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Noclevername
2015-Jun-29, 11:33 AM
A question for my current story: suppose you have a manned station or spacecraft. Solar powered and with a cooling radiator set up for human occupancy. Now suppose you want to bring aboard a freezer capable of reaching liquid air temperatures. Assuming that you can connect the freezer directly to the radiator, what is the smallest size heat pump that can do that job? And what is the quietest noise level that can achieve this temperature using current technology?

swampyankee
2015-Jun-29, 11:54 AM
A question for my current story: suppose you have a manned station or spacecraft. Solar powered and with a cooling radiator set up for human occupancy. Now suppose you want to bring aboard a freezer capable of reaching liquid air temperatures. Assuming that you can connect the freezer directly to the radiator, what is the smallest size heat pump that can do that job? And what is the quietest noise level that can achieve this temperature using current technology?

How big is the freezer?

There are several technologies, many commercially available.

cjameshuff
2015-Jun-29, 12:51 PM
A question for my current story: suppose you have a manned station or spacecraft. Solar powered and with a cooling radiator set up for human occupancy. Now suppose you want to bring aboard a freezer capable of reaching liquid air temperatures. Assuming that you can connect the freezer directly to the radiator, what is the smallest size heat pump that can do that job? And what is the quietest noise level that can achieve this temperature using current technology?

It can be done with something the size of a shoebox...it depends on how quickly you want to make liquid air. Some sound pretty much like a small aquarium pump: https://www.youtube.com/watch?v=51a7X7lblMc

Noclevername
2015-Jun-29, 01:43 PM
How big is the freezer?

There are several technologies, many commercially available.

About 1.5 cubic meters.

John Mendenhall
2015-Jun-29, 03:08 PM
You intend to radiate the heat into space? Just keep the sun off it and most of the battle is won.

swampyankee
2015-Jun-29, 10:57 PM
At a rough guess, you're probably going to need about a kilowatt of cooling; most of the cryocoolers in my (very brief and superficial) look seem to need to have coefficients of performance of about 0.1, so the 1 kW of cooling will require about 10 kW of input power. If your radiator is running at 300 K, it will take about 500 m^2 just for the cryocooler.

Here's one place to look a bit: http://www.lorentzcenter.nl/lc/web/2012/512/problems/4/Cryocoolers%20the%20state%20of%20the%20art.pdf

profloater
2015-Jun-29, 11:18 PM
Why not point an insulated box into space? It will get very cold you have a wonderful cold sink there. Insulation also very easy, you have vacuum available.

cjameshuff
2015-Jun-29, 11:40 PM
Power requirements are going to depend on how well insulated it is (and on a space station, a good quality vacuum insulated enclosure probably isn't hard to arrange) and how quickly you want it to cool things.

John Mendenhall
2015-Jun-29, 11:55 PM
Why not point an insulated box into space? It will get very cold you have a wonderful cold sink there. Insulation also very easy, you have vacuum available.

My point from my previous post. If you are not in a hurry, there is pkenty of cold available.

Noclevername
2015-Jun-30, 12:12 AM
It was smuggled aboard, now the crew have to keep it frozen indoors until they can arrange proper vacuum storage.

Noclevername
2015-Jun-30, 12:15 AM
It can be done with something the size of a shoebox...it depends on how quickly you want to make liquid air. Some sound pretty much like a small aquarium pump: https://www.youtube.com/watch?v=51a7X7lblMc

I have no experience with either cryo freezers or aquariums, how much noise would it make?

profloater
2015-Jun-30, 05:03 PM
You can make liquid air from a compressed air gas bottle and a coiled up copper pipe, the expansion causes the cooling which bootstraps. Peltier coolers can also do it, stacked up.

Noclevername
2015-Jun-30, 11:43 PM
You can make liquid air from a compressed air gas bottle and a coiled up copper pipe, the expansion causes the cooling which bootstraps. Peltier coolers can also do it, stacked up.

The point is not to make liquid air, but to keep the freezer's contents at that temperature under less than ideal circumstances.

swampyankee
2015-Jul-01, 01:19 AM
The point is not to make liquid air, but to keep the freezer's contents at that temperature under less than ideal circumstances.

If you have a compressor, you can use compressed air: expand the air through a nozzle (better, a turbine: you can recover some energy), then use the cold air coming out of the nozzle to cool the room-temperature air going into the nozzle (it's a regenerative cycle). For an example, see http://www.instructables.com/id/Homemade-liquid-nitrogen-generator/step6/Regenerative-Cooling-Tower/
http://satish0402.weebly.com/uploads/9/4/6/7/9467277/bsc_i_paper_ii_nov10.pdf and http://rsnr.royalsocietypublishing.org/content/64/1/43

VQkr
2015-Jul-02, 06:28 AM
You can't just put the container outside, in the shadow of the ship/station, to keep it frozen?

Maybe the crew could sneak some cryogenic fuel to keep the payload cool. With a space-generated vacuum jacket, a little liquid hydrogen would go a long way...

ETA - what about a solid-state Peltier cooler? Completely silent.

Van Rijn
2015-Jul-02, 07:04 AM
A question for my current story: suppose you have a manned station or spacecraft.

Where is the spacecraft or station? As some have pointed out, it may be easy to stash something outside, but not near a warm world. Sunlight wouldn't be much of an issue either in the outer solar system, especially if the object has a white surface.

Noclevername
2015-Jul-02, 09:47 AM
Where is the spacecraft or station? As some have pointed out, it may be easy to stash something outside, but not near a warm world. Sunlight wouldn't be much of an issue either in the outer solar system, especially if the object has a white surface.

Halfway between Earth and Mars. The crew are busy at the moment, and the freezer was smuggled aboard as cargo in the life supporting section. They have to use what the smugglers used until such time as they can suit up and get the box outside.