Sent: Tuesday, December 09, 2003 11:54
AM
Subject: [FlyRotary] Re: Air Density at
altitude
Ed another factor which will help in this
situation is the fact that the air at 25K will be alot colder than at S.L.
That will help as well won't it? I've read somewhere that liquid cooled
a/c cool better at altitude than their aircooled counterparts. Anyone else
heard this?
Jarrett Johnson
Interesting point. It certainly has to help
as the colder incoming air will provide a larger Delta T between the
temperature of the incoming air and the walls/fins of the cooler core
(which would stay at approx the same temp - if using a thermostat). The
question is would is how much would it help and would it help enough to make
up for the lesser air mass flow? The mass flow at 20,000 ft is approx 30% less
than that at sea level for the same indicated air speed.
Heat transfer equation Q =W*DeltaT*Cp, with W =
mass flow down by 30%. So to get rid of the same Q of heat (and since Cp
doesn't change that much) it would appear that means the delta T term
would need to increase by 30% for Q quantity to remain the same. But, I
don't know exactly how a 79Deg colder incoming air would affect the Delta T
term.
BIll??
Ed Anderson