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

The car has a quad rotor, the first to be built in NZ, it was built here in Tauranga by the same guys that put my single rotor together.
It uses a Davis Craig 115 lts/ min pump these are made in Australia. daviescraig.com.au Check them out.
I do not know for certain what the fuse is rated at, but I imagine it will be no more than 10 Amps. 120 Watts or there about.
That is a hell of a lot less than 3Hp 745x3=2235 Watts.
No one that is interested in efficiency would use such a crude design with an open impellor on clean water.
Again the reason for the automotive industry doing so is to allow the water to bypass impellor at high RPM thus saving them the cost of a nearly constant speed impellor, and the cost of a more efficient design that with their set up would be of a detriment.
Andrew Campbell.

Sounds like drag racing. I am sure they do not run any NASCAR races
in Tauranga :-) No cooling system is needed with drag racing.

It takes HP to pump the water through the block at a high rate to
be an effective cooling in aircraft engine.

The news letter will be delayed for the next few days as I have
to take care of some high priority stuff.

Paul Lamar



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