Jim Sower wrote:

I need a little help here.  I may have got lost back a ways.  Tell me if

this is

true:
1.  Cavitation happens when the pump can't "suck" (read "accelerate") the

coolant

into the impeller with the flow rate (velocity) that is required by output

flow

rate.

2.  The event under discussion took place with the coolant being drawn

>from and

returned to an open tank with coolant level at some distance below the

impeller.

If these things are so, it occurs to me that in a closed system, the coolant
supply to the pump would not be stagnant as in the experiment, but moving

at the

same flow rate as the output side of the pump, and under steady state

conditions

(no acceleration of the coolant supply) no cavitation would or could occur.

I intuit that the coolant supply to the pump being a stagnant pool rather

than a

flowing, closed stream rendered the experiment bogus at the rpm where the

onset of

cavitation occurred.

Where did I go wrong?           Jim S.
PS finally got my date/time straightened out ;-)

Jeff Spitzer wrote:

Your intuition is correct but the magnitudes may be wrong.  Sucking from a
stagnant source will cause the pressure to be lower at the inlet due to
accelerating the fluid.  If the inlet line is of reasonable size this
should be less than 1 psi though.  You are likely to get more pressure drop
from the fittings to close the loop than from the re-acceleration of the
flow from stagnant.

Jeff Spitzer

 
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