<p>A highly accurate centrifugal compressor polytropic performance approximation method has been developed that is easy to employ. The method is based upon a constant efficiency, temperature-entropy path. The elegance of this method is its exceedingly simple way of calculating polytropic efficiency with sufficiently high precision as required for ASME PTC-10 compressor performance testing. A constant efficiency polytropic path is modeled using&nbsp;sequential cubic polynomial segments, which provides closed form solutions that allow for determining thermodynamic state variables along a continuous path. New analytic terms have been developed for slope and curvature of temperature versus entropy along the constant efficiency polytropic path. Also, a new screening method has been developed to assist in determining if a single or multiple sequential cubic polynomial segments may be required to provide sufficient accuracy for a given application. Example cases are used to demonstrate accuracy and comparisons to other polytropic performance calculation methods.&nbsp;The method presented in this paper provides not only overall polytropic compression performance results but has the ability to predict fluid state parameters at any point along the polytropic compression path. The analysis is based upon an inlet flange to discharge flange constant efficiency path for a single, uncooled, compressor section that may contain multiple impellers. Thermodynamic state parameters used in the calculations are based upon total conditions at inlet and discharge measurement locations.</p>

Centrifugal Compressor Polytropic Performance Evaluation Using Cubic Polynomial Approximation for the Temperature-Entropy Polytropic Path

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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