METHOD OF DETERMINING THERMOPHYSICAL PROPERTIES OF SUBSTANCES IN PHASE TRANSITIONS Russian patent published in 2024 - IPC G01N25/02 G01N25/18 

FIELD: measuring.

SUBSTANCE: invention relates to thermophysical measurements and can be used to determine properties of solid substances, liquids and gases during phase transitions. Disclosed is a method for determining thermophysical properties of substances in the region of phase transitions, comprising steps of placing the analysed substance into a container with a heating element in the form of a metal wire, wherein the container itself is immersed in the thermostating liquid of the thermostat with a temperature close to the temperature of the beginning of the phase transition of the investigated substance, depending on the phase transition under study, heating or cooling of the thermostating liquid of the thermostat is started at a constant rate. At the same time, direct current pulses are periodically supplied to the ends of the metal wire with such an interval between them that, before the next pulse is supplied, the heat from the previous one is completely dissipated in the environment, before each pulse, temperature T₀ of the heating element, which simultaneously serves as a resistance thermometer, and temperature of the thermostating liquid T_T are measured, and the difference between T₀ and temperature of the thermostating liquid is determined ΔT_F = T₀ – T_T. During each pulse, voltage U at the ends of the metal wire and current intensity I are measured at regular time intervals, and density of heat flux from the surface of the heating element q_L = (I U/L) is calculated, where L is the length of the wire. For each heating pulse, wire temperature increment values are calculated ΔT to T₀ for time τ from the beginning of the pulse and plotting the dependence ΔT = f (lnτ), to which heat conductivity coefficient is calculated by formula λ = q_L/(4π tgϕ), where ϕ is the angle of inclination of the straight section of the obtained graph, then a thermogram is plotted ΔT_F = f (τ*), where τ* is current time of passage of phase transition. From thermogram ΔT_F = f (τ*) calculating the integral ∫ ΔT_F d τ* and determining the volumetric heat of the phase transition r' from the relationship r' = (λ_av ∫ ΔT_F d τ*), where λ_av is the average value of the heat conductivity coefficient, calculated as the arithmetic mean of the values λ for each pulse during phase transition, F is the surface area of one metre of the length of the heating element. Phase transition temperature of the pure substance is determined from the curve λ from T₀, temperature, at which λ ceases to depend on T₀ and all values λ are located on a straight line parallel to the axis λ, corresponds to the phase transition temperature of the pure substance.

EFFECT: invention makes it possible to determine volumetric heat of phase transition, temperature of phase transition of pure substance, as well as heat conductivity coefficient in one measurement with high accuracy.

1 cl, 5 dwg, 2 tbl