Efficiency Uncertainty of a Turbine Driven Compressor in a Supercritical CO2 Brayton Cycle

by Gregory D. Wahl
Knolls Atomic Power Laboratory

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Compressor fluid performance is a fundamental issue of the supercritical CO2 Brayton cycle. Tests to accurately describe the performance of the compressor require the proper instrumentation to enable the accurate efficiency calculations required for analytic model validation. There are several ways to calculate compressor efficiency. They all require input power measurements. For a turbine driven compressor, input power can be measured by torque and speed, or by fluid property changes. When torque measurements are unavailable, the efficiency must be calculated using fluid property measurements. This paper investigates the efficiency uncertainties associated with this technique. Test predictions are used to simulate the fluid property test data for two sets of instrumentation with different precision. An uncertainty reduction technique is applied and the compressor efficiency uncertainty is calculated for a range of compressor speeds, mass flow rates, and inlet fluid conditions. It has been shown that accurate efficiency measurements can be made over a large range of operational conditions using fluid property measurements with the proper instrumentation selection.