cell unit with a non-uniform stack temperature (hereafter the stack temperature has the same meaning of the cell temperature since only single cell is considered). Based on this model, the following parameters can be predicted along the channels on both cathode and anode sides: current density, output voltage, stack temperature, stream pressure and temperatures, stream velocity, relative humidity, water vapor mole fraction, water liquid fraction, density, viscosity, Reynolds number, required pumping power, and so on. Also, the results from uniform stack temperature model and non-uniform stack temperature model are compared in this research. (c) 2006 Elsevier B.V. All rights reserved.