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#1 2014-11-28 07:58:11

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,210
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Desalinating water

I found this source on the energy cost of desalinating water. It seems to suggest that desalinating seawater costs on the order of 10Wh/gallon... I'm actually surprised, I though it would be more. That's about 10kJ/litre. That seems to be much more efficient than boiling the water, though I suppose on Mars you'd be able to boil it in a much lower pressure


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#2 2014-11-28 14:13:52

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
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Re: Desalinating water

Hi Terraformer:

The cost of membrane desalination includes the cost of periodically replacing the membranes when the become too contaminated.  The membranes are expensive already.  When you add in the cost of transporting replacement membranes to Mars (or elsewhere),  boiling might actually be the better choice for off-world desalination.

Although,  on Mars,  extreme cold is readily available.  The first ice that forms from freezing seawater is always quite fresh.  Why not freeze local brine for freshwater ice,  even if you have to reject over half your throughput?  On Mars,  you pay zero for the freezer.  Your energy costs are (1) pumping liquid and (2) some heat (80 cal /gram) to melt the freshwater ice plus (3) perhaps some heat to get the brine in the first place.

GW


GW Johnson
McGregor,  Texas

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

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#3 2014-12-03 17:34:52

Void
Member
Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

Hi Terraformer,

Another potential option, might get you other things as well.
I said this in another thread:
http://phys.org/news/2014-11-protons-fu … pects.html … pects.html

The above technique wants a moist atmosphere to produce Hydrogen, and they have not proved that they can get it yet.  However, I recall one of our persons here suggests a plastic greenhouse that does not block UV.  That would be good.  a moist greenhouse that produces Hydrogen that could be harvested by the means suggested in the above link.  Perhaps organisms would grow under a translucent sand layer at the top of the soil, to provide another useful purpose.  (Shielded by the sand from UV).  Or, perhaps a plastic layer inside the greenhouse to provide protection from the UV, but letting the volume above it be exposed to UV.

However, I want to go another direction with some of the above.

I was thinking at one point of creating a usable dynamic window to receive the focused output of a concentrating mirror.

Here is the dynamic window smile It is a squirrel cage fan:
images?q=tbn:ANd9GcRqDsP7UNolMmZraS9fsMifGpYZCyhMKm4QW6WHBXaRbuTK4zTP4Q

https://www.google.com/search?q=squirre … CAcQ_AUoAg

The objective would be to suck Martian air in that is heated very hot, and to then blow that hot air over a containment which holds the water you want to boil.  The air will be very hot.  Also the Squirrel cage and motor assembly will be very challenged by heat.  However you might water cool those components and dump that heat into the boiler process.

What I was actually after was moist air which is hard to come by on Mars.  So from the boiler should come steam which can be vented into the inlet port of the squirrel cage fan, moistening the air being sucked in, and perhaps according to the article listed above about collecting Hydrogen from moist air, providing Hydrogen.  Most of the boilers steam however might be quenched in cold water, and just maybe might run a turbine.

Out in the open this might be a problem but if you enclose the whole operation in a ambient pressure greenhouse, probably not a problem.

If it were a greenhouse which lets most of the UV in, then that would be good.  A concentrated focus of Martian sunlight with most of the UV, would be a very powerful molecule splitting agent.  Then you might consider enhancing that with catalysts of some kind.

I am thinking of a "PCTFE film" which was spoken of by RobertDyke in his own thread about indoor farming.  I am under the impression it will let a lot of UV light through, but it is very strong.

However I don't want to pressurize the tent, just use it to cover the apparatus, and limit the flows of raw Martian air into the process.

Anyway, you could boil and condense water.  Of course I am also wanting to create and capture fuels, and by doing that I presume also Oxidized compounds.

It's a bit wild, but maybe someone will revise it and make it practical.  I actually discarded if for a better process that gets water another way, but no talkie on that.

Hmm...

I originally thought the hot air would heat a tank.  However, I see that hot low Relative Humidity air if blown over water at a pressure of say ~20 to ~70 mb would evaporate water.  It would then be very easy to cool that air from say hundreds of degrees to quite cool on Mars.  That would release the water vapor to condensation.  Perhaps the tent could be somewhat pressurized, and serve as a radiator?

Oh well. there would be lots of options.

An alternative would be to have the tent that covers the machine at ambient pressure, but use a squirrel cage compressor to push the hot moist air into a second pressurized tent, using compression and thermal losses to the Martian Environment promote condensing.

Last edited by Void (2014-12-03 18:10:36)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#4 2014-12-03 20:24:05

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

Why, would we want to use electrical power to do this when solar can do the same and use less power.

http://www.greendiary.com/solar-powered … stems.html

http://en.wikipedia.org/wiki/Solar_desalination

http://www.businessinsider.com/californ … ell-2014-3

Use the heat generated from the concentrator to heat the ice in a chamber to evaporate then cool it just like in a stil....

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#5 2014-12-04 09:01:49

Void
Member
Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

Spacenut,

I will attempt to justify what was previously presented by me against the benchmark you have provided.

First of all Mars is not Earth.  The methods presented as challenge are specifically adapted to provide a solution to problems that exist on Earth, and may not be suited to Mars.  No swamps on Mars, no oceans.

