1. For refrigeration systems using expansion valves, liquid return is closely related to the selection and use of expansion valves. If the expansion valve is too large, the superheat setting is too small, the installation method of the temperature sensor package is incorrect, or the insulation package is damaged, and the expansion valve fails, the liquid may be returned.
2. For a small refrigeration system using a capillary tube, the amount of liquid added is too large to cause liquid return.
3. If the evaporator is severely frosted or the fan fails, the heat transfer will be poor, and the liquid that has not evaporated will cause liquid return.
4, frequent fluctuations in the cold storage temperature will also cause the expansion valve reaction failure and cause liquid return.
For refrigeration systems that are difficult to avoid with liquid return, the installation of a gas-liquid separator and the use of an evacuation shutdown (ie, allowing the compressor to drain the liquid refrigerant in the evaporator before shutdown) can effectively prevent or reduce the hazard of liquid return.
Start with liquid
1. When the return air-cooled compressor is started, the phenomenon that the lubricating oil in the crankcase is violently foamed is called starting with liquid.
2. The blistering phenomenon with liquid start can be clearly observed on the oil sight glass.
3. The root cause of liquid start-up is that a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil suddenly boils when the pressure suddenly drops, and causes foaming of the lubricating oil. The duration of foaming is related to the amount of refrigerant, usually a few minutes or ten minutes. A large amount of foam floats on the oil surface and even fills the crankcase. Once the cylinder is drawn through the intake port, the foam is reduced to a liquid (a mixture of lubricating oil and refrigerant) that can easily cause a liquid impact. Obviously, the liquid blow caused by the start of the liquid only occurs during the start-up process.
4. Unlike the liquid return, the refrigerant that causes the liquid to start is entered into the crankcase by means of "refrigerant migration". Refrigerant migration refers to the process or phenomenon in which the refrigerant in the evaporator is in the form of a gas, enters the compressor through the return line and is absorbed by the lubricating oil, or is mixed with the lubricating oil after condensation in the compressor.
5. After the compressor is stopped, the temperature will decrease and the pressure will increase. Since the partial pressure of the refrigerant vapor in the lubricating oil is low, the refrigerant vapor on the oil surface is absorbed, causing the crankcase air pressure to be lower than the evaporator air pressure. The lower the oil temperature, the lower the vapor pressure and the greater the absorption of refrigerant vapor. The vapor in the evaporator slowly "migrates" into the crankcase. In addition, if the compressor is outdoors, the weather is cold or at night, the temperature is often lower than the evaporator in the room, and the pressure in the crankcase is low. After the refrigerant migrates to the compressor, it is easily condensed into the lubricating oil.
6. Refrigerant migration is a very slow process. The longer the compressor downtime, the more refrigerant will migrate into the lubricant. This process proceeds as long as liquid refrigerant is present in the evaporator. Since the lubricating oil that dissolves the refrigerant is heavy, it sinks to the bottom of the crankcase, and the lubricating oil that floats on it can absorb more refrigerant.
7. Due to structural reasons, the crankcase pressure is much slower when the compressor starts, the foaming phenomenon is not very severe, and the foam is difficult to enter the cylinder. Therefore, the air-cooled compressor does not have the problem of liquid-starting liquid hammer.
8. In theory, the compressor is equipped with a crankcase heater (electric heater) to effectively prevent refrigerant migration. After a short downtime (such as at night), maintaining the crankcase heater energized can cause the lubricant temperature to be slightly above the rest of the system and refrigerant migration will not occur. After long-term shutdown (such as a winter), heating the lubricant for several or ten hours before starting the machine can evaporate most of the refrigerant in the lubricating oil, which can greatly reduce the possibility of liquid attack when starting with liquid. Sex can also reduce the damage caused by refrigerant flushing. However, in practical applications, it is difficult to maintain the heater power supply after the shutdown or power the heater for more than ten hours before starting the power. Therefore, the actual effect of the crankcase heater will be greatly reduced.
