From: Paul Doherty (pauld@exploratorium.edu)
Date: Fri Feb 04 2005 - 09:27:52 PST
Message-Id: <l0311074dbe2960564369@[192.168.112.4]> Date: Fri, 4 Feb 2005 09:27:52 -0800 From: Paul Doherty <pauld@exploratorium.edu> Subject: Re: pinhole Cooling satelites in space?
One type of "heat pipe" works like this:
Inside is a small amount of liquid that evaporates at the hot end,
absorbing thermal energy and cooling the hot end, then the gas fills the
pipe where it condenses at the colder end releasing the thermal energy.
Convection of the gas carries a large quantity of heat from one end of the
pipe to the other.
Now on earth gravity is used to return the liquid to the hot end, I wonder
how the return works in freefall?
Paul D
>Some satellites use what they call "heat pipes" to
>move heat around the satellite. They were basically
>tubes that carry liquid (or a gas, I can't remember
>what goes through the pipes) through the panels.
>Having large temperature differences on different
>parts of a spacecraft is troublesome because of how
>materials expand and contract. A reflective foil with
>several layers is sewn together and covers the outer
>surfaces. The outer layer often contains a thin layer
>of gold (Gold is quite good at reflecting). They also
>use thin layers of insulating material between the
>foil layers so the outer layer does not conduct heat
>inward as it is warmed by the sun. I used to work on
>those things but I haven't thought about that stuff
>for a while.
>
>wayne
>
>--- Paul Doherty <pauld@exploratorium.edu> wrote:
>
>> Hi Mike
>>
>> A satellite with no internal heat sources and an
>> albedo equal to the earth
>> would reach an equilibrium temperature similar to
>> the earth at the earth's
>> distance from the sun. (about 0 ƒC) (The surface of
>>> the earth is warmer due
>> to the greenhouse effect.)
>>
>> Apollo 13 had a problem which removed internal heat
>> sources, the
>> temperature dropped in the spacecraft and the
>> astronauts got cold.
>>
>> The problem comes in when there are heat sources on
>> the spacecraft. They
>> must get rid of the generated heat or the
>> temperature of the spacecraft
>> will increase.
>>
>> Spacecraft use black radiators not in sunlight to
>> radiate excess heat.
>> The insides of the space shuttle hatch doors open in
>> space because they are
>> covered with radiators. If the doors don't open the
>> shuttle has to return
>> to earth or it will overheat.
>>
>> The spacecraft going to Mercury has a metal foil
>> shield on the sun side to
>> reflect sunlight.
>>
>> Paul D
>>
>>
>>
>> >Hello,
>> >
>> >I have a question about space satellite design. I
>> understand that despite the
>> >super low temperatures in space, satelites actually
>> have a problem with
>> >overheating because without air, they can't lose
>> heat by conduction or
>> >convection. They are stuck with radiative heat
>> loss as the only mechanism to
>> >cool off. Furthermore, with the intense radiation
>> above the atomosphere, they
>> >are subject to a lot of radiative warming and their
>> electronics generate heat
>> >too.
>> >
>> >I'd like to pose an engineering problem to my
>> students but figure I ought to
>> >understand the answer first. What kind of design
>> features do satelites use to
>> >thermoregulate properly? They are often covered in
>> some sort of foil. Is
>> >part
>> >of the idea here to reduce warming by radiative
>> absorbtion? I wonder, are the
>> >backs of the solar arrays black? This would
>> increase cooling by radiative
>> >emission on a part of the satelite that isn't
>> exposed to the sun but I wonder
>> >if they are actually designed this way.
>> >
>> >Cheers,
>> >Mike Geluardi
>> >
>> >
>> >
>> >
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