Centrifugal pump question

snipped-for-privacy@gmail.com wrote on 5/28/2017 10:27 AM:

??????? ? ?? ??????? ??AJF eU wrote:

?????? ? ? ?????? ?? lBYWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

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pumps threw me. Since water isn't compressible, I don't see how the mult i-stage pumps work. For gas, no problem, but I don't get it for liquids.

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ure/volume relationship, though, isn't in agreement with Boyle's law. Gas es approximate it. It's easy to imagine a multi-stage non-positive-displa cement compressor that keeps building pressure in a material that obeys B oyle's law. It's much harder to imagine it with liquids.

id.

ldn't hold pressure that way.

the kinetic aspects of a turbo pump (velocity) and the potential aspects (pressure). A turbine pump that's pumping a liquid must be producing pote ntial energy from kinetic energy.

way that an ordinary turbine pump can hold the pressure generated by a p revious stage, unless the entire thing is kinetic, which we're then measu ring as potential energy (pressure).

) >>>>

e-d_309.html>

essor efficiency, which ranges from 0.70 to 0.85 in the best turbo machin ery, including stationary and aircraft gas turbines. At the high end, 85% compressor efficiency, they're losing 15% to gas friction.

tween pressure and volume (Boyle's law). Compressing gas with a machine, whether it's positive or non-positive displacement, like a turbo compress or, is not a problem. An example of positive displacement types is a vane -type supercharger. An example of non-positive-displacement types is a tu rbocharger. Or the compressor stage of a gas turbine engine, such as an a ircraft jet engine.

g
or

If you daisy-chain two centrifugal pumps together, I am sure you will get a lot higher pressure output than using just one (too optimistic to expect 2 times the pressure).
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snipped-for-privacy@gmail.com wrote on 5/28/2017 10:27 AM:


I suggest you watch this centrifugal pump video to clear up your brain fog:
<http://www.wermac.org/video/how-does-a-centrifugal-pump-work.html
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On Sunday, May 28, 2017 at 7:05:42 PM UTC-4, ZScPb?? ? ?????? ? ?? ?????? ??tLolr wr ote:

?????? ? ? ?????? ??AJ FeU wrote:

?????? ? ? ?????? ??lB YWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

s
t of

rong?

will be

y be

he

duce 10

dd any

flowing

pumps threw me. Since water isn't compressible, I don't see how the multi- stage pumps work. For gas, no problem, but I don't get it for liquids.

ge as

leads

ility

ure/volume relationship, though, isn't in agreement with Boyle's law. Gases approximate it. It's easy to imagine a multi-stage non-positive-displaceme nt compressor that keeps building pressure in a material that obeys Boyle's law. It's much harder to imagine it with liquids.

id.

ldn't hold pressure that way.

the kinetic aspects of a turbo pump (velocity) and the potential aspects (p ressure). A turbine pump that's pumping a liquid must be producing potentia l energy from kinetic energy.

way that an ordinary turbine pump can hold the pressure generated by a pre vious stage, unless the entire thing is kinetic, which we're then measuring as potential energy (pressure).

) > >>>>

e-d_309.html>

essor efficiency, which ranges from 0.70 to 0.85 in the best turbo machiner y, including stationary and aircraft gas turbines. At the high end, 85% com pressor efficiency, they're losing 15% to gas friction.

tween pressure and volume (Boyle's law). Compressing gas with a machine, wh ether it's positive or non-positive displacement, like a turbo compressor, is not a problem. An example of positive displacement types is a vane-type supercharger. An example of non-positive-displacement types is a turbocharg er. Or the compressor stage of a gas turbine engine, such as an aircraft je t engine.

g
or

g:

I know how a centrifugal pump works. That video doesn't address the issue i n 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.
--
Ed Huntress

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On May 28, 2017, snipped-for-privacy@gmail.com wrote
<huge snip>

I think that the missing piece is Bernoulli?s 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
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On Monday, May 29, 2017 at 10:11:42 AM UTC-4, Joseph Gwinn wrote:

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Thanks, Joe. That is a good way to deal with the conversion and conservatio n 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 par tly 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 invol ute -- only velocity and mass.
If they *are* correct, then the velocity must *decrease* as you progress fr om center to periphery, to conserve energy with the larger mass involved. T hat'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 increasi ng. If that's the case, the energy is imparted by the second stage by the v elocity imparted by radial acceleration -- which is what we're often told i s the way a centrifugal turbomachine works.
Now, if that's true, then what is the effect of feeding the second stage wi th water at high pressure? What happens with that pressure inside of the in volute? It can't be conserved because, if the involute isn't filled, it's u nconstrained and it simply fills up the empty volume near the periphery. En ergy is conserved because the mass*velocity is conserved: greater mass, les s velocity.
Is that what happens? I've found no explanation or illustration of it so fa r.
--
Ed Huntress

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On May 29, 2017, snipped-for-privacy@gmail.com wrote

Model isn?t quite right - water is incompessible, which means that the volume of a package of water is constant - mass does not change either. And Bernoulli?s equation is a direct consequence of the conservation of energy applied to the flow of an incompressible fluid.