The Idea with the heated mineral oil might have application on Mars.  However, after heating the mineral oil, the final process I believe is to just boil non potable water and condense it into potable water.  Which is just fine, a good plan for a place on Earth.

I presented something which I think is rather new. a portal where both a gas flow and a concentrated solar flow pass from a lower pressure environment to a higher pressure environment.  True, you must supply electrical or steam force to spin the fan, but I think it may have useful potential for specific purposes.

A small amount of steam is also added to the flow at its upstream side in the hopes of producing a presence of free Hydrogen which according to the link I supplied can exist in warm moist air.

Further the whole process can occur with less than 100 mb pressures, perhaps much lower than that.  That could matter as the materials that you create a machine from would be expensive on Mars.

So, what I would hope to get out of this effort would be

1) Hydrogen (And an Oxidizer).
2) Distilled water
3) Possibly a thermal power system.

I had asked the other members to try to help me complete the machine.  That is no longer necessary.  I think I have the main variations in mind.

I stipulate that #1 can exist without implementing #2 or #3.

It makes sense however to do #2 if you are doing #1.

It may make sense to do #3 as well, if you have sufficient distilled water, and your installation is large.

I request your indulgence to redefine a variation of the machine/process, one which will suit life support much more I think.

I will start with the plastic film enclosure.  I will change it from being filled with Martian air to being filled with Oxygen, at a higher than ambient pressure so as to inflate it.  However it will be desired to keep the pressure low enough to escape the dangers of combustion or explosion. The enclosure should allow as much of the solar spectrum to pass through as possible.  Particularly I want the U.V. spectrum, because it is very powerful at messing with water molecules.
In the thread atmospheric separations,

A potential modification of the above:
I have proposed how to extract Nitrogen and Argon, etc from the atmosphere of Mars.  Here would be an application to use those.  Instead of having a pure Oxygen filler, I would alter the scheme to one where a mixture of Oxygen, Nitrogen, and Argon are maintained to make the process less corrosive, flammable, and explosive.

Inside of that low pressure plastic film enclosure  will suppose a solar concentrating mirror.  As a first try, I will suppose a parabolic circular mirror, but it should be possible also to use a rectangular mirror, it would require some adaptations however.

That mirror being focused on a Squirrel Cage rotor and it's chamber.  It should be noted that both the rotor and the chamber which encloses it may have a catalyst substance added to their surfaces to aid the process of splitting water molecules.  The turbulence of the air in contact with the rotor and the induced turbulence of the air in the chamber should enhance the contact of  water molecules with the rotor and enclosure surfaces which may include a catalyst surface layer.  The water will of course be squirted into the opening . This is not the distillation process, so don't be confused it is to mix some water molecules into the portal.

The objective of the dynamic portal is to suck in a low pressure mixture of Oxygen, Nitrogen, Argon, and water vapor, pressurize it inside of a compartment defined by the static enclosure walls and the dynamic wall created by the rotating squirrel cage rotor.  The concentration of solar energy focused into this pressurized chamber, is to raise the temperature of the pressurized mixed gasses, and also the content of that concentrated focused light mixture presumed to be including a significant portion of U.V. light , the production of temporary liberated Hydrogen should be expected. 

So, at some point you would want to use the process where an electric current will convert a Hydrogen atom to a Proton.  It is suggested that this is expected to be possible, and useful in the link below.  Without that this whole described process might not be as useful, and in the absence of the ability to collect Hydrogen, it might be wise to chose an altered process.  However, I am going to run with the idea that it will be possible to extract Hydrogen from moist warm air.
http://phys.org/news/2014-11-protons-fu … pects.html

It should be noted that if you are adding water vapor to a gas mix of Oxygen, Nitrogen, and Argon, and then splitting some of the water molecules, and then capturing the temporariliy liberated Hydrogen out of that mix, you are then causing the mix to have more Oxygen. So, again;

A potential modification of the above:
I have proposed how to extract Nitrogen and Argon, etc from the atmosphere of Mars.  Here would be an application to use those.  Instead of having a pure Oxygen filler, I would alter the scheme to one where a mixture of Oxygen, Nitrogen, and Argon are maintained to make the process less corrosive, flammable, and explosive.

So you add more Nitrogen and Argon to the mix, and you have more "Air".

So if this works, you have captured Hydrogen, and have manufactured Air, without plants or Electrolysis.

So item #1 is completed!

Next item #2 wants some water distilled.  Specially salty water which is likely available on Mars, but to broaden it could be non potable water.  We want to distill it into usable water.

An easiest way to do this would be to pass the hot air over a tray of contaminated water and evaporate from it.  In fact this might be superior to actual boiling, because if you boil, you must utilize de-misters to remove the brine mist that gets included into the steam.  But if you want to boil it I suppose you could blow the hot air over a pressure vessel's outer surface and create a pressurized boil.  Since water is being evaporated/boiled the temperature of the hot air is reduced to accomplish this.

I prefer the open basin evaporation method.  Should work very well when you hot air is ~800 Degrees Fahrenheit (~426.667 degC), and your pressure of the output air is ~20 to ~100 mb.

So you then have your evaporated water in a air flow.  Condensation is the next effort to be made.

