1、 Refluxing

1. For refrigeration systems that use brain expansion valves, liquid return is closely related to the selection and improper use of the follow-up valve. Excessive selection of the brain expansion valve, low setting of superheat, incorrect installation method of the temperature sensor, damaged insulation wrapping, and malfunction of the body valve may all cause liquid return.

2. For small refrigeration systems using capillaries, excessive liquid addition can cause liquid return.

3. When the evaporator frosts severely or the fan malfunctions, the heat transfer deteriorates, and the unexpired liquid can cause liquid return.

4. Frequent fluctuations in cold storage temperature can also cause the expansion valve to malfunction and cause liquid return.

For refrigeration systems where dry return liquid is difficult to avoid, installing a gas-liquid separator and using evacuation shutdown (i.e. letting the compressor dry the liquid refrigerant in the evaporator before the signal) control can effectively prevent or reduce the harm of return liquid

2、 Start with liquid

1. The phenomenon of severe foaming of lubricating oil in the crankcase during start-up of a return air cooled compressor is called liquid start.

2. The bubbling phenomenon during start-up with droplets can be clearly observed on the oil sight error.

3. The fundamental reason for starting with liquid is that a large amount of refrigerant is dissolved in the lubricating oil and settles under the lubricating oil. When the pressure suddenly decreases, it suddenly rises and causes the lubricating oil to bubble. The duration of foaming is related to the content of the agent, usually a few minutes or more. Dali foam floats on the oil surface and even fills the crankcase. When the air cylinder is sucked in through the air inlet one day, the foam will be reduced to liquid (the mixture of bone lubricating oil and refrigerant), which is easy to cause liquid hammer. Obviously, the liquid hammer caused by start-up with liquid only occurs during the start-up process.

4. Unlike liquid return, the refrigerant that causes liquid start enters the crankcase in a "refrigerant migration" manner. Refrigerant migration refers to the process or phenomenon where the refrigerant in the evaporator enters the compressor as a gas through the return pipeline and is absorbed by the lubricating oil when the compressor stops running, or is mixed with the lubricating oil after condensation in the compressor.

5. After the compressor stops, the temperature will decrease and the pressure will increase. Due to the low partial pressure of the refrigerant vapor in the bone lubricating oil, it will absorb the refrigerant vapor on the oil surface, causing the pressure of the crankcase to be lower than that of the evaporator. The lower the oil temperature, the lower the steam pressure, and the greater the absorption of refrigerant vapor.

The temperature of the vegetable gas part in Lingzhuo fruit will shift slightly towards the oil tank. In addition, during cold weather or at night in Anwai, the temperature of the Jiaguo press machine is lower than that of the indoor air conditioner, and the pressure in the oil tank is also lower. After the refrigeration is moved to the pressure phase, it is also easy to be contaminated with oil.

6. Refrigerant may be a very picturesque design. As the check-in time increases, the amount of refrigerant in the oil will increase. I want to cry in English, and this will be carried out by the National Institute of Refrigeration. The electricity generator will sink at the bottom of the crankshaft circuit and prove it to be on top of it after solving the electrical audit of the refrigeration system

The lubricating oil can also absorb more refrigerant.

7. Due to the structure, the crankcase pressure will decrease much more slowly when the air cooling compressor starts, the foaming phenomenon is not very serious, and the foam is difficult to enter the air compressor, so the air cooling compressor does not have the problem of liquid hammer when starting with liquid.

8. In theory, installing a crankcase heater (electric heater) on a compressor can effectively prevent refrigerant sweating. After a short shutdown (such as at night), maintaining the heating of the crankcase can increase the temperature of the lubricating oil and dry other parts of the system, preventing refrigerant displacement. After a long-term shutdown (such as a winter), heating the lubricating oil for a few or more hours before starting can evaporate most of the refrigerant in the lubricating oil, greatly reducing the possibility of liquid shock during start-up with liquid and reducing the harm caused by refrigeration. However, in practical applications, it is difficult to maintain the heater supply after shutdown or to supply power to the heater more than ten hours before startup. Therefore, the actual effect of the crankcase heater will be greatly reduced.

