The critical point

[sniffnoy]

I really want to see a critical point demonstration where you have, like, a rectangle of some fluid, and somehow you have a temperature gradient across one dimension, and a pressure gradient across another, with the critical point in the middle, so that like you can see that there is a phase boundary that runs across part of it until it stops in the middle.

...is that possible? Because I really want to see what that looks like.

Comments

[pklemica]

I'm not sure how you could maintain a pressure gradient across a rectangle of fluid, unless it was actually a bunch of small rectangles near each other each with their own separated regulated environment?

[sniffnoy]

Yeah I dunno! But if they were all separate you wouldn't get to see the phase boundary, which defeats the point. Annoying.

I mean, you can do just a pressure gradient, right? But it's both at once that seems difficult...

(Also hi! :) )

[pklemica]

(hi!)

Ok wait now that I've said idk how you'd do a pressure gradient, I have a really easy way to do a very specific pressure gradient, but it's a super-subtle one and I don't know how to do a different one... maybe with a big enough rectangle it'd give you enough differentiation?

But anyways, orient the rectangle vertically and gravity will do the work for you

[sniffnoy]

Ha, yeah! That'd have to be big, but... the question then is there anyway to somehow keep the temperature constant vertically while varying it horizontally...

[pklemica]

maybe not perfectly constant but I think you could have temperature-regulating structures just outside the tank, like, pumping the right temp up along its back the whole time? If it's a thin enough tank that'll get you something close to what you want

This is growing into a pretty big-budget experiment

[sniffnoy]

Yeah it doesn't have to be perfect it just has to be good enough that you can see a boundary with an endpoint! :)

This is growing into a pretty big-budget experiment

Haha I suppose it is!

[sniffnoy]

Hm so I was talking to someone about this the other day and they suggested that maybe a centrifuge would work as a smaller way to get the needed pressure gradient, rather than relying on just gravity...? Hm...

[armiphlage]

Maybe divide the rectangle of fluid into an array of sealed containers, to allow you to maintain the temperature and pressure separately in each one? Not continuous, but it'd let you show them closer to what's on a phase diagram.

[sniffnoy]

Yeah but the point is to see the *boundary* and its end.