Comparison of working principle of single screw and twin screw refrigeration compressors
1. Twin screw compressor
Twin-screw refrigeration compressor is an energy-adjustable oil-injected compressor. Its three continuous processes of inhalation, compression and exhaust are realized by periodic volume changes when a pair of intermeshing female and male rotors rotate. Generally, the male rotor is the active rotor and the female rotor is the driven rotor.
Main components: double rotor, body, main bearing, shaft seal, balance piston and energy adjustment device.
The capacity is 15～100% stepless adjustment or two-stage or three-stage adjustment, adopting hydraulic piston increase and decrease load.
Conventional use: both radial and axial bearings are rolling bearings; the open type is equipped with an oil separator, an oil storage tank and an oil pump;
Closed:
is the differential pressure oil supply for lubrication, oil injection, cooling and piston movement for adjusting the capacity of the drive slide valve.
Compression principle:
Inhalation process: The gas enters the volume between the teeth of the yin and yang rotors through the air inlets.
Compression process: When the rotor rotates, the volume between the female and male rotor teeth is connected (V-shaped space). Due to the mutual meshing of the teeth, the volume gradually decreases and the gas is compressed.
Exhaust process: The compressed gas moves to the exhaust port to complete a working cycle.
Two, single screw compressor (single screw compressor)
Using the meshing of an active rotor and two star wheels to produce compression. Its three continuous processes of inhalation, compression and exhaust are realized by the periodic volume changes when the rotor and the star wheel rotate.
The rotor has six teeth and the star wheel has eleven teeth.
The main components are a rotor, two star wheels, and two energy slide valves.
The capacity can be steplessly adjusted from 12.5% to 100% and four-stage adjustment.
Compression principle:
Inhalation process: The gas enters the rotor tooth slot through the suction port. As the rotor rotates, the star wheel enters the state of meshing with the rotor tooth grooves in turn, and the gas enters the compression cavity (the enclosed space formed by the rotor tooth groove surface, the inner cavity of the casing and the tooth surface of the star wheel).
Compression process: As the rotor rotates, the volume of the compression chamber decreases, and the gas is compressed until the front of the compression chamber turns to the exhaust port.
Exhaust process: After the front of the compression chamber turns to the exhaust port, the exhaust starts, and a working cycle is completed.
Due to the symmetrical arrangement of the star wheel, the cycle will be compressed twice every time it rotates, and the displacement is correspondingly twice that of the aforementioned cycle.
3. Comparison of the characteristics of single screw refrigeration compressor and twin screw refrigeration compressor
Features of twin screw refrigeration compressor:
requires fuel injection compression (a small amount of liquid injection can also be used). Once oil is lost, metal-to-metal meshing friction may occur, which will seriously affect operation and rotor life.
The rotor radial load and axial thrust are large, especially the axial thrust is very large. Bearings and balanced pistons with large volume and strength are needed to offset the axial force, and the service life of the bearings will be affected. Generally, the bearing life is only 20,000 hours (imported machine), and 20,000 hours require overhaul.
There is a leaky triangle hole between the rotor meshing, there is leakage and pressure loss, which reduces the compression efficiency.
oil is not only used for cooling and sealing between the male and female rotors of the screw, but also for lubrication and power transmission (25-60% of the power).
Generally, the oil pump needs to be started continuously during operation. Due to the large fuel consumption, the oil circuit system is complicated, and the maintenance investment is large.
It is necessary to adopt an oil return system to avoid that the efficiency of the heat exchanger will not drop rapidly after the refrigerating oil enters the evaporator when the liquid supply is too large or the load changes.
The single-stage compression ratio is high. In low temperature conditions, a unique economizer structure can be adopted, which has good energy saving performance, but the cost is correspondingly increased.
It is difficult to repair, and generally needs to be disassembled for repair.
