Calculation of screw air compressor power and exhaust volume converted into intake volume

The conversion between the power, exhaust volume (exhaust volume) and intake volume of a screw air compressor involves multiple parameters and working conditions. The following is the detailed calculation method and formula derivation:

1. Definition of core parameters

1. Power (P)
   The nameplate power of the drive motor, usually in kW, reflects the energy consumption of the air compressor.

2. Exhaust volume (Q ˇ)
   Volume of compressed air discharged per unit time (converted to intake state), in m³/min.

3. Air intake volume (Q)
   The volume of air entering the air compressor per unit of time (actual working conditions), in m³/min.

2. Conversion relationship formula

1. Relationship between power and exhaust volume

Derived from energy conservation and air compressor efficiency:

P=367Q2​⋅p2​⋅k​(kW)

• p2​: Exhaust pressure (MPa)
• k: Thermal insulation index (1.4 for air)
• 367: Unit conversion factor (converts m³/min·MPa to kW)

2. Relationship between exhaust volume and intake volume

Consider compression ratio and leakage losses:

Q1​=T2​⋅ηv​Q2​⋅T1​​⋅(p2​p1​​)1/k

• T1​,T2​: Intake and exhaust temperature (K)
• ηv​: Volume efficiency (typical value 0.85-0.95)
• p1​,p2​: Intake and exhaust pressure (absolute pressure, Pa)

3. Example of calculation steps

known conditions：

• power P=22kW
• exhaust pressure p2​=0.8MPa
• intake pressure p1​=0.1MPa(Atmospheric pressure)
• intake air temperature T1​=293K, exhaust temperature T2​=313K
• volumetric efficiency ηv​=0.9

calculates a target: Air intake volume Q1​

1. Calculate exhaust volume Q2​
   Deformation from the power formula:

Q2​=p2​⋅kP⋅367​=0.8×1.422×367​≈7.14m³/min

2. Calculate compression ratio correction term

(p2​p1​​)1/k=(0.80.1​)1/1.4≈0.62

3. Insert into the intake air quantity formula

Q1​=313×0.97.14×293​×0.62≈4.89m³/min

4. Key influencing factors

1. temperature correction: Increasing the intake air temperature will cause the density to decrease, so the intake air volume needs to be increased.
2. leakage loss: When the volumetric efficiency decreases, higher speed compensation is needed to increase energy consumption.
3. pressure ratio: When the compression ratio increases, the intake air demand increases exponentially.

5. Engineering application suggestions

1. Selection verification: The actual intake air volume needs to be adjusted for altitude (such as thin air in plateau areas).
2. energy efficiency monitoring: Install flow meters and pressure sensors to calculate air compressor efficiency in real time.
3. energy-saving renovation: Adjust the air intake volume through frequency conversion control to avoid “big horses and small cars”.

conclusion: The power, exhaust volume and intake volume of the screw air compressor can be converted by theoretical formulas, but need to be corrected in conjunction with working conditions parameters. It is recommended to optimize equipment selection and operation strategies through sensor data collection and efficiency analysis in practical applications.