Mercury stream in space

[Acme]

If we take a gallon of mercury into space and squirt it out from a circular orifice, will it stay all together as a 'string'?

 

All the ifs, ands, and buts entertained. Like... a string will form if the pressure is right, and the orifice is smooth, but not if too close to mass x.

[Moontanman]

I will guess no, surface tension would pull it into a string of spheres...

[imatfaal]

Surely it would freeze - I believe, if I have read the phase diagrams correctly, into a body-centred tetragonal lattice. Not sure how long this would take with no atmosphere to aid heat dispersion so perhaps your spheres or other shapes would form first

[DrP]

I would think you are right that it would have something to do with the pressure it is squirted at and also the aperture size. High pressure and small hole and you would end up with a atomised mist I suppose. Too slow and it will freeze and block the exit. Somewhere in between would give something similar to what moontanman describes. Get it right and get a long mercury sausage.

[imatfaal]

... Get it right and get a long mercury sausage.

 

Sorry, but my infantile mind loves that sentence!

[John Cuthber]

Some of the mercury will be lost by evaporation

[imatfaal]

Some of the mercury will be lost by evaporation

 

That was my immediate thought - I looked at the phase diagram

 

 

Phase diagram of mercury (1975) [Public domain], by David A. Young, from Wikimedia Commons

 

and couldn't see any gas phase. Pretty sure this is because I am misreading the diagram - or don't understand the assumptions inherent but would appreciate more information / explanation if this is the case

[swansont]

The vapor pressure of mercury is 10^-8 torr at 200K, which is close to Rb vapor pressure at room temperature. We have 1g ampoules of Rb in vacuum that have lasted a decade.

 

 

[John Cuthber]

The vapor pressure of mercury is 10^-8 torr at 200K, which is close to Rb vapor pressure at room temperature. We have 1g ampoules of Rb in vacuum that have lasted a decade.

 

At 200K mercury is a solid so that's clearly not a sensible temperature to consider it being squirted about.

The vapour pressure at room temperature (which is the temperature I'd choose for my space ship) it's about 10^-3 torr.

In the vacuum of spcae heat los from the mercury can only take place by radiation or evaporation.

Something shiny like mercury is a poor radiator(it's far from being a "black body".

So, evaporative cooling will take place.

 

Just out of idle curiosity, the Rb in that sealed ampule- if you raised the temperature until the vapour pressure was, say, half an atmosphere, how much would you "lose" and where would it go?

Once the headspace was full of vapour, how long would it last, and why would 10 years be relevant to that timescale?

[swansont]

At 200K mercury is a solid so that's clearly not a sensible temperature to consider it being squirted about.

The vapour pressure at room temperature (which is the temperature I'd choose for my space ship) it's about 10^-3 torr.

In the vacuum of spcae heat los from the mercury can only take place by radiation or evaporation.

Something shiny like mercury is a poor radiator(it's far from being a "black body".

So, evaporative cooling will take place.

 

 

 

emissivity of mercury is about 0.1 So it will underperform a black body by one order of magnitude.

 

A small drop with a surface area of 1 mm^2 will radiate about 50 microwatts in space instead of 500. That's about 0.1g. Specific heat capacity of .14 J/gK, so the drop needs to shed 0.014 J to drop 1 degree. That will take less than 5 minutes, without accounting for evaporative cooling. Even though the cooling rate slows, it'll be pretty cold in several hours, and the vapor pressure will have dropped a couple orders of magnitude. (edit: off by x100. Drop by a degree in a few seconds. See below)

 

So, how fast will it evaporate?

[Sensei]

A small drop with a surface area of 1 mm^2 will radiate about 50 microwatts in space instead of 500. That's about 0.1g.

I tried reproducing your calcs on piece of paper, and getting 0.282 mm radius, and then 0.094 mm^3 volume of drop.

Shouldn't you multiply volume by density 13.5 g/cm^3 = 0.0135 g/mm^3 to get mass of sphere?

I am getting mass of drop (sphere) 0.00127 g.

Or I misunderstood what you meant by 0.1g?

[John Cuthber]

From time to time we see threads about "What would happen to someone exposed to the vacuum of space?" and there's a discussion about whether or not they would explode because of the vacuum etc.

 

Imagine that there's a life form somewhere with blood made of mercury, and that they were having the same discussion. They may well come to a similar conclusion. Exposed body fluids would boil.

 

 

In principle, any liquid exposed to a good enough vacuum will boil.

