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Small-sized axial fans are used as air coolers for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although it causes the deterioration of the efficiency and the increase of noise. Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of the performance. In the present paper, the performance and the internal flow condition of the small-sized axial fan are shown as a first step of the research for the contra-rotating small-sized axial fan and the important points to apply contra-rotating rotors to the small-sized axial fan are discussed. Furthermore, the numerical flow analysis is conducted to investigate the performance of the contra-rotating small-sized axial fan and internal flow conditions and pressure distributions are clarified and the effect of contra-rotating rotors is considered.

The effect of angle and length of the inlet guide vane on the performance of the crossflow fan was examined. By installing guide vane of one sheet in tongue division side in the suction region, the performance of the cross-flow fan becomes more high pressure and high efficient than the case without the guide vane. The prerotation of the inlet flow which is counter directional with the rotation of the rotor is generated by the guide vane. In the high flow region, the high pressure and high efficiency are obtained since the suction cascade work increases by the prerotation of the flow, and since the leading edge separation of the suction cascade is more avoided to high flow. Moreover, in the low flow region, it is possible to suppress the circulating flow in scroll side in the rotor suction inlet. Therefore, the high efficiency is obtained in the low power compared to the result without the guide vane.

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