The Screw Chiller is mainly composed of a screw compressor, a condenser, an evaporator, an expansion valve and an electric control system. The original cooling diagram of the water-cooled twin-screw chiller is as follows:
(1) Twin screw compressor
The twin-screw refrigeration compressor is an energy-adjustable injection compressor. Its three successive processes of inhalation, compression, and exhaust are achieved by a periodic volume change caused by the rotation of a pair of intermeshing male and female rotors in the body.
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 the second and third stage adjustment. The hydraulic piston is used to increase or decrease the load. Conventional adoption:
Radial and axial are rolling bearings; open type with oil separator, oil storage tank and oil pump; closed type for differential pressure oil supply for lubrication, fuel injection, cooling and piston movement to drive spool capacity adjustment.
Inhalation process: The gas enters the interdental volume of the male and female rotors through the suction port.
Compression process: When the rotor rotates, the volume between the male and female rotor teeth is connected (V-shaped space). Due to the mutual meshing of the teeth, the volume is gradually reduced and the gas is compressed.
Exhaust process: The compressed gas moves to the exhaust port to complete a working cycle.
(2) Single screw compressor
Compression is produced by the engagement of an active rotor and two star wheels. Its three successive processes of suction, compression and exhaust are realized by periodic volume changes caused by the rotation of the rotor and the star wheel.
The rotor has six teeth and the star wheel is eleven teeth.
The main components are a rotor, two star wheels, the body, the main bearing, and energy conditioning devices.
Capacity can be adjusted from 10% to 100% stepless and three or four segments.
Suction process: Gas enters the rotor slot through the suction port. As the rotor rotates, the star wheels enter the state of meshing with the rotor slots, and the gas enters the compression chamber (the closed space formed by the rotor slot curved surface, the casing cavity and the star tooth surface).
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 is turned to the exhaust port.
Exhaust process: After the front of the compression chamber is turned to the exhaust port, the exhaust is started, and a working cycle is completed. Due to the symmetrical arrangement of the star wheels, the cycle undergoes two compressions per revolution, and the displacement is twice the amount of circulation per week.
(1) Simple structure, high refrigeration efficiency, less wearing parts, small volume and light weight;
(2) The single machine has a large compression ratio and is not sensitive to wet travel;
(3) The vibration is small, the basic requirements are low, and vibration isolation measures are usually not required;
(4) The gas transmission coefficient is high and the exhaust gas temperature is low;
(5) There are few moving parts, the total number of machined parts is only 1/10 of the piston type, the maintenance period is long, the trouble-free running time can reach 20,000-50,000 hours, and the trouble-free running time of the new fully enclosed compressor can reach 100,000 hours;
(6) The cooling capacity can be adjusted steplessly in the range of 10%-100%. Due to the characteristics of the machine structure, it realizes the economic system of the intermediate intake air, and has the advantages of small footprint;
The noise is high, the fuel consumption is large, and the oil circuit system and auxiliary equipment are more complicated. However, the new type of machine after the 1980s, especially the full-closed machine, has made the noise level and fuel consumption of the screw machine gradually approach and exceed the piston refrigerator.
Because of its outstanding advantages, it has developed rapidly at home and abroad in the past 20 years, and has now surpassed the piston machine, and has a tendency to catch up with centrifuge chillers.
3 types of screw chillers:
(1) Open type:
Advantages: low cleanliness, low moisture content, easy maintenance, etc.
Disadvantages: shaft seal is easy to leak, low efficiency, loud noise, complicated oil circuit, and more oil cooling auxiliary equipment;
Advantages: the shaft sealing mechanism is eliminated, the airtightness is good, the efficiency is high, and the maintenance is convenient;
Disadvantages: The motor has high cleanliness and water content requirements, complicated oil passages, and oil-cooled auxiliary equipment;
(3) Fully enclosed:
Advantages: good airtightness, high efficiency, low vibration, light weight and low noise, which solves the shortcomings of complicated screw oil passages and many auxiliary equipments, and the weight of the whole machine is greatly reduced;
Disadvantages: The motor has high requirements for cleanliness and moisture content of the system and cannot be repaired.