Determination of enthalpy–temperature–composition relations in incongruent-melting phase change materials

•H-T data can also be used to obtain valuable liquidus region T-x data.•Applies to all incongruent-melting compounds with known thermodynamic properties.•Reduces the effort and cost of assessing full suite H-T-x data for PCMs.•Uses existing T-x or H-T data of incongruent-melting PCMs to determine the other.

This paper demonstrates that liquidus line (T-x) data can be obtained from calorimetric determinations of phase transition enthalpy profiles (H-T) for incongruent-melting phase change materials (PCMs) more efficiently than using traditional cooling curves. An accurate and reliable equilibrium mixture enthalpy model bridges the H-T and T-x gap to provide a full suite of high density H-T-x data to assist latent heat energy storage researchers to evaluate composition-dependent two-phase equilibrium processes. The proposed method is validated for T-history method H-T determinations of 1:1 diluted sodium acetate trihydrate in water, and can also be used with other laboratory calorimetric techniques used to determine the phase transition enthalpy profiles of incongruent-melting compounds.