Working Principle and Characteristics of Screw Compressors

Introduction to Screw Refrigeration Compressors:
The screw refrigeration compressor is also known as the screw compressor. In the 1950s, oil - injected screw refrigeration compressors were applied in refrigeration units. Due to its simple structure, few vulnerable parts, low exhaust temperature under working conditions with large pressure differences or pressure ratios, insensitivity to a large amount of lubricating oil in the refrigerant (often called a wet stroke), and good regulation of gas delivery volume, it quickly occupied the application range of large - capacity reciprocating compressors and continuously extended to the medium - capacity range. It is widely used in refrigeration units such as refrigeration, cold storage, air - conditioning, and chemical processes. The screw heat pump with it as the main unit has been used in heating and air - conditioning since the early 1970s, including air - source type, water - heat - pump type, heat - recovery type, ice - storage type, etc. In the industrial field, in order to save energy, screw heat pumps are also used for heat recovery.

Working Principle of Screw Refrigeration Compressors:
Inside the cylinder of a screw compressor, there is a pair of meshing spiral male and female rotors. Both rotors have several concave teeth and rotate in opposite directions. The gaps between the rotors and between the casing and the rotors are only 5 - 10 silk. The main rotor (also known as the male rotor or convex rotor) is driven by an engine or an electric motor (mostly an electric motor), and the other rotor (also known as the female rotor or concave rotor) is driven by the oil film formed by oil injection from the main rotor, or by the synchronous gears at the ends of the main rotor and the concave rotor. So there is no metal - to - metal contact (theoretically) during the driving process.
The length and diameter of the rotors determine the exhaust volume (flow rate) and exhaust pressure of the compressor. The longer the rotors, the higher the pressure; the larger the rotor diameter, the larger the flow rate.
The grooves of the screw rotors are filled with gas when passing through the suction port. When the rotors rotate, the rotor grooves are sealed by the casing wall, forming a compression chamber. After the rotor grooves are sealed, lubricating oil is sprayed into the compression chamber to play the roles of sealing, cooling, and lubrication. When the rotors rotate to compress the lubricant - gas mixture (abbreviated as the oil - gas mixture), the volume of the compression chamber decreases, and the oil - gas mixture is compressed towards the exhaust port. When the compression chamber passes through the exhaust port, the oil - gas mixture is discharged from the compressor, completing an intake - compression - exhaust process.
Each rotor of the screw machine is supported by antifriction bearings, and the bearings are fixed by end covers near the end of the shaft. The intake end is supported by roller bearings, and the exhaust end is supported by a pair of tapered roller bearings. Usually, the bearings at the exhaust end position the rotor, that is, the thrust bearings, which resist axial thrust, bear radial loads, and provide the necessary minimum axial running clearance.

The working cycle can be divided into three processes: intake, compression, and exhaust. As the rotors rotate, each pair of meshing teeth successively completes the same working cycle.