9. For larger systems, allowing the compressor to dry the liquid refrigerant in the base generator before shutdown (referred to as evacuation shutdown) can fundamentally avoid refrigerant migration. Installing a gas-liquid separator on the return pipeline can increase the negative force of refrigerant migration and reduce the migration amount.

Slowly and slowly:

3、 Return oil

1. When the compressor is higher than the evaporator, the oil return bend on the vertical return pipe is indispensable. The oil return bend should be as compact as possible to reduce oil storage. If the spacing between the return bends is appropriate, and there are many return bends, some lubricating oil should be added.

2. The return oil pipeline of the variable load system also needs to be careful. When the load decreases, the return air speed will decrease, and too low a speed is not conducive to dry return oil. In order to ensure oil return under low load, a vertical suction pipe can be used with double risers.

3. Frequent start-up of the compressor is not conducive to dry oil return. Due to the short continuous operation time, the compressor stopped, and there was no time to form a stable high-speed airflow in the return pipe, so the lubricating oil could only remain in the pipeline. If there is less return oil, the compressor will run out of oil. The shorter the operating time, the longer the pipeline, the more complex the system, and the more prominent the problem of oil return.

4. Lack of oil can cause serious lubrication shortage, and the root cause of oil shortage is not the amount and speed of oil flow in the dry compressor, but the poor return oil of the system. Installing an oil separator can quickly return oil and extend the compressor's oil free operation time.

5. The design of the evaporator and return pipeline should consider the return oil. Maintenance measures such as avoiding frequent starts, timed defrosting, timely replenishment of refrigerant, and timely replacement of worn piston components can also help dry and return oil.

4、 Evaporation temperature/return air temperature/return air pressure

1. Every 10 ℃ increase in the temperature of the Yingrong product can be increased by 30% from the machine backup to the electrical point, resulting in a phenomenon of small mouth holding large vehicles. Therefore, the installation time of the work binding machine is extended by using a direct temperature binding and cold removal method, and the pressing time is in the state of super loading, without the use of the machine's products, so that the machine can be enclosed to

It is easy to burn out in sudden situations such as voltage fluctuations and surges.

2. The lower the evaporation temperature, the smaller the refrigerant mass flow rate, and the smaller the actual motor power required. Therefore, when using air conditioning compressors and medium to high temperature refrigeration compressors at dry low temperatures, although the actual power consumption of the motor is much reduced compared to the nominal power, the actual power demand and cooling situation at low temperatures are still too large, and motor cooling is prone to problems.

3. The return air temperature is relative to the dry evaporation temperature. In order to prevent liquid return, a return air superheat of 20 ℃ is generally required in the return air pipeline. If the insulation of the return air pipeline is not good, the superheat will far exceed 20 ℃.

4. The higher the return air temperature, the higher the cylinder suction temperature and exhaust temperature. For every 1 ℃ increase in return air temperature, the exhaust temperature will increase by 1-1.3 ℃.

5. For a return air cooled compressor, the refrigerant vapor is heated by the motor as it flows through the motor cavity, and the suction temperature is once again increased. The heat output of a motor is influenced by power and efficiency, while the power consumption is closely related to displacement, volumetric efficiency, working conditions, friction resistance, etc.

6. Some users have a biased belief that the lower the evaporation temperature, the faster the cooling rate, which actually has many problems. Although reducing the evaporation temperature can increase the freezing temperature difference, the refrigeration capacity of the compressor decreases, so the freezing speed may not be fast. Moreover, the lower the evaporation temperature, the lower the refrigeration coefficient, while the load increases, the running time prolongs, and the power consumption increases.

