Ivanov S. System for determining the heat of evaporation and heat capacity of wet materials

The thesis is devoted to the development of the measurement system for investigating the heat capacity and the heat of evaporation from inhomogeneous materials. Thesis describes existing methods and devices for investigating the heat of evaporation. On this basis decided to use method of synchronous thermal analysis. The factors influencing the result of the measurement are analyzed by using the mathematical modeling. It is shown that the influence of unevenness of heat supply to the sample is significant in the study of non-uniform materials. One of the most effective ways of ensuring the uniformity of temperature conditions in a calorimetric cell is the placement of a cell on a high-conductivity platform. The influence of the additional heat exchange of the sample with the gas environment of the working chamber and the method of compensation of the influence of the heat exchange of the sample on the gas environment in the research process have been developed. It is proposed to add a comparison surface in the environment of evaporation, the characteristics of which are close to the characteristics of the measuring cells, and the surface temperature is set close to the surface temperature of the sample. Suggested method of compensating the effect of the heat exchange conditions nonidentity in calorimetric cells based on the direct recording of the temperature change of the cells. The measurement system for investigating the heat of evaporation and the heat capacity of a wide range of humid inhomogeneous materials are presented. For investigating the different samples materials using a single measurement system, a replaceable calorimetric platforms with different configurations of cells was proposed. The method of calibration of heat flow sensors built into the device based on a method of comparison using a reference heat flow sensor and a set of thermal collectors are presented. In thesis suggested the method of calibration by the heat capacity and by the heat of evaporation, which is based on testing of reference samples with known characteristics. An estimation of the metrological characteristics of measurement system was made, according to which the heat capacity determining error on the presented device does not exceed ± 1.5%, and the heat of evaporation determining error does not exceed ± 2.5%. The procedure for preparing and conducting experimental research, as well as the algorithms for processing the measurement information, is developed, depending on which type of sample is being investigated and what value needs to be determined. Experimental results was been obtained of the evaporation heat and heat capacity of wet inhomogeneous materials with various structures, such as plant raw materials, food products, biofuel components, building materials. Key words: drying, heat capacity, heat of evaporation, heat flow sensor, inhomogeneous materials, synchronous thermal analysis, STA, measurement error.