Hi
Bill,
Had seen your nice data
before, but one thing finally awoke in my old brain when I looked at it this
time that I had not considered before. We know that parallel cores give
slightly better efficiency than a serial core set because the
DT decreases for the
second core in the series compared to both parallel cores having the same
DT (at least in
theory). However, what jumped out at me this time was the real
significance of the parallel cores in cooling. In this case, I am assuming
no thermostat in the coolant flow.
If I understood your
graphs correctly, it looks like you are getting around 20 gpm flow with a single
core (so presumably you would get a bit less with two cores in series – but
perhaps not significantly), but looks like with parallel cores you are getting
around 32 gpm flow. That is a 20/32 = approx 37 % more mass
coolant flow through the engine. That means (all else being equal),
you should transfer 37% more heat out of the engine per unit time with the
parallel cores compared to the serial cores (assuming cores of same type and
size).
Now the engine is
producing X amount of waste heat at Y HP that it needs to get rid of. That
won’t change for a given power setting Y. So Q (waste heat X) produced by
the engine should be a constant at Y Hp.
So taking Q =
M*Dt/Cp and since Q (waste
heat) = constant at power setting Y, then with M (mass flow up 37%)
implies that in this case Dt = (Temp of coolant
out of engine – temp of coolant into engine) should decrease by 37%.
When you increase the mass flow and are removing the same quantity of heat, the
DT is of necessity a
lower value.
If that is the case,
then the question is - does this mean the temp of coolant into the engine increases – not necessarily desirable, or
does the Temp of coolant out of
the engine decrease? Or a bit of
both? I suspect it’s a bit of both depending on the radiator’s
performance. If your radiators/air flow are the limiting factors, then
transferring more heat per unit time to the radiators is not going to buy you
much. The reason is that if it is not able to get rid of the heat at the
faster rate and the DT between the coolant and air will be less.
But, my guess is that
this theoretical increase in heat removal by using parallel cores could be
useful in some situations – again if you are already limited in the airflow
situation, then this won’t make much difference. It does suggest
that using parallel cores could result in the need for core sizes 37%
smaller. OR did I miss something here?
Like your data in
any case
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Schertz
Sent: Thursday, May 13, 2010 10:39
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: alternative water
pump
Back in 2002 I measured the flow
from a 13-B pump, attached to the engine but driven with an electric motor. The
curve is attached. I ran the pump at 3 different RPM, established by changing
the pulley size on the motor. At 5594 rpm, the pump produced 19 psi at zero
flow, and 44 gpm at 0 psi. At lower RPM, the pump of course pumps
less.
The other test I did was to measure
the flow through one core of the two I was using for my installation. That is
the curve going up to the right with the red dots as the experimental points.
Since I am running my cores in parallel, the right hand rising curve is a
'calculated' flow response for the parallel
cores.
Finally, I hooked up the cores to
the system, and pumped water through them. The single large point represents
where the flow and pressure came out, very close to the calculated expected
response.
All flow measurements were done by
the "bucket and stop-watch" technique, with multiple runs to get the
flow.
Bill Schertz
KIS Cruiser
#4045
N343BS
Phase I testing
Sent:
Wednesday, May 12, 2010 11:54 AM
Subject:
[FlyRotary] Re: alternative water
pump
Al,
Are
you sure of the 40 GPM? That seems like a lot. My radiator in/out is
1.25 inches, so the water would be traveling at 628 feet per minute at that flow
rate. That is over 7 miles per hour!
Bill
B
When my 20B (with a
13B pump that Atkins referred to as ‘high flow’) was on the dyno the measured
flow was 48 gpm with the standard pulleys. I expect the dyno cooling loop
was fairly low pressure drop compared to our typical systems, so I’m just
guessing 40 gpm is in the ballpark. 628 fpm (10.5 ft/sec) would not be
considered very high - - above 15 ft/sec I’d consider
high.
Al