Compressor pressure ratio terminology What is the term for the ratio of discharge (delivery) pressure to inlet (suction) pressure in a compressor?

Introduction / Context:
Pressure ratio is a fundamental parameter that defines the duty of a compressor, influences work requirement, discharge temperature, and determines staging in multistage designs.

Given Data / Assumptions:

• Discharge pressure and suction pressure are absolute values unless specified otherwise.
• Steady operation at the stated pressures.

Concept / Approach:
The ratio r = p_discharge / p_suction is called the compression ratio. It is used in performance correlations and to select the number of stages and intercooling requirements. Larger ratios generally imply higher work input and higher discharge temperatures for a given inlet state.

Step-by-Step Solution:

Verification / Alternative check:
Performance maps are often plotted against pressure ratio. Gas turbine compressors likewise use overall pressure ratio across the compressor train.

Why Other Options Are Wrong:

Expansion ratio applies to turbines, not compressors.Efficiency terms are dimensionless performance metrics, not raw pressure ratios.

Common Pitfalls:
Using gauge pressures in the ratio without converting to absolute can produce large errors. Always use absolute pressures in thermodynamic calculations.

Final Answer:

Compression ratio