7. Reducing the resistance of the return air pipeline can also increase the return air pressure. Specific methods include timely replacement of dirty and blocked gas filters, and minimizing the length of the evaporation and return air pipelines as much as possible.

8. In addition, insufficient refrigerant is also a factor in low return pressure.

Slowly and slowly:

9. The main reasons for high suction temperature are:

(1) The refrigerant charge in the system is insufficient, and even if the foot valve is opened to * *, there will be no change in the supply liquid. This causes the refrigerant vapor to overheat in the evaporator and increase the suction temperature. (2) If the opening of chest expansion smoke is too small, the circulation of refrigerant in the system is insufficient, and there is less refrigerant entering the evaporator, resulting in high superheat and high suction temperature.

(3) The filter screen at the foot expansion valve port is blocked, resulting in insufficient supply of liquid in the evaporator, a decrease in refrigerant liquid, and a portion of the evaporator being occupied by excess steam, resulting in an increase in suction temperature.

(4) Other reasons that cause the suction temperature to be too high, such as poor insulation of the return pipeline or excessively long pipeline, can all cause the suction temperature to be too high. Under normal circumstances, the red cover of the compressor should be half cold and half hot. If the suction temperature is too high, all the covers will heat up.

10. The reasons for the low suction temperature are:

(1) There is too much refrigerant filling, which occupies a portion of the volume inside the condenser and increases the condensation pressure, resulting in an increase in the amount of liquid entering the evaporator. The liquid in the evaporator cannot be completely vaporized, causing the gas absorbed by the compressor to contain liquid micro quotient. In this way, the temperature of the return gas pipeline decreases, but the evaporation temperature remains unchanged due to the pressure not decreasing, resulting in a decrease in superheat. Even if the expansion valve is turned off, there is no significant improvement.

(2) The opening of the Shengchang valve is too large. Due to the loose binding of the temperature sensing element, small contact area with the return pipe, or the temperature sensing element not being wrapped with insulation material and its incorrect position, the temperature measured by the temperature sensing element is inaccurate and close to the ambient temperature, which increases the opening degree of the expansion lubrication action and leads to excessive liquid supply.

11. The basic temperature has a significant impact on the refrigeration efficiency. For every 1 degree decrease, the same cooling weight increases by 4%. Therefore, if conditions permit, increasing the evaporation temperature is beneficial for improving the zero cooling efficiency of the air conditioning system. The evaporation temperature of household air conditioners is generally 5-10 degrees lower than the temperature at the air outlet of the air conditioner. During normal operation, the evaporation temperature is 5-12 degrees and the outlet temperature is 10-20 degrees.

5、 Exhaust temperature/exhaust pressure/exhaust pressure

1. The reasons for the high exhaust temperature are as follows: high return gas temperature, large heating capacity of motor, high compression ratio, high condensation pressure, heat capacity ratio of refrigerant, improper selection of refrigerant.

2. For dry R22 compressors, when the evaporation temperature decreases from -5 ° C to -40 ° C, the COP will generally increase by four times, while other parameters have little change. The temperature rise of the gas in the motor control will increase by three or four times. The exhaust temperature can increase by 1-1.3 ℃ for every 1 ℃ increase in dry gas injection temperature. Therefore, if the base temperature decreases from -5 ° C to -40 ° C, the exhaust temperature will increase by about 30-40 ° C. The temperature rise range of the refrigerant in the motor cavity of the return air cooled semi sealed compressor is approximately between 15~45 ℃.

3. In air cooled (air-cooled) compressors, the refrigeration system does not pass through the winding, so there is no problem with motor heating.

4. The exhaust temperature is greatly affected by the compression ratio (cold comfort pressure/English pressure, usually 4). Under normal circumstances, the exhaust pressure of the press machine is very close to the cold comfort pressure. When the cold air pressure increases, the exhaust temperature of the compressor also increases. The higher the compression ratio, the higher the exhaust temperature, and the smaller the static power of the gas transmission system, thereby reducing the refrigeration capacity of the compressor and increasing its power consumption.

