First, the precautions when the refrigeration system is running:
Expansion valve is one of the four major components of the refrigeration system. It is an important device for regulating and controlling the flow and pressure of the refrigerant into the evaporator.Its adjustment is not only related to the normal operation of the entire refrigeration system, but also an important indicator of the operator's skill level.The adjustment of the expansion valve must be performed carefully and patiently. The adjustment of the pressure must take place through the evaporator and the temperature of the warehouse to produce boiling (evaporation), and then enter the compressor suction chamber through the pipeline to reflect on the pressure gauge, which requires a time process.Each time the expansion valve is adjusted, it usually takes 15-30 minutes to stabilize the adjustment pressure of the expansion valve on the suction pressure gauge.
The suction pressure of the compressor is an important reference parameter for the adjustment pressure of the expansion valve.The expansion of the expansion valve is small, and the flow rate of the refrigerant is small, and the pressure is low;The larger the opening degree of the expansion valve, the larger the flow rate of the refrigerant and the high pressure.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 expansion valve outlet pressure is too low, the corresponding evaporation pressure and temperature are too low.However, due to the decrease in the flow into the evaporator and the decrease in pressure, the evaporation rate slows down, the cooling capacity per unit volume (time) decreases, and the cooling efficiency decreases.Conversely, if the expansion valve outlet pressure is too high, the corresponding evaporation pressure and temperature are too high.The flow and pressure into the evaporator are increased. Due to the excess evaporation of liquid, excessive moisture (or even liquid) is sucked into the compressor, which causes the wet stroke (liquid strike) of the compressor, causing the compressor to fail to work properly, causing a series of problems The condition is bad and even damages the compressor.
From this perspective, correct adjustment of the expansion valve is particularly important for the operation of the system.In order to reduce the pressure and temperature loss of the expansion valve after adjustment, the expansion valve should be installed on the horizontal pipe from the entrance of the cold storage as much as possible.During normal operation of the expansion valve, the frost on the valve body is inclined, and the frost on the inlet side should not be frosted, otherwise it should be considered that there is ice blocking or dirty blocking in the inlet filter.Under normal circumstances, the expansion valve is very quiet when working. If a more pronounced \"\" Sisi \"\" sound, it means that the refrigerant in the system is insufficient.The expansion valve should be replaced when there is a problem with the air leakage of the temperature sensing system or malfunction of the adjustment.
Second, the exhaust temperature of the compressor is too high:1. The suction pressure is too low, the compression ratio of the cylinder is large, the opening degree of the expansion valve is small, and the adjustment pressure is low;2. The suction temperature is too high, that is, the suction is too hot, the suction pipe is too long or the insulation effect is poor;3. The amount of cooling water is insufficient or the water temperature is too high;4. Too much non-condensable gas (air) in the system;5.The condensation pressure is too high, and the corresponding condensation temperature is also high, which causes the exhaust temperature to rise;6. The compressor cylinder or valve group is faulty.
Third, the exhaust pressure of the compressor is too high:1. Too much non-condensable gas (air) in the system;2. The amount of cooling water is insufficient or the water temperature is too high;3. The condenser is too dirty with excessive scaling;4. Too much refrigerant in the system.
Fourth, the oil temperature of the compressor is too high:1. The suction and exhaust temperature of the compressor is too high;2. The lubricant is too dirty or the oil quality is too poor;3. The compressor parts are severely worn.
V. Evaporation temperature and pressure:Adjusting the evaporation temperature is actually adjusting the temperature difference between the evaporation temperature and the temperature of the cooled medium.From the perspective of heat transfer, the temperature difference is large, and the heat transfer effect is good and the temperature is reduced quickly.However, increasing the heat transfer temperature difference will reduce the evaporation temperature.For the refrigeration capacity of the compressor, when the condensing temperature is constant, the lower the evaporation temperature, the smaller the refrigeration capacity.Due to insufficient cooling capacity, the temperature of the medium to be cooled cannot be lowered.The smaller the temperature difference, the worse the heat transfer effect. Although the refrigeration capacity of the compressor increases, the heat exchange of the evaporator is insufficient.Therefore, according to the different refrigeration equipment, the temperature difference is reasonably selected.
