Development of an automated thermal storage system
Students Name: Kost Vasyl Ivanovych
Qualification Level: magister
Speciality: Technologies and Means of Telecommunications
Institute: Institute of Telecommunications, Radioelectronics and Electronic Engineering
Mode of Study: full
Academic Year: 2022-2023 н.р.
Language of Defence: ukrainian
Abstract: The object of research is an automated thermal accumulation system. The subject of the study is the use of thermal accumulators for the accumulation and storage of heat obtained from the conversion electricity power from solar panels and a wind generator. The purpose of the research: studying the possibility of creating a technical means - an automated thermal storage system that will ensure the thermal regimes of the thermal storage: optimal use of electricity for heating the thermal medium, compliance with heating limits, thermal reduction, etc. The purpose research: studying the possibility op creating a technical means - an automated thermal storage system that will ensure the thermal regimes of the thermal storage: optimal use electricity for heating the thermal medium, compliance with heating limits, thermal reduction, etc. The main part of the automated system is a thermal accumulator. It has two sections: the upper one is filled with quartz nose, the lower one is filled with paraffin. Between these sections, heat exchange takes place, which provides thermal reduction of temperatures (upper section ?500 oС, lower section ?100 oС). A system of nichrome wire heaters is used to heat quartz sand. The controller switches the heaters in such a way as to ensure the optimal selection of energy from the solar panels and the wind generator. Surplus energy from solar panels and a wind generator is used to generate thermal energy. The automated system must provide an algorithm for performing the following operations: - conversion of excess energy from solar panels and wind generator into thermal energy, - optimization of heating of the heat-accumulating material, - optimization of the heating of the thermoreducer material, - thermoreduction for the use of heat, 8 - temperature control of heat-accumulating material and thermoreducer material, - automation of the optimal connection of heaters, - automation of maintaining coolant temperatures within working limits. Thermoaccumulation involves receiving, storing and subsequent use of accumulated heat. Heat accumulation will occur when the incoming thermal energy exceeds the outgoing thermal energy. The output includes the useful thermal energy used by the consumer and the thermal energy of losses due to the transmission and dissipation of heat in the external environment. Nichrome wire heaters are most often used for obtaining heat. The heater can be made in the form of a tena, which has a body, insulating material - dry sand - is used to isolate the nichrome wire spiral from the body of the tena. An alternating current network with a voltage of 220 V is mostly used to power the tena. The analysis of the types of heaters showed that in the automated system, which is being developed in the master’s thesis, it is most appropriate to use a heater made of nichrome wire, since the output voltage of the solar panels and the wind generator, which is used to power the heaters, does not exceed the safe voltage limit of 42 V direct current. The wire is used in the thermoaccumulator made of nichrome with a diameter of 1.4 mm. The resistance of a wire 1 m long is 0.734 Ohm. Water is often used for heat accumulation. For example, in thermal accumulators for solid fuel boilers. Such thermoaccumulators are produced serially. Water has a high heat capacity (Table 1), allows you to efficiently store heat, and has a low cost. Table 1. Thermal properties of substances Substance Density, kg/m3 Specific heat capacity, kJ/ kg• оС Amount of heat per 1 degree C, kJ kJ/ m3• оС Temperature Debaya, оС Water Dry sand Paraffin 1000 4,18 4180 2400 – 2800 0,8 800 500 – 700 2,72 2720 – 81 (ice) 367 (silicon) – The disadvantage of using water is its low operating temperature range, which is conventionally in the range from 0 oC to 100 oC, that is, in the range from the freezing point to the boiling point of water. Possible freezing of water creates problems of transportation, storage and operation of the thermal accumulator in which water is used as a heat carrier. Also, despite the high heat capacity of water, the efficiency of its use for heat storage is limited by a relatively low upper temperature limit of 100 oC and a low Debye temperature of minus 81 oC. According to Debye’s law, the amount of heat (Cv) up to a certain limit has a cubic dependence of growth on temperature 12??4 ??3 ????(??)= 5 ??????3 9 where, T is the Kelvin temperature, ? is the Debye temperature. At temperatures higher than the Debye temperature, this dependence (Cv) becomes linear. Thus, a material with a high Debye temperature should be used for thermal storage. At the same time, it should have insulating properties, not release harmful substances at high temperatures, and be affordable. Analysis of the thermal characteristics of various substances showed that silicon has a relatively high Debye temperature. For it, the Debye temperature is 367 oC. The closest material in which the content of silicon dioxide is more than 98% is quartz sand. Such sand is white in color, it has high insulating properties. If it contains iron impurities, it acquires a yellow color. The analysis of information sources showed that it is most appropriate to use quartz sand for thermoaccumulation. Maximum heating of sand to a temperature of 500 oC. In this case, the cubic dependence of heat capacity growth at temperatures lower than the Debye temperature is effectively used. For effective heat storage, the body of the thermoaccumulator is made in the form of a thermos with an inner and outer body made of AISI 304 stainless steel with a melting point of 1400-1450 oС. Between the cases, a 120 mm thick non- flammable mat is laid, for example, PAROC Pro Wired Mat 65 based on stone wool with a maximum temperature of 640 oС. To heat the sand in the thermoaccumulator, it is planned to use electric energy from two types of sources: solar panels and a wind generator. Two RSM120-8-605M solar panels with a nominal power of 605 W, a supply voltage of 35 V and a maximum supply current of 17.29 A can be used for modeling, manufacturing and research of a prototype of an automated thermal storage system. The overall dimensions of the solar panel are 2172x1303x35 mm. A wind generator [2] with a nominal power of 800 W and a nominal voltage of 12/24 V is also used for electricity production. To heat the sand in the thermoaccumulator, 10 heaters made of nichrome wire with a diameter of 1.4 mm and a length of 1 m are used. The resistance of one heater is 0.734 Ohm. At a voltage of 12 V, the current passing through the heater is 16.3 A. In this case, the heater consumes 195.6 W. The maximum consumption of all heaters at a supply voltage of 12 V is 1965 W, which is within the limits of the total power of the solar panels and the wind generator. For optimal selection of electricity from solar panels and a wind generator, heaters are automatically connected in such a way as to ensure maximum energy yield. Switching of 6 heaters for solar panels and 4 heaters for wind generator is used. Electricity consumption for heating the sand in the thermal accumulator occurs when it is redundant, when it is not used for direct electricity consumption needs. An example of such a mode can be the energy supply of a country house.