In phosphoric acid fuel cell (PAFC) stack, reduction of the phosphoric acid that is impregnated in the cell is a major factor to restrict the operating life. In this paper, the phosphoric acid reduction by the evaporative and condensational dissipation on the effect of liquid phase migration was evaluated by numerical analysis. The calculations that include the behavior of evaporation, condensation, and liquid phase migration for the phosphoric acid, and the behavior of gas flow and heat transfer were conducted for the model cell with conditions that correspond to an on site stack. The diffusion coefficient of liquid phase migration was derived from the activation energy and frequency factor based on the experimental results. The phosphoric acid distributions in the vapor phase and liquid phase at the process gas and electrode were calculated for the duration of 3136 h, and as a result of those, the exhausting and remaining amount of phosphoric acid for the cell were evaluated. The effects of liquid phase migration on the phosphoric acid dissipation were evaluated by analysis for various diffusion coefficients, and the analysis results were compared with the experimental results for the model cell. (C) 2011 Elsevier B.V. All rights reserved.