Adjusting the difference between the evaporation temperature and the temperature of the cooled medium is actually adjusting the opening of the orifice of the throttle valve.During the commissioning operation, it is mainly determined by observing the change of evaporation pressure to determine whether the opening degree of the expansion valve is appropriate.If the valve opening is too small and the liquid supply is insufficient, the evaporation pressure and evaporation temperature will decrease, the compressor suction will overheat, and the exhaust temperature will also increase;When the liquid supply is too much, the evaporation pressure and evaporation temperature will increase, and the excess liquid will also cause the compressor to produce liquid hammer.So correctly controlling the opening degree of the throttle valve is one of the main methods to adjust the evaporation temperature and evaporation pressure during operation.In addition, when the cooling equipment load and the capacity of the compressor are unchanged, if the heat exchange area of the evaporator is too small or the internal and external surfaces are dirty, the evaporation temperature will be reduced;If the heat exchange surface is too large, the evaporation temperature will increase;If the cooling equipment load and evaporator heat exchange area are unchanged, the compressor capacity increases, the evaporation pressure and temperature decrease, and when the capacity decreases, the evaporation temperature and pressure increase.
6. Condensing temperature and pressure:The condensing pressure of the refrigeration system is the pressure indicated by the high pressure gauge, expressed in absolute pressure.In general, the condensing temperature is 5-7 ° C higher than the cooling water inlet temperature and 10-15 ° C higher than the cooling air inlet temperature for forced ventilation.When the evaporation temperature does not change, the condensing temperature increases, the condensing pressure also increases, the compression ratio of the compressor increases, the gas transmission coefficient decreases, the refrigeration capacity of the compressor decreases, and the power consumption increases.In addition, the condensing pressure increases, and the temperature of the compressed exhaust gas increases.If the exhaust temperature is too high, the compressor lubricant will be diluted and affect the lubrication. When the exhaust temperature is close to the lubricant door point, some of the lubricant will be carbonized and accumulated in the exhaust valve, which will affect the sealing performance of the valve. .
The condensation temperature is too high. From the design perspective, it is because the condensation area is too small.At this time, the superheated gas entering the condenser from the compressor cannot be condensed into a liquid at a specified pressure, but only at a higher pressure and temperature.In this case, only increase the condenser area or reduce the number of compressors running in the parallel system.
During operation, if there is dirt on the inner surface of the condenser or a small amount of non-condensable gas such as air in the system, both can increase the heat transfer heat resistance and prevent the refrigerant vapor from condensing in time.The usual treatment method is to regularly drain oil, air, and remove scale according to the water quality.
Seven, the suction temperature of the compressor:
The suction temperature of a compressor refers to the temperature of the refrigerant gas in the suction chamber of the compressor for a displacement compressor.The suction temperature is high and the exhaust temperature is also high. The specific volume of the refrigerant when it is sucked is large. At this time, the refrigeration capacity per unit volume of the compressor becomes smaller;Conversely, when the compressor suction temperature is low, the refrigeration capacity per unit volume is large.However, the suction temperature of the compressor is too low, which may cause the refrigerant liquid to be sucked into the compressor and cause a liquid hammer phenomenon in the reciprocating compressor.
In addition, the length of the compressor suction pipe and the performance of the wrapped insulation material also have a certain effect on the degree of superheat.The intake temperature is generally controlled at the intake superheat degree of the refrigerating device of 5 to 10 ° C, and the intake superheat degree of a Freon system with a regenerative heat exchanger is more suitable at 15 ° C.Therefore, in the operation of the machine, we must pay attention to the control of the compressor suction temperature. Usually, the adjustment screw of the thermal expansion valve is used to adjust the superheat degree.
Eighth, the exhaust temperature of the compressor:The discharge temperature of the compressor is the high-pressure superheated steam after the refrigerant is compressed.Since the refrigerant discharged by the compressor is superheated steam, there is no corresponding relationship between its pressure and temperature.The discharge temperature of the compressor can be read from a thermometer on the discharge line.
The exhaust pressure is generally slightly higher than the condensation pressure, and the exhaust temperature is much higher than the condensation temperature.Except for the type of refrigerant, the exhaust temperature is mainly related to the intake temperature, pressure, and pressure ratio, and it increases with their increase.Excessive condensing and exhaust temperatures are detrimental to the operation of the compressor.
Nine, other matters needing attention:1. The suction temperature of the compressor should be 5-15 ° C higher than the evaporation temperature;2. The exhaust temperature R22 system of the compressor must not exceed 150 ℃;3. The maximum oil temperature of the compressor crankcase must not exceed 70 ° C; 4. The suction pressure of the compressor should correspond to the evaporation pressure;5. The compressor's exhaust pressure R22 system must not exceed 1.8MPa;6. The oil pressure of the compressor is 0.15-0.3MPa higher than the suction pressure;7. Pay attention to the amount of cooling water and the temperature of the water. The outlet temperature of the condenser should be 2-5 ℃ higher than the temperature of the inlet water.8. Pay attention to the oil level of the compressor crankcase and the oil return of the oil separator;9, the compressor should not have any knocking sound, the body should be normal fever;10. Condensing pressure must not exceed the discharge pressure range of the compressor.