1. The frost on the surface of the refrigeration evaporator is too thick or there is too much dust, and the heat transfer effect is reduced
Another important reason for the slow drop of the storage temperature is the low heat transfer efficiency of the evaporator, which is mainly caused by the thick frost layer or excessive dust accumulation on the surface of the evaporator. Since the surface temperature of the evaporator in the refrigeration cold storage is mostly lower than 0 ℃, and the humidity in the warehouse is relatively high, the moisture in the air is easily frosted or even frozen on the surface of the evaporator, which affects the heat transfer effect of the evaporator. In order to prevent the surface frost layer of the evaporator from being too thick, it needs to be defrosted regularly. Two relatively simple defrosting methods are introduced below: ① Stop defrosting. That is, stop the operation of the compressor, open the door of the warehouse, let the temperature of the warehouse rise, and restart the compressor after the frost layer automatically melts. ② Rinse cream. After moving the goods out of the warehouse, directly rinse the surface of the evaporator pipe with tap water with a higher temperature to dissolve or fall off the frost layer. In addition to the poor heat transfer effect of the evaporator due to the thick frost, the heat transfer efficiency of the evaporator will also be significantly reduced due to the excessive dust accumulation on the surface of the evaporator because it has not been cleaned for a long time.
2. Due to poor thermal insulation or sealing performance, the refrigeration cold storage has a large loss of cooling capacity
The poor thermal insulation performance is due to the insufficient thickness of the thermal insulation layer of pipes and warehouse thermal insulation walls, and the poor thermal insulation and thermal insulation effect. It is mainly caused by the improper selection of the thickness of the thermal insulation layer during design or the poor quality of thermal insulation materials during construction. In addition, in the process of construction and use, the thermal insulation and moisture-proof performance of the thermal insulation material may be damaged, resulting in the thermal insulation layer being damp, deformed, or even eroded. slow down. Another important reason for the large cooling loss is the poor sealing performance of the warehouse, and more hot air intrudes into the warehouse from the leak. Generally, if there is condensation on the sealing strip of the warehouse door or the sealing of the cold storage insulation wall, it means that the sealing is not tight. In addition, frequent opening and closing of the warehouse door or more people entering the warehouse together will also increase the loss of cooling capacity in the warehouse. Avoid opening the warehouse door as much as possible to prevent a large amount of hot air from entering the warehouse. Of course, when the warehouse is frequently stocked or the stock is too large, the heat load increases sharply, and it generally takes a long time to cool down to the specified temperature.
3. 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 rate 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 is also reduced, the cooling capacity of the system is also reduced, and the temperature drop rate of the warehouse will also slow down. Generally, it can be judged whether the refrigerant flow rate of the throttle valve is appropriate by observing the evaporating pressure, evaporating temperature and the frosting condition of the suction pipe. The blockage of the throttle valve is an important factor affecting the flow of refrigerant. The main reasons for the blockage of the throttle valve are ice blockage and dirty blockage. Ice blockage is due to the poor drying effect of the dryer, and the refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0 °C, and the moisture in the refrigerant freezes into ice and blocks the throttle valve hole; dirty blockage is Due to the accumulation of more dirt on the filter screen at the inlet of the throttle valve, the flow of refrigerant is not smooth, resulting in blockage.
4. The efficiency of the refrigeration compressor is low, and the cooling capacity cannot meet the load requirements of the warehouse
Due to the long-term operation of the refrigeration compressor, the cylinder liner and the piston ring and other components are seriously worn, and the matching clearance increases, the sealing performance will decrease accordingly, the gas transmission coefficient of the refrigeration compressor will also decrease, and the cooling capacity will decrease. When the cooling capacity is less than the heat load of the warehouse, the temperature of the warehouse will drop slowly. The refrigeration capacity of the compressor can be roughly judged by observing the suction and discharge pressures of the compressor. If the refrigeration capacity of the compressor decreases, the commonly used 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, or even dismantling and overhauling, and troubleshooting.
5. There is more air or refrigeration oil in the evaporator, and the heat transfer effect is reduced
Once more refrigeration 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 be reduced, and its heat transfer will be reduced. Efficiency will also drop significantly, and the rate of drop in warehouse temperature will slow down. Therefore, in daily operation and maintenance, attention should be paid to timely removal of oil stains on the inner surface of the evaporator heat transfer tube and discharge of the air in the evaporator to improve the heat transfer efficiency of the evaporator.
6. The amount of refrigerant in the system is insufficient, and the cooling capacity is insufficient
There are two main reasons for insufficient refrigerant circulation. First, the refrigerant charge is insufficient. 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 leak point, focus on checking the connections of each pipeline and valve, and then fill in a sufficient amount of refrigerant after repairing the leaked parts.
Post time: Jan-14-2022