Energy 29 (2004) 1785–1804 www.elsevier.com/locate/energy Phase transition temperature ranges and storage density of paraffin wax phase change materials Bo He  , Viktoria Martin, Fredrik Setterwall Department of Chemical Engineering and Technology, Division of Energy Processes, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Received 18 March 2003 Abstract Paraffin waxes have been used in many latent thermal energy storage applications because of their advantageous thermal performances. In this paper, the liquid–solid phase diagram of the binary system of tetradecane and hexadecane has been used to obtain information of the phase transition processes for cool storage applications. The analysis of the phase diagram indicates that, except for the minimum-melt- ing point mixture, all mixtures melt and freeze in a temperature range and not at a constant temperature. The latent heat of fusion evolves throughout this temperature range. Differential scanning calorimetry (DSC) was used to determine the thermophysical properties of the binary system. Depending on the DSC settings throughout the measurements, varying results were obtained. For example, when the DSC runs at a high heating/cooling rate, it will lead to erroneous information. Also, the correct phase transition temperature range cannot be obtained simply from DSC measurement. By combining phase equilibrium considerations with DSC measurements, a reliable design method to incorporate both the heat of phase change and the temperature range is presented. # 2004 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, the use of phase change material (PCM) thermal energy storage has gained considerable attention. This is because PCMs have high storage density (amount of energy stored per unit mass), and a narrow temperature range for charging and discharging the stor- age. This range corresponds to the phase transition temperature of the PCM. The compactness of the PCM storage system allows for a greater flexibility in choosing a location for the storage system [1].  Corresponding author. Tel.: +46-8-790-9480; fax: +46-8-723-0858. E-mail address: bohe@ket.kth.se (B. He). 0360-5442/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2004.03.002