文章來源： 作者：羅茨機電 發布時間：2022-01-21 瀏覽次數：477
Centrifugal fan has huge energy-saving space and can obtain very considerable social and economic benefits. Shaanxi fan? There are four main loss types of centrifugal fan, namely flow loss, volume loss, bearing friction loss and disc loss. The latter two are sometimes collectively referred to as mechanical losses, because the bearing friction loss is the external mechanical loss caused by the bearing rotation friction, and the wheel cover loss is the internal mechanical loss caused by the friction between the impeller and the surrounding gas when the impeller rotates.
1. Flow loss
Shaanxi fan? The main loss is the flow loss, which is rooted in the viscosity of the gas. The flow loss can be divided into boundary layer friction loss and vortex loss. The latter includes the loss caused by boundary layer separation, "jet wake" and secondary flow, as well as the impact loss caused by the difference between air inlet angle and blade inlet angle when the fan works under non rated working conditions. The flow loss is closely related to the boundary layer. On the one hand, the thickening of the boundary layer will increase the gas friction loss in the boundary. On the other hand, when the boundary layer develops to a certain extent, there will be backflow near the wall, resulting in the separation of the boundary layer from the wall, forming a fixed vortex area and causing great losses.
2. Secondary flow loss
There is a pressure gradient in the blade path of centrifugal impeller. The inertial force formed by the fluid in the boundary layer on the blade surface and the wheel cover disc surface cannot be balanced with the pressure gradient in the blade path, resulting in the flow from the pressure surface to the suction surface in the boundary layer. The flow is perpendicular to the main flow direction in the blade channel, which is called secondary flow. Secondary flow is that the low-speed fluid micro mass near the pressure surface in the boundary layer on the surface of wheel cover and wheel disc is sucked away, and the boundary layer on the suction surface becomes thicker, resulting in separation and loss. The reason for the jet wake phenomenon is that the boundary layer separation on the suction surface affects the flow in the mainstream area. A squeeze area is formed near the pressure surface, and the high velocity is called jet. The relative velocity near the suction surface is low, which is called wake.
There is a certain gap between the collector and the impeller inlet, and a small part of the gas flowing out of the impeller will flow back to the impeller inlet through the gap. This loss caused by the gap is called volume loss. The friction loss between the wheel disc and the wheel cover will cause power loss, but does not reduce the pressure. In addition, the kinetic energy at the outlet of the volute free fan impeller for roof ventilation and fan wall is not converted into static pressure. When the air flow rushes out of the impeller, the kinetic energy is completely lost, and there is also dynamic pressure loss.
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