Screw refrigeration compression belongs to the positive displacement refrigeration compressor, which uses a pair of interlocked male and female rotors to rotate in the body, periodically changing the volume between each pair of teeth of the rotor to complete the suction, compression, and exhaust processes.

1. Inhalation process

When the rotor rotates, the slot volume gradually expands with the rotation of the rotor and is connected to the suction port. The gas from the evaporation system enters the slot volume through the orifice for the gas suction process. After the rotor rotates to a certain angle, the interdental volume crosses the suction port position and disconnects from the suction port. The suction bearing rotor energy slide valve shaft seal body content ratio slide valve suction filter is completed.

2. Compression process

When the rotor continues to rotate, the gas in the tooth groove enclosed by the body, suction end seat, and exhaust end seat is compressed towards the exhaust end due to the mutual meshing of the female and male rotors and the mutual filling of the teeth, while the pressure gradually increases for the compression process.

3. Exhaust process

When the rotor rotates to connect the tooth slot space with the exhaust port on the exhaust end seat, gas is forced out and discharged from the exhaust flange, completing the exhaust process. Due to the occurrence of the above three processes in the working cycle of each tooth slot space, during high-speed operation of the compressor, several pairs of tooth slot working volumes repeat the suction, compression, and exhaust cycles, thereby ensuring continuous and smooth gas delivery of the compressor.

When the screw refrigeration compressor works, a large amount of lubricating oil is sprayed and discharged together with refrigerant vapor, so an oil separator is installed between the compressor and the condenser. The function of the oil separator is to separate the lubricating oil carried in the compressor exhaust, making the refrigerant entering the condenser pure and avoiding the lubricating oil from entering the condenser and reducing its efficiency. The oil separator also has the function of an oil reservoir.

The lubricating oil separated from the high-temperature and high-pressure oil and gas mixture discharged from the compressor has a high temperature and cannot be directly sprayed into the compressor. It needs to be cooled by an oil cooler to reach the viscosity and temperature required by the compressor before it can be reused. There are generally several ways to cool oil:

（1） Water cooled oil cooler

Water cooled oil cooler is a horizontal shell and tube heat exchanger, with oil outside the tube and water inside the tube. The tube bundle is fixed on both end tube plates, and there are baffle plates inside the oil cooler cylinder, which can improve the heat exchange between oil and cooling water. Due to impurities in the water forming scale in the cooler water pipes and reducing the heat transfer coefficient, regular inspection and cleaning are necessary. When the winter unit is not running, please pay attention to unscrewing the drain plug on the water cover to drain the water in the oil cooler to prevent freezing and damage to the equipment. The inlet temperature of the cooling water for the oil cooler should be less than 32 ℃, and the oil temperature of the unit should be controlled between 40-65 ℃. If WL series special lubricating oil is used, the oil temperature can be controlled between 40-70 ℃.

（2） Hot Rainbow Oil Absorption Cooler

The structure of a thermal siphon oil cooler is similar to that of a water-cooled oil cooler, which is a horizontal shell and tube type with oil outside the tube and refrigerant inside the tube. The refrigerant liquid that flows out after being condensed by the condenser flows into the thermosiphon receiver and then splits into a liquid path that enters the thermosiphon oil cooler. Along the way, it absorbs the heat of the high-temperature oil outside the tube and evaporates. The density of the refrigerant gradually decreases during the evaporation process, and the density of the gas-liquid mixture in the oil cooled return pipe is lower than that of the liquid in the oil cooler supply pipe. This imbalance creates a pressure difference that causes the refrigerant to flow in the oil cooler. The temperature of the oil cooled by the thermal siphon oil cooler is generally 10-20 ℃ higher than the condensation temperature. When designing and installing a thermosiphon system, attention should be paid to:

（3） Spray cooling

In a unit with spray cooling, there is a high-pressure refrigerant liquid that is drawn out from the condenser or accumulator in the unit or system. After passing through a filter, throttle valve, or high-temperature expansion valve, it is sprayed into a middle hole of the compressor to absorb compression heat and cool the oil temperature. The opening degree of the high-temperature expansion valve is determined by the exhaust temperature. When the exhaust temperature is too high (above 55 ℃), the opening degree of the expansion valve increases; When the exhaust temperature is low (below 50 ℃), the opening degree of the expansion valve decreases. There are two liquid injection ports on the compressor - a high-level liquid injection port and a low-level liquid injection port. When refrigerant liquid is injected from the low-level liquid injection port, it is injected from the high-level liquid injection port. The unit with a spray device eliminates the need for an oil cooler, resulting in a simple appearance and smaller volume.

Guidelines for Screw Refrigeration Compressor Malfunctions