Through means of 3-D CFD (Computational Fluid Dynamics) method, a novel axial compressor with different impeller shapes compressing water vapor as refrigerant was investigated. The numerical simulation focuses on the fluid flow from compressor impeller inlet to outlet. The overall performance level and range are predicted. Different blade patterns with different hub sizes were compared regarding the aerodynamic performance. Independent of the blade pattern, in this numerical investigation the largest hub diameter shows the highest pressure ratio and efficiency at narrowest operating range. (C) 2011 Elsevier Ltd. All rights reserved.