While it is true that "heat transfer is directly proportional to temperature
difference" that does not tell the whole story. First, remember that the
relevant temperature difference is the difference between the temperature of
the fluid on the inside and the air on the outside, and even with pre-heated
air the second radiator could have the same delta T as the first radiator.
I'll grant you that there is probably a difference, however.
Also relevant, and non-trivial, are the area of the heat transfer surface,
the flow rate of the liquids inside the heat exchangers (radiators, in
common aircraft and automotive parlance), the flow rate of the air outside
these heat exchangers, the heat transfer coefficients for each of the fluids
involved, the heat transfer coefficients of the materials from which the
radiators are made, the effect of any scale or similar deposits on the heat
transfer surfaces (both inside and outside), Reynolds numbers for the
flowing fluids (a function of flow rates and fluid properties), and the
physical properties the radiators and of the coolant and oil flowing within
the heat exchangers.
Having said all of that, there is no doubt that "re-using" the cooling air
will affect heat transfer within the radiator using pre-heated air, and this
is undoubtedly why Europa recommend placing one below the other.
Best regards,
Rob Housman
Irvine, CA
Europa XS Tri-Gear
A070
Airframe complete
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Robert Borger
Sent: Saturday, June 05, 2010 11:02 AM
Subject: Re: Europa-List: Cooling issues, once again!
Paul,
I don't see how it can. Simple thermodynamics is against it. Heat transfer
is directly proportional to temperature difference. Both radiators are at
about the same temperature. Once the air has been heated by the first
radiator its ability to accept heat from the second has been greatly reduced
if not eliminated.
And this is assuming that the area below the radiators has been sealed so
that the air goes through the radiators and not under them, doing no good at
all.
Check six,
Bob Borger
http://www.europaowners.org/N914XL
Europa XS, Short Wing, Intercooled Rotax 914
rlborger@mac.com
Cel: 817-992-1117
On Jun 5, 2010, at 11:43 AM, Paul McAllister wrote:
Hi All,
I am curious to know if there are any examples of standard XS cooling set
up's that do not have the oil radiator lowered that work fine.
Thanks, Paul
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