Fan surge
Thread Content
Excuse me, is there any difference between centrifugal fans and centrifugal compressors? If not, why do some of them need to be protected against surge, while some fans aren’t even mentioned in this context?； There are also air fans, axial flow fans, air compressors, and centrifugal fans – what are the differences between them?
The difference between centrifugal compressors and centrifugal fans lies only in their pressure ratings. The same phenomenon of \"surge\" occurs, as it is determined by the characteristics of its working principle. When the outlet pressure exceeds the centrifugal force generated by the impeller, gas flows back momentarily, causing a sudden drop in current. When the outlet pressure reverses and drops, the current increases again, thus creating a periodic \"surge\" phenomenon. As for some fans not mentioning this issue, it is because ordinary fan manufacturing is rather rough; some air currents can circulate through the gaps, so there is no occurrence of \"surge\" phenomenon. The same is true for axial flow fans; as long as the precision is sufficient, this kind of phenomenon can occur. For positive-displacement fans and compressors, due to the special nature of their structural principles, \"surge\" does not occur. Mock language, for reference only.
When the flow rate drops to its minimum value, the outlet pressure drops suddenly; the pressure in the downstream pipeline then becomes higher than the outlet pressure, causing the medium being transported to flow back into the machine, until the outlet pressure rises again and the medium is sent forward through the pipeline； When the pressure in the pipeline returns to its original level, the flow rate decreases again, causing the fluid in the pipeline to flow backward, and this cycle repeats itself.