IPB

Welcome Guest ( Log In | Register )

11 Pages V  < 1 2 3 4 > »   
Reply to this topicStart new topic
Temperature and pressure at Gale, Suitable (for short periods) for liquid water?
udolein
post Sep 30 2012, 11:59 PM
Post #16


Junior Member
**

Group: Members
Posts: 40
Joined: 29-December 11
Member No.: 6295



CO2 won't be a liquid at normal conditions due to the 5.1 bar triple point. This is the reason why dry ice sublimates directly to gaseous CO2. There would be no liquid phase in between. The phase transition would happen from D to F as well.

Udo


--------------------
But to be a lament on the lips of the loved one is glorious, For the prosaic goes toneless to Orcus below. (Friedrich Schiller: Naenie)
Home of marspages.eu and plutoidenpages.eu
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 12:14 AM
Post #17


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (udolein @ Sep 30 2012, 11:19 PM) *
BTW: This site has the current weather readings: marsweather.com

Udo

They also have ground temperatures, true ?
It would be nice to see ground temperatures also.
One reason, for instance, is that the temperature of the bottom, sides and other parts of the rover facing the surface and not in direct sunlight is largely in radiative equilibrium with the ground. Heat conduction via the atmosphere is negligible regardless of air temp.
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 12:33 AM
Post #18


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (udolein @ Oct 1 2012, 12:44 AM) *
The phase transition under the conditions mentioned would happen directly from ice to gas. It evaporates. There would be no boiling at all. At 40c a liquid phase is impossible at 6-10 mbar air pressure.
In my above phase diagram the phase transition would happen from point D to F. No liquid phase at all.

Udo

Note that I am talking about magically placing a glass of ice water ( temp 1c or so) on the surface. Please see earlier post.
As I state, the 40c temp I mentioned is the temp of the sand, not the water. Radiative heating from the surrounding sand would probably be more important than conduction thru the bottom of our glass.

And I'm not clear on why you are referring to the phase diagram of CO2 in some of your post
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 01:36 AM
Post #19


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (djellison @ Sep 30 2012, 11:25 PM) *
Quite- we''re dancing around a tiny tiny wedge at the low pressure end of the liquid part of the H2O phase diagram. Even with dramatic salt content, that end of the diagram doesn't change much.

Are you looking at a phase diagram designed for engineers ( most of them are as is the one udolien is using). If so the area of interest to atmospheric scientist will always be a "tiny tiny wedge". On one designed for Martian use the "tiny wedge" will occupy a whole page.
Go to the top of the page
 
+Quote Post
nprev
post Oct 1 2012, 02:41 AM
Post #20


Senior Member
****

Group: Admin
Posts: 8004
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Um. Let's put it this way, Eyes: We ain't gonna see any liquid water at Gale. We're a few billion years too late.

Let's deal with what is real.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
djellison
post Oct 1 2012, 04:13 AM
Post #21


Administrator
****

Group: Chairman
Posts: 14019
Joined: 8-February 04
Member No.: 1



QUOTE (Eyesonmars @ Sep 30 2012, 05:36 PM) *
On one designed for Martian use the "tiny wedge" will occupy a whole page.


Yes it would - and on that page you would see that at these very low pressures, the temperature difference between melting and boiling is very small.
Go to the top of the page
 
+Quote Post
Juramike
post Oct 1 2012, 02:01 PM
Post #22


Senior Member
****

Group: Moderator
Posts: 2780
Joined: 10-November 06
From: Pasadena, CA
Member No.: 1345



QUOTE (Eyesonmars @ Sep 30 2012, 07:33 PM) *
Note that I am talking about magically placing a glass of ice water ( temp 1c or so) on the surface.


Or take a glass of ice water and put it in a vacuum chamber and suddenly expose it to vacuum. [Done the equivalent lotsa times in a rotary evaporator].

Doug's right, it would boil. Bubbles of water vapor would form at imperfections in the glass of the surface and it would bloop up out of the glass and go everywhere. A combination of sudden cooling due to more evaporative surface area would make all the flung water droplets quickly turn to ice, which would then sublimate away.

[When this happens in the lab, it is due to the receiver trap bumping, and there is usually a "Dangit!" if any of the water drops land back in the previously dried compound].

(Water-->bloop--->freeze--------------------->sublimate)

The water-bloop-droplet-freeze sequence would happen on the order of a few seconds. If the glass has a rougher surface, it would foam and froth smoothly due to all the nucleation sites. If it was a really smooth surface, it would sit quietly for a second and then just release it in a massive spasm of boiling due to the fewer nucleation sites.


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
Go to the top of the page
 
+Quote Post
ElkGroveDan
post Oct 1 2012, 02:13 PM
Post #23


Senior Member
****

Group: Admin
Posts: 4732
Joined: 15-March 05
From: Sloughhouse, CA
Member No.: 197



QUOTE (Eyesonmars @ Sep 30 2012, 06:36 PM) *
Are you looking at a phase diagram designed for engineers ( most of them are as is the one udolien is using). If so the area of interest to atmospheric scientist will always be a "tiny tiny wedge". On one designed for Martian use the "tiny wedge" will occupy a whole page.

I can make one the size of a highway billboard and it won't change the state of matter anywhere in the universe. As Doug has repeated several times you are talking about a miniscule portion of the phase diagram in every practical sense. You might as well obsess over how many angels could break-dance in that portion of the diagram without bumping into each other.


--------------------
If Occam had heard my theory, things would be very different now.
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 05:07 PM
Post #24


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



Hey guys come on
Before you all pile on Please read my posts from the beginning.
I've never suggested that liquid water would be stable on mars in any realistic scenario.
I am addressing the question posed by the author of this thread.
In it I clearly state why liquid water is all but impossible on mars.
Then I offer some physical insight into my statement by offering a thought experiment.

