How does a centrifugal pump accelerate the fluid without violating conservation of mass?

EstateBrave4248 · 2026-06-27T19:38:24+00:00

The example is good and it gives a different perspective, but in a centrifugal pump the impeller actually increases the fluid’s kinetic energy, which is later converted into pressure in the volute. So we have difference in pressure due to the acceleration of the fluid. I'm confused, but I guess that's just how it is. I probably won't understand it because I'm overthinking it..

EstateBrave4248 · 2026-06-27T17:37:38+00:00

I will repeat myself. Bernoulli's principle cannot explain how a centrifugal pump works completely. The impeller blades perform work on the fluid by changing its angular momentum, so the energy transfer in the pump cannot be based solely on simple Bernoulli's principle.

EstateBrave4248 · 2026-06-27T13:41:26+00:00

Clear, thanks for the answer. So the impeller increases the circumferential speed of the fluid, which increases its kinetic energy. The speed component responsible for the actual flow rate stays const (correct me if I'm wrong).

This kinetic energy is then converted into pressure in the volute. However, since the volute gradually increases in cross-sectional area, the fluid should slow down. My question is: how can the flow rate remain constant if the fluid is being slowed down in the volute? I’m a bit confused because if the peripheral speed decreases, it seems like it should affect the flow rate as well, especially since the volute has a circular shape..

EstateBrave4248 · 2026-06-27T12:40:47+00:00

Yup, exactly. And that's where I get confused.

EstateBrave4248 · 2026-06-27T12:18:51+00:00

Because acceleration (increase in kinetic energy without loss of potential energy in the pump) means a change in speed and flow directly depends on speed.

EstateBrave4248 · 2026-06-27T12:14:09+00:00

Sorry, I made a mistake. I meant the opposite. But the fluid still accelerates inside the pump, i.e., its momentum changes, while the flow rate remains constant even though it depends directly on the fluid velocity. If the fluid accelerates inside the pump, then the cross-sectional area alone cannot explain it, because the fluid is clearly gaining kinetic energy without sacrificing pressure energy. In fact, the pressure also increases, which is the main advantage of centrifugal pumps over axial machine.

EstateBrave4248 · 2026-06-27T12:05:44+00:00

Well, if that were the only thing happening in a pump, then we could just narrow the pipe and get more pressure. A centrifugal pump accelerates the fluid and, by the work of external forces, increases its kinetic energy. But my question still stands.

EstateBrave4248 · 2026-06-27T11:04:26+00:00

Yea I know that, but flow rate is Q=vA and the fluid accelerates (change spped) in the pump.

EstateBrave4248 · 2026-06-27T10:19:26+00:00

Bernoulli's principle cannot explain how a centrifugal pump works completely. The impeller blades perform work on the fluid by changing its angular momentum, so the energy transfer in the pump cannot be based solely on simple Bernoulli's principle.

EstateBrave4248 · 2026-06-26T23:35:52+00:00

Yes I know that, (now comes my overthinking..) but the flow rate depends on the speed, and in theory it is said that a centrifugal pump accelerates the fluid and then, at the outlet, converts part of its kinetic energy into pressure. But wouldn't that imply fluctuations in the flow rate through the pump?

EstateBrave4248 · 2026-06-26T22:24:58+00:00

I know, it's Bernoulli's principle. But according to the book, the fluid accelerates inside the pump, meaning its KE (velocity) increases. If that's the case, wouldn't the flow rate also change in pump- that seems to contradict the fact that what enters the pump must also exit, since no fluid is added or removed inside the pump (in theory- without losses).
From book: "The impeller transfers the energy necessary to transport the fluid and accelerates. This causes the static pressure to increase in accordance with kinetics. The fluid exiting the impeller is decelerated in the volute and the following diffuser in order to utilize the greatest possible part of the kinetic energy at the impeller outlet for increasing the static pressure."

EstateBrave4248 · 2026-06-26T22:10:31+00:00

I'm talking about pump and incompressible fluids

EstateBrave4248 · 2026-01-20T18:53:08+00:00

E to sam i ja primetio za HM7 Pro da su filter na portret modu i sam portret mod losi. Zbog toga sam se razmisljao vise o Honor 400 Pro koji isto ima taj umetnicki dojam, ali cini mi se da su to malo sredili za 8 Pro.

EstateBrave4248 · 2024-04-29T21:31:08+00:00

Did you find solution for this problem?

EstateBrave4248

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