Влияние термоциклирования на выбор рабочего тела с фазовым переходом для теплоаккумуляторов систем солнечного теплоснабжения

Abstract

The present work is aimed at analysing the characteristics of known thermal storage materials featuring phase transition and studying the effect of the main operational parameters (thermal cycling, insufficient long-term stability, phase segregation, corrosion, supercooling) on the thermophysical and operational properties of these materials. Here, analytical research methods are applied based on the generalisation and analysis of a significant amount of empirical information on thermal storage materials, the classification of materials according to their main properties and the synthesis of recommendations on the practical use of thermal storage materials in heat supply systems using solar energy. The selection criteria for a medium using the latent heat of the phase transition for thermal receivers are considered. One of the main requirements formulated by the authors for the medium consists in the preservation of thermophysical properties, such as melting point, latent heat of melting, as well as their variation ranges, during in-operation repeated phase transitions. The effect of the transition number (100-1500 thermal cycles) on the stability of the thermophysical properties of materials is demonstrated with the recommendations provided on the selection of thermal storage materials for thermal energy storage in solar heat supply systems. In terms of heat storage materials with a phase transition for solar energy systems operating at relatively low temperatures (30-60°C), both organic (paraffins, fatty acids) and inorganic (crystalline hydrates of salts) materials are applicable. In order to increase the efficiency of thermal transfer processes in thermal storage systems based on materials with a low thermal conductivity coefficient (0.148-0. 6 W/m•K), the application of special technical solutions is recommended, including an increased area of thermal transfer surfaces, the introduction of inclusive additives (for example, inserting a porous metal foam and a metal matrix in the thermal storage material, the addition or dispersion of nanoparticles), etc.