GRANITE HEAT ACCUMULATORS FOR AIR HEATERS

Abstract

The article deals with one of the ways to improve the energy situation in agriculture of Ukraine, namely to increase the energy efficiency of solar air heaters through the use of granite heat accumulators. In the world, in recent years, the share of energy produced by non-traditional sources has been steadily increasing. Unfortunately, in Ukraine this proportion is much smaller than in the first world countries. This problem is especially relevant for agriculture. The main renewable energy sources for Ukraine's agricultural sector are biofuels (solid, liquid, gaseous), wind and solar. The latter is the most attractive for widespread use in agriculture. After all, for the production of biofuels requires at least land, mechanization and chemistry, etc., for the production of wind energy requires appropriate weather conditions that are not available in most regions of the country. And only solar energy is everywhere and almost always. The difficulty of using solar energy at night is one of the main constraints on the widespread use of solar installations. The use of heat accumulators (in devices that accumulate heat during the day and give it away at night for production purposes) for solar heaters greatly enhances their technological capabilities. Battery material is a variety of materials - from soil to plastic water bottles. This article discusses the theoretical justification (confirmed by experimental studies) of the choice of rational size and shape of granite heat accumulator elements. To simplify the task, it was assumed that the battery element has a spherical shape and its thermophysical characteristics remain constant throughout the process of heating and cooling. As a result of the solution of the differential equation of thermal conductivity for these conditions, the dependence of the liquid temperature distribution depending on the radius and time of heating was obtained. The battery element is fully charged when the liquid temperature in the center and on the surface is equal. The temperature distribution in the middle of the liquid was also determined when cooled. Theoretical calculations were confirmed by experimental studies. To determine the rational parameters of the battery cells, a criterion was proposed, the value of which depends on the ratio of heating and cooling time, heating and cooling temperatures, the location of thermocouples. As a result of theoretical and experimental studies, it is established that the rational size of the granite element of the heat accumulator is an equivalent diameter of 0.3 m. The use of a heat accumulator of this type allows to evaporate more than 300 kg of moisture, which allows to reduce the hay ventilation period, to reduce nutrient losses.