Enthalpy–Temperature Characterisation of Organic Phase Change Materials Using a Common T-History Framework

Phase change materials can exhibit markedly different thermal responses during cooling, ranging from narrow single-stage transitions to broad or multistage behaviour, which requires the analysis procedure to account for differences in response structure. This study applies a common water-referenced T-history framework to the enthalpy–temperature characterisation of six organic phase change materials: RT35HC, RT45HC, lauric acid, beeswax, palmitic acid and soy wax. Five experiments were reported for each material. The enthalpy was obtained from small, matched temperature intervals in the same way for every material, while the low-temperature calorimetric boundary was derived from the measured cooling response rather than imposed as a fixed temperature criterion. Thermal responses were described by cumulative temperatures at the 5%, 50% and 95% levels of the detected thermal effect. The T-history enthalpy changes were 207.35 ± 32.31, 197.59 ± 23.31, 224.11 ± 32.48, 200.38 ± 17.47, 191.50 ± 15.16 and 109.37 ± 13.33 J/g for RT35HC, RT45HC, lauric acid, beeswax, palmitic acid and soy wax, respectively. Comparison with differential scanning calorimetry measurements of the tested samples, independent calorimetric studies, manufacturer data and published thermal data supported the identified temperature regions and response structures. The enthalpy values were interpreted separately, taking into account differences in calorimetric definitions and temperature intervals. Changing the detector settings changed the mean primary midpoint temperature by less than 0.03 K for every material, while changing the matched temperature interval from the nominal 0.250 K to 0.125 K or 0.500 K changed the mean enthalpy by at most 2.29%. The results show that a common T-history framework can characterise substantially different cooling behaviours of the phase change materials when calorimetric boundaries are derived from the measured thermal response. The resulting characteristics also provide material-level information relevant to the selection of PCMs for electronic thermal management applications.