What is the volumetric efficiency of screw compressor?

The volumetric efficiency of screw compressors is usually 0.75~0.95 the specific value is affected by multiple factors such as compressor type, operating conditions, design parameters and operating status. The following is a detailed analysis:

core Definition of 1. Volumetric Efficiency

the volumetric efficiency is the ratio of the actual gas transmission volume of the compressor to the theoretical gas transmission volume, which reflects the utilization efficiency of the compressor to the geometric size. The calculation formula is:

volumetric efficiency = theoretical intake volume, actual intake volume × 100%

• theoretical intake volume: Determined by compressor speed and rotor geometry.
• Actual intake volume: Affected by factors such as leakage, flow loss and heat exchange, it is usually less than the theoretical value.

2. Key Factors Affecting Volumetric Efficiency

1. leakage
   • external leakage: High-pressure gas leaks to the suction channel or primitive volume, directly reducing the actual gas delivery.
   • Internal leakage: The leakage between the high-pressure primitive volumes only affects the power consumption and does not directly affect the volumetric efficiency.
   • Oil injection seal: Oil injection can fill the gap, reduce leakage, and improve volumetric efficiency (oil-injected compressors are usually more efficient).
2. gas flow loss
   • the suction pipe resistance causes the suction pressure to drop, the gas specific volume increases, and the actual suction volume is reduced.
3. heat exchange
   • the rotor and the casing are heated by the compressed gas, resulting in an increase in the temperature of the suction gas and an increase in the specific volume, further reducing the actual suction volume.
4. Working conditions and structural parameters
   • pressure ratio: When the pressure ratio increases, the volumetric efficiency decreases slowly (because the screw compressor has no clearance volume).
   • Speed: Increased speed can reduce leakage, but too high may increase flow losses.
   • Gas properties: The gas with large molecular weight has less leakage and higher volumetric efficiency.
   • Compressor type:
     • oil-injected screw compressor: Volumetric efficiency is usually in 0.85~0.95 between.
     • dry screw compressor: No oil seal, more serious leakage, volumetric efficiency is usually 0.75~0.85 between, the need for high speed compensation.

3. the efficiency range under different application scenarios

• screw compressor for refrigeration: Volumetric efficiency approx. 0.75~0.9, Affected by evaporation temperature and pressure ratio.
• Industrial large screw compressor: Efficient models up more than 0.9(e. g. fuel injection type, optimized design).
• Dry high pressure ratio condition: May be as low 0.75 it needs to be improved by high speed or sealing optimization.

Optimization Direction of 4. Lifting Volumetric Efficiency

1. design optimization: Reduced rotor clearance, optimized profile design, variable volume ratio technology.
2. Operation control: Reasonably match the pressure ratio, avoid over-compression or under-compression.
3. auxiliary measures: Oil injection cooling, increase oil film sealing, optimize the design of suction pipe.

Summary

the volumetric efficiency range of screw compressors is roughly 0.75~0.95 the specific value needs to be comprehensively evaluated in combination with compressor type, operating conditions and design optimization. Under optimized design and operating conditions, high-efficiency models can reach more than 0.9, while dry or high pressure ratio conditions may be as low as 0.75. In practical applications, it is recommended to refer to the performance curve or experimental data provided by the compressor manufacturer to match the specific needs.