THERMAL PROPERTIES IN THE Zn(NO3)2–Co(NO3)2–H2O SYSTEM WITH LIMITED SOLUBILITY

10.25712/ASTU.1811-1416.2026.03.006

Abstract

. This paper proposes an integral model for calculating the thermal properties of phase change materials from cooling curves using a modified T-history method. Unlike existing techniques, the developed model introduces a heat transfer calibration coefficient UA determined for a (reference+tube) measuring cell. This approach enables the recording of sample cooling curves without a physical reference, relying on a cell calibrated under identical experimental conditions. The model was tested using crystalline hydrate mixtures of Zn(NO₃)₂·6H₂O/Co(NO₃)₂·6H₂O at various mass fractions. The obtained enthalpies and temperatures of crystallization and melting demonstrate agreement with differential scanning calorimetry data. Within the temperature range of 20–60 °C, the mean integral values of thermal conductivity decrease from 0.374 to 0.254 W·m^-1·K^-1 as the Zn(NO₃)₂·6H₂O mass fraction increased from 0 to 100 wt.%, as well as for the heat transfer coefficient, which decreased from 20.5 to 13.9 W·m^-2·K^-1, and the thermal diffusivity. Thus, empirical equations for the temperature dependence of the liquid-phase specific heat capacity were derived during heating up to 60 °C. The experimental findings show that the studied mixture forms a solid solution with mutual solubility limits of approximately 15 wt.% for Zn²⁺ ions in Co²⁺ and about 10 wt.% for Co²⁺ ions in Zn²⁺.