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botrous
16-01-2005, 11:38 PM
Guys think about this . . .
You are invited to design a compression air conditioning system for a space ship , the indoor unit is without problem , the outdoor unit (condenser) is in the space (considered as vaccum), how would it act with no fluid to transfer the heat from the condenser ????
I am asking this to myself , semiconductors cooling has 4% efficiency , so if a space ship or city is built immagine what a huge surface of semiconductors it should have only to give good climate for people , huge surfaces of semiconductors ==> huge surface of the ship or city ==> less population density.
If we consider absorption , the same problem occurs , where to reject the heat of the condenser . . .
Is compression and absorption fittibal for space applications ???

Brian_UK
17-01-2005, 12:14 AM
The condenser would operate under the laws of :-
Radiation

Radiation (http://en.wikipedia.org/wiki/Radiation) is a means of heat transfer. Radiative heat transfer is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.

For room temperature objects (~300 K), the majority of photons emitted (and involved in radiative heat transfer) are in the infrared spectrum, but this is by no means the only frequency range involved in radiation. The frequencies emitted are partially related to black-body radiation. Hotter objects—a campfire is around 700 K, for instance—transfer heat in the visible spectrum or beyond. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting and RF hair removal.

< stolen from en.wikipedia.org ><STOLEN from en.wikipedia.org>

botrous
17-01-2005, 12:58 AM
Remember , the surface of the condenser is somehow critical in the design , using the 3 methods of heat transfer here (on the earth) and still sometimes the condenser will not work 100% properly what if you are using only the radiation , and let me say that the refrigerant tempreture isn't that hight to make the condenser emitts considerable ammount of energie by radiation (radiation ammout of a body raises with it's tempreture) but still your idea is somehow reasonnable

Argus
17-01-2005, 10:37 AM
My understanding is that NASA used a form of heat pipe array to address this issue in the 1960s
________
Yamaha PSR-3000 history (http://www.yamaha-tech.com/wiki/Yamaha_PSR-3000)

Peter_1
17-01-2005, 12:23 PM
Well, outside temperature is low enough to condens or just make an air/air HX but I think Botrous asked a pure hypothetical question.
Another perhaps stupid question then: if you have a vacuum, suppose almost absolute, then what temperature can that vacuum achieve? There are no molecules anymore, so....?

Superheatman
17-01-2005, 08:30 PM
Hi Peter...I did some work on chillers a few years ago at the joint european torus at Culham (experimental fusion reactor)...the heated substance...a circular plasma about 2 or three mm across was suspended by elecromagnets inside the centre of the torus and pulsed by a huge floor mounted generator...using twelve inch bus bars which used to whine with the amount of energy flowing in them....the torus in which the plasma was suspended was pulled to a very low vacuum by long banks of vacuum pumps to prevent heat transfer to the walls of the torus.....they were using Trane centrifugals using 3Kv motors with a 12 volt control and also a few mark 2 hallscrews....there were 40 foot high very thick concrete doors that dropped down before actuation as the temperatures reached were in millions of degrees and carried the subsequent dangers if any problems occured with the magnetic field or the vacuum whilst undergoing an experimental run.

Superheatman
17-01-2005, 08:56 PM
I guess I would have to ask someone or something that would know....maybe schrodingers cat :-))

chemi-cool
17-01-2005, 09:06 PM
How about a Vortex tube?

Chemi :)

chemi-cool
17-01-2005, 09:26 PM
When I think about seriously, its cooling they need in space,
Space crafts are always painted dark so it absorbs heat.

Any heat exchanger on the outside with inside air getting cool outside.
Its an air/vacuum heat exchanger :D

ChemI :)

Superheatman
17-01-2005, 09:40 PM
I have "The elegant universe" on two dvd's....I managed the first dvd but have never managed to complete watching the second...when they start trying to explain ten dimensions my brain liquifies and only returns to normal state (bone) after a rest....ah me....old and senile does it for me :-)

rbartlett
17-01-2005, 09:47 PM
nice to see you around mark

i thought you were coming to see us??

