----- Original Message -----
Sent: Friday, October 10, 2003 2:30
AM
Subject: [FlyRotary] solo's & Delta
T... no more emergencies
Hey
Guy's;
Well today we had very high winds (30Kts) so we sat on the ground most
of the day watching SNIP
What I
found was somewhat surprising. I found that the coolant rads (2 Ford evap
cores plumbed in parallel) had a delta T of 20C, while the Oil cooler only had
a delta T of 5C.
SNIP
The oil cooler is a little disappointing to have only a Delta T of 5C
or 9F. I'd expected much higher. Ed were you planning on measuring deltaT
through the oil as well or just the coolant? I'd like to know what others are
getting. I hope to get out again tomorrow afternoon and if the weather is
better with higher ceilings, I'll do a longer climb followed by a longer run
at cruise speed to allow temps to stabilize a little better. Tonight's
circuits were admittedly not the ideal run for gathering data, but I thought
some may be interested in my results. I'll try to gather more data in the days
to come.
The EWP continues to function perfectly.
S. Todd Bartrim
Turbo 13B
RV-9Endurance
C-FSTB
Thanks for the data, Todd.
I use a delta T of 20F for coolant drop
across the GM cores as an estimate for my cooling calculations. I had not
thought about the oil cooler, but it would be fairly simple matter to just
switch a couple of the thermocouples. I'll put that on my list of "to
dos"
I wouldn't worry too much about
the oil delta T only being 9F so long as your oil out of your cooler
stays below 210F (180F being ideal). I suspect that the flow rate
through the oil cooler is higher (Lynn do you have figures on the GPM
for the oil pump - or anybody?) - which would mean more heat
removed from the engine even with the smaller delta T.
Q = M*(Tout-Tin)*Cp, the heat transfer equation indicates
that the heat removed (Q) is dependent on mass flow (M) and Delta
T(Tout-Tin). Specific heat (CP) is fixed for the cooling
medium. (One implicit assumption is that the mass flow
(air/water/oil) is carrying away as much heat as it theoretically can - not
always the case in the real world as things like boundary layers, laminar
flow, etc can reduce the theoretical transfer of heat to the
medium)
In any case, Q will remain the same so long
as the product of M*(Tout-Tin) remains the same. So if M is less
- then the Delta T would need to be higher (better transfer of heat to
the medium), if M is more then the Delta T can be less for the same amount of
Q removed. So while you can get a greater Delta T by slowing the coolant flow
through the radiator, that means you have decreased M - which means less heat
removal (Q) from the engine. For a given Delta T, the equation shows you
always remove more heat with increase mass flow (M) (all else being
equal).
So the 36F is certainly greater
than the 20F. Now, the question is whether that 36F means the system is
cooling better? I would say based on the flow rates you got when
experimenting the answer is definitely - yes. However, as just stated,
just because you get a greater Delta T in coolant temp across the radiators
does not Necessarily mean you have better cooling.
While it is always possible to show a greater Delta T by slowing the
flow of coolant through a radiator (exposing it to the cooling air longer),
the crucial cooling performance factor is how much heat (Q) is
being removed from the engine. If the flow (M) is too low, clearly
you impede heat removal from the engine no matter what the Delta T is across
the radiators.
It would appear there is an optimum flow rate
factor. If its too slow the delta T across the radiators looks great -
but, the slower cooling flow does not remove as much heat from the
engine. It appears that more flow always results in more heat removed
from the engine - however, above certain flow rates, you start to encounter a
lot of losses due to turbulence, friction, etc. and more power is
required to pump the coolant.
Since it appears that the flow rates are comparable
(I can't recall for certain, but, I think you found the Ford cores even flowed
a bit better than the GM cores) between the two type cores and if the 36F
represents the delta T for the Ford Vs 20F for the GM cores for the same flow
rate, then you are clearly getting more heat rejection.
So, I would say that if your coolant temp coming
out of the engine stays at or near the 180F or less mark, then you are
getting close to optimum cooling. If the coolant temp varies significant
from that then you may need to check things closer.
Its great to get this type of data. It could
mean me swapping out my old GM cores for Ford Cores (it would make my Ford
Areostar and Windstar happier {:>))
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews,
NC
eanderson@carolina.rr.com