1. For the refrigeration system using expansion valve, the return fluid is closely related to the selection and improper use of expansion valve.Too large selection of expansion valve, too small overheat setting, improper installation method of temperature sensing package or damage of adiabatic packing, failure of expansion valve may lead to liquid return.
For small refrigeration systems using capillaries, excessive amount of
adding liquid will cause liquid return.When the evaporator frosts badly
or the fan fails, the heat transfer becomes worse.Frequent temperature
fluctuations can also cause the expansion valve reaction failure and
cause the fluid return.
The machine starts with liquid
The phenomenon of severe blistering of lubricating oil in a compressor is called starting with liquid.The bubbling phenomenon during the start-up of the liquid can be clearly observed in the oil scope.The fundamental reason is that a large amount of refrigerant is dissolved in the lubricating oil and is immersed in the lubricating oil. When the pressure drops suddenly, it suddenly boils.
1. When the position of the compressor is higher than that of the evaporator, the vertical oil return bend on the return pipe is necessary.Return oil bend as tight as possible to reduce oil storage.The distance between the oil return bend should be appropriate, the amount of oil return bend is large, some lubricating oil should be added.
2. Frequent starting of compressor is not conducive to oil return.Because the compressor stopped running for a very short period of time, there was no time to form a stable high speed air flow in the return pipe, so the lubricating oil could only be left in the pipeline.The compressor will run out of oil if the return oil is less than the running oil.The shorter the operation time, the longer the pipeline, the more complex the system, the more serious the problem of oil return.
3. Lack of oil will cause serious lubrication deficiency. The fundamental reason for lack of oil is not the amount and speed of the compressor, but the bad oil return of the system.Installation of oil separator can quickly return oil, to extend the compressor running time without oil return.
Evaporation temperature has a great influence on refrigeration efficiency. Every time it decreases by 1 degree, the same amount of cooling needs to increase power by 4%.Therefore, it is beneficial to increase the cooling efficiency of air conditioner by increasing the evaporation temperature appropriately under the condition of permitting.
Blindly lowering the evaporation temperature can cool the temperature difference, but the amount of compressor cooling is reduced, so the refrigeration speed is not necessarily fast.In addition, the lower the evaporation temperature, the lower the cooling coefficient, but the load has increased, the longer the running time, the higher the electricity consumption.
Excessive exhaust temperature
The reasons for the high exhaust temperature are as follows: high return temperature, high heat added by motor, high compression ratio, high condensing pressure, heat adiabatic index of refrigerant, improper choice of refrigerant.
1. In order to ensure the safe operation of the compressor and prevent the occurrence of liquid percussion, the suction temperature is required to be a little higher than the evaporation temperature, that is, a certain degree of superheat is required.
2. The inhalation temperature should be too high or too low.Too high suction temperature, that is, too much overheating, will lead to higher compressor exhaust temperature.If the inhalation temperature is too low, it indicates that the refrigerant does not evaporate completely in the evaporator, which not only reduces the heat exchange efficiency of the evaporator, but also forms the liquid shock of the compressor.Suction temperature under normal circumstances should be 5 ~ 10 ℃ higher than the evaporation temperature.
When there is little fluoride or its regulating pressure is low (or partially blocked), the valve cover of the expansion valve (bellows) or even the inlet of the valve will frosting.When the amount of fluorine is too small or basically free of fluorine, the appearance of the expansion valve does not respond, only a little air flow can be heard.
See which end of the ice start from, from the nozzle or from the compressor back to the trachea, if from the nozzle is a lack of fluorine, from the compressor is a lot of fluorine.
Low suction temperature
1. The refrigerant filling amount is too much, occupying part of the condenser volume and increasing the condensing pressure, and the liquid entering the evaporator will increase accordingly.The liquid in the evaporator can not be completely vaporized, so that the compressor sucks the gas with the liquid droplet.Thus, the temperature of the return gas pipeline decreases, but the evaporation temperature remains unchanged because the pressure does not decrease, and the superheat decreases.Even close the small expansion valve did not improve significantly.
2. The expansion valve is opened too large.Due to loose binding of temperature sensing elements, small contact area with the return air pipe, or improper packing position of temperature sensing elements without adiabatic materials, the temperature measured by temperature sensing elements is not accurate and close to the ambient temperature, which increases the opening degree of expansion valve movement and leads to excessive liquid supply.
High suction temperature
1. In the system, the refrigerant filling amount is insufficient, or the expansion valve is opened too small, resulting in the insufficient circulation amount of the refrigerant of the system, and the refrigerant dosage of the evaporator is low and the superheat is high, so the suction temperature is high.
2. The filter screen at the expansion valve port is blocked, the amount of liquid supplied in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and part of the evaporator is occupied by the superheated steam, so the suction temperature is increased.
3. For other reasons, the inhalation temperature is too high, such as bad heat insulation of the return air pipeline or too long pipe, which may cause the inhalation temperature to be too high.Under normal circumstances, the compressor cylinder cover should be half cool, half hot.
Low Exhaust temperature
The exhaust pressure is too low, although its phenomenon is manifested in the high pressure end, but the reason is most often in the low pressure end.The reasons are:
1. Ice block or dirty block of expansion valve, filter block, etc., will inevitably reduce the suction and exhaust pressure;Insufficient charge of refrigerant;
2. The expansion valve hole is blocked, and the supply of liquid is reduced or even stopped. At this time, the suction and exhaust pressure are reduced.
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