cheers

richard

botrous
17-01-2005, 09:47 PM
Let me remember you , that the tempreture and the radiation in the space are huge if we compare it to those on earth , so the space tempreture is much higher than the tempreture in our atmospher ( if the elemntery space we are talking about is touched by sun radiations)cause the flux of radiation is much more than those that reaches the earth , With that i can assume that no heat transfer from the condenser via radiation could be made , as a matter of fact i think that the condenser will absorb heat from the sun . . .
As for ironic answers that i hear , it seems that someones aren't willing to scratch their brains ;) . . . it's a scientefic matter guys

rbartlett
17-01-2005, 09:55 PM
my ex father was involved with the hubble space thingy and was part of the european space agency

he once gave me a chat on how the space probes etc were cooled..

buggered if i remember..

http://www.oup.co.uk/isbn/0-19-850792-5?view=rights
http://books.guardian.co.uk/aventisprize2004/

cheers

richard

botrous
17-01-2005, 10:15 PM
Well , your idea seems reasonnable to me Marc , we can take an example the moon , a side with high tempreture and the other side with ultra low tempreture , so if the space ship have 2 black bodies , the one and the sun side must be covered with reflective material , (if we consider that the second one isn't by any mean influenced by sun radiations or other thermal radiations) theoricly the heat will flows out of the ship to the outside using the heat transfer low (energy flows from hight temp side to low temp side ) but how big should the space ship be to have differents temps on both of it's sides ???

botrous
17-01-2005, 10:38 PM
Sorry , Marc i didn't understand what you mean :(

botrous
17-01-2005, 10:56 PM
hehe , what i was saying is that your theory about the black bodies is in doupt because no considerable climate change will occure in a space ship , if one side is exposed to the sun and the other side isn't

botrous
17-01-2005, 11:47 PM
Haleluya YES YES someone understood my question

Brian_UK
17-01-2005, 11:51 PM
If I remember rightly, it does happen - honest, don't they have a heating problem in space more than a cooling one. The ship is covered with reflective material to prevent over heating when receiving sunlight, which is only on on one side of the vessel; the other side of course is loosing heat.

As to how big must the ship be for a temperature difference between to two black balls..... it needs to be large enough to cause one ball to be in shade, or the balls must be in perfect alignment with the sun, i.e. one balls shadow covers the other ball.

botrous
18-01-2005, 12:03 AM
We can't be certain that the second side is loosing heat . . . unless we assume that the sun is the only emmitter of thermal radiations . . . I read a long time ago about a technology to cool sensors in military satellites , i'll dig for that article to see what i can find and refresh my memory

Brian_UK
18-01-2005, 12:14 AM
. unless we assume that the sun is the only emmitter of thermal radiations .I think that we have to assume that that is correct, or rather that it is the largest, unless we go outside of our solar system. Personally I think that is taking the discussion too far ;)

botrous
18-01-2005, 01:51 AM
You are right Brian , that takes the discussion too far , but what about reflector of solar thermal radiation , the moon for example , should we neglect the moon to ??

Tejbir Singh
19-01-2005, 06:29 PM
Guys think about this . . .
You are invited to design a compression air conditioning system for a space ship , the indoor unit is without problem , the outdoor unit (condenser) is in the space (considered as vaccum), how would it act with no fluid to transfer the heat from the condenser ????
I am asking this to myself , semiconductors cooling has 4% efficiency , so if a space ship or city is built immagine what a huge surface of semiconductors it should have only to give good climate for people , huge surfaces of semiconductors ==> huge surface of the ship or city ==> less population density.
If we consider absorption , the same problem occurs , where to reject the heat of the condenser . . .
Is compression and absorption fittibal for space applications ???

Have a Look at This
http://science.nasa.gov/headlines/y2001/ast21mar_1.htm

Tejbir

botrous
19-01-2005, 11:45 PM
Tejbir , thanks for the link , it's very useful and contains good information about space ship thermal balance designs , i recommend it to be read .

Alt Concepts
25-02-2005, 07:17 PM
Your question triggered my own interest in future tech. for space and here at ground 0. Ive read, but not sure how advanced it has become that, sound wave frequencies will someday replace conventional refrigeration altogether. NASA I believe currently utilizes it but on a much smaller scale. Anyone know of this?