Can a Boat Float In Supercritical Fluid?

this is liquid CO2 just before reaching its super critical point. The most fascinating part of watching a liquid become super critical to me is that before the super critical point there is obviously a liquid below with a gas above separated by a line or a meniscus, but once. becomes super critical, that line just fades away and becomes a super critical

fluid

state, but this gave me an idea and raised a question: if the line just disappears, what would happen if there was a ship?

float

ing on the surface of the liquid just as it spins Super critical, what happens to the

boat

?

Does it stay right where it was

float

ing before or would it now float to the surface since the entire tank is now full or would it sink to the bottom? Since there is no layer of liquid to float on today, I am going to test this by floating a small Styrofoam

boat

in liquid CO2 and then heating it to its super critical point in order to do this, I have to hold a lot. of pressure, the super critical point of CO2 is at 73 atmospheres, which means I need to hold over 1,000 lb per square in my container, so to do that I'm going to use this container here, it has two thick pieces of acrylic windows and I can screw them onto the body that has a valve and a pressure gauge right here.

This tank has been tested at more than double the pressure I'm going for today, but I'm still a little nervous about using it to get to this. a high pressure, so to start we need some CO2, when it's solid we call it dry ice, so I'm going to take some pieces of dry ice and put them in the container. Now I'm going to tighten these bolts and then close the valve. as soon as the pressure increases the dry ice stops going from solid straight to gas, there it goes, but now it can turn into a liquid, so now we have liquid CO2 here, if I release the pressure it freezes into solid CO2.

Again, okay, now let's do this for real, let's put in our dry ice and I'm going to add this Styrofoam half sphere to act as our boat floating in the liquid. Okay, now let's put our little boat in, let's close it. this styrofoam is very squashed but it's floating, okay, now I'm heating it up to see if we can get to a super critical pressure here, it'll be around 1.00 PSI, okay, we're above 500 PSI, we're about Half way. and look, the meniscus is still there, it's not even cold anymore, we're getting very close right now, we're at 68° F, we're waiting to get to around 87° F, look how the liquid is splashing, we're getting very close, the super critical state, okay, here it is. it's going to move a little bit look how it looks whoa what's going on it's like dripping from the top it's condensing and dripping look that's like a waterfall that's so weird it means it's super critical on the right side but then it condenses again in liquid on the left side because the right side is where my heat is, so what is happening is that the refractive index of the gas and the liquid are becoming the same, so it is not seen. a meniscus or you don't see the light.

It bends as it passes through the liquid, so even when I shake it you don't see a real difference between the refractive indices, but you can still see the styrofoam floating on top. the styrofoam is sinking deeper now, it's like disappearing, look, the line is disappearing, that meniscus is just disappearing, but the styrofoam stays in a pretty similar place to where it was okay, the line is literally disappearing, you can still see it alter the background though in this shot, so there's still a slight meniscus there, but it's moving away W and rising above the surface of the styrofoam oh, the styrofoam sank, sank into the liquid, but now I can't see a meniscus at the top anymore, you can't really tell where the gas and liquid separate, okay, it's completely super critical now, over 1,000 PSI and the styrofoam is in the bottom.

You can still see it being heated from the side, so you can see some little waves happening from the hot

fluid

going up, but it's all super critical, there's no meniscus. If I pick up the container and move it around, you can see that there are no longer two states here, it's just one state that's a little bit viscous and the Styrofoam can just fall out. through it slowly, okay, now let's let it cool a little and it should go back from its super critical state to a liquid with gas on top again and I think the styrofoam should float once again, okay, I'm going to put an ice cube on top. oh, out of sight, gone, oh, there it is.

I saw it start to float and it's back on top. Look at it, as soon as it comes out of the super critical phase, it floats back on top of the meniscus that is so cool, totally again. up okay now I'm going to release the pressure okay 3 2 1 wow the styrofoam got sucked into the little hole it tried to get out here is our styrofoam canister that survived that's where it tried to get sucked out by that little one hole in the end, so why did this boat sink when it went super critical? Well, if you think about it before it gets super critical, there is a liquid at the bottom and a gas at the top, since the boat is floating right on the surface of the meniscus, which means the average.

The density of the ship is denser than that of the gas but less dense than that of the liquid, but once it becomes super critical, these two states suddenly become one, so it would make sense that the density of the remaining fluid would be a average of these two states and Sure enough, if you look at the density of liquid CO2, it is around 800 G per liter at room temperature, but then once it reaches its critical point, it suddenly drops to just over 400 G per liter. This average density is less dense than the average ship density so it sinks to the bottom, this would also be the case for any real ship that had an open top, so here we go, now we know that ships sink into super critical fluids, so next time you're in a lake that suddenly goes super critical.

Make sure you get to shore quickly for more handy tips like this. Make sure to subscribe to my channel if you haven't already and I'll see you next time.