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
You May well be using at least 3 Hp to drive the pump and possibly much
more. But that energy is not being used to cool the engine,
The piston engine aircraft runs at a considerably lower RPM than a rotary,
so the centrifugal pump is not being overdriven by the same extent.
If the automotive pump could be run on a variable speed drive your power
consumption would reduce dramatically, but not the cooling ability. At high
RPM these pumps are acting as a water break similar but way cruder than the
water breaks we used to use for engine testing.
Andrew Campbell.
So far I have not seen a picture of Davis Craig impeller.
The Mazda 2nd gen RX7 impeller is about as good as they get.
That preclude a better impeller. The Mazda engineers are no dummy's
when it comes to designing anything. The last time I looked at a electric
water pump the impeller was nowhere near as good as the 2nd gen
The RPM of the pump has nothing to do with it, Less RPM more torque.
HP = RPM * Torque / 52 52
That is the bottom line.
The HP of the pump must be there.
1 HP = 746 watts
3 HP 2238 watts.
Watts = Voltage * Current
If it is coming from the battery
the current must be there. Since the battery is only 12 volts the current
must be 200 AMPS!!!
Please tell me what fuse he is using :-)
It takes a lot of HP to pump water through the engine at high velocity
sufficient
to cool it under worse case conditions. Climbing the Grape Vine in
SoCal in a car
when the temperature is 100 degrees F at high speed is a worst case
condition.
You see at least one car pulled over to the side
with cooling problems. Taking off on a hot day and then running the
aircraft engine
70 to 80 % continuous is another problem. Usually the system would fail
during
taxing.
We have been over and over about all this years and
years ago. By writing the book I fixed the problem forever :-)
.
Pumping water from one container to another is super easy.
Paul Lamar
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