Usually the cold storage temperature of the cold storage system depends on the cold storage rate and the state characteristics of the cold storage tank at this time. For the external ice melting system, it refers to the amount of ice on the inner tube wall. For ice storage systems with short cold storage time, a higher cold storage rate is generally required, which means cold storage at a lower (average) cold storage temperature; conversely, a slow cold storage rate means a higher cold storage temperature. Generally, cold storage equipment manufacturers can provide the lowest cold storage temperature values ??at various cold storage rates. For cold storage equipment such as container type and high-quality salt type, supercooling will occur in the early stage of the cold storage process. Supercooling only occurs when the cold storage equipment has completed releasing the cold and there is no ice left in it. The result is that the start of the cold storage is reduced. stage heat transfer rate. Supercooling can be reduced by adding nucleating reagents. According to foreign information, a certain patented nucleating agent can limit the degree of subcooling to between -3°C and -2°C.
For ice storage systems, during the cooling cycle, if the cooling temperature remains constant, the cooling amount will gradually decrease; or when the cooling rate remains constant, the cooling temperature will gradually decrease. rise. This is particularly obvious for completely frozen and container-type cold storage equipment. This is because most of the ice outside the coil and inside the ice ball is melted by heat exchange through a layer of water, and the heat exchange area is changing dynamically; For ice-making slide-down and refrigerant coil-type cold storage equipment, warm water and ice are in direct contact to melt the ice, and the cooling temperature remains relatively stable.
In fact, cold storage equipment rarely maintains a constant cooling rate. The actual cooling rate depends on the air conditioning load curve, especially the air conditioning load value in the last few hours is the most important, which determines the cooling rate. The maximum cooling temperature value of the cold cycle. Therefore, for the same type of cold storage equipment, which one maintains a constant cooling temperature for a longer time under the actual cooling rate condition, the better the performance of the equipment. Whether a cold storage air conditioning system uses partial or full cold storage, its initial investment is usually higher than that of a conventional air conditioning system. This requires designers to correctly grasp the time-varying characteristics of the building's air conditioning load and determine reasonable cold storage equipment and its system configuration. Develop system operation strategies and make accurate economic analysis so that investors can recover excess investment in a short period of time in the form of electricity bill savings. Generally speaking, in a designed cold storage system, the cost of the cold storage equipment can be measured by the cost per unit of available cold storage capacity. In addition, the configuration of the cold storage system also affects the size of the cold storage equipment.
10. Regarding the selection of secondary refrigerant in ice storage; 1) The secondary refrigerant is required to be in a liquid state at the operating temperature and does not undergo phase change. 2) The solidification temperature of the secondary refrigerant is required to be at least 4 to 8°C lower than the evaporation temperature of the refrigerant, and the standard evaporation temperature is higher than the maximum temperature that the refrigeration system can achieve. The specific heat is larger. When transferring a certain amount of heat, the circulation volume of the secondary refrigerant can be reduced, which reduces the power consumption of the pump transporting the secondary refrigerant and reduces the amount of consumable materials in the pipeline, thus improving the economic efficiency of the cycle. In addition, when a certain amount of fluid carries a certain amount of heat, a large specific heat can reduce the heat transfer temperature difference. 3) The thermal conductivity should be large to increase the heat transfer effect and reduce the heat transfer area of ??the heat exchange equipment. 4) The viscosity should be small to reduce flow resistance and delivery pump power. 5) The chemical properties are required to be stable. The brine does not decompose within the working temperature; it does not combine with oxygen in the air, and it is required not to corrode equipment and pipelines. Thanks to the teachers at the School of Environment and Engineering of Donghua University for providing information.