That's true of room-temperature mercury in space.

So, the answer to the question "So, how fast will it evaporate?" is an interesting one, but if there's something to nucleate boiling- perhaps the vortexes produced by squirting it, the answer might be "quite fast".

There's certainly nothing to stop it doing so.

 

Also, when it cools to about -39 C the temperature will stop dropping for a short while because heat needs to be removed in order to freeze the material.

That's about 2.3 KJ/mol

So, for the 1 degree change near the mp the heat it needs to lose is about 12 J/g

It will take roughly 100 times as long to cool through -39C as to cool by a degree near room temp

[swansont]

I tried reproducing your calcs on piece of paper, and getting 0.282 mm radius, and then 0.094 mm^3 volume of drop.

Shouldn't you multiply volume by density 13.5 g/cm^3 = 0.0135 g/mm^3 to get mass of sphere?

I am getting mass of drop (sphere) 0.00127 g.

Or I misunderstood what you meant by 0.1g?

 

 

No, it's my error. I started working with a 1 mm radius and switched to 1 mm^2 surface area, and copied the wrong number.

 

So there's ~1/100 as much I calculated, and the cooling happens 100x faster.

[Moontanman]

From time to time we see threads about "What would happen to someone exposed to the vacuum of space?" and there's a discussion about whether or not they would explode because of the vacuum etc.

 

Imagine that there's a life form somewhere with blood made of mercury, and that they were having the same discussion. They may well come to a similar conclusion. Exposed body fluids would boil.

 

 

In principle, any liquid exposed to a good enough vacuum will boil.

That's true of room-temperature mercury in space.

So, the answer to the question "So, how fast will it evaporate?" is an interesting one, but if there's something to nucleate boiling- perhaps the vortexes produced by squirting it, the answer might be "quite fast".

There's certainly nothing to stop it doing so.

 

Also, when it cools to about -39 C the temperature will stop dropping for a short while because heat needs to be removed in order to freeze the material.

That's about 2.3 KJ/mol

So, for the 1 degree change near the mp the heat it needs to lose is about 12 J/g

It will take roughly 100 times as long to cool through -39C as to cool by a degree near room temp

 

 

I have my doubts about mercury boiling in a vacuum, I have been googling this and so far everything points at mercury being a liquid that will not boil in a vacuum. Evaporate faster possibly but that is not the same as boiling...

[Raider5678]

From time to time we see threads about "What would happen to someone exposed to the vacuum of space?" and there's a discussion about whether or not they would explode because of the vacuum etc.

Can you give me a link to that thread? I'd like to read it.

[Bender]

The surface tension between mercury and air is about 7 times larger than between water and air. I'm not sure how it works in a vacuum, but I seriously doubt that the mercury would remain a long sausage. On the other hand, the inertia is also considerably larger.

Could there be a critical diameter for the string: if it is larger, the mercury would separate before it can cool down too much; if it is smaller, it would freeze before it can move?

[John Cuthber]

 

 

I have my doubts about mercury boiling in a vacuum, I have been googling this and so far everything points at mercury being a liquid that will not boil in a vacuum. Evaporate faster possibly but that is not the same as boiling...

You can't have tried searching for "vacuum distilled mercury" which shows that you can boil it in a vacuum.

 

I wonder how you would think it could fail to boil in a vacuum.

Things boil if their vapour pressure exceeds the local "atmospheric" pressure.

 

In any event, there is going to be some evaporation loss.

Can you give me a link to that thread? I'd like to read it.

This sort of thing

https://physics.stackexchange.com/questions/91215/how-does-blood-saliva-boil-in-outer-space

Edited April 13, 2017 by John Cuthber

[Acme]

...In principle, any liquid exposed to a good enough vacuum will boil.

That's true of room-temperature mercury in space.

So, the answer to the question "So, how fast will it evaporate?" is an interesting one, but if there's something to nucleate boiling- perhaps the vortexes produced by squirting it, the answer might be "quite fast".

There's certainly nothing to stop it doing so.

...

So I was thinking to minimize vortices by using a laminar flow nozzle like they use in those dancing fountains. >>

 

So if we get a laminar flow stream at a rate that freezes before it boils away, we have a sublimating sausage?

[Moontanman]

You can't have tried searching for "vacuum distilled mercury" which shows that you can boil it in a vacuum.

 

I wonder how you would think it could fail to boil in a vacuum.

Things boil if their vapour pressure exceeds the local "atmospheric" pressure.

