If the rotational speed remains constant while the inlet flow rate continues to increase, will surge occur?

With the rotational speed unchanged and the inlet flow rate increased, the outlet pressure will not drop; in this case, surge does not occur

“Surge occurs because a decrease in flow leads to a drop in outlet pressure; when this pressure falls below that of the pipeline, the pressure from the pipeline flows back into the unit, and this cycle repeats itself. ”. First of all, your conclusion regarding surge is flawed. There are two types of surge phenomena in turbine compressors (fans): one is the change in vacuum pressure at the inlet when the air supply is severely insufficient. This phenomenon occurs mostly during the initial startup phase, due to the inlet valve (guide vane) being opened too little or being fully closed. Another common cause is excessive outlet pressure in turbine compressors (fans). The principle is that an increase in outlet pressure leads to a decrease in flow rate, rather than surge occurring due to changes in outlet pressure resulting from a reduction in flow rate. If that is the case, surge will not occur. It is the special principle of this machine that gives rise to the specific term “surge”. When the pressure reaches a certain value, the centrifugal force generated is no longer sufficient to increase the pressure any further; as a result, the compressed gas expands instantaneously through the impeller channels and flows from the inlet to the atmosphere. When this portion of pressure expands, it reduces the pressure at the outlet, which in turn generates centrifugal force and causes the pressure to rise; this cycle repeats itself, resulting in the periodic phenomenon of \"surge\". The above is an imitation version of the explanation; there are many different versions for explaining this principle of surge, and the level of knowledge required varies accordingly. The imitation versions are for reference only.

A reminder from the design institute: You have understood only half of it. When the inlet flow rate drops below the surge point, it causes a drop in pressure; if this pressure falls below the outlet backpressure, surge occurs. Then why does pressure drop occur when the flow rate is very low at the same rotational speed? Think about pumps: why isn’t it said that the pressure drops significantly when the flow rate is low? The ultimate reason lies in the properties of gases: they have low viscosity and poor cohesion. When the flow rate decreases, if the velocity remains constant, rotational stall occurs, causing the gas to separate from the working surface of the impeller, which prevents an increase in the gas’s velocity. That’s why surging occurs. In cases of high flow, rotational stall does not occur. (Stonewalling is a different situation.) 2. Generally, compressor curves do not have a surge zone; if such a zone is present, it can be observed that the pressure drops sharply, while when the flow rate increases, the decrease in pressure head is minimal, thus meeting the backpressure requirements of the process. Therefore, surge does not occur at high flow rates. Only a blocked condition will occur. And the hazards of blocked conditions are much less severe than those of surge.

Think about it the other way around: isn’t opening the anti-surge valve meant to increase the inlet flow? With high inlet flow, the system can’t handle it, but the compressor equipment is likely to be fine. But in terms of the manufacturing process, does an overall voltage increase of the system meet the requirements? Economically speaking, if you can’t consume it over a long period of time, storing it just means wasting money, right?:o

1. Increasing the inlet flow rate while keeping the rotational speed constant results in little change in the outlet pressure. 2. With the rotational speed remaining constant, an increase in flow rate will inevitably lead to an increase in the power of the unit, which in turn requires an increase in the input power of the prime mover.

This is a somewhat problematic question. An increase in incoming flow, if not accompanied by an increase in compressor power, will inevitably lead to pressure buildup upstream. If a safety valve is installed there, it might be forced to open, resulting in the shutdown of the system.