altitude vs. temperature
altitude vs. temperature
(OP)
I am modeling an electronic heat sink specified to 10,000 ft. How should I change the pressure to handle this? Will lowering the environmental pressure correct the elevation change?
-R
-R





RE: altitude vs. temperature
However are you considering the effect of temperature changes?
RE: altitude vs. temperature
RE: altitude vs. temperature
TTFN
RE: altitude vs. temperature
RE: altitude vs. temperature
TTFN
RE: altitude vs. temperature
RE: altitude vs. temperature
You'll probably need to enter the correct air density. This can be calculated from temperature and altitude. If you don't have the formulas, you can try this little calculator: http://www.denysschen.com/catalogue/density.asp
ko (www.ecooling.biz)
RE: altitude vs. temperature
Thanks,
Rodney
RE: altitude vs. temperature
RE: altitude vs. temperature
The relationships between temperature, pressure and altitude that are used in air pollution dispersion modeling are presented in the book "Fundamentals of Stack Gas Dispersion", Fourth Edition, 2005 available at www.air-dispersion.com, and the following is a direct quote from that book:
Atmospheric pressure decreases with increasing altitude, and any air rising from the warm surface of the earth will expand as it rises to lower atmospheric pressure levels. Taking the atmospheric pressure at sea level to be 14.696 psia, we can obtain the atmospheric pressure at any altitude from this approximation:
(1) Pa = 14.696 (0.963)a
We can obtain the temperature which will be acquired by dry air rising from sea level to any given altitude from this expression which assumes that the rising air expands adiabatically:
(2) Ta =Ts (Pa/14.696)(k-1)/k
where:
a = altitude in 1000's of feet
Pa = atmospheric pressure at altitude a, in psia
Ta = air temperature at altitude a, in degrees R
Ts = sea level ambient temperature, in degrees R
k = 1.4 for air
Using the above relationships, one finds that from sea level to 8000 feet, the atmospheric pressure decreases 0.5 psi per 1000 feet ... and the temperature of dry air will decrease 5.5 degrees F per 1000 feet.
Milton Beychok
RE: altitude vs. temperature
You need a psychrometric chart to find the relation between humidity and density. In most environments (5-95% humidity, 15-50C) humidity has a negligble effect on heat sink performance.
A tutorial on psychrometric charts: https://www.uwsp.edu/it/tlrn/LOs2003/paperlo/
ko (www.ecooling.biz)
RE: altitude vs. temperature
ht
RE: altitude vs. temperature
R
RE: altitude vs. temperature
RE: altitude vs. temperature
His worst-case scenario might be a heat sink at the top of an electronic cabinet on a hot day with an A/C failure in a crowded computer room in La Paz, Bolivia...
ko (www.ecooling.biz)
RE: altitude vs. temperature
RE: altitude vs. temperature
ko (www.ecooling.biz)
RE: altitude vs. temperature
Here is a good article on heatsink selection. Check out the box at the bottom of the page it has derating values for heatsinks at altitude.
http: