Windage loss model for S-CO$_2$ turbomachinery

Abstract

A supercritical CO2 (S-CO$_2$) Brayton cycle has high compactness, simple configuration and competitive efficiency. The advantages are originated from S-CO$_2$ non-ideal gas properties, and enable to utilize the S-CO$_2$ Brayton cycle for distributed power generation in remote regions. However, the design of the cycle and components becomes challenging because of the strong real gas effect. Especially, turbomachinery is the key component for the expansion and compression processes and is most affected by the real gas effects of S-CO$_2$. In order to obtain precise design of the turbomachinery, accurate loss models are necessary. Windage loss is one of the external losses that determines motor load and heat generation due to friction. The overall turbomachinery efficiency is greatly affected by the windage loss especially in an S-CO$_2$ power cycle, since the windage loss is more significant due to high fluid density and high rotational speed. Therefore, an accurate windage loss model which reflects the real gas effect of S-CO$_2$ is essential to obtain precise design of the turbomachinery. In this thesis, existing windage loss models are compared under the S-CO$_2$ condition to understand the turbomachinery performance uncertainty due to the windage loss models. Then, they are corrected to reflect the S-CO$_2$’s real gas effect. Finally, the improved models are verified and new models are suggested based on the S-CO$_2$ windage loss experiments.