I suggest involving Item #3.  An Ammonia water power generator could be considered, although their are other alternatives.  An Ammonia/Water boiler system will require piping and will of course be self enclosed against outside conditions.  The heating coils of the Ammonia/Water electric generator will have the very hot air blow over them so as to boil Ammonia, and to partially cool the hot air.  The condenser side of the Ammonia water system will have to be a heat sink, which is quite do-able on Mars.  The heat could be dumped to the outside environment around the clock, or into a cold water reservoir.

So Item #3 is potentially satisfied  (Electric power generation from thermal differentials.)

But Item #2 may still be open.  The Ammonia water boiler system which is used to partially cool the air may not cool it enough for water to condense.

The final cooling process could likely involve cold water from a reservoir, mixing the air with water at a substantially cold temperature, even as low as 32 degF (0 degC).

So Air, Hydrogen, cleaned water, and electric power from both a turbine, and from fuel cells (If you have made air, and have captured Hydrogen, then you might choose to recover energy using a fuel cell).

One of the problems with making a living on Mars, is either you must have pressurized greenhouses with plants in them, or you must have artificial lights and have indoor gardens.  I don't propose to dispose of any of those options, but this is yet another method to obtain what is needed.

But if this works, (The Hydrogen and air parts in particular), then there will be much less need for high pressure greenhouses, or electrically demanding indoor artificially lighted gardens.  If you have Hydrogen and air, and electricity and fresh water, you can manufacture food and plastics as well.  And your "GreenHouse" enclosures could be at ambient pressure or just a bit higher, requiring less strength, and less materials.


Your question was "Why, would we want to use electrical power to do this when solar can do the same and use less power.

Really the only mentioned component is the dynamic portal (Squirrel cage rotor).   It's consumption of energy should be rather small compared to the energy and resource value that could be captured by the above system.

The substitute process you mentioned would also have to involve electricity consuming technological devices.  The question is, is it worth it?  Is the value out greater than the value expended to capture the value out?

But I understand, you wanted me to explain better, and to give better "Evidence" of value.

Last edited by Void (2014-12-04 09:24:17)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#6 2014-12-08 09:22:18

Void
Member
Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

Self correction.

At some point I misinterpreted what RobertDyke presented in the greenhouse thread.

I assumed that one of the materials he presented "PCTFE film", which was very durable could allow in UV light.  It appears that that was not his intention.  Rather he was going to block the UV using a protective coating.  I suppose if the UV was allowed in it would damage the greenhouse "PCTFE film" material over time.

So, I still think the machine proposed here could be of value but unfortunately it appears that UV cannot be conveyed into the mirror, to be focused onto the "Dynamic Portal".  That's a pity.  Anyway the machine should work without it.

Last edited by Void (2014-12-08 09:23:27)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#7 2015-02-08 18:58:30

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

I was right you did post something with simular content:

Void wrote:

I have my own ideas about obtaining water.
I have seen;
-Glaciers (Dig)
-Bake soil (Dig and bake soil)
-Get it out of the atmosphere. (Small amounts, lots of effort)

I suggest looking at salt pans, and salt domes.

Some of the salt pans in the southern low latitudes are calculated to at times have enough moisture in them, and sufficient elevation of temperature that they could support life.  So, to investigate them would be supported by both the people who want to settle Mars, and those who wish to investigate the chances of life on Mars.

The machine I propose to extract water from the salt flats, or maybe a salt dome, would use;
-Solar Heat
-An electrostatic capacitor
-A flowing electrical circuit
-Vacuum.
-The salt pan itself and the moisture in it.

-A bag of water placed on the salt pan (For now I will ignore the problems of corrosion of salt on the plastic.  I think that could be solved).
-Electrons extracted from the ambient environment.  Either from the air (Preferred) or from an electrode placed some distance from the water bag.
-Electrons injected into the water of the bag, forming a capacitor, where the water within has a charge of electrons (-) greater than the environment outside the water bag.
-The outside skin of the bag will develop a skin of condensed positive ions (+) and will be relatively pressurized.
-If electrons are extracted from the atmosphere, it will release a plume of positive ions that will travel downwind.
-Additionally, under the bag, an electrode charged negative (-).
-While electrons will try to travel towards the positively charged contact point of the plume, and also in all directions away from the underside of the bag, Positive ions of various sorts will try to travel towards the underside of the bag.  Among these should be positive ions of water.

So, I am presuming that ion collection is favored by the electrical circuit of the (-) electrode under the bag, and the downwind (+) plume, and conductance of both electrons (-) and the downwind plume ions (+) pushing (+) H20 ions though the salt pan or salt dome.  Something like this was done by the Germans during WWII, to dry up wet ground so that they could drive tanks over it.

The water bag can also serve as a solar collector.  The bag will have to be able to tolerate internal pressures for 0 degrees Centigrade and up.
The underside will also be heated up by heat conducted from the bag to the area below it.  So, you then have a situation similar to a solar still which is demonstrated on Earth by pulling moisture from dry sand, and condensing it on a film of plastic above it.

The dielectric pressure of the thin film on the outside of the bag, might even allow for liquid phase water, if it is not too warm, but that is not the method of extraction I contemplate.

