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Article #144Re: nasa-celebrates-successful-mars-landing
From: Phil Hobbs
Date: Tue, 07 Aug 2012 23:57
Date: Tue, 07 Aug 2012 23:57
54 lines
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3910 bytes
Adrian Jansen 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. > Thermal conduction is independent of pressure until the mean free path becomes comparable to the dimension of the object, or to the gap between objects. A 5-torr atmosphere is as good as a 760 torr one for conductive cooling. Convection is more complicated--as pressure increases, you win by having more air mass per unit volume, but you lose by the diffusion length getting shorter--you can't heat as much volume in a given time. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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Date: Tue, 07 Aug 2012 19:57:40 -0400
From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
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Subject: Re: nasa-celebrates-successful-mars-landing
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