 

In any event, there is going to be some evaporation loss.

This sort of thing

https://physics.stackexchange.com/questions/91215/how-does-blood-saliva-boil-in-outer-space

 

 

With mercury surface tension is an important consideration. As i said from what I've been able to find so far mercury would have to be heated quite hot for it to boil in a vacuum. Something like 225C...

[DrP]

 

Could there be a critical diameter for the string: if it is larger, the mercury would separate before it can cool down too much; if it is smaller, it would freeze before it can move?

 

exactly - when I said a sausage I was thinking more along the lines of an extruded wire. I do not even know if it is possible under the right conditions with mercury or not. I would 'guess' that it would be possible under the right temps and pressures to extrude it into a longer wire. You can do it with most other metals, so why not mercury,

[swansont]

 

I wonder how you would think it could fail to boil in a vacuum.

 

 

I personally have seen mercury not boil in a vacuum. Take a tube of mercury, closed at the bottom. Invert it. The gap at the top of the tube, as you know, will be a vacuum. The mercury in it is not boiling.

[Bender]

Could it be that the internal pressure inside the mercury, caused by surface tension, is large enough to keep it from boiling.

[John Cuthber]

 

 

I personally have seen mercury not boil in a vacuum. Take a tube of mercury, closed at the bottom. Invert it. The gap at the top of the tube, as you know, will be a vacuum. The mercury in it is not boiling.

The top, as I know and you should know, will contain mercury vapour at about 0.002 mmHg pressure.

That's (exactly) enough pressure to stop the mercury boiling.

It's also a very high pressure compared to some systems that both of us have worked with; I'm a little surprised to see you describe it as a vacuum.

 

Also, here on earth if you heat a beaker with some mercury in it the pressure at the bottom of the beaker is significantly more than at the top.

That will influence the behaviour significantly. The stuff at the top will evaporate quickly before the stuff at the bottom reaches its boiling point.

However- in space where gravity doesn't create a meaningful hydrostatic pressure, that doesn't happen.

 

The surface tension may be enough to stop it boiling (at least for small droplets- the effect depends on the radius of curvature of the surface and is zero for a flat surface.)

 

That still will not stop it evaporating, and there will in spite of all the arguments, still be a a loss of mercury by evaporation.

[swansont]

The top, as I know and you should know, will contain mercury vapour at about 0.002 mmHg pressure.

That's (exactly) enough pressure to stop the mercury boiling.

It's also a very high pressure compared to some systems that both of us have worked with; I'm a little surprised to see you describe it as a vacuum.

Which is, of course, one of the reasons we label the quality of vacuums. But we still call them vacuums.

 

That still will not stop it evaporating, and there will in spite of all the arguments, still be a a loss of mercury by evaporation.

The argument is not that evaporation won't take place, it's that it will not be at a significant rate. Not sure what "all the arguments" are that you're referring to.

[John Cuthber]

Which is, of course, one of the reasons we label the quality of vacuums. But we still call them vacuums.

 

 

The argument is not that evaporation won't take place, it's that it will not be at a significant rate. Not sure what "all the arguments" are that you're referring to.

OK, would you use the same labels for space and the relatively huge pressure at the top of a mercury barometer?

 

What I said at the outset was "Some of the mercury will be lost by evaporation"

Your reply was

"The vapor pressure of mercury is 10^-8 torr at 200K, which is close to Rb vapor pressure at room temperature. We have 1g ampoules of Rb in vacuum that have lasted a decade."

 

You seemed to be arguing that evaporation would not take place: in the same way that it hadn't taken place in a sealed Rb ampule.

 

Then there was Bender's comment that "The surface tension between mercury and air is about 7 times larger than between water and air."

​Which might change the boiling point, but the original assertion was that it would evaporate.

For what it's worth the effect goes the "wrong" way to stop it boiling.

"The vapor pressure at a convex curved surface is higher than that at a flat surface. "

from

https://en.wikipedia.org/wiki/Kelvin_equation

So, the little drops that form will be more likely to boil and/ or evaporate.

 

And we had Moontanman's argument that it won't boil "With mercury surface tension is an important consideration. As i said from what I've been able to find so far mercury would have to be heated quite hot for it to boil in a vacuum. Something like 225C... "

which (probably relies on the assumption of normal gravity.

 

Notwithstanding all that; as I said before

"Some of the mercury will be lost by evaporation"

Let me know if anything changes.