in this study, direct contact melting of hydrocarbon mixtures as phase change materials was investigated experimentally. Tetradecane and hexadecane binary mixtures, and pentadecane and octadecane binary mixtures were used as phase change materials, with various mixing ratios. It was found that the heat flux decreased significantly in the low surface temperature range. In addition, a rough and uneven melting surface was observed in the low surface temperature range. The convex portions at the melting surface were collected, and the ingredients of this region were measured by using differential scanning calorimetry (DSC). It was found that the DSC curve shifted to a higher temperature region, and the concentration of higher melting point material increased at the convex portions. Therefore, it seems that the melting point around the convex portions increased due to the higher concentration of higher melting point material, and this resulted in the decrease in the heat flux. (c) 2005 Elsevier Ltd. All rights reserved.