Development of a large-scale, low-noise, cross-flow fan

点击翻译按钮获取中文摘要

Cross flow fans have been frequently used in the inner units of air conditioners and strongly requested to be quiet. In this research projict the relation between the geometrical parameters of a cross flow fan and the generated fan noise level as well as the fluid-dynamic characteristics has been experimentally investigated to create the designing method of large-scale, low-noise, cross-flow fans. The results are summarized as follows :1. On the effects of the geometry of the fan casing it is clarified : (a) There is an optimum divergent angle of the diffuser part of the fan casing, at which both the fluid dynamic and the noise characteristics become optimum. (b) The geometry of the casing upstream of the tongue controls the center of the vortex, which affects the fluid-dynamic performance. (c) The location of the vortex affects both the noise and the fluid dynamic characteristics. Farther from the center of the rotation of the rotor and the closer to the tongue, the higher the both pe … More rformances become.2. The investigation of the internal flow pattern reveals that : (a) The static pressure decreases sharply at the boundary between the scroll and the diffuser in the casing wall and asymptotically increases up to the atmospheric pressure toward the exit of the fan. (b) The rate of this sharp decrease is smaller in the case of the better geometry of the scroll casing. (c) In the case both the noise and the fluid dynamic characteristics are better the internal flow becomes more uniform across the duct.3. The investigation of the similarity by using the two cross-flow fans which are geometrically similar but different in size reveals that : (a) In the same fan the similarity holds good in the case the Reynolds number exceeds the critical number, which is about 1.6*10^4. (b) The similarity of both the noise and fluid dynamic characteristics holds good between the two geometrically similar but different in size if the flow rate does not exceed the maximum efficiency point of the smaller fan, but not in the flow rate region over it. Less