Heat capacities of potential organic phase change materials

The heat capacity of a material is an important factor for many applications, including phase change material (PCM) selection for thermal energy storage. Aside from storing energy via the latent heat of a phase transition, significant sensible heat can be stored using the material's heat capacity outside the transition temperature region. Furthermore, accurate heat capacity values are required to model and thereby optimize PCM heat storage systems. Various group additivity models can be used to estimate the heat capacity of organic liquids. However, these methods do not distinguish isomers built of the same base units. In the present study the liquid phase heat capacities of five isomeric, 12-carbon, linear, saturated fatty esters (potential PCMs) have been measured experimentally, and the results are compared to calculations from several group additivity methods. It was found that the heat capacities of the liquid esters are well described by the group additivity models, and that each of the esters had approximately the same heat capacity at a given temperature, despite their structural differences. The heat capacity of another isomer, dodecanoic acid, was also compared to the ester isomers, and found to be significantly different. The group additivity methods also were able to accurately represent the heat capacity of the acid isomer.