Liquid–solid phase equilibrium study of tetradecane and hexadecane binary mixtures as phase change materials (PCMs) for comfort cooling storage

Abstract

Phase diagrams (equilibrium diagrams) are a convenient way of depicting the concentration–temperature–pressure relationships of a chemical system at equilibrium. They are invaluable to PCMs thermal storage researches and developers. In the present paper, the liquid–solid phase equilibrium of binary mixture system of tetradedcane and hexadecane has been studied. For theoretical evaluation of the thermodynamic equilibrium between the liquid phase and solid phase of tetradecane and hexadecane, several methods were compared: the UNIFAC group-contribution method, the model of Won, and Pedersen’s model. The temperature–composition phase diagram of the binary system has been obtained by the calculation. The diagram illustrates a binary, isomorphous system with a temperature minimum. Differential scanning calorimetry (DSC) was used to study the phase transformation of the binary system. DSC was run at different ramp rates and results indicate that these mixtures melt and freeze over a temperature range and the temperature range depends on the DSC ramp rate, and in a short mixture concentration interval appears low temperature solid–solid peaks. From the DSC results presented, it is concluded that the behaviour of binary mixtures of n-alkanes is far more complicated than considered in earlier studies. The phase diagram and all information from DSC are very important for designing PCM storage system.