Here is a plot of temperature data, all taken with CHT
thermocouples.
Rad_in is clamped to the water pipe just before it splits to
go to the two radiators
Rad_out is clamped to the exit water pipe after the flow
from the two rads has been recombined.
Oil_filter is clamped to the oil line as it exits the filter
and enters the engine, and
Oil Cool left end is bonded to the end away from the
entrance/exit on the oil cooler to tests that the oil cooler is working. As you
know the standard Mazda oil cooler sends the oil down to the end and
back. I was getting high oil temperatures on one of my (non thermocouple
) oil sensors, and wanted to verify that the oil cooler was working.
Bill Schertz
KIS Cruiser #4045
N343BS
Phase I testing
Sent: Friday,
May 14, 2010 5:32 PM
Subject:
[FlyRotary] Re: alternative water pump
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