I know it is so easy to take a single post out of context - who hasn't ?

(yet another Doug here)
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 05:20 PM
Post #25


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (Juramike @ Oct 1 2012, 02:01 PM) *
Or take a glass of ice water and put it in a vacuum chamber and suddenly expose it to vacuum. [Done the equivalent lotsa times in a rotary evaporator].

Doug's right, it would boil. Bubbles of water vapor would form at imperfections in the glass of the surface and it would bloop up out of the glass and go everywhere. A combination of sudden coo anling due to more evaporative surface area would make all the flung water droplets quickly turn to ice, which would then sublimate away.

[When this happens in the lab, it is due to the receiver trap bumping, and there is usually a "Dangit!" if any of the water drops land back in the previously dried compound].

(Water-->bloop--->freeze--------------------->sublimate)

The water-bloop-droplet-freeze sequence would happen on the order of a few seconds. If the glass has a rougher surface, it would foam and froth smoothly due to all the nucleation sites. If it was a really smooth surface, it would sit quietly for a second and then just release it in a massive spasm of boiling due to the fewer nucleation sites.

Juramike,
I have followed your posts for years and have learned a great deal from you, especially the thought experiments you pose.

In your opinion what would happen to a glass of water with a temperature of 4c put into that chamber at a pressure of say 12mb. ? ignore other variables for the moment
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 05:46 PM
Post #26


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (djellison @ Oct 1 2012, 04:13 AM) *
Yes it would - and on that page you would see that at these very low pressures, the temperature difference between melting and boiling is very small.

Yes
The temperatures and pressures we are used to dealing with on earth in engineering, meteorology, you name it,are rarely near the triple point of water. But on Mars we have an entire PLANET and atmosphere which is never very far from the triple point of H20. Small changes in conditions near the triple point can have major effects. I would imagine future residents of mars would see H20 behave in ways that would seem alien to us. Their very existence might depend on understanding how H20 behaves under Martian conditions.
Go to the top of the page
 
+Quote Post
marsophile
post Oct 1 2012, 05:49 PM
Post #27


Member
***

Group: Members
Posts: 362
Joined: 10-September 08
Member No.: 4338



I think one can make a case for transient wetting under certain conditions. Suppose there is overnight frost concentrated , let's say, in a cold trap area. In the early morning while the air temperature is still well below freezing, the thin frost cover might produce a green house effect on the soil beneath, especially for an east-facing slope, so that it warms above freezing. So there might be brief wetting underneath a vanishing frost cover.

Obviously this can only happen at locations and times where there is overnight frost. The Opportunity rover has shown this can occur even in equatorial regions. It would be nice to have orbital surveys of where and when frost occurs.
Go to the top of the page
 
+Quote Post
Juramike
post Oct 1 2012, 06:53 PM
Post #28


Senior Member
****

Group: Moderator
Posts: 2780
Joined: 10-November 06
From: Pasadena, CA
Member No.: 1345



QUOTE (Eyesonmars @ Oct 1 2012, 12:20 PM) *
In your opinion what would happen to a glass of water with a temperature of 4c put into that chamber at a pressure of say 12mb. ? ignore other variables for the moment


(Assuming bp. of H2O at 12 mb is at 10 C)

It would probably behave similar to a low boiling liquid under terrestrial conditions. I'd use diethyl ether as an example (b.p. 35 C). It won't boil at a normal room temperature of 25 C, but it will evaporate very quickly.
As it evaporates, it will cool.

Water should do the same thing under vacuum, but water's melting point is pretty high, so it will evaporatively cool and then freeze. After it is frozen it will sublimate. Some wierdness might occur if the glass of water is deep enough, the water would freeze on top and maybe you'd get liquid water sealed up in the ice? (Sublimation will also suck heat out of the system, eventually the whole thing should freeze solid then sublimate.)

BTW, a very similar phenomenon is predicted for any Titan ponds of pure methane. They would evaporatively cool, freeze (from the bottom up), then the totally frozen methane pond would slowly sublimate.


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
Go to the top of the page
 
+Quote Post
Eyesonmars
post Oct 1 2012, 07:27 PM
Post #29


Junior Member
**

Group: Members
Posts: 85
Joined: 5-September 12
Member No.: 6635



QUOTE (Juramike @ Oct 1 2012, 06:53 PM) *
(Assuming bp. of H2O at 12 mb is at 10 C)

Water should do the same thing under vacuum, but water's melting point is pretty high, so it will evaporatively cool and then freeze. After it is frozen it will sublimate. Some wierdness might occur if the glass of water is deep enough, the water would freeze on top and maybe you'd get liquid water sealed up in the ice? (Sublimation will also suck heat out of the system, eventually the whole thing should freeze solid then sublimate.)

Do you think it is possible that by exposing the glass to simulated Martian sun the evaporative cooling could be offset enough to keep it liquid until it all evaporated ?
Go to the top of the page
 
+Quote Post
Juramike
post Oct 1 2012, 07:39 PM
Post #30


Senior Member
****

Group: Moderator
Posts: 2780
Joined: 10-November 06
From: Pasadena, CA
Member No.: 1345



Hmmm. That's a good question, but off the top of my head I'd guess no, it wouldn't. Local airspeed is probably a bigger factor, with faster winds increasing sublimation (and evaporation).


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
Go to the top of the page
 
+Quote Post

11 Pages V  < 1 2 3 4 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 25th November 2017 - 05:55 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.