Implementation of T-history method to determine the thermophysical properties of the phase change materials

Abstract

Phase-change materials (PCM) are an easy-to-integrate heat storage medium for buildings. In the present study, the thermophysical properties of the coconut oil (Tm = 25 °C) and commercial paraffin-based RT28HC PCM (Tm = 27–29 °C) are analysed through the T-history method. Various criteria are considered for experiments, such as heating/cooling medium, sample quantity, PCM container alignment, temperature gradient, and thermocouple placement to record PCM temperature. The experimental procedures considered standardise the T-history method and help for obtaining the appropriate cooling curve to evaluate thermophysical properties. Further, PCM melting fraction is analysed by image processing. The results show that the investigation performed in an air-cooled medium with vertical alignment of the PCM container meets the Biot number condition (Bi<0.1). The experiment with 15 g (same mass) samples yields 10% lower results than a 20 ml sample (same volume) selection due to the difference in convective length of the PCM container. RT28HC (242.004 kJ/kg) stores higher latent heat than coconut oil (71.15 kJ/kg), which is found by processing the cooling curve. Thermophysical results are validated against literature and manufacturer data. Supercooling is studied, revealing a degree of 0.1–0.7 °C in RT28HC and 2.7–3.1 °C in coconut oil. It results from poor nucleation and is reduced when the temperature gradient is less.