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Water cold storage is to use the sensible heat of water to realize the storage of cold energy. Therefore, a properly designed cold storage system should obtain the cold storage efficiency by maintaining the largest possible temperature difference in the storage water and preventing the mixing of cold water and hot water. In the water cold storage technology, the key issue is that the structure of the cold storage tank should be able to prevent the mixing of the stored cold water and the returning hot water. To achieve this, the following methods are commonly used:

One, Multi-tank method

The cold water and hot water are stored in different tanks to ensure that the temperature of the cold water sent to the load side remains unchanged. Multiple water storage tanks have different connection methods, one is the empty tank method. As shown in Figure 1a, it maintains that there is always one tank in the storage tank system that is empty at the beginning of the storage or discharge cycle. As the cold storage or cooling proceeds, the tanks are emptied in turn. Another way to connect is to connect multiple tanks in series or divide a storage tank into several interconnected compartments. During cold storage, cold water enters the tank from the bottom inlet of the storage tank, and the hot water overflowing at the top is sent to the bottom inlet of the second tank, and so on. Finally, all the tanks are cold water; when cooling, the direction of water flow Instead, cold water flows from the bottom of the tank. The return hot water is fed from the top of the last tank. Since the hot water is on the top and the cold water is on the bottom in all the tanks, the density difference caused by different water temperatures can prevent the cold and hot water from mixing. When the multi-tank system is running, its individual water storage tanks can be separated from the system for maintenance and repair, but the pipeline and control of the system are more complicated, and the initial investment and operation and maintenance costs are relatively high.

Second, the maze method:

The water storage tank is divided into many cells by partitions, and the water flows through each cell in turn according to the designed route. The labyrinth method can better prevent the mixing of hot and cold water. But in the process of cold storage and cooling, one is that hot water enters from the bottom inlet or cold water enters from the top inlet. This is easy to cause mixing due to buoyancy; in addition, the high flow rate of the water will cause disturbance and the mixing of hot and cold water; if the flow rate is too low, a dead zone will be formed in the cells, reducing the capacity of the cold storage system

Three, natural stratification

Natural stratification is achieved by utilizing the different density of water at different temperatures. The system consists of adding a water storage tank to the conventional refrigeration system. When the cold storage cycle is performed, the cold water sent by the refrigeration equipment enters the water storage tank from the bottom diffuser, and the hot water is discharged from the top, and the water volume in the tank remains unchanged. In the cooling cycle, the water flows in the opposite direction, the cold water is sent from the bottom to the load side, and the return hot water enters the water storage tank from the top diffuser. Fig. 3b is a graph of the cold storage characteristic. The ordinate is the temperature, and the abscissa is the percentage of water storage