Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans. Three impellers (Ⅰ,Ⅱ,Ⅲ) having same outer diameter, but different radius ratio and blade angles were employed for the investigation. Each impeller was tested with two tongue shapes. Flow survey was carried out for each impeller and tongue shape at two flow coefficients, and for each flow coefficient at different circumferential positions. The flow is two-dimensional along the blade span except near the shrouds. The total pressure developed by the impellers in each case is found to be maximum at a circumferential position of around 270°. The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry, but they vary considerably at exit of the impellers. Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure. Higher diffusion and sma Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans. Three impellers (Ⅰ, Ⅱ, Ⅲ) having same outer diameter, but different radius ratio and blade angles were employed for the investigation. Each Flow survey was carried out for each impeller and tongue shape at two flow coefficients, and for each flow coefficient at different circumferential positions. The flow is two-dimensional along the blade span except near the shrouds. The total pressure developed by the impellers in each case was found to be maximum at a circumferential position of around 270 °. The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry, but they vary substantially at exit of the impellers. Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure. H igher diffusion and sma