Stall and surge are two different concepts. Stall is a hydrodynamic phenomenon caused by the structural characteristics of the blade. Some basic characteristics of stall, such as the rotation speed of the flow separation zone, the starting point and the vanishing point of the flow separation, have their own laws, and are not affected by the capacity and shape of the pipeline system of pumps and fans.
[practical operation of fan surge, stall and windbreak]
Surge is a manifestation of oscillation characteristics after the performance of pump and fan is coupled with pipeline system. Its amplitude, frequency and other basic characteristics are dominated by the capacity of pipeline system of pump and fan. The fluctuation of flow, total pressure and shaft power is caused by unstable working conditions. However, the experimental results show that the surge phenomenon is always closely related to the rotating flow separation in the blade passage, and the increase of the attack angle is also related to the decrease of the flow rate. Therefore, in the unstable working condition region with surge, there must be rotating flow separation.
Stall does not necessarily appear surge, surge must have occurred; stall only belongs to the internal flow characteristics of axial flow fan, and surge is the coupling result of internal and external characteristics of axial flow fan, and has inevitable connection with outlet pipeline characteristics. In the actual operation, when the fan surge, the fan and pipe will produce great vibration and noise. The stalled fan will not produce great vibration and noise, as long as the rotor blade or speed is adjusted, it can continue to run.
The wind snatching must happen in the parallel pipeline, and the stall and surge may not occur during the wind snatching, which is related to the pipeline condition. In general, the phenomenon of rushing wind is mainly caused by the change of resistance and local resistance of pipeline system from the outlet of two fans to the load point. If one side of air preheater is seriously blocked, denitration and desulfurization system is blocked, booster fan fails in the system with booster fan. Both the resistance along the way and the local resistance. A typical pulverizer system is arranged in line along the front and rear walls of the boiler. Because the distance between the primary air inlet of each pulverizer and the primary air main pipe is very large, when one pulverizer trips, the two primary air fans with balanced output may be forced to resist the wind of one fan with high resistance and the output of the two fans will be deviated. Generally, when there is a large flow, the wind snatching will not be very serious.
However, if the flow rate is small, the fan may enter the stall and surge zone, causing the fan to stall and surge and form a serious phenomenon of rushing wind. Therefore, if one of the two fans stalls and surges, it will definitely happen the phenomenon of rushing wind.
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