Solidification of phase change materials encapsulated in a vertical shell which contains also the heat transfer fluid tubes is studied using a fixed grid numerical model. The solution of the system consists of adopting a velocity field of a complete developed flow coupled with the energy equations of the heat transfer fluid (HTF), the pipe wall and the phase change material (PCM). The control volume finite difference approach is used to solve the equations describing the phase change thermal system. The radial temperature distribution, the phase change interface position and the latent and sensible heat accumulated along the system axial length in function of time period, Reynolds and Stefan numbers and tube materials are presented. It is also shown in this work a procedure for thermal performance prediction of a vertical tube type phase change material thermal unit.