This paper reports the results of a numerical optimization and experimental investigation of phase change material (PCM) based composite pin fin matrix heat sink. The main objective of this study is to determine the optimized configuration of the matrix type heat sink that will stretch the operation time during the heating cycle and minimize the time during the discharging cycle. The PCM used is n-eicosane. The heat sink is made of aluminium. A constant heat flux of 1.9 kW/m(2) is applied at the bottom of the heat sink. The numerical results were matched up with the experimental results to determine the overall heat transfer coefficient with the help of commercially available ANSYS FLUENT 14.0 software. For constant power level and constant volume of the PCM, 40 different geometrical configurations of heat sinks were considered and temperature time histories were obtained for both the charging and discharging cycles by using full three dimensional simulations of flow and conjugate heat transfer including phase change using FLUENT 14.0. The output of these simulations was given as an input to a neural network and a multi objective optimization was carried out to determine the optimum configuration of the heat sink, that maximizes the charging period and minimizes the discharging period simultaneously. (C) 2015 Elsevier Ltd. All rights reserved.