Low temperature cold storage usually use exhaust pipes as heat exchangers, and the external heat transfer forms are natural convection and radiation heat transfer.In general, multiple circulation of refrigerant is used for liquid supply in the pipeline, which is mainly phase change heat exchange, with large local heat exchange. Generally, the cooling and temperature return are relatively fast.There will be a big difference when the heat exchange of exhaust pipe is used in the coolant system.The most intuitive feedback is that the temperature of the cold storage cannot be reached, or the cooling is relatively slow.In fact, it has a great relationship with the arrangement of system exhaust pipe, the pipe form of heat exchange exhaust pipe and the physical parameters of coolant.Glacier coolant through cold storage laboratory tests, different evaporator, different heat exchange pipe, different coolant, different pump circulation system found the following phenomenon.
Under the same heat exchange area, the cooling time of aluminum row tube is longer than that of smooth row tube, and the efficiency of aluminum row tube fin of load coolant system decreases obviously.
Under the same working condition and the same coolant, the cooling time of steel row pipe is close to that of aluminum row pipe. Considering the cost, the economic value of using ordinary seamless steel pipe is better.
The efficiency of the plate heat exchanger is significantly higher than that of the shell and tube heat exchanger. The channel in the shell and tube is several millimeters. The boundary layer of the coolant is relatively small, and the main thermal resistance of the heat exchanger is on the side of the coolant. The reduction of the measured thermal resistance of the coolant significantly improves the efficiency.
According to some comprehensive test data, during the transformation or design of the cold storage, the heat exchange exhaust pipe needs to be reasonably used. First, ensure the flow rate in the exhaust pipe, and then ensure that the cooling in the exhaust pipe is not too large or the single circuit is not too long.
The volume of coolant in the cold storage is small, and the finned tube is used. If it is really needed, the calculated heat exchange area needs to be increased by 30%.In addition, the pressure of the coolant system is generally 2 ~ 3bar. In fact, the pipe used can have less wall thickness and reduce the heat conduction and thermal resistance.
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