Performance characteristics comparison
In the refrigeration system, because the working principle of the reciprocating refrigeration compressor and the screw refrigeration compressor are different, it affects them.
The reasons for our pressure loss and leakage loss are also different.
For reciprocating refrigeration compressors, the main reasons that affect its pressure loss and leakage loss are the quality of the valve and the tightness of the valve when it is closed. This is because when the suction valve is opened, it is necessary to overcome the spring resistance (compression spring) and when the gas flows through the valve, due to the small passage section and high flow speed, a certain flow resistance is generated. Therefore, the reciprocating refrigeration compressor During the suction process, the pressure of the gas in the cylinder is always lower than the gas pressure in the suction pipe; in the same way, the pressure of the gas in the cylinder of the reciprocating refrigeration compressor is always higher than the gas pressure in the suction pipe during the discharge process. If the passage section of the air valve is smaller, the resistance loss is greater. If the valve plate is large and the spring force of the valve is also large, the resistance loss will increase, so that the compression coefficient value will decrease.
For screw-type refrigeration compressors, the main reason that affects its pressure loss and leakage loss is the gas flow rate.
In screw refrigeration compressors, the performance of the screw is the key. If the tooth profile of the screw is a symmetrical arc type, then it
The manufacturing is simple. If the tooth profile of the screw is asymmetrical, then its air delivery screw is large and the efficiency is high. If you reduce the length of the screw
The diameter ratio can make the screw have good strength, increase the reliability of the operation of the screw refrigeration compressor, and facilitate the development of the screw refrigeration compressor in the direction of high pressure ratio.
In a screw-type refrigeration compressor, two pairs of screws with the same diameter and length dimensions, the rotor area utilization coefficient value of the pair,
Its displacement is large. On the surface, the larger the rotor area utilization coefficient, the better the performance of the screw refrigeration compressor. However, if the rotor area utilization factor is too large, the strength and rigidity of the screw will be reduced.
In the screw refrigeration compressor, reducing the number of teeth of the screw can increase the area between the teeth of the screw and improve the screw refrigeration compressor
The displacement. On the surface, the fewer the number of teeth of the screw, the better the performance of the screw refrigeration compressor. However, if the number of teeth of the screw is too small, the bending strength and rigidity of the screw will be reduced.
In a screw refrigeration compressor, increasing the circumferential speed of the screw can reduce the size and quality of the screw refrigeration compressor, and the relative leakage of gas through the gap in the screw refrigeration compressor will be reduced. , It is beneficial to improve the volumetric efficiency and thermal efficiency of the screw refrigeration compressor. On the surface, the faster the circumferential speed of the screw, the better the performance of the screw refrigeration compressor. However, if the peripheral speed of the screw is too fast, it will correspondingly increase the flow loss of the gas in the peripheral speed between the suction and exhaust ports and between the teeth.
Among the three common refrigeration compressors (reciprocating, screw, and centrifugal), the inertia generated by reciprocating motion is the reciprocating system.
The main disadvantage of cold compressors. Because they are often subjected to inertia caused by reciprocating motion, the valve and crank connecting rod mechanism in reciprocating refrigeration compressors are most susceptible to damage.
In the three common refrigeration compressors (reciprocating, screw, and centrifugal), the huge noise generated during operation is the screw system.
The main disadvantage of cold compressors. Because it is often affected by the periodic high-speed passage of the refrigerant gas through the suction and exhaust ports, and the leakage through the gap, a reasonable screw operating speed must be selected in the screw refrigeration compressor.
Among the three common refrigeration compressors (reciprocating, screw, and centrifugal), surge is the main disadvantage of centrifugal refrigeration compressors.
point.
The reason for the surge of the centrifugal refrigeration compressor is that when the cooling water inlet of the condenser is reduced to a certain extent, the flow rate of the centrifugal refrigeration compressor is reduced to a small amount, and serious gas desorption occurs in its passage. Flow, its outlet pressure suddenly drops. Although the centrifugal refrigeration compressor and the condenser work together, the pressure of the gas in the condenser is not reduced at the same time, so the pressure of the gas in the condenser is greater than the outlet pressure of the centrifugal refrigeration compressor, causing condensation The gas in the condenser flows back into the centrifugal refrigeration compressor until the pressure of the gas in the condenser drops to equal to the outlet pressure of the centrifugal refrigeration compressor. This is, the centrifugal refrigeration compressor starts to send air to the condenser again, the flow rate increases, and the centrifugal refrigeration compressor resumes normal operation. However, when the gas pressure in the condenser is also restored to the original gas pressure, the flow rate of the centrifugal refrigeration compressor decreases again, the outlet pressure of the centrifugal refrigeration compressor begins to drop, and the gas flows back again. This goes back and forth, generating periodic oscillations of the airflow. Therefore, in the centrifugal refrigeration compressor, the cooling water volume of the condenser should not be too small, otherwise it will cause strong vibration when the centrifugal refrigeration compressor is in operation, and even cause damage to the centrifugal refrigeration compressor in severe cases. Broken.
Summary: In the refrigeration system, because the three common refrigeration compressors (reciprocating, screw, centrifugal) have their own differences
specialty. Therefore, they have their own advantages and their own shortcomings in performance.
