Causes of abnormal cold storage temperature

Causes of abnormal cold storage temperature

In daily life, there are many problems with abnormal temperature in cold storage. Common common problems are usually: 1. No cooling or poor cooling effect; 2. Slow cooling speed; 3. The cooling temperature stays high and cannot drop; 4. The cooling temperature Decrease slowly; under normal circumstances, the first two abnormal problems are relatively rare. The current refrigeration mechanism has a good refrigeration effect. The refrigeration effect and refrigeration speed are the main products of many manufacturers. Today we cannot reduce the temperature of the cold storage. Analysis of the abnormal phenomenon of slow decline:

　　 1. The cold storage has poor heat insulation or sealing function, and large cooling loss

　　 Poor thermal insulation performance is due to insufficient insulation thickness of pipes, warehouse insulation walls, etc., and poor thermal insulation and thermal insulation effects. It is mainly caused by improper selection of insulation layer thickness during design or poor quality of insulation materials during construction. In the process of construction and use, the thermal insulation and moisture-proof function of the thermal insulation material may be damaged, causing the insulation layer to be damp, deformed, or even eroded. Its thermal insulation capacity will decrease, and the loss of cold storage capacity will increase, and the temperature drop will be significantly slowed down. In addition, an important reason for the large cold loss is the poor sealing function of the warehouse, and more hot air invades the warehouse from the leak. Under normal circumstances, if you see condensation on the seal of the warehouse door or the seal of the cold storage insulation wall, it means that the seal is not tight. In addition, frequent opening and closing of the warehouse door or more people entering the warehouse together will increase the cooling capacity loss of the warehouse. Try to avoid opening the warehouse door frequently to prevent a large amount of hot air from entering the warehouse. Of course, when the warehouse stocks frequently or the stock volume is too large, the heat load increases sharply, and it usually takes a long time to cool down to the specified temperature.

　　2. The surface of the evaporator is too thick or dusty, and the heat transfer effect is reduced

　　 Another important reason for the slow drop in temperature is the low heat transfer efficiency of the evaporator, which is mainly caused by the thick layer of frost or excessive dust on the surface of the evaporator. Because the surface temperature of the cold storage evaporator is mostly lower than 0℃, and the humidity of the warehouse is relatively high, the moisture in the air is very easy to frost or even freeze on the surface of the evaporator, which affects the heat transfer effect of the evaporator. In order to prevent the frost layer on the evaporator from being too thick, it is necessary to defrost it regularly.

　　 introduces two defrosting methods that are simpler and easier to operate:

　　①Stop defrosting. That is, stop the operation of the compressor, open the warehouse door, let the warehouse temperature rise, and restart the compressor after the frost layer automatically melts.

　　②Frost. After the goods in the warehouse are moved out, the surface of the evaporator pipe is directly washed with hot tap water to dissolve or fall off the frost layer. In addition to excessively thick frosting will cause poor heat transfer in the evaporator, the evaporator surface will have too thick dust due to long-term uncleaned, and its heat transfer efficiency will also be significantly reduced.

　　 3. There is more air or refrigerant oil in the evaporator, and the heat transfer effect is reduced

Once more refrigerant oil is attached to the inner surface of the heat transfer tube of the evaporator, the heat transfer coefficient will be reduced. Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will decrease and the heat transfer will be reduced. Efficiency will also drop significantly, and the rate of temperature drop in the warehouse will also slow down. Therefore, in daily operation and maintenance, attention should be paid to timely removing the oil on the inner surface of the evaporator heat transfer tube and exhausting the air in the evaporator to improve the heat transfer efficiency of the evaporator.

　　4. The throttle valve is improperly adjusted or blocked, and the refrigerant flow is too large or too small

　　 Improper adjustment or blockage of the throttle valve will directly affect the refrigerant flow into the evaporator. When the throttle valve is opened too large, the refrigerant flow is too large, the evaporating pressure and evaporating temperature will also increase, and the temperature drop rate of the warehouse will slow down; at the same time, when the throttle valve is opened too small or blocked, the refrigerant The flow rate also decreases, the cooling capacity of the system also decreases, and the temperature drop rate of the warehouse will also slow down. Generally, you can determine whether the throttle refrigerant flow rate is appropriate by observing the evaporating pressure, evaporating temperature, and frosting of the suction pipe. Throttle valve blockage is an important factor affecting refrigerant flow. The main cause of throttle valve blockage is ice blockage and dirty blockage. The ice blockage is caused by the poor drying effect of the dryer. The refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0°C. The moisture in the refrigerant freezes and blocks the throttle valve hole; Because a lot of dirt is accumulated on the filter at the inlet of the throttle valve, the refrigerant is not smoothly flowed and clogged.

　　 5. The amount of refrigerant in the system is insufficient, and the cooling capacity is insufficient

　　 There are two main reasons for the lack of refrigerant circulation: one is the insufficient refrigerant charge, and only a sufficient amount of refrigerant is needed. Another reason is that there are many refrigerant leaks in the system. To catch up with this situation, you should first find the leaks, and focus on checking the connections of the pipes and valves. After the leaks are repaired, they can be filled with sufficient refrigerant.

　　6. ​​The compressor efficiency is low, and the cooling capacity cannot meet the load requirements of the warehouse

　　 Because of the long-term operation of the compressor, the parts such as cylinder liner and piston ring are severely worn and the fit clearance increases. The sealing performance will be correspondingly reduced, and the air delivery coefficient of the compressor will also be reduced, and the cooling capacity will be reduced. When the cooling capacity is less than the thermal load of the warehouse, the temperature of the warehouse will decrease slowly. The refrigeration capacity of the compressor can be roughly determined by observing the suction and discharge pressure of the compressor. If the refrigeration capacity of the compressor decreases, the common method is to replace the cylinder liner and piston ring of the compressor. If the replacement still does not work, other factors should be considered, and even the machine should be disassembled for inspection and troubleshooting.