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Sorry, looking back on my centrifugal pump curves, the head (pressure)
usually doesn't drop ....... so you can restrict too far ....... it's
the efficiency that peaks and then drops as backpressure is increased,
so you want to make sure you don't restrict flow through the cooling
tubes any more than the max efficiency point of the pump (a specific
gpm/head relationship for a specific hp); any more restriction and the
pump begins to start beating btu into the water, until, at shutoff, you
have lots of pressure, no flow, and lots of beating of the water.
phil stitzer wrote:
Higher flow rates increase turbulence in the water tubes (many tubes
are scored or raised inside to increase mixing of water during flow)
which means more mixing and more water that 'sees' the tube surface, so
more opportunity for heat conductance ..... all at the cost of
increased pressure required. This should work until the centrifugal
pump begins to stall (pressure increases causing flow to decrease to
the point that pump head pressure begins to fall, at which point the
pump begins to add heat to the system. All radiators have 'ideal'
flow rates for resultant 'ideal' pressure drops for best heat
rejection.
Summary: Turbulent flow in radiators provides much more heat rejection
potential than laminar flow, whether it's the water inside the tubes or
the air going around the tubes. And the key on both sides is to allow
for a good low pressure area on the downstream side so all the pressure
drop is located where you want it in the radiator.
Phil Stitzer
ex plumber
Lehanover@aol.com wrote:
Mark, if you really had excess air flowing through your
radiators the coolant would drop more than 4 Deg F. In fact, the more
air flow the more coolant Delta T you would drop through the radiator.
<snip>
That's exactly what I HAD thought, until I was told that the
air could pass through too fast and not pick up as much heat. This
didn't make sense to me. Maybe I wasn't listening closely and missed
the point altogether (wouldn't be the first time).
This is one of the oldest
myths around - that air or coolant will flow too fast to pick up the
heat. It just IS NOT factual. The more mass flow you have, the more
heat you will carry away. It appears that some early experimenters
noted that if you slowed the flow of coolant through a radiator that
there was a greater temperature drop of the fluid than if it flowed
through faster. better myth. I once had an debate
Ed, Could you comment on this?:
On race cars I modify the radiators to be double or triple
pass.
By inserting baffles in the tanks, to force the coolant through a fewer
number of tubes, and therefore at a higher velocity. The effect is that
the radiator has 1/3 or 1/2 the tube count but the tubes are twice or
three times as long and have exactly the same area exposed the airflow.
It has never failed to work for me.
My thinking is that the flow rate remains very energetic and
is
scrubbing the inside of the tubes with gusto, dumping more heat than a
slower flowing coolant.
What do you think?
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