Why can't the cold storage temperature drop The evaporator is very important!

Why can't the cold storage temperature drop The evaporator is very important!

There are many reasons why the temperature of the cold storage cannot drop. The editor of okmarts.com lists the following six common phenomena for your reference:

　　 1. The evaporator surface has too thick frost or too much dust, and the heat transfer effect is reduced

　　 When the frost layer on the surface of the evaporator is too thick or the dust accumulates, it will inevitably cause the heat transfer effect of the evaporator to decrease. Since 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 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 surface of the evaporator from being too thick, it needs to be defrosted regularly.

　　 Two simpler defrost methods are introduced below:

　　 1. Shut down and defrost. That is, stop the compressor, open the warehouse door, let the warehouse temperature rise, and restart the compressor after the frost layer automatically melts.

　　 2. Flushing. After removing the goods in the warehouse, directly rinse the surface of the evaporator pipe with hot tap water to dissolve or fall off the frost layer.

　　3. In addition to excessively thick frosting will lead to poor heat transfer effects of the evaporator, the evaporator surface will not be cleaned for a long time and the dust will be too thick, and its heat transfer efficiency will also be significantly reduced.

　　2. The cold storage has a large loss of cooling due to poor heat insulation or sealing performance

　　 Poor thermal insulation performance is due to insufficient insulation thickness of pipes, warehouse insulation walls, etc., and poor thermal insulation and insulation effects. It is mainly caused by improper selection of insulation layer thickness during design or poor quality of insulation materials during construction. In addition, during the construction and use process, the thermal insulation and moisture-proof performance of the thermal insulation material may be destroyed, causing the insulation layer to be damp, deformed, or even eroded, and its thermal insulation capacity will decrease, and the loss of cold storage capacity will increase, and the temperature drop will be significantly slowed . Another important reason for the large cold loss is the poor sealing performance of the warehouse, and more hot air invades the warehouse from the leak. Generally, if condensation occurs at 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 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 generally takes a long time to cool down to the specified temperature.

　　 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, its heat transfer coefficient will decrease. Similarly, if there is more air in the heat transfer tube, the heat transfer area of ​​the evaporator will decrease, and its heat transfer Efficiency will also drop significantly, and the rate of temperature drop in the warehouse will slow down accordingly. 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, and 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 judge whether the throttle valve refrigerant flow 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 due to the poor drying effect of the dryer. The refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0℃. The moisture in the refrigerant freezes and blocks the throttle valve hole; Due to the accumulation of more dirt on the inlet filter of the throttle valve, the flow of refrigerant is not smooth, causing blockage.

　　5. The compressor has low efficiency and the cooling capacity cannot meet the load requirements of the warehouse

　　Due to the long-term operation of the compressor, the cylinder liner, piston ring and other parts will be severely worn and the fitting clearance will increase. The sealing performance will be correspondingly reduced. The compressor's air delivery coefficient 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 judged by observing the suction and discharge pressure of the compressor. If the refrigeration capacity of the compressor drops, 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 maintenance and troubleshooting.

　　 6. The refrigerant in the system is insufficient, and the refrigeration capacity is insufficient

　　 There are two main reasons for the insufficient refrigerant circulation. One is the insufficient refrigerant charge. At this time, only a sufficient amount of refrigerant needs to be added. Another reason is that there are many refrigerant leaks in the system. In this case, 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.