Orifice plate effect on impeller flow rate

[Spimon]

Hi everyone,

Hoping someone can point me in the right direction.

I'm trying to find (a theoretical approximation of) the flow rate through a pipe where the pressure is provided by an axial flow impeller, but restricted by an orifice plate.

I have (or can get hold of) all the physical parameters - pipe dimensions, motor power, impeller power number, impeller pressure drop, pumping capacity, orifice area, etc..).
I know the flow rate through the open pipe with no orifice plate.

I imagine placing an orifice plate over the open pipe will create a higher pressure, more drag, put more load on the motor and reduce the flow rate.

How will I find out the new flow rate?

I guess I need to somehow find the new pressure difference either side of the orifice plate. I don't know how to do this.

Any ideas/suggestions/equations/text book references would be a great help!

Thanks!

 

[scutterbob]

Strangely enough orfice plates are often used for flow rate measurement ;)

http://en.wikipedia.org/wiki/Orifice_plate

Also, the pump curve would be useful, should come with your pump.

 

[Spimon]

Thanks for the link.
Unfortunately it's the pump I'm designing (not intended to be a pump, but has a pumpig effect).
I may need some experimentation to figure out my pressure drop. Thanks anyway :)

 

[jim hardy]

I imagine placing an orifice plate over the open pipe will create a higher pressure, more drag, put more load on the motor and reduce the flow rate.

Actually most pump motors experience less load when flow is throttled.
When you were a kid did you put your hand over exhaust from Mom's vacuun cleaner and wonder why motor sped up? Vacuum cleaners are centrifugal, but this Wiki shows similar curve for axial..

http://en.wikipedia.org/wiki/File:Axial_1.png

Ther must be a way to get your pump curve. They've been designing them for well over century.

Are you familiar with Crane handbook, "Flow of Fluids"? Where i worked It was on every mechanical engineer's desk.
http://www.flowoffluids.com/publications/crane-tp-410.aspx