This paper deals with an entropy and exergy efficiency analysis of a latent heat storage system (around a cylindrical tube) during charging process. First, a numerical model is developed and solved through the governing equations for the heat transfer fluid (HTF), pipe wall and phase change material for different parameters (shell radius and pipe length, Re number, inlet temperature of HTE etc.). Second, extensive parametric studies are conducted to investigate how the solidification fronts, heat stored, heat transfer rates, entropy generation number and exergy efficiency change with time, particularly dimensionless time (the Fourier number). Third, the model results are compared with some experimental data of one of the authors, and a good agreement is obtained for various parameters. The results show that entropy generation is crucial in such systems and should be minimized in order to increase the exergy efficiency and hence the system performance. (c) 2007 Elsevier Masson SAS. All rights reserved.