For cooling electronic equipments and computers, a simple axial flow fan, which consists of a single impeller, is widely used. With an increase in the performance of electronic equipments and computers, the capacities of these fans are also increasing. The discharge must be maintained for the increasing demands of pressure differences, without increasing the fan diameter or numbers of revolutions.
In this research, a single axial flow fan without a stationary blade is designed with a flow pattern of mixed free vortex and solid vortex of the ratio of 1:3. To prevent secondary flow in the blade passage and to get the high pressure difference, blade lean was applied. Two types of blade lean, i.e., dihedral and sweep, were applied. Changing the combinations of dihedral and sweep and their angles, 15 impellers were designed and used for this research. Performance tests and CFD calculations of flow through blade were also made.
Among the impellers with constant blade chord and with dihedral or sweep, the best performance was acquired for the impeller with no dihedral or sweep, i.e., the center of gravities at every section arranged in the radial direction. The arrangement of the center of gravity of every section in the radial direction has been taken as the usual design method. It was made clear that this method is also better one suitable for getting larger pressure difference and high efficiency. The large pressure difference was acquired for the impeller with dihedral of negative angles and sweep with positive angle. But their performances could not exceed that of no dihedral or sweep. But for impellers with mixed negative dihedral and positive sweep, the larger pressure differences and larger efficiency were found to be acquired. The reason why the performance improvement could be acquired were explained by the results of CFD calculation. For the impellers with constant solidities along the radius the similar conclusions were acquired.

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It is considered that the lower limit of specific speed for a centrifugal pump is 80(min^-1, m³/min, m). A centrifugal pump with a much lower specific speed than this has been developed. In this development, a combination of trial calculation using a method of performance estimation for an impeller and the idea to ditch the spiral grooves on the impeller to maintain adequate tip clearance was adopted. The result of tests using two kinds of impeller shows that the maximum efficiency of both impellers is 28% and 25%, and that the specific speeds at that point are 55.7 and 51.0, respectively, even though it is a palm-sized pump. Moreover, the noise level of both impellers is 52 dB (A).

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