Optimizing the storage methods for excess heat energy and associated technical and technological solutions has a significant impact on the development of LHTES systems. New technologies for storing thermal energy are increasingly an alternative to the classic methods of providing thermal infrastructure facilities. In this paper we analyze the results of experimental studies of heat-storage materials for their further integration into the Smart Grid heating system of infrastructure objects and use in the M-TES. The conducted literary review showed that the thermophysical parameters of the investigated substances for the conservation of heat from different authors are very different. We conclude that this is due to the quality of the materials being studied and the errors of laboratory measurements. This negatively affects the design of LHTES systems and greatly complicates the calculation and modeling of heat transfer processes. It is especially important to correctly determine the amount of heat that can be obtained during the charging and discharge cycles of TES, as well as the lifetime of the material that accumulates heat. Therefore, the purpose of this work is to identify the appropriate material for energy storage applications between 0 0C and 115 0C and evaluate it, depending on the thermophysical properties and the time of stable operation. Taking into account the economic aspects, only the available technical materials are considered within the framework of this study, since the choice of material is aimed at the use of M-TES in real conditions of operation. Figure 1 summarizes the results of research on heating and cooling cycles of heats of heat storage substances. High thermal power and, hence, high thermal conductivity are important for the storage efficiency of PCM, especially in the process of solidification, because in a heat transfer predominant solid layer that grows continuously. However, both PCMs are not suitable for mobile thermal storage systems in this form. The huge disadvantages are the emergence of different values of the melting point, the high retention time of both candidates, as well as their prices. Therefore, further research should be directed to eliminate these negative effects. Despite the relatively low density of heat storage with aqueous solutions of antifreeze, they are beneficial candidates for waste heat transfer systems within the framework of this study. Addition of NaCl salt practically does not affect the speed of heating and cooling of the coolant. The addition of bischofite worsens the thermophysical properties of water and shows a small density of heat accumulation. It has been experimentally established that after 3 ... 4 cycles of heating and cooling from a solution of technical bischofite, a dark yellow, insoluble precipitate forms, which creates problems during the operation. Significant increase in TES discharge time was obtained when testing ozokerite. All of the above substances have shown a stable state after 30 cycles of heating / cooling and indicate overcooling below the melting point by about 30 °C. Trihydrate sodium acetate shows no stable results. Subsequently, after 20 cycles of heating and cooling, it loses its properties.
EXPERIMENTAL RESEARCH OF THERMAL STABILITY OF SUBSTANCES FOR THERMAL ENERGY STORAGE
