On Monday, May 29, 2017 at 10:11:42 AM UTC-4, Joseph Gwinn wrote:
On May 28, 2017, wrote
(in ):

huge snip

I know how a centrifugal pump works. That video doesn't address the issue in
question: What happens when the input pressure is higher than the example in
your video? And how does it work?

Notice that you did not address the issue of the involute volume increasing
as the liquid flows from the center to the periphery, and the effect that has
on pressure.

I think that the missing piece is Bernoullis Equation:

.http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
.https://en.wikipedia.org/wiki/Bernoulli%27s_principle

For water (and air at low velocity compared to the speed of sound), read the
stuff about incompressible flow.

Joe Gwinn

Thanks, Joe. That is a good way to deal with the conversion and conservation of energy. If I can find out what the dynamics are inside of that second stage, it may help.

Without going into details, here's the basic dilemma. Note that the volume of the involutes increases as you progress from the center to the periphery.. Illustrations usually show that volume filled at the center, but only partly filled at the periphery. I don't know if the illustrations are correct or not. If they are, then there is no pressure involved inside of the involute -- only velocity and mass.

If they *are* correct, then the velocity must *decrease* as you progress from center to periphery, to conserve energy with the larger mass involved. That's the static view. It's possible that a dynamic view allows for both an increase in volume and an increase in velocity, due to the energy added by the rotation of the wheel.

I don't think that's what happens. I think it's a case of velocity increasing. If that's the case, the energy is imparted by the second stage by the velocity imparted by radial acceleration -- which is what we're often told is the way a centrifugal turbomachine works.

Now, if that's true, then what is the effect of feeding the second stage with water at high pressure? What happens with that pressure inside of the involute? It can't be conserved because, if the involute isn't filled, it's unconstrained and it simply fills up the empty volume near the periphery. Energy is conserved because the mass*velocity is conserved: greater mass, less velocity.

Is that what happens? I've found no explanation or illustration of it so far.