Investigation of T-history Method Application for Sub-zero Phase Change Material Thermal Properties

Abstract

The T-history method, first proposed by Zhang & Jiang, is a simple method used to determine the latent heat, specific heat, thermal conductivity, melting point, and degree of supercooling of a phase-change material (PCM). The method is based on the measurement of the temperature of the material over time. It assumes that the PCM sample and the reference material exchange thermal energy with the environment in a similar manner, because it is based on the lumped capacitance method, and the temperature distribution inside the sample is uniform. There are multiple advantages that the T history method has over conventional methods; however, the T history method also has some downfalls, which have been improved over the years by different authors. This study experimentally investigates the reliability of this technique for PCM with a phase change temperature below 0 ° C. The technique is used to first determine the properties of denoised water with a phase change temperature of 0 ° C, using ethylene glycol with a mixture ratio of 50/50 as reference material. Second, by determining the properties of KCl with a concentration of 19.5% salt to water for a phase change temperature of -10 ° C. Two analytical approaches were used, one by immersing the samples in antifreeze during the charging process and the other by exposing the samples to ambient air during the discharging phase. The experimental results were further validated using the known literature to determine the latent heat of KCl. This study found that the latent heat of KCl measured using the technique has a 6.2% difference from the known results determined by the DSC. This study recommends the use of the T history method when designing latent heat thermal energy storage systems (LHTESS), because the sample size is an important characteristic for accurate thermophysical properties during the design process.