The failure of refrigeration system in small cold storage

The failure of refrigeration system in small cold storage

Small cold storage, including movable cold storage, generally have a capacity of less than 100 tons. The cold storage evaporator adopts a platoon type or a combined type of air cooler, and a complete refrigeration system is composed of a compressor unit (water-cooled or air-cooled), a throttle expansion valve, etc. Most of the compressors are of semi-closed type, larger systems also use open type, and smaller systems use fully enclosed type. R22 is a common refrigerant.

　　 1. Reasons for failure of refrigeration system in small cold storage

　　The most common operating failures of the refrigeration system of the cold storage are: the slow drop of the refrigeration temperature, the abnormal operating conditions or the inoperability caused by the system blockage, etc.

　　The cold storage temperature drops slowly, mostly due to improper operation adjustment, of which the adjustment of the expansion valve is the most critical. The opening degree of the expansion valve is small, the flow rate of the refrigerant passing through is small, and the pressure is also low; the opening degree of the expansion valve is large, the flow rate of the refrigerant passing through is more, and the pressure is also high. According to the thermal properties of the refrigerant, the lower the pressure, the lower the corresponding temperature; the higher the pressure, the higher the corresponding temperature. According to this law, if the outlet pressure of the expansion valve is too low, the corresponding evaporation pressure and temperature are also too low. However, due to the decrease of the flow into the evaporator and the decrease of the pressure, the evaporation speed slows down, the refrigeration capacity per unit volume (time) decreases, and the refrigeration efficiency decreases. On the contrary, if the outlet pressure of the expansion valve is too high, the corresponding evaporation pressure and temperature are also too high. The flow and pressure entering the evaporator are both increased. Due to the excessive liquid evaporation, the excessive moisture gas (or even the liquid) is sucked into the compressor, causing the wet stroke (liquid hammer) of the compressor, making the compressor unable to work normally, causing a series of work The condition is bad and even damages the compressor. The opening degree of the expansion valve should be adjusted according to the current storage temperature, that is, under the pressure corresponding to the storage temperature.

　　 2. The troubleshooting method of small cold storage:

　　 Close the main liquid supply valve and open the compressor to run. When the suction pressure stabilizes below 0, close the discharge valve of the compressor, and stop the compressor at the end of the closing (the fluorine collection is complete). Disassemble the liquid inlet of the expansion valve, take out the filter, clean it, and reinstall it, and replace the infusion dry filter or filter, check the performance of the infusion solenoid valve and restore it (check and clean). Open the exhaust bypass port of the compressor (others are still in the state when fluorine is collected), start and run, so that all the air from the main valve of the liquid supply to the compressor body is drawn from the exhaust bypass port until the suction pressure stabilizes at 0 When the vacuum is below (pumping is complete), close the exhaust bypass port, open the exhaust valve and the main valve of the compressor, and the system resumes operation.

If the expansion valve itself is working normally, it is just a blockage caused by excessive water or dirt in the system, causing serious ice blockage or dirty blockage, making the system work abnormally, and the temperature of the liquid pipe before the expansion valve is lower than normal temperature, or even Condensation, there is no temperature response in the pipeline behind the valve, the suction pressure of the compressor is below 0, the machine operating temperature and exhaust temperature are high, and even knocking sounds occur, the cooling temperature does not drop, and the operating conditions are bad.

Excessive water in the system is mainly due to the incomplete maintenance of the vacuum; leakage causes low pressure to continue to operate under negative pressure and inhale moisture; the system is left for too long after disassembly; the mechanical parts are regained and sticky; the moisture content of the refrigerant Excessive volume; caused by cracked condenser tube of water-cooled condenser. The main reason for the excessive pollution of the system is the precipitation of iron oxides in the pipe evaporator and water-cooled condenser and other dirt of the system along with the working fluid circulation.

　　 To deal with the above faults, the system's sewage and water removal operations can be carried out at the same time. The specific method: connect the bypass port of the compressor low pressure valve to discharge fluorine. When the pressure reaches 0 gauge, it can be regarded as the system working fluid has been discharged. Open a by-pass port with the same diameter as that of the evaporator pipe in advance at the lowest part of the evaporator pipe, and install the corresponding valve for fluorine; Replacement) Three-way ports of the same diameter and related valves should be installed. Turn on the compressor (the water supply valve of the water-cooled condenser should be opened), suck in the air from the suction bypass port, press the compressor to increase the pressure, and stop when the pressure rises to 1.2MPa gauge pressure, and quickly fully open the evaporation pipe The lowest bypass valve and the condenser three-way outlet, the compressed air followed by the system's dirt and water are quickly discharged from the high pressure and low pressure sides respectively (the sewage outlet of the cold storage pipe in a small space can be temporarily connected to the leather pipe to lead out the storage In addition, pay attention to the hose not higher than the drain outlet). When the system pressure is close to 0, restart the compressor to increase the pressure and discharge the sewage, and repeat this several times until the water and dirt in the system are confirmed to be discharged. After shutdown, immediately replace the dry filter or new filter, clean the expansion valve filter and solenoid valve, remove and wash the compressor suction filter, replace the compressor lubricating oil, close the drain valve of the discharge pipe and the condenser outlet tee Connect the fluorine cylinder to the compressor's low-pressure valve bypass port, close the compressor's exhaust valve, open the exhaust bypass port, other valves of the system should be opened, and start the compressor to operate the system for vacuum and fluorine operations , To resume the production of the system.

　　 In addition, the oil and air discharge operation of the system should be performed frequently or regularly to improve the heat exchange performance and cooling effect of the heat exchanger. Because the refrigerating oil has a large viscosity, it is usually adsorbed on the inner surface of the pipeline or container to form an oil film layer. Especially on the low pressure side (expansion valve outlet to compressor inlet), due to the low temperature, the viscosity of the oil is greater, and the oil film layer formed is of course larger, which increases the heat exchanger (evaporator and condenser) Thermal resistance affects heat transfer performance and reduces the cooling effect. The more oil in the system, the greater this disadvantage, so it is very detrimental to refrigeration. The presence of air or other non-condensable gases in the system will cause the condensing pressure and temperature to increase, the power consumption increases, the compressor's operating temperature is high, the load is heavy, and the refrigeration efficiency is reduced. The pipe-type evaporator can use the drain outlet at the lowest point to drain the oil; the lowest liquid outlet of the combined air cooler evaporator usually has an oil (soil) outlet. Both the oil and air discharge operations should be carried out when the system is stopped and the air discharge should be carried out when the temperature is lower, so that the effect will be better. For systems without special air discharge equipment, the air discharge is generally selected at the highest outlet on the high-pressure side. The evaporative tube and the finned tube of the cold storage must be defrosted in time (timing) to ensure good heat transfer.