I think it is time to take a look at the
automotive water pump.
There are 2 major types of pumps,
centrifugal and positive
displacement, we are interested in the
centrifugal group.
Within that group there are 2 types of
designs; open impellor and closed
impellor. Open impellor are used in almost
all automotive water pumps.
The open impellor type are used for their
low cost of manufacture and
their relative ease of cleaning, should they
become blocked.
The closed style is however far more
efficient but is substantially far
higher in cost to produce, and far harder
to clean if they become
blocked. Blockage in our situation is not
a factor. Open style impellor
pumps are never used on flammable or
explosive materials as the
clearance between the impellor and the
volute can be reduced to zero by
thermal expansion. Automotive pumps run
with very high clearances to
avoid the same problem, this makes them
low efficiency.
We must now consider the application they
are being used on.
In Industry the pump is designed around a
set of parameters that suit
the customers requirements, and in
general used at a constant speed.
In the case of the automobile and other
internal combustion engines this
speed can vary considerably.
The automotive pump must be able to
deliver sufficient flow at low rpm
and or low speed and high engine load to
cool adequately.
If you double the speed of this pump
you require the cube in energy,
i.e. 2x2x2=8.
Consider an engine running at 2000 rpm at
idle and then at 6000rpm or
higher as we do at cruise, the auto
environment never for domestic use
run at so high rpm for any length of
time.
You have increased the speed by a factor
of 3, so now you require the
cube of 3, 3x3x3=27.
I have no argument with Pauls formulae
for Volts x Amps = watts, and the
conversion between HP to Watts, what is
in dispute is that you have
increased the rpm by a factor of 3 but
have not increased the flow by
anywhere near that factor, but are
consuming 27 times the power. You
could only possibly hope to increase the
flow rate by a factor of 3 by
using variable geometry impellors and
volute. This aint going to happen.
In any case to increase the flow by this
amount and be able to exchange
3 times the heat is also not going to
happen with a heat exchanger
designed to suit the output of the pump
So where does this leave us.
It leaves us with a pump that is highly
inefficient and a vast waste of
energy, but is acceptable to the auto
manufactures, and where do you
think all that energy goes? Some is lost
in slippage within the pump due
to high clearances, the higher pressure
is able to pass easily to the
low pressure side thus reducing pumping
efficiency, but the rest goes
into heating the cooling water!!!
Some European car manufactures have
woken up to this and are using
electric pumps, also many of the rotary
racing boys here and probably
elsewhere are using electric pumps.
They consume a fraction of the power of a
mechanical pump, but are
highly efficient.
I will be running an electric pump made
by Davis Craig of Australia,
check them out.
I also Know of a tri rotor here in
Tauranga that is a race car that has
run an electric pump for some years.
Andrew. Campbell
What kind of race car? What brand of
electric pump? What size is the
fuse?
Paul Lamar
Hi!: thanks for the good info.
I'd always consider having hot water
going out of block from the upper
part, then entering, as usual, radiator
in its upper part, and the
return piping from lower radiator part,
entering the low part of block
or housing, in order that, provided the
case in pumping failures, no
wall in pipes exist, some Thermal-siphon
effect always exists, making
liquid circulate.
is this a reasonable concern, or too
childish, already implemented from
very early times?
Regards, Salut †
Jose Gros-Aymerich
Madrid, Spain
The liquid cooled aircraft engines of WW
II have pump impellers that
look just like
the pump impellers available today.
Therefor the same pump HP needed per
prop HP
out is the same. The Mazda impellers have
proven to be effective in
aircraft use. Use a smaller impeller or
less pump HP at your own peril.
If you want to try an electric pump use
a small starter motor.
They will develop 3 HP at 200 amps out
of the battery.
You will need two alternators :-) I know of
no car alternators that will put
out 200 amps. There may be one out there
but check the weight :-)
Paul Lamar
A starter motor is not designed for
continuous duty, and will likely burn up in about 10
min of use.
Craig. Smith
I agree. I know that:-) Just an illustration.
Maybe it could be water cooled :-)
Paul Lamar
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