Numerical study of heterogeneous condensation in the de Laval nozzle to guide the compressor performance optimization in a compressed air energy storage system

Compressed air energy storage technology (CAES) has an enormous possibilities in terms of energy conversation, environmental protection, and economic benefits. Air compressor, as a core component, is of great significance for the CAES system efficiency. The impact of the non-equilibrium condensation of steam contained in the air on the blade erosion and thermal efficiency drop in the compressor is not to be missed. The compressor flow characteristics in blade-to-blade channels can be reproduced by the flow in the Laval nozzle, which can verify the accuracy of the condensation model based on similar flow characteristics and subcooling conditions in the non-equilibrium condensation flow. Firstly, the homogeneous condensation flow is numerically investigated by different condensation models, and the Blend model is used to investigate the heterogeneous condensation because of its higher accuracy. Secondly, the physical properties in the heterogeneous condensing flow are analyzed in detail by the particles number, radius, and types. The result presents that the foreign particles promote the heterogeneous condensation while the homogeneous condensation is weakened. Finally, the flow loss coefficients and thermal efficiency are calculated, and the guide to optimize compressor operation is proposed. It is concluded the heterogeneous condensation with liquid droplets as condensation nuclei can weaken the non-equilibrium condensation greatly and reach a higher thermal efficiency compared to the heterogeneous condensation with solid particles as condensation nuclei. The huge amount of air mass flow rate in compressors and expanders used in the CAES systems makes it difficult to filter out the solid particles and to dry air therefore, investigating the impact of steam condensation on the flow characteristics is recommended.