Volumetric efficiency of screw and scroll compressors

There is a significant difference in volumetric efficiency between screw and scroll compressors. The following is a detailed comparison of the volumetric efficiency of the two compressors:

1. screw compressor volumetric efficiency

1. definition and Scope:

   • volumetric efficiency refers to the ratio of the actual gas delivery of the compressor to the theoretical gas delivery.
   • Screw refrigeration compressors are mainly used in screw chillers, and their volumetric efficiency is generally in the range of 0.75 to 0.9.

2. Influencing factors:

   • leakage: The leakage of gas through the gap can be divided into two types: external leakage and internal leakage. The external leakage directly affects the volumetric efficiency of the refrigeration compressor of the screw chiller.
   • Suction pressure loss: The gas flow loss generated when the gas passes through the suction pipe and the suction hole causes the suction pressure to decrease, thereby reducing the suction volume of the compressor and reducing the volumetric efficiency.
   • Preheating loss: The temperature of the rotor and the casing is increased due to the heating of the compressed gas, which causes the gas to expand during the suction process, reduces the amount of gas inhaled, and reduces the volumetric efficiency.
   • Other factors: such as compressor structure, size, speed, type of refrigerant, cylinder fuel injection volume, oil temperature, accuracy of body processing and manufacturing, degree of wear and operating conditions, etc.

2. scroll compressor volumetric efficiency

1. definition and Scope:

   • volumetric efficiency of scroll compressors is usually as high as 90% to 98%, and even 95% in some cases.

2. Reasons for high volumetric efficiency:

   • there is no clearance volume and intake and exhaust valves, so there is almost no volume loss from re-expansion.
   • The process of suction, compression and exhaust is continuous and unidirectional, the harmful overheating is small, the pressure difference between adjacent working chambers is small, and the gas leakage is small.
   • The flexible seal is used to prevent leakage and the leakage is small.

3. comparison summary

• although the volumetric efficiency of the screw compressor is within an acceptable range, it is lower than that of the scroll compressor. This is mainly due to the screw compressor leakage, suction pressure loss and preheating loss and other issues.
• Because of its unique design and working principle, such as no clearance volume and intake and exhaust valves, continuous one-way suction, compression and exhaust process and flexible seal, the volume efficiency of scroll compressor is much higher than that of screw compressor.

In summary, the scroll compressor has a significant advantage in terms of volumetric efficiency. However, when choosing a compressor, in addition to volumetric efficiency, other factors need to be considered comprehensively, such as use requirements, cost, and maintenance difficulty.