Matviienko S. Improvement method for determination of the substances composition by their thermal conductivity

This work devoted to scientific substantiation and improvement of the method for control and determining the thermal conductivity of substances with thermistor use as a sensitive element and development an instrument which makes the process of measuring the thermal conductivity of substances by a nondestructive method much simpler and enables the simultaneous research of large number of samples with improved measurement accuracy. In the work, the direct heating thermistor method for control the thermal conductivity of substances is scientifically justified. The choice and design of sensitive elements for measuring their thermal and physical characteristics (TPC) is substantiated. Developed mathematical model for calculating the thermal conductivity of substances based heating thermistor thermogram. Calculated formula for improved method that determines the coefficient of substance thermal conductivity is generalized relative dependence of heating thermistor power consumed to its geometric dimensions and values of the thermogram heating temperature at control points. In order to increase the accuracy of TPC substances determination under investigation, were introduced into the mathematical model a number of correction factors, which was obtained by measuring on reference substances with known TPC. The use of correction coefficients in the mathematical model for determining the thermal conductivity of substances taking into account the test sample temperature, the compensation of temperature difference measured by thermistor to it`s average value, the value at the ADC output, the temperature of the thermistor self-heating caused by presence of the shell, and sensitivity of the probe thermistor to thermal conductivity of test substance , allowed to get a general error measurement that does not exceed 3%. An design developed multi-channel instrument for measuring substances TPC studied, which is based on the results of research testing stand and the appropriate software and mathematical software for process control measurements and processing of research results. Presented methodology of experimental research for determining the thermal conductivity of substances by direct heating thermistor method. The results of measuring the thermal conductivity of the test substances ratios ranging from 0.1 W/m*K to 1.0 W/m*K, which confirmed the possibility of using the improved method and device designed to determine the thermal conductivity of substances.