9. For larger systems, let the compressor drain the liquid refrigerant in the evaporator before stopping (called evacuation shutdown), which can fundamentally avoid refrigerant migration. The installation of a gas-liquid separator on the return line can increase the resistance of refrigerant migration and reduce the amount of migration.
Return oil
1. When the compressor is at a higher position than the evaporator, the oil return bend on the vertical return pipe is necessary. The oil return bend should be as compact as possible to reduce oil deposits. The spacing between the oil return bends should be appropriate. When the number of oil return bends is relatively large, some lubricants should be added.
2. The return line of the variable load system must also be careful. When the load is reduced, the return air speed will decrease, and the speed is too low to be good for oil return. In order to ensure oil return under low load, the vertical suction pipe can adopt double riser.
3, the frequent start of the compressor is not conducive to oil return. Since the compressor is stopped for a short running time, and the return air pipe does not have a stable high-speed airflow, the lubricating oil can only remain in the pipeline. If the oil is less than the oil, the compressor will be short of oil. The shorter the running time, the longer the pipeline, the more complicated the system, and the more serious the oil return problem.
4, lack of oil will cause serious lubrication shortage, the root cause of lack of oil is not how much and how fast the compressor is running, but the system is not good. The oil separator can be installed to quickly return oil and extend the compressor's return-free operation time.
5. The design of the evaporator and return line must take into account the return oil. Maintenance measures such as avoiding frequent starts, timing defrosting, replenishing refrigerant in a timely manner, and replacing worn piston components in a timely manner also contribute to oil return.
Evaporation temperature / return air temperature / return air pressure
1. For every 10°C increase in evaporation temperature, the motor load can be increased by 30% or even higher, causing the phenomenon of small horse-drawn carts. Therefore, the low temperature compressor is used in the medium and high temperature system, and the cooling process of the cold storage is too long. The compressor is in an overload state for a long time, which is very harmful to the motor, so that the motor will encounter voltage fluctuations, surges, etc. in the future. Easy to burn.
2. The lower the evaporation temperature, the smaller the mass flow rate of the refrigerant, and the smaller the actual motor power required. Therefore, when the air conditioner compressor and the medium and high temperature refrigerating compressor are used for low temperature, although the actual power consumption of the motor is much lower than the nominal power, the actual power demand and cooling condition at the low temperature are still too large, and the motor cooling is easy. problem appear.
3. The return air temperature is relative to the evaporation temperature. In order to prevent backflow, the return air line generally requires a return air superheat of 20 °C. If the return line is not well insulated, the degree of superheat will far exceed 20 °C.
4. The higher the return air temperature, the higher the cylinder suction temperature and exhaust temperature. For every 1 °C increase in the return air temperature, the exhaust gas temperature will increase by 1 to 1.3 °C.
5. For a return air-cooled compressor, the refrigerant vapor is heated by the motor as it flows through the motor cavity, and the cylinder suction temperature is once again increased. The heat generated by the motor is affected by power and efficiency, and the power consumption is closely related to displacement, volumetric efficiency, working conditions, and frictional resistance.
6. Some users believe that the lower the evaporation temperature, the faster the cooling rate. This idea has many problems. Although lowering the evaporation temperature can increase the freezing temperature difference, the refrigeration capacity of the compressor is reduced, so the freezing speed is not necessarily fast. Moreover, the lower the evaporation temperature, the lower the refrigeration coefficient, the higher the load, the longer the operation time, and the higher the power consumption.
7. Reducing the resistance of the return air line can also increase the return air pressure. The specific methods include timely replacement of the dirty return air filter and minimizing the length of the evaporation tube and the return air line.
8. In addition, insufficient refrigerant is also a factor in low return air pressure.
Inspiratory temperature is too high
(1) The refrigerant charge in the system is insufficient. Even if the expansion valve is opened to a large size, the liquid supply amount will not change, so that the refrigerant vapor is superheated in the evaporator to raise the suction temperature.
(2) The opening degree of the expansion valve is too small, resulting in insufficient circulation of the refrigerant of the system, the refrigerant amount of the evaporator is small, the degree of superheat is large, and the intake temperature is high.
(3) The expansion valve port is clogged, the amount of liquid supply in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the intake temperature is increased.
