RUS New site

Advanced search

[ New messages · Forum rules · Members ]
Page 1 of 11
Forum » SpaceEngine » Science and Astronomy Discussions » Supercritical Substances (Discussion of scCO2; consequences for planets)
Supercritical Substances
WatsisnameDate: Tuesday, 30.12.2014, 23:16 | Message # 1
Galaxy Architect
Group: Global Moderators
United States
Messages: 2611
Status: Offline
Split from the General Suggestions thread.

For anyone wondering how supercritical substances look/behave, this is an excellent youtube video where a guy creates supercritical CO2 in a transparent pressurized vessel. (His method is also extremely dangerous, don't try it at home.)

JCandeias, slight misinterpretation going on here. What the research team found with their computational methods is that there may be distinct boundaries on the PV diagram where supercritical CO2 changes from "gas-like" to "liquid-like" behavior. I.e. small change in temperature or pressure will cause dramatic change in whether the fluid behaves more like liquid or gas. This is not the same as saying that there is a distinct interface, as seen between actual liquid and gas phases. So no obvious shorelines and sea surfaces as on Earth. Definition of supercritical fluid is that this interface disappears (because the density change approaches zero), as seen in the video demonstration.

Supercritical CO2 has some really interesting properties. It is a strong solvent for many substances, and also permeates materials very easily. (One of the reasons why the above demonstration is rather dangerous -- the supercritical CO2 eats through the acrylic and eventually causes failure, which due to high pressure and no release valve, can be catastrophic.)

edit: I said PV diagram where I meant to say phase diagram. Which would be a PT diagram. smile





 
JCandeiasDate: Wednesday, 31.12.2014, 14:13 | Message # 2
Pioneer
Group: Translators
Portugal
Messages: 382
Status: Offline
Quote Watsisname ()
JCandeias, slight misinterpretation going on here. What the research team found with their computational methods is that there may be distinct boundaries on the PV diagram where supercritical CO2 changes from "gas-like" to "liquid-like" behavior. I.e. small change in temperature or pressure will cause dramatic change in whether the fluid behaves more like liquid or gas. This is not the same as saying that there is a distinct interface, as seen between actual liquid and gas phases. So no obvious shorelines and sea surfaces as on Earth. Definition of supercritical fluid is that this interface disappears (because the density change approaches zero), as seen in the video demonstration.


I see.

It's not so easy to wrap one's head about planet-sized consequences of that. For instance, if slight changes in pressure and temperature lead to dramatic changes in behaviour, there should still be boundaries because in planets substances aren't pure and the kind and amount of impurities is affected by the properties of the stuff those impurities are in. But those boundaries would likely be subtle and probably pretty unstable, very easily affected or disrupted by turbulence. I guess you'd be able to see them if you can see far enough (like up to the horizon, or something like that), but at short ranges they'd be very hard to or even impossible to see.

So no familiar landscapes, no. And probably no Mars-like landscapes either, except in areas above supercritical levels. Which means such planets would indeed look different from how SE is showing them.

Or maybe I'm still missing something.





They let me use this!
 
WatsisnameDate: Wednesday, 31.12.2014, 22:19 | Message # 3
Galaxy Architect
Group: Global Moderators
United States
Messages: 2611
Status: Offline
It is very hard to say what this could look like on a planetary scale. There would be no obvious sharp interface between supercritical and ordinary liquid/gas phase, since this boundary vanishes in the supercritical regime. However, where the gas-like to liquid-like supercritical boundary occurs, there could be some visual effects. My best guess is that there might be a blurry, hazy, or turbulent area, perhaps similar to a halocline, or heat haze. Its precise nature will depend on how rapidly the conditions change with position, and how rapidly the density changes with temperature/pressure along this boundary of the phase diagram.




 
Forum » SpaceEngine » Science and Astronomy Discussions » Supercritical Substances (Discussion of scCO2; consequences for planets)
Page 1 of 11
Search: