Centrifugal Compressor Polytropic Head & Power Calculator
Calculate polytropic head (ft-lbf/lb & kJ/kg), discharge temperature (T2), gas horsepower (GHP), and required brake power using the Schultz polytropic method per ASME PTC 10.
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Frequently Asked Questions
Why is polytropic analysis preferred over isentropic for centrifugal compressors?
Isentropic efficiency assumes zero entropy generation, which is physically unrealistic across multiple compressor stages where frictional heat alters the gas density in subsequent stages. Polytropic efficiency represents the true aerodynamic quality of each incremental pressure rise independent of overall pressure ratio.
What is the Schultz polytropic method per ASME PTC 10?
The Schultz method introduces a compressibility correction factor (X and Y functions) to the classical polytropic head equation. It accurately models real gas behavior and deviation from ideal gas laws under high pressures without requiring complex thermodynamic chart integration.
What is the maximum allowable discharge temperature for uncooled compressors?
Per API 617, the maximum predicted discharge temperature for centrifugal compressors should not exceed 300°F to 350°F (150°C to 175°C). Exceeding this limit degrades dry gas seal elastomers, accelerates polymer fouling, and causes thermal rotor distortion.