[DeTomaso] Any rocket scientists out there

[Michael Shortt]

Yes, one will run cooler,
I am no rocket scientist ( but I did build several model rockets and I
stayed in a Holiday Inn Express last night )

here's what I found that should be applicable to radiators which are heat
sink type devices as well.


Michael in Savannah


Since the density of air varies with altitude, so does the efficiency of a
heat sink. I wonder how many consumer equipment makers take this into
consideration?  As can be seen from the table below, the effects are not
insignificant.
    *Altitude (Metres)* *Altitude (Feet)* *Derating Factor* 0 (sea level) 0
1.00 1,000 3,000 0.95 1,500 5,000 0.90 2,000 7,000 0.86 3,000 10,000 0.80
3,500 12,000 0.75 *Altitude Derating Factors*

The altitude effect should be considered in all cases, since many electronic
systems are installed at an elevated altitude, it is necessary to derate the
heat sink performance mainly due to the lower air density caused by the
lower air pressure at higher altitude. The table shows the performance
derating factors for typical heat sinks at high altitudes. For example, in
order to determine the actual thermal performance of a heat sink at
altitudes other than sea level, the thermal resistance values read off from
the performance graphs should be divided by the derating factor before the
values are compared with the required thermal resistance.

Example:  A 1° C/W heatsink would become 1.16° C/W at an altitude of 2,000
metres, or 1.25° C/W at 3,000 metres.



On 6/14/07, Lynn Wall <lwall at wt-inc.com> wrote:
>
> All,
>
>
>
> This may be a stupid question and probably covered in the past but I have
> not read anything related and those I have asked are not sure either so
> here
> goes:
>
>
>
> Two virtually identical cars (or the same car if it helps), one at sea
> level
> and one at 6,000' elevation.  80 degree day in both locations, exact same
> driving, exact same humidity, timing, tuning, etc.  Will one car run
> cooler
> than the other?
>
>
>
> Basically I'm trying to find out what effect elevation and therefore
> thinner
> air has on the cooling (if any) of a car.  It strikes me that if there is
> less air going through the radiator due to the thinner air then you would
> have less cooling.  Am I wrong or crazy?
>
>
>
> Just curious,
>
>
>
> Lynn, maybe the thinner air is getting to me
>
>
>
>
>
> Lynn R. Wall, President
> Western TelCom Inc.
> Phone 801-288-2001
> Fax 801-288-2002
>
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-- 
Michael L. Shortt
Savannah, Georgia


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