Instead I propose a vacuum line with a collection nozzle under the bag near the (-) electrode.  The bag pressing against the ground with the weight of the water in it is intended to resist the flow of atmospheric air under the bag to the vacuum nozzle.  The intention is to create a vacuum chamber under the bag, to promote evaporation of water bound to salt, and any which might be bound in any phase to the underside of the bag.

The materials vacuumed from under the bag should include water vapor.  A machine to pressurize the mix and extract the water as a liquid should be possible.  Then the liquid can be injected into the bag for storage, up to the point that the bag has maximized it's volume.  Presumably it would then be tapped for human use.

Interestingly bushmen use a vacuum method to extract water from soil at times, but I don't think it is quite the same process.

It would not be prohibited to grow simple life forms in the water in the bag at the same time if that was considered to be of value.

Problems:
-Perchlorate Salts may be attracted.  However, maybe this could be turned around as a method to extract value from them.
-Corrosion of the underside of the bag.  I guess this has to be figured out.
-Freeze up of the bag.  This may or may not damage it.  By applying insulation in places that do not collect solar energy, this might be improved.
During dust storms, it is very possible the bag would freeze up.  One fix would be to drain it before freeze up.
-U.V. Deterioration of the bag.  (I suggest a simple tarp with U.V. protection on its top side, that can be replaced as needed to be put over the bag).

I have specified salt pans and salt domes, but I also observe that the soils of Mars and particularly the crust above are rather salty.  Perhaps this can be less location specific.  Maybe it could be done near the equator, which could be nice.

The areas dried by this process would be primed to collect more water from the atmosphere, during instances of higher humidity, caused by seasonal changes, and by nighttime atmospheric processes.  So, this is after all an atmospheric condenser, but it uses the existing winds, and the existing humidity in the salt to make it more practical than a small machine which must pump air though it and has to use exotic materials to absorb moisture from the atmosphere.

The value of this method could be that except for construction and normal maintenance, humans in suits, and expensive mobile machinery would not be required.  Those activities are both dangerous to humans, and costly.

Done

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#8 2015-02-08 19:33:25

Tom Kalbfus
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Registered: 2006-08-16
Posts: 4,401

Re: Desalinating water

How do you desalinate water on Mars?
Simple, you take the salty water outside and watch it boil away, and then you have a pile of salt in your container, the water has been desalinated!

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#9 2015-02-08 20:34:47

louis
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From: UK
Registered: 2008-03-24
Posts: 5,487

Re: Desalinating water

Tom Kalbfus wrote:

How do you desalinate water on Mars?
Simple, you take the salty water outside and watch it boil away, and then you have a pile of salt in your container, the water has been desalinated!

I thought the droplets on the Mars Polar Lander were brine?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#10 2015-02-08 21:25:31

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

lol big_smile cool Tom Kalbfus thanks but it think we will need the water more than the salt but sure that works....

I was searching for another topic that I had made a post about the use of a solar still  but could not find my post ended up searching my hard drive and located a topic by Dryson : but its no longer here as it was in the crash years. So reposting what I have here....

dryson wrote:

   Post subject: Harvesting water on the Moon and or Mars Posted: Wed Aug 18, 2010 6:08 pm

Here is an idea that might be cheap and effective to harvest water on Mars. Last week I had hot water in a plastic container. I placed the lid on the container and left it sit for awhile. When I returned the water had condensed on the lids surface.

How the harvester would function is as follows:

http://en.wikipedia.org/wiki/Solar_still


Quote:
A solar still is a low-tech way of distilling water, powered by the heat of the sun (more precisely, the heat & humidity of the soil, and relative cool of the plastic or glass or other transparent material).


The top of the unit would be like any other solar still designed to collect the water as the water evaporates from the soil and condenses on the transparency pane. Once the water condenses on the transparency the water would drain down into a channel at the bottom edge of the transparency and then into a stainless steel vessel that would be pressurized and kept above freezing temperatures but below the point of evaporation.

The next part of the idea revolves around heating the soil to create humidity. After you have completed your road runner thrust manuever...Before placing the solar still in the ground two trenches would be dug the width of the solar still allowing the heating elements to be lowered into the ground. The heating elements are in red as shown in the Sketch Up model. Once lowered into the ground regolith or Martian soil would be packed around the legs so that the heat would not escape through the trench openings while not being packed around the heating elements. Once in place the heating elements would turn on thus heating and providing the soil with humidity within the enclosed unit.

Once the area had been harvested of the water the unit would be removed and moved to another location.

Here are some Sketch Up images that shows the basic idea or design

The first is the unit built as a whole unit.

MartianWaterHarvesterFullUnit.png

The second image is from the top portion, dorsal or overhead view.

MartianWaterHarvester3.png

Also would using different chased of transparency created more condensation instead of using jsut a clear piece of glass or plastic?

The next two image's shows the legs and heating elements

MartianWaterHarvester2.png

MartianWaterHarvester1.png

To reach water at lower depth's additions to the heating element legs can be added as needed.

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#11 2015-02-08 21:43:46

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

Rune wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Thu Aug 19, 2010 11:03 am 
You do know that at Mars surface conditions, water would not condensate, right? It cannot exist in liquid form, unless it has a high salt content.

Rune. It would need to be a pressurized solar still, at least.