5. Low compression ratio can significantly reduce exhaust temperature, including increasing milk gas pressure and reducing exhaust pressure. The suction pressure is determined by the evaporation pressure and the resistance of the repair pipeline. Increasing the base temperature can enhance the gas pressure, reduce the compression ratio, and thus lower the exhaust temperature.

6. Real ball control, by increasing the suction pressure to enhance the quality of breath, is simpler and more effective than other methods.

7. The main reason for the high exhaust pressure is that the cooling pressure is too high (there is air in the system; refrigerant (there is too much injection in the vehicle, which occupies the effective cooling area; the cooling area of the cooler is insufficient, scale is accumulated, the cooling air volume or water volume is insufficient, and the temperature of the cooling water or air is too high). It is very important to choose a suitable condensation area and maintain sufficient cooling medium flow.

8. The exhaust pressure is too low, although the phenomenon is manifested in the high-pressure end, the reason is often caused by the low-pressure end. The reason for this is (1) foot swelling, water blockage or dirt blockage, as well as filter blockage, which inevitably leads to a decrease in suction and exhaust pressure; (2) Insufficient refrigerant charge;

(3) During the successful expansion of the Min hole blockage race, the liquid supply volume was reduced until it stopped, and at this time, the extreme and exhaust pressures both increased and decreased.

9. The insufficient exhaust capacity is mainly due to the fact that compared to the designed air capacity of the compressor, the compressor's milk duct is too long and the pipe diameter is too small, which increases the negative force of good air and easily leads to a decrease in exhaust capacity due to the whitening of the intake volume cluster.

Slowly and slowly:

6、 Liquid hammer

1. In order to ensure the reliable operation of the compressor and prevent liquid hammer phenomenon, it is required that the suction temperature be slightly higher than the evaporation temperature, which should have a certain degree of superheat. The magnitude of superheat can be achieved by adjusting the opening degree of the expansion valve.

2. Avoid high or low suction temperature. If the suction temperature is too high, that is, if the pressure is too high, it will lead to an increase in the discharge temperature of the compressor. If the suction temperature is too low, it indicates that the refrigerant does not evaporate completely in the evaporator, which not only reduces the efficiency of evaporator transfer, but also causes the suction of wet steam to form compressor liquid hammer. Under normal circumstances, the suction temperature should be 5-10 ℃ higher than the evaporation temperature.

7、 Superheat degree

1. For the commonly used R22 refrigerant, the cooling capacity of the compression mechanism decreases with the increase of effective superheat. When the superheat is 10 ℃, the cooling capacity is 99.5% of the cooling capacity under saturated evaporation. When the superheat is 20 ℃, the cooling capacity is 99.3% of the cooling capacity under saturated evaporation. It can be seen that the cooling capacity decreases very little with the increase of superheat.

2. For R502 refrigerant, the cooling capacity of the compression mechanism increases with the increase of effective superheat.

3. Maintaining a certain degree of superheat in the refrigerant can further prevent liquid hammer phenomenon in the cylinder, and for low-temperature refrigeration systems, appropriately increasing the effective superheat can ensure that the lubricating oil returns to the compressor smoothly. But as the suction superheat of the compressor increases, its exhaust temperature also increases. Excessive exhaust temperature can cause the viscosity of the lubricating oil to become thinner or even carbonized, affecting the normal operation of the compressor. Therefore, the suction superheat should be controlled within a certain range.

8、 Fluorination

1. When the fluorine content is low or the regulating pressure is low (or partially blocked), the valve cover (corrugated pipe) of the expansion valve and even the inlet will frost; When there is too little or almost no fluoride, the surface of the expansion valve has no reaction, and only a slight sound of airflow can be heard.

2. Which end does icing start from? Is it from the separation head or from the compressor return pipe? If there is a lack of fluorine from the liquid separation head, then there is an excess of fluorine from the press.