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246 points world2vec | 3 comments | | HN request time: 0.733s | source
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mlhpdx ◴[] No.44357730[source]
It’s very odd to think of something extremely hot but with almost no density, and therefore very little heat transfer.
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jordanb ◴[] No.44357945[source]
That's actually most of space. Space is a very hot environment, especially where we are so close to the sun. Think about it. When you stand outside in the sun you heat up. All that heat is coming from the sun. But a lot of it was filtered by the atmosphere, so if you're in space near earth it will be hotter than standing at the equator on a sunny day, in terms of radiation.

Then there's the fact that heat is very difficult to get rid of when in space. The ISS's radiators are much bigger than its solar panels. If you wanted to have a very-long eva spacesuit you'd have to have radiators much bigger than your body hanging off of it. Short evas are handled by starting the eva with cold liquids in the suit and letting them heat up.

All of the mockups of starships going to Mars mostly fail to represent where they're going to put the radiators to get rid of all the excess heat.

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im3w1l ◴[] No.44358464[source]
Okay this may sound silly but what about a solar powered ac for cooling? Like solar radiation is 6000K right, so if you used that to pump your waste heat into say a 1000K radiator (aimed away from the sun obviously) I'm thinking it might give you plenty of negentropy but also radiate away heat at a decent pace.
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thatguy0900 ◴[] No.44358531[source]
Acs don't get rid of heat, they just move it around. At some point you need to put the heat somewhere and then your just back to giant radiators
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eesmith ◴[] No.44358635[source]
https://en.wikipedia.org/wiki/Absorption_refrigerator

> An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. Solar energy, burning a fossil fuel, waste heat from factories, and district heating systems are examples of heat sources that can be used. An absorption refrigerator uses two coolants: the first coolant performs evaporative cooling and then is absorbed into the second coolant; heat is needed to reset the two coolants to their initial states.

https://www.scientificamerican.com/article/solar-refrigerati...

> Fishermen in the village of Maruata, which is located on the Mexican Pacific coast 18 degrees north of the equator, have no electricity. But for the past 16 years they have been able to store their fish on ice: Seven ice makers, powered by nothing but the scorching sun, churn out a half ton of ice every day.

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mrguyorama ◴[] No.44358864[source]
It literally doesn't matter what your refrigeration process is. You have to "reject" the heat energy at some point. In space, you can only do that with large radiators.

There is no physical process that turns energy into cold. All "cooling" processes are just a way of extracting heat from a closed space and rejecting it to a different space. You cannot destroy heat, only move it. That's fundamental to the universe. You cannot destroy energy, only transform it.

Neither link is a rebuttal of that. An absorption refrigerator still has to reject the pumped heat somewhere else. Those people making ice with solar energy are still rejecting at minimum the ~334kj/kg to the environment.

An absorption refrigerator does not absorb heat, it's called that because you are taking advantage of some energy configurations that occur when one fluid absorbs another. The action of pumping heat is the same.

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eesmith ◴[] No.44359742[source]
The question was 'what about a solar powered ac for cooling?', yes?

Giant radiators don't make ice.

The proposed method of pumping heat into someplace hot to make it hotter doesn't work. But there area definitely ways to do solar powered ac for cooling.

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1. IAmBroom ◴[] No.44370033[source]
The Second Law of Thermodynamics would like a word with you.
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2. eesmith ◴[] No.44370693[source]
I provided links. It's how propane-powered fridges work. And it was a homework problem in thermodynamics class.
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3. im3w1l ◴[] No.44372903[source]
Since this discussion is still active, I think hwillis was the only one that got my idea. Pumping heat into the radiators will make them hotter then they would be by just passive conduction, and then the T^4 radiation scaling means that the radiators will start radiating a lot, i.e. a lot of heat will be sent into deep space.