Chris Clute wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Thu Aug 19, 2010 8:39 pm


Zubrin has a simpler idea in "The Case for Mars." He advocated putting a transparent tent over a section of ground. Several mirrors would stand alonside the tent to maximize heat from the sun. The water would get baked out of the regolith and gather on a cold piece of metal on one side. A refrigeration unit would need to keep it cold, but you wouldn't need to dig or provide heat.

dryson wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Sun Aug 22, 2010 2:31 pm

Quote:
You do know that at Mars surface conditions, water would not condensate, right? It cannot exist in liquid form, unless it has a high salt content.
Rune. It would need to be a pressurized solar still, at least.

I was reading about Mars and surface freezing and sublimation. Would the water freeze underneath of the surface when heat is added to the soil to create the humidity needed to create the evaporation process which would then lead to condensation? Or would the water rise to the surface first and then freeze?

Have any reports from Nasa confirmed that there is a level at which the water under the surface of Mars or Moon is protected from the coldness of space?

If the water on Mars or the Moon melts and rises to the surface and then re-freezes the unit would then eject a gaseous compound into the chamber of the unit where the molecular compound would be similar to the rock salt used to keep snow and ice off of the roads and pavement during winter time.

Road Salt

The difficult area to determine would be how much gaseous salt would be needed to keep the water from freezing. Too little salt and the water still freezes. Too much salt and the water freezes still.

One way to get around the problem of keeping the water from freezing could be to drill exploratory holes to the appropriate depth where the water is located at. The holes would drilled in a 38. special cylinder pattern. One hole would be drilled in the center with six other holes drilled around it that would be tangent to the center hole. The hole spacing would need to be in relation to the temperature of the are drilled as well as the heat effective zone where the water would contineu to rise to the surface while being heated by the heating elements on the legs without freezing. The water would come in contact with the road salt columns that were placed in the exploratory drilling holes. Once the water reaches the surface the heat from the unit would cause the water to evaporate and condense on the unit's transparent paneling.

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#12 2015-02-08 22:03:43

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

dryson wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Sun Aug 22, 2010 2:36 pm
Quote:
Zubrin has a simpler idea in "The Case for Mars." He advocated putting a transparent tent over a section of ground. Several mirrors would stand alonside the tent to maximize heat from the sun. The water would get baked out of the regolith and gather on a cold piece of metal on one side. A refrigeration unit would need to keep it cold, but you wouldn't need to dig or provide heat.

That's basically the same idea that I was going for with my idea the only difference is that with "The Case for Mars." idea there would be a mraginal amount of water collected that would only come from a few inches below the surface.

Does Zurbin's idea go into details about the paticular's of the amount of heat needed comparable to the area being harvested along with the volume of water that could be harvested with his idea?

My idea is basically the same as Zurbins but it is layered to harvest water from deeper depths to provide a sustainable water harvesting farm.

Just imagine drinking a cool glass or bottle of Martian or Lunar water.

Chris Clute wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Sun Aug 22, 2010 10:24 pm
Quote:
Does Zurbin's idea go into details about the paticular's of the amount of heat needed comparable to the area being harvested along with the volume of water that could be harvested with his idea?

p 192 of The Case fo Mars, " If the tent is a hemisphere 25 meters in diameter, and the tent greenhouse plus reflector arrangement causes the equivalent of an extra 200W/m2 of heating [for a total of 700W/m2] to occur eithin the tent, the total effective power would be 98kW. This is enough to release 224 kilograms of water from 3 percent grade soil in the cours of an eight hour day. This amount of water would be available within the first centimeter of soil within the tent."

That's about 25 gallons, right? Not bad I think. If we had several of these, we could get a fair amount of water per day.

Your idea would go deeper, but that water might be harder to get at. Well, I guess it depends on how much water is in the soil in reality. Your system should be able to get more water.

louis wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Sun Aug 22, 2010 10:31 pm 
It's just a lot easier to park up close to a mile high glacier.

Rune wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Mon Aug 23, 2010 5:38 am 
The problem is not the water freezing, it's the water sublimating. In the low pressure of martian atmosphere, liquid water just can't exist. It is either a solid (under the pressure of soil) or it sublimates slowly into water vapor if exposed to the surface almost-vacuum. So if your dome isn't pressurized, water just can't condensate, no matter how you do it.

You could collect water vapor, of course, and pressurize it to condensate it later, for storage. I suspect that's what Zubrin suggests.

Still, I'm with louis on this one:

louis wrote:
It's just a lot easier to park up close to a mile high glacier.

And just use a pick and shovel.

dryson wrote:
Just imagine drinking a cool glass or bottle of Martian or Lunar water.

Should be pretty much like any other water bottle. Only more expensive. 

Rune. I should read The Case for Mars, if only to criticize it more properly.

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#13 2015-02-08 22:10:31

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

el_slapper wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Mon Aug 23, 2010 8:50 am 
Rune wrote:
(.../...)
You could collect water vapor, of course, and pressurize it to condensate it later, for storage. I suspect that's what Zubrin suggests.

he's not absolutely clear on the topic - at least on french translation. But yeah, you need the pressure to have it work, sooner or later.

Rune wrote:
Still, I'm with louis on this one:

louis wrote:
It's just a lot easier to park up close to a mile high glacier.

