In this paper, a simple computational model for isothermal phase change of phase change material (PCM) encapsulated in a single container is presented. The mathematical model was based on an enthalpy formulation with equations cast in such a form that the only unknown variable is the PCM's temperature. The theoretical model was verified with a test problem and an experiment performed in order to assess the validity of the assumptions of the mathematical model. With very good agreement between experimental and computational data, it can be concluded that conduction within the PCM in the direction of heat transfer fluid flow, thermal resistance of the container's wall, and the effects of natural convection within the melt can be ignored for the conditions investigated in this study. The numerical analysis of the melting time for rectangular and cylindrical containers was then performed using the computational model presented in this paper. Results show that the rectangular container requires nearly half of the melting time as for the cylindrical container of the same volume and heat transfer area. (C) 2001 Published by Elsevier Science Ltd.