Pumps in series do work, but the stages must be correctly matched for the cascade to be effective. A good example is an axial-flow turbine - each fan disk stage gives the passing fluid a kick (increases its velocity). If this flow is impeded, the pressure will rise, until the stagnation (max) pressure is reached.
If you look at the performance curve for any fan, it will be max flow at zero head, and max head at zero flow, and max delivered aerodynamic power somewhere between.
I?d dig up a college intro to physics textbook and read the chapter about Bernoulli?s equation. This will clarify the issue.
Joe Gwinn
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On Sunday, May 28, 2017 at 9:23:49 AM UTC-4, snipped-for-privacy@gmail.com wrote:

??????? ? ?? ??????? ??lBYWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

of

ng?

ll be

be

ce 10

any

lowing

umps threw me. Since water isn't compressible, I don't see how the multi-st age pumps work. For gas, no problem, but I don't get it for liquids.

as

eads

ity

e/volume relationship, though, isn't in agreement with Boyle's law. Gases a pproximate it. It's easy to imagine a multi-stage non-positive-displacement compressor that keeps building pressure in a material that obeys Boyle's l aw. It's much harder to imagine it with liquids.

t hold pressure that way.

kinetic aspects of a turbo pump (velocity) and the potential aspects (press ure). A turbine pump that's pumping a liquid must be producing potential en ergy from kinetic energy.

that an ordinary turbine pump can hold the pressure generated by a previou s stage, unless the entire thing is kinetic, which we're then measuring as potential energy (pressure).

> >

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So what do you think happens if you have a centifical pump with a pressure gauge on the output and the output blocked off so there is no flow?
Dan
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wrote:


So what do you think happens if you have a centifical pump with a pressure gauge on the output and the output blocked off so there is no flow?
Dan =======================That depends on the geometry of the impeller. A centrifugal fan may stall, not couple as well to the air and draw -less- power. The discharge curve gives the relationship between flow rate and pressure rise. https://mechanicalengineeringblag.wordpress.com/2015/12/26/why-are-most-centrifugal-pump-vanes-backward-curved/ -jsw
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Jim Wilkins wrote on 5/29/2017 2:30 PM:

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A centrifugal pump is spinning the fluid 'round and 'round inside an enclosed housing. It will never stall unless you feed solid debris like straws and sticks into it.
A centrifugal pump is generating pressure by spinning the fluid to generate centrifugal force. It is different from a turbo pump.
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On Monday, May 29, 2017 at 5:01:14 PM UTC-4, LcISQw?? ? ??????? ? ?? ??????? ??nPkuk O wrote:

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A centrifugal pump is a type of turbomachine.
https://en.wikipedia.org/wiki/Turbomachinery
--
Ed Huntress

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snipped-for-privacy@gmail.com wrote on 5/29/2017 5:11 PM:

??????? ? ?? ??????? ??nPk ukO wrote:

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"Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid"
You are confusing yourself by reading too much and overloading your brain, again.
The rotor in a turbine functions much like an electric fan or a ship's propeller. It is designed to propel fluid in a direction perpendicular to its plane of rotation.
On the other hand, the rotor (impeller) in a centrifugal pump is throwing fluid radially outward parallel to its plane of rotation.
They are different in the principle they work. That's why one is called a "turbo pump", the other is called "centrifugal pump", Ed.
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On Monday, May 29, 2017 at 6:04:16 PM UTC-4, zzCjnt?? ? ??????? ? ?? ??????? ??xPofs D wrote:

?????? ? ? ?????? ??nP kukO wrote:

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Right. That's why I used the term.

I'm not overloaded. I'm trying to figure out the fluid dynamics within the involutes of a pump.

No shit? <g>

If you're comfortable with your understanding of it, that's fine. I'm not c omfortable with it. Something in the explanations is being oversimplified t o the point where they make no sense.

They're both turbomachinery. In the context in which I used the term, it's correct. I was quite careful about how I used it.
--
Ed Huntress


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snipped-for-privacy@gmail.com wrote on 5/29/2017 6:14 PM:

??????? ? ?? ??????? ??xPo fsD wrote:

?????? ? ? ?????? ?? nPkukO wrote:

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the involutes of a pump.

ot comfortable with it. Something in the explanations is being oversimpli fied to the point where they make no sense.

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t's correct. I was quite careful about how I used it.