And just use a pick and shovel.
(.../...)

and come back to pressurized area before

Rune wrote:
Rune. I should read The Case for Mars, if only to criticize it more properly.

iOf course you should. Despite being slowly but surely slipping in the "obsolete" category, it remains a book very cool to read.

dryson wrote:

   Post subject: Re: Harvesting water on the Moon and or MarsPosted: Thu Dec 23, 2010 12:47 pm
Would Barnes and Noble still have a copy for the Case for Mars? I would really like to read it.

We know that the polar ice caps and the surface of Mars contains water. But what about the valley's and crater impact's? More water is thought to be located within the craters on the Moon than in the surface of the Moon itself. Would we possibly be able to harvest better water yields by harvesting the water from deep inside the craters as well as from the valley's and deep trenches of Mars such as the Valles Marineris?

In Closing on the final post that I have a copy of the website is missing lots of good creative conversation as well as problem solving that would help to stop all the repeat topics that we here once long ago.

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#14 2015-02-10 06:34:32

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Desalinating water

Interesting.  I generally find that I have insufficient time to explore these topics to the sort of depth that they deserve.

I wonder if desalination could be integrated into a power cycle such that waste heat is used to drive the boiling?  Waste heat is probably a misleading expression of Mars as it suggests that the heat is worthless, whereas in reality it will be a valuable biproduct.

The Martian environment possesses some useful qualities so far as power production is concerned.  The atmosphere is dominated by CO2 and it is the most logical working fluid for stationary power cycles.  The ambient temperatures are far beneath the supercritical point of CO2 (308K) and approach the triple point (~250K).  This suggests that solar thermal power cycles could using CO2 could achieve good efficiency (10% or more) even at modest temperatures, as the CO2 liquefies ion the condenser and pumping losses are small.  The condensor could still operate above the freezing points of most brines and could therefore use waste heat for desalination without impacting efficiency.

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#15 2016-08-06 15:51:29

elderflower
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Registered: 2016-06-19
Posts: 1,169

Re: Desalinating water

Desalination on Earth generally involves reverse osmosis or distillation and recondensation. it is, however, possible to exclude most contaminants from a dilute brine by partial freezing, producing fresh ice which can be crushed, washed to remove residual salts and then melted again. This happens to old sea ice in the arctic on earth which can be used as a potable water source, despite being formed from sea water. On Mars water is all frozen but brine would have been expelled during the freezing process so the ice may be available for mining with fairly low levels of contamination.

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#16 2016-08-06 16:24:53

RobertDyck
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From: Winnipeg, Canada
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Re: Desalinating water

National Snow & Ice Data Center: All About Sea Ice

When sea ice forms, most of the salt is pushed into the ocean water below the ice, although some salt may become trapped in small pockets between ice crystals. Water below sea ice has a higher concentration of salt and is more dense than surrounding ocean water, and so it sinks. In this way, sea ice contributes to the ocean's global "conveyor-belt" circulation.

Wikipedia: Sea ice

In the freezing process, much of the salt in ocean water is squeezed out of the frozen crystal formations, though some remains frozen in the ice. This salt becomes trapped beneath the sea ice, creating a higher concentration of salt in the water beneath ice floes. This concentration of salt contributes to the salinated water’s density, and this cold, denser water sinks to the bottom of the ocean. This cold water moves along the ocean floor towards the equator, while warmer water on the ocean surface moves in the direction of the poles. This is referred to as “conveyor belt motion”, and is a regularly occurring process.

So it's not absolute.

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#17 2016-08-06 16:50:59

RobertDyck
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From: Winnipeg, Canada
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Re: Desalinating water

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#18 2016-08-10 05:06:21

elderflower
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Registered: 2016-06-19
Posts: 1,169

Re: Desalinating water

You are right, Robert, it isn't absolute, but it is effective, especially with a wash step. If not sufficient in one stage, repeat. It would use less energy than evaporation. Recrystallisation is widely used to purify materials is the chemical industries.

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#19 2016-08-10 10:26:24

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,768
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Re: Desalinating water

Freezing is easy on Mars,  hard here (except at the poles).  Sounds like desalination by freezing is the way to go on Mars. 

Perhaps by careful control of motions,  the efficiency in one step can be increased.  Salt gets incorporated in the freezing sea ice because it is moving around in the waves.  If held very still inside a machine,  it might separate quite a bit better.  Plus,  you can always shave off the bottom contaminated zone and recycle it. 

GW

Last edited by GW Johnson (2016-08-10 10:27:31)


GW Johnson
McGregor,  Texas

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

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#20 2016-08-10 14:17:27

Void
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Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

I am a pest no doubt.

Anyway if you are going to use freezing as a step to purify brine to fresher water here is a way to make a power source in association with that process:
https://www.bing.com/videos/search?q=el … ORM=VRDGAR

I think this is just one version in a family of developing processes, but it suggests a direction to take.
Some of these schemes also can use waste water as the fresh component.

Doing this however could introduce chemicals which might not entirely be pushed out of the freezing ice, so I would suggest that a simple heating process be used to produce distilled water as well.  I would think that a very low pressure steam produced in a simple solar thermal collector would do this well.

Sublimating the surface of an already processed top of a ice sheet would actually require a lot of energy, since you would be going from solid to vapor, but the source of the energy would be simple, reliable, and very available during normal days.

