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On Monday, May 29, 2017 at 2:13:31 PM UTC-4, Jim Wilkins wrote:
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On Monday, May 29, 2017 at 1:47:17 PM UTC-4, Jim Wilkins wrote:
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On Monday, May 29, 2017 at 8:13:36 AM UTC-4,
wrote:
On Sunday, May 28, 2017 at 4:04:30 PM UTC-4,
wrote:
On Sunday, May 28, 2017 at 11:35:39 AM UTC-4,
wrote:
You are over thinking the situation. A multistage pump has a
bunch of identical sections all turning at the same speed.
Each
stage increases the pressure. So you might have a 6 stage
pump
with each stage increasing the pressure by 10 psi. Which
makes
for a fairly efficient pump which will supply water at 60
psi.
Google it.
From Wik
Multistage centrifugal pumps
Multistage centrifugal pump[5]
A centrifugal pump containing two or more impellers is called a
multistage centrifugal pump. The impellers may be mounted on
the
same shaft or on different shafts. At each stage, the fluid is
directed to the center before making its way to the discharge
on
the
outer diameter.
For higher pressures at the outlet, impellers can be connected
in
series. For higher flow output, impellers can be connected
parallel.
A common application of the multistage centrifugal pump is the
boiler feedwater pump. For example, a 350 MW unit would require
two
feedpumps in parallel. Each feedpump is a multistage
centrifugal
pump producing 150 l/s at 21 MPa.
All energy transferred to the fluid is derived from the
mechanical
energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in
addition
to the pressure increase).
Dan
Thanks, Dan. I read that -- and maybe 100 more pages over the
past
few
days. None of them really explain it. To say that the energy is
derived from the impeller is axiomatic. It doesn't explain what's
going on inside the second stage.
Rather than try to go through it in detail, I'll post something
if I
find a good explanation.
--
Ed Huntress
======
http://www.engineeringtoolbox.com/ve...ead-d_916.html
Thanks, Jim. That was one of the things I looked at. The problem
with
applying the formula for velocity head is that it assumes the flow
is
constricted (in a pipe, for example), while the expanding volume of
a
compressor involute presents an entirely different situation.
I'll bet I've read 100 pages over the past three days. g No joy
yet.
--
Ed Huntress
If the flow is unrestricted and just gushes out then it isn't
pressurized. If you want pressure you need to restrict the flow.
https://blog.craneengineering.net/ho...gal-pump-curve
"As pressure increases, the flow decreases moving your performance
point to the left of the curve. As pressure decreases, the
performance
point runs out to the right of the curve and flow increases."
-jsw
Right. So what is the condition inside of one involute in the second
stage? Is it completely full when it's operating?
--
Ed Huntress
Why does that matter? The pump will force out all the air it can and
compress any that's trapped. If you want to build up pressure you have
to restrict the outlet, according to the discharge curve. The
Grundfoss manual showed that two identical stages will add their
pressures. Are you being distracted by imagining an improper mismatch?
-jsw