You are hopelessly thick.
Please look at this impeller of a centrifugal water pump. The fins are acting like pedals, not blades. It is designed to throw fluid outward, instead of pushing fluid forward.
<
http://www.iboats.com/mall/image/vendor/16/bigger/18-3087_big.jpg

Would you do us a favour? Please beat your head against the wall 10 times to clear your mind and then think again before you get back to us.
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On Monday, May 29, 2017 at 2:10:17 PM UTC-4, snipped-for-privacy@krl.org wrote:

?????? ? ? ?????? ??lB YWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

s
t of

rong?

will be

y be

he

duce 10

dd any

flowing

pumps threw me. Since water isn't compressible, I don't see how the multi- stage pumps work. For gas, no problem, but I don't get it for liquids.

ge as

leads

ility

ure/volume relationship, though, isn't in agreement with Boyle's law. Gases approximate it. It's easy to imagine a multi-stage non-positive-displaceme nt compressor that keeps building pressure in a material that obeys Boyle's law. It's much harder to imagine it with liquids.

d.

n't hold pressure that way.

e kinetic aspects of a turbo pump (velocity) and the potential aspects (pre ssure). A turbine pump that's pumping a liquid must be producing potential energy from kinetic energy.

ay that an ordinary turbine pump can hold the pressure generated by a previ ous stage, unless the entire thing is kinetic, which we're then measuring a s potential energy (pressure).

> > >

-d_309.html>

e gauge on the output and the output blocked off so there is no flow?

You have static pressure. That, too, is axiomatic. But this is a dynamic ma chine.
--
Ed Huntress

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snipped-for-privacy@gmail.com wrote on 5/29/2017 3:28 PM:
?????? ? ? ?????? ?? lBYWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

s
t of

rong?

will be

y be

he

duce 10

dd any

flowing

pumps threw me. Since water isn't compressible, I don't see how the mult i-stage pumps work. For gas, no problem, but I don't get it for liquids.

ge as

leads

ility

ure/volume relationship, though, isn't in agreement with Boyle's law. Gas es approximate it. It's easy to imagine a multi-stage non-positive-displa cement compressor that keeps building pressure in a material that obeys B oyle's law. It's much harder to imagine it with liquids.

id.

ldn't hold pressure that way.

the kinetic aspects of a turbo pump (velocity) and the potential aspects (pressure). A turbine pump that's pumping a liquid must be producing pote ntial energy from kinetic energy.

way that an ordinary turbine pump can hold the pressure generated by a p revious stage, unless the entire thing is kinetic, which we're then measu ring as potential energy (pressure).

) >>>>

e-d_309.html>

sure gauge on the output and the output blocked off so there is no flow?

c machine.

You are talking nonsense. If you feed the output to storage tank, can you tell the difference whether the storage tank is pressurized by a turbo pump, a piston pump, a diaphragm pump, or a centrifugal pump?
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On Monday, May 29, 2017 at 5:08:50 PM UTC-4, Dcbfdd?? ? ??????? ? ?? ??????? ??tZsGT V wrote:

?????? ? ? ?????? ??lB YWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

s
t of

rong?

will be

y be

he

duce 10

dd any

flowing

pumps threw me. Since water isn't compressible, I don't see how the multi- stage pumps work. For gas, no problem, but I don't get it for liquids.

ge as

leads

ility

ure/volume relationship, though, isn't in agreement with Boyle's law. Gases approximate it. It's easy to imagine a multi-stage non-positive-displaceme nt compressor that keeps building pressure in a material that obeys Boyle's law. It's much harder to imagine it with liquids.

id.

ldn't hold pressure that way.

the kinetic aspects of a turbo pump (velocity) and the potential aspects (p ressure). A turbine pump that's pumping a liquid must be producing potentia l energy from kinetic energy.

way that an ordinary turbine pump can hold the pressure generated by a pre vious stage, unless the entire thing is kinetic, which we're then measuring as potential energy (pressure).

) > >>>>

e-d_309.html>

sure gauge on the output and the output blocked off so there is no flow?

c machine.

My response to Dan's question is exactly correct. Static pressure cannot "f eed the output" to anything. To "feed," it must be dynamic.
--
Ed Huntress

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snipped-for-privacy@gmail.com wrote on 5/29/2017 5:13 PM:

??????? ? ?? ??????? ??tZs GTV wrote:
e:

?????? ? ? ?????? ?? lBYWJ wrote:

? ?????? ? ? ??????? ?? ?DiDrO wrote:

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ge pumps threw me. Since water isn't compressible, I don't see how the mu lti-stage pumps work. For gas, no problem, but I don't get it for liquids .

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ssure/volume relationship, though, isn't in agreement with Boyle's law. G ases approximate it. It's easy to imagine a multi-stage non-positive-disp lacement compressor that keeps building pressure in a material that obeys Boyle's law. It's much harder to imagine it with liquids.

luid.

e.

ouldn't hold pressure that way.

t the kinetic aspects of a turbo pump (velocity) and the potential aspect s (pressure). A turbine pump that's pumping a liquid must be producing po tential energy from kinetic energy.

no way that an ordinary turbine pump can hold the pressure generated by a previous stage, unless the entire thing is kinetic, which we're then mea suring as potential energy (pressure).

si) >>>>>>

ure-d_309.html>

essure gauge on the output and the output blocked off so there is no flow ?

mic machine.

t "feed the output" to anything. To "feed," it must be dynamic.

Think, Ed. If a centrifugal pump is registering 50 psi at the gauge while the output valve is closed, what do you think the gauge at the storage tank will register after it has been pressurized by the centrifugal pump? It will be 50 psi, Ed. How is it different from any other pump, Ed?
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