I am not sure to what degree brine would help to eliminate some micro-organisms emitted by the human body and also industrial processes, but that might be a helpful effect as well.

Then there is the small amount of O2 and CO in the Martian atmosphere.  If you had a somewhat extreme brine at the bottom of the process, you might support extreme micro-organisms in that brine which would process organic materials introduced by waste water.  I believe there is 2 times as much O2 as CO, so there should be enough extra Oxygen to achieve that.

And the electrical source should work around the clock.

As for chipping ice from the top, that is not forbidden, as for some purposes, it would be pure enough.


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#21 2016-08-11 04:46:23

Antius
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From: Cumbria, UK
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Re: Desalinating water

The latent heat of melting is about 1/5th of the latent heat of boiling and will always take place at a lower temperature.  So freezing is a less energy intensive method of purification and can make use of non-concentrated solar heat, provided you are relatively close to the equator.  Most of the water you find will be frozen anyway.

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#22 2016-08-11 10:49:33

Void
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Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

First of all may I apologize to the other previous posters, I did not intend to end your participation, and I hope you will continue.

That is a good reminder, a statement which provides awareness of efficiency, which is always important.

But, efficiency should be balanced against capability, and opportunity.

Lets say I had a shopping list.  I want the following:
1) Survival water (Water I can get even in most equipment failure modes, to continue life).
2) Normal Drinking water (Water which is healthy to use long term).
3) Wash water (Water to clean average things, my body for instance).
4) Distilled water, for industrial uses, Chemical processes, etc.
5) An electrical source which works 24/7 year around (Barring systems failures).
6) A process to recycle used water, or at least "Grey Water".
7) Biological use of Martian O2 & CO for whatever useful substances that could produce.

A question to you then:
If I suggest a containment, which includes a pool of brine, covered with ice, and in this case having a roof which allows daily thermal cycles to be felt inside the containment, the hot and the cold, is that in line which what you are describing?  I see that this is likely to be implemented at a low Martian latitude, so as to have a ~24+ hour cycle?

If this is similar to your plan, I can see then how you might produce useful water ice, and you might extract that mechanically, and then melt it, with your 1/5 energy cost, to produce some useful water.  This water might satisfy items 1, 2, and 3.  I am very supportive of that good notion you have produced (Presuming that I do understand what you intend).

But what if you could add capability, and expand efficiency?

DESERT+MONOLITH.png

Disclaimer: Apes not provided with your black monolith kit. smile

Now put a shiny surface on the ground around it, on the sunward sides, add insulation to it on the other sides.

Now inverted gutters around this object, as radiator fins, periodically from top to bottom, but angle them down a bit like a roaring 20's flapper dress.

s-l1000.jpg

Each gutter angled out more than the flaps on her dress, and of course the whole device black.

So, then a Radiator/Solar collector, sufficient to generate temperatures in it's interior significantly above freezing during at least part of the Martian day, and to also radiate heat to the universe at night, so the interior of the object (Hollow) to be experiencing large temperature cycles.

No moving parts so far. 

To be useful however you would fill it with some atmospheric gas.

Of course then you might couple this, or many of them to your brine containment.  To do that you will need ducts, and Fans/Pumps/Valves.

For evaporating ice, and then condensing water during the day, the process might be rather easy.  You can either simply evaporate the surface of the ice, and then condense water from the air flow by using cold from the brine or the ice.  Or you could actually form steam inside the solar collector by injecting water, that steam on encountering the ice would either condense to it or evaporate it depending on the balance of heating power, and the air pressure you are using.  For the evaporating process, I would think rather low air pressures would work better, in the case of using steam.  If you are simply to use air, then higher pressures might suit the situation since denser air can dissolve more water vapor into it.

For the nighttime cold sub cycle, you would either have to have a containment roof which could hold a higher air pressure, and pour very cold Martian nighttime cooled air onto the ice surface, or if your containment cannot hack higher pressures (Up to 1 bar), you might try to also have piping in the brine just under the ice which might conduct a cold liquid through them.  Of course in that case the Radiator/Solar collector/(Monolith), would need to have similar tubing attached to it's insides.  The piping would precool the brine and perhaps generate loose ice crystals, but in this case, where you would operate under low pressures, you would still want to radiate heat through the roof of the containment to process the ice slab itself.

Actually, if you were to just use Martian air, you might use higher pressure at night, and lower pressure during the day, and a steam process during the day.

So, now you should be able to satisfy "4) Distilled water, for industrial uses, Chemical processes, etc.".

If you did something like this, and energy processor which uses solar & day night energy, it produces brine and fresh water for you. (If it works smile).

So, I would think you might want to add a process which will offer electrical power fairly well, on demand 24/7 (Barring a dust storm, or system failure).
5) An electrical source which works 24/7 year around (Barring systems failures).

And that then gets us to #6
6) A process to recycle used water, or at least "Grey Water".
Where at least "Grey Water" can be used instead of totally fresh water, allowing it to serve another useful purpose.

And if you should have more electricity than you need, could you use some of it to obtain O2 and CO from the Martian atmosphere for:
7) Biological use of Martian O2 & CO for whatever useful substances that could produce.

