The non-dimensional width B and the inlet flow angle αi are the important parameters influencing the losses and the stability of radial vaneless diffusers. Their effects on diffuser losses are analyzed in this paper. The portions of the various flow losses change with the variation of non-dimensional width parameter B and flow angle αi. In a diffuser with small width B, the loss is primarily due to wall friction loss. In a diffuser with large B, the wall friction loss becomes a small part of the total loss, especially when αi is large. Comparison with experimental data shows that it is better to calculate the performance parameters of radial vaneless diffusers by using Dou’s method than by Senoo’s method in the design of centrifugal compressors. Senoo’s method is found to be only suitable for the conditions of small B values because it calculates simply the wall friction loss and the secondary flow loss and neglects diffusion loss.

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