(4) Other reasons cause the inspiratory temperature to be too high. If the air return duct is not well insulated or the pipeline is too long, the inhalation temperature may be too high. Under normal circumstances, the cylinder head of the compressor should be half cold and half hot.
If the intake temperature is too high, the cylinder head will heat up.
Inspiratory temperature is too low
(1) The refrigerant charge is too much, occupying a part of the volume inside the condenser, so that the condensing pressure is increased, and the liquid entering the evaporator is increased. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. Thus, the temperature of the return air duct drops, but the evaporating temperature does not change because the pressure does not fall, and the degree of superheat decreases. Even if the small expansion valve is closed, there is no significant improvement.
(2) The expansion valve opening degree is too large. Because the temperature sensing element is loosely tied, the contact area with the return air pipe is small, or the temperature sensing element is not wrapped with the heat insulating material and the wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate, close to the ambient temperature, and the expansion valve is operated. The degree of opening increases, resulting in too much liquid supply.
Effect of evaporation temperature on refrigeration efficiency
1. The evaporation temperature has a great influence on the cooling efficiency. For every 1 degree reduction, the same cooling capacity is required to increase the power by 4%. Therefore, if the conditions permit, it is beneficial to improve the cooling efficiency of the air conditioner. of. The evaporating temperature of the household air conditioner is generally 5 to 10 degrees lower than the temperature of the air outlet, and during normal operation, the evaporating temperature is 5 to 12 degrees, and the outlet temperature is 10 to 20 degrees.
Exhaust temperature / exhaust pressure / displacement
1. The reasons for excessive exhaust gas temperature are as follows: high return air temperature, large motor heating, high compression ratio, high condensing pressure, adiabatic index of refrigerant, and improper refrigerant selection.
2. For the R22 compressor, when the evaporation temperature is lowered from -5 °C to -40 °C, the general COP will be reduced by 4 times, while other parameters will not change much, and the temperature rise of the gas in the motor cavity will increase by three or four times. The exhaust gas temperature can be increased by 1 to 1.3 ° C for every 1 ° C increase in the cylinder suction temperature. Therefore, the evaporation temperature is lowered from -5 ° C to -40 ° C, and the exhaust gas temperature rises by about 30 to 40 ° C. In the return air-cooled half-sealed compressor, the temperature rise of the refrigerant in the motor cavity is approximately between 15 and 45 °C.
3. In the air-cooled (air-cooled) type compressor, the refrigeration system does not pass through the winding, so there is no motor heating problem.
4. The exhaust gas temperature is greatly affected by the compression ratio (condensation pressure/evaporation pressure, generally 4). Under normal conditions, the compressor discharge pressure is very close to the condensing pressure. As the condensing pressure increases, the compressor discharge temperature also rises. The larger the compression ratio, the higher the exhaust gas temperature and the smaller the gas transmission coefficient, so that the refrigeration capacity of the compressor is reduced and the power consumption is increased.
5, reduce the compression ratio can significantly reduce the exhaust temperature, specific methods include increasing the suction pressure and reducing the exhaust pressure. The suction pressure is determined by the evaporation pressure and the suction line resistance. Increasing the evaporation temperature can effectively increase the suction pressure and rapidly reduce the compression ratio, thereby reducing the exhaust gas temperature.
6. Practice has shown that reducing the exhaust gas temperature by increasing the suction pressure is simpler and more effective than other methods.
7. The main reason for the excessive exhaust pressure is that the condensing pressure is too high (there is air in the system; the refrigerant charge is too much, the liquid occupies the effective condensation area; the condenser heat dissipation area is insufficient, the scale, the cooling air volume or the water volume is insufficient , cooling water or air temperature is too high, etc.). It is important to choose the right condensing area and maintain a sufficient flow of cooling medium.
8. The exhaust pressure is too low, although the phenomenon is manifested at the high pressure end, but the cause is mostly caused by the low pressure end. The reason:
(1) The ice or blockage of the expansion valve, as well as the clogging of the filter, will inevitably reduce the suction and exhaust pressures;
(2) insufficient refrigerant charge;
(3) The expansion valve hole is blocked, the liquid supply volume is reduced or even stopped, and the suction and exhaust pressures are reduced at this time.