This then gets a bit nasty, but not too bad.  In the process of generating electricity from your grey water and brine, the grey water gets salty, and do you dump it into the brine, or mix it into it, and if the mix is gentle enough, micro-organisms can live in it, so as to perhaps process it biologically.  It would hopefully be unfriendly to organisms which come from the human body, so that the extreme organisms in the mix would eat them and get rid of a pathogen cycle.  And to help this you may or may not introduce O2 and CO from the atmosphere.

The entire amount of O2 might be entirely consumed by the process, or not.  If not then you might have a useful source of O2, with the CO entirely consumed by the micro-organisms.

And finally you might generate a organic material which is useful from the micro-organisms.

Life Support.

Note, I really want to back out of much more posting at NewMars for a time, as it is time consuming, and I have other necessary things to do.  But I do enjoy it much, but I also fear that I annoy much as well.

Last edited by Void (2016-08-11 11:56:38)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#23 2016-08-11 19:53:40

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Desalinating water

Previously posted as it relates to waste recovery, which you do speak too......

It would appear that we could do a lot more with a little help from our ecological freinds namely baterium of various extreme forms.

Bacteria Eat Human Sewage, Produce Rocket Fuel

But Brocadia anammoxidans, or anammox bacteria, survive without oxygen, producing energy from nitrites and ammonia, which is found naturally in human waste.

Of course all this takes place in chambers specially designed for the intended processing....This one pole in the list is power and the more we can do without its use the better off as we need that ability to survive if and when its not operating.....

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#24 2016-08-12 04:52:00

elderflower
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Registered: 2016-06-19
Posts: 1,169

Re: Desalinating water

Any designs for  human support systems (and for some industrial ones) need to avoid closed loops. These allow build up of undesirable substances/bacteria etc within the loop. So there must always be some discard and fresh make up.

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#25 2016-08-12 13:42:20

Void
Member
Registered: 2011-12-29
Posts: 3,011

Re: Desalinating water

I will respond.  I am not sure what scale your device is in your mind.
It most likely is a starter device, and in that case you would like to perhaps only use the freeze thaw method, to service a very small population of humans.  In that case I am imagining that you are contemplating digging ice out of the ground, or obtaining it's vapors by some heating method.  Or perhaps extraction from a RSL.

Scaling up, you could go all the way to extracting ice from the polar caps, and moving it to a more favorable location.  That would be the maximum scale, I think.

But if there are indeed fossil ice deposits in the rift valley, and perhaps similarly at other locations of a similar latitude, then you might use a vacuum line to transport it from the extracting point to the location of use.  As for discarding some of the water, there are maybe some useful things to do with that, but I will not deviate to that.

I have been pondering "Elon Musk's" hyper loop system.  I have been considering how the tubing might be used to lift water to high elevations in mountains, from a low elevation water source.

The hyper loop system appears to be intended to move people and perhaps cargo.  But what if it just moved a cargo, namely water vapor, at a very high speed.

In the Earth version of this, I would anticipate using wind power in the mountains, to transfer vacuum into the tube.  I do have a version where cryogenics would be involved, but I won't bother with that. 

So presumably, vapor pressure generated by water heated would supply the vapor.  Such a system would become air bound, due to small components of non-condensing gasses which would accumulate, but as I indicated windmills would supply the vacuum, so by various methods it should be workable.

Although the vapor would be thin, it would travel at a very high speed, perhaps near the speed of sound, and this would help to keep the interior of the vapor tube warm, inhibiting condensation.

For the Mars version, I would anticipate deep chilling a strong solution of brine with night time temperatures, and quenching the water vapor into it.

In this version, I would anticipate that you would have a sizable impoundment of water, such as an ice covered lake.  So, it is possible that if you had a biological activity in that lake somewhere, that might absorb some or all of the non-condensable gasses (CO2, N2, etc.) by using their metabolism.  Otherwise a degassing process would be needed, which should not be too harsh a burden.

As for the input side, I would imagine solar heat used to produce a liquid, perhaps, and most likely this would need to be degassed before inputting into the vapor tube.  But on Mars, the air pressure is not very high, so again I do not think that that burden would be overwhelming.

Ideally a long term major sources of fossil ice would be available at the equator, but eventually, perhaps during a summer season, it might be possible to go full scale with such a system, and draw water vapor from the poles, and to the equator, to provide very major ice covered bodies of water.

Then perhaps radiator / solar collectors could be distributed on the ice at periodic intervals.

DESERT+MONOLITH.png

I am aware that the above representation cannot be highly pressurized without distorting it's shape.  It is just a place holder to represent versions which would be compatible with the actual physical circumstances that need to be handled.

But with such devices, you could have sections of ice which would experience a freeze/thaw cycle, like on the north polar ice pack.  Perhaps they would actually be cylindrical, or pseudo cone shaped.

A system like that could support an electrical system, either using brine / fresh water, or steam driven.

And really I did not previously mention it, but during the night, vapors would migrate from the ice surfaces, and condense as frost on the interior surfaces of the Monolith, cylinder, or pseudo cone.  By day then that might thaw, and then provide something like a distilled water.

And if the surface of the ice were to melt during the day, then you would have your normal water which you could siphon off for use.

Last edited by Void (2016-08-12 14:14:47)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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