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elderflower

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Registered: 2016-06-19

Posts: 1,262

Re: How Do We Pressurize a Greenhouse?

The problems of compressing gases from very low inlet pressures have been solved on earth. The mechanical ones are called vacuum pumps and most labs have small ones. Industrial scale machines are also available.
Another method would be to use a chemical adsorbent which would be regenerated at a higher pressure. On earth we use amines for doing this with carbon dioxide, but they wouldn't work the same on Mars. Probably a solid adsorbent would be preferred. Heat is expected to be available as a by product of the nuclear reactor system.

GW Johnson

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From: McGregor, Texas USA

Registered: 2011-12-04

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Re: How Do We Pressurize a Greenhouse?

Hi Elderflower: 

Yeah,  that's the direction my compressor sizing was headed.  What I came up with was intermediate between compressor and vacuum pump.  All the mechanical vacuum pumps I ever saw processed very little massflow at all,  through a fairly-limited pressure ratio. 

The easiest way I know of to compress Mars CO2 is a self-compression process driven by low-grade heating.  Spread out something cold at night to catch CO2 frost,  and collect and put that frost into a closed space of limited volume.  Let it sublime upon heating,  which will modestly pressurize the closed container.  You're out the low grade sublimation heat,  and whatever high-grade energy refrigerates your collection surface below the frost point. 

But as I said above,  you need more in that greenhouse atmosphere than CO2.  You need some amount of oxygen.  I don't know how much.  But plant metabolism does require both gases as feedstocks,  not just CO2. 

GW

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GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

RobertDyck

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From: Winnipeg, Canada

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Re: How Do We Pressurize a Greenhouse?

Modern wheat requires as much partial pressure of oxygen as humans do. Other plants are different. Cyanobacteria do not require any oxygen at all, but that's not a food. Plants don't require nitrogen, but it's recommended. Legumes such as beans and peas usually have a nitrogen-fixing bacterial called Rhizobia growing in nodules in their roots. This bacteria grows symbiotically with the plant. The bacteria feeds on carbohydrates from the plant, and combines nitrogen from the air with water to form ammonia. The plant uses this ammonia to produce protean. Clover is another legume, it also uses this same bacteria to fix nitrogen.

Root nodules on a Wisteria plant (a hazelnut pictured for comparison)

I've argued that capturing CO2 from Mars atmosphere is most efficiently done with a freezer at night (Robert Zubrin's idea). However, capturing nitrogen requires a compressor.

Last edited by RobertDyck (2017-04-20 07:15:12)

elderflower

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Registered: 2016-06-19

Posts: 1,262

Re: How Do We Pressurize a Greenhouse?

GW
I suspect that the cold surface will get water frost on it as Mars atmosphere is pretty much saturated with water vapour. This will reduce its ability to condense CO2 due to latent heat of water.
See Busch Cobra- Industrial for a large screw type vacuum pump.