🚀 go-pugleaf

On Wed, 8 Aug 2012 05:16:57 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Aug 7, 7:57 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
>> On Wed, 08 Aug 2012 09:42:05 +1000, Adrian Jansen
>>
>>
>>
>>
>>
>> <adr...@qq.vv.net> wrote:
>> >On 8/8/2012 7:04 AM, Jon Kirwan wrote:
>>
>> >>>> Which reminds me of another thing. How do they convect the
>> >>>> internally generated heat away. I recall hearing about
>> >>>> multiple power systems, operating around 32V at near 2A. More
>> >>>> than one. This power must be convected/conducted away -- no
>> >>>> way they want to radiate it. I wonder if they push it
>> >>>> (costing more heat) towards a vane or arm and drag it around
>> >>>> on the surface to get rid of it?
>>
>> >>> The atmosphere won't help much.
>>
>> >>> Why not?  Thermal conductivity of air is pretty much constant till you
>> >>> get below 1 Torr or so.  Wiki says the mean pressure on mars is about
>> >>> 0.1 psi, which is ~5 torr.
>>
>> >> Good point.
>>
>> >In earth atmosphere, I understand most heat above around 300K ( 'room'
>> >temp ) is carried by radiation and convection.  Conduction is a minor part.
>>
>> >No idea what convection is like at 5 torr in a CO2 atmosphere, but I
>> >suspect its a lot lower.
>>
>> Then that begs the question, again. Perhaps George spoke too
>> soon.
>
>Sure, I'm always putting my foot in my mouth!
>(I must enjoy the taste of toe jam :^)

Nah. You nailed it, George. As I'd guessed earlier, it WAS
about mean free path. And I was the ignorant one. Not you. I
just needed an additional clue from Phil (characteristic
size) to put the pieces together again.

Makes me feel the fool.

But then, not for the first time or the last. Been there so
many times now.

>On Earth once the temp difference is above a few degrees I think
>convection is the biggest source of heat transfer.  But I have no idea
>of how that changes with pressure.  Maybe some day I can build a
>convectron pressure gauge.  The patent on that must be expired.

I got a chance in re-studying to see a beautiful 3D chart
with pressure on one side, temperature on another, and the
height being a constant of heat flow. Very interesting (non
trivial) shape to it.

Thanks so much for taking a moment to knock me on the head!

Jon