9. The shortage of exhaust gas is mainly due to the fact that the compressor suction pipe is too long and the pipe diameter is too small, which causes the suction resistance to increase, which affects the intake air volume and reduces the exhaust gas volume. .
Liquid blow
1. In order to ensure the safe operation of the compressor and prevent the occurrence of liquid hammer, the inhalation temperature is required to be higher than the evaporation temperature, that is, it should have a certain degree of superheat. The degree of superheat can be achieved by adjusting the opening of the expansion valve.
2. Avoid inhaling temperatures that are too high or too low. Excessively high inspiratory temperatures, ie excessive superheat, will cause the compressor discharge temperature to rise. If the suction temperature is too low, it means that the refrigerant is not completely evaporated in the evaporator, which reduces the heat exchange efficiency of the evaporator, and the suction of the wet steam will form a compressor liquid hammer. The suction temperature should be 5 to 10 ° C higher than the evaporation temperature under normal conditions.
Superheat
1. For the commonly used R22 refrigerant, the compressor cooling capacity decreases with the increase of effective superheat. When the superheat degree is 10 °C, the cooling capacity is 99.5% of the cooling capacity under saturated evaporation, when the superheat degree is 20 At °C, the cooling capacity is 99.3% of the cooling capacity under saturated evaporation. It can be seen that the cooling capacity is small with the increase of superheat.
2. For R502 refrigerant, the compressor cooling capacity increases with the increase of effective superheat.
3. The refrigerant maintains a certain degree of superheat, which can further prevent the liquid hammer phenomenon generated in the cylinder, and for the low temperature refrigeration system, appropriately increasing the effective superheat degree can make the lubricating oil return to the compressor smoothly. However, as the superheat of the suction of the compressor increases, the exhaust temperature also rises. Excessive exhaust temperature will make the viscosity of the lubricating oil thin or even carbonized, which will affect the normal operation of the compressor, so the suction superheat should be controlled. Within a certain range.
Fluorine
1. When the amount of fluorine is small or the regulating pressure is low (or partially blocked), the valve cover (corrugated pipe) of the expansion valve and even the inlet port will be frosted; when the amount of fluorine is too small or substantially no fluorine, the appearance of the expansion valve No reaction, only a little sound of the airflow can be heard.
2, to see from which end of the icing, is from the liquid separation head or from the press back to the gas tube, if the liquid separation head is the lack of fluorine, from the press is more fluorine.
Xiamen Longlong Jiuding Refrigeration has many years of chiller production and installation experience and professional after-sales service team, can provide all kinds of screw chillers, low temperature chiller repair and maintenance services; maintenance and reasonable price, complete accessories, is your maintenance cold water Good choice of business;
Xiamen Xiaolong Refrigeration specializes in manufacturing all kinds of industrial chillers, low temperature chillers, cascaded cryogenic refrigerators, low temperature brine units, undertaking large-scale refrigeration and refrigerating storage, ammonia cold storage renovation, process cooling, gas recovery engineering, ice storage air conditioning units. , gas condensation recovery equipment, medium and low temperature chillers (-35 ° C ~ 0 ° C), industrial chillers (0 ° C ~ +25 ° C), cascade ultra-low temperature refrigeration unit (-35 ° C ~ -80 ° C);
Peptone Basic Information
CAS: 73049-73-7
MF: C13H24O4
MW: 244.32726
EINECS: 615-895-9
Mol File: 73049-73-7.mol
Peptone Structure
solubility H2O: 50 mg/mL
form powder
color Dark cream powder
Odor Odorless
PH 6.5-7.5 (2% in H2O)
Water Solubility Soluble in water. Insoluble in alcohol.
Sensitive Moisture Sensitive & Hygroscopic
EPA Substance Registry System Peptones (73049-73-7)
Peptone Water,Peptone Composition,Peptone Water Composition,Peptone Meaning,Peptone Water Preparation
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