A systematic investigation to understand the use of a novel axial impeller as a part of counter-rotating axial compressor to compress water vapor as refrigerant was undertaken. Blade angle was investigated at first to understand this novel impeller's geometry. A commercial CFD package, which solves the Reynolds-averaged Navier-Stokes equations, was used to compute the complex flow field of the impeller. Two hub/shroud tip ratios with different speed ratios were numerically simulated. The numerical simulation focused on the water vapor flow from compressor impeller inlet to outlet and the overall performance level and range were predicted. The numerical investigation revealed that at hub/shroud tip ratio of 0.54, maximum pressure ratio reached about 1.24 with isentropic efficiency around 75% at its design point. Detailed investigation into flow structure showed that a serious secondary flow exists between span ranges of 30-50%. An enlargement of hub/shroud tip ratio to 0.75 showed that pressure ratio had been improved significantly. By comparing different speed ratios and hub/shroud tip ratios, the study shows potential to utilize this novel axial impeller to compress water vapor as refrigerant. (C) 2011 Elsevier Ltd. All rights reserved.