Evaluation of supercritical CO_2 compressor off-design performance prediction methods

摘要

A supercritical CO_2 (S-CO_2) Brayton cycle has a compact and simple layout, which suggests the possibility to serve as a small scale distributed power conversion system. Off-design behaviors of each component determine the system off-design performance in the S-CO_2 power cycle. Among components, compressor performances have the largest impact on the system off-design analysis since it operates nearest to the critical point of CO_2. In the system analysis, the off-design performance of a compressor is usually pre-calculated for the fixed inlet conditions. The performance map is then converted for the off-design performances prediction using corrected mass flow rate and corrected rpm. Similitude models are used for the conversion. Several similitude models have been developed mostly for air conditions previously, but the applicability of these models to S-CO_2 still needs to be tested. In this paper, to evaluate the existing models for the S-CO_2 conditions, experimentally validated 1D mean-line code is used to generate wide range of S-CO_2 compressor data set. As a result of the evaluation, Pham model showed the most accurate enthalpy rise prediction resulting in the best pressure rise prediction, and the efficiency prediction could be modified with density correction to improve the off-design performance prediction.