When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

I'm thinking as one side floats to the edge of the puddle it must be
warmer (thinner water layer due to surface tension?), which makes it melt
faster and rockets it off to the other side. But that explanation seems
kind of weak.


--
"Let us learn to dream, gentlemen, then perhaps we shall find the
truth... But let us beware of publishing our dreams before they have been
put to the proof by the waking understanding." -- Friedrich August Kekulé

Gregory L. Hansen wrote:

When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

It's probably not just ice, but has oxygen and CO2 in it too.
Not to mention acetylene, and all other sorts of traces.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
What a wonderfull world it is that has girls in it! -- Robert A Heinlein.

(Gregory L. Hansen) wrote in message ...
When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

I'm thinking as one side floats to the edge of the puddle it must be
warmer (thinner water layer due to surface tension?), which makes it melt
faster and rockets it off to the other side. But that explanation seems
kind of weak.

If I understand your question right, you're on the right track. The
"ice" could be melting so fast it boils at the same time. More likely,
whatever the substance is, the atmosphere is probably below the
critical pressure, the same reason dry ice doesn't melt, it goes
straight from solid to gas. So you have this little chunck of "ice"
boiling rapidly, and that creates a blanket of gas around it, allowing
it to behave like a little hovercraft. Any little "pop" in the boiling
of the ice would make it dance.

(Gregory L. Hansen) wrote in message ...

When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

Any ideas why the ice would contain trapped compressed micro-bubbles?

It seems to me I've seen something similar, but with dry ice ...

OK ... check that. Given the temperature of LN2, maybe your water ice
contains bits of solid CO2. Or maybe there are trapped microbubbles
after all ... ordinary ice cubes are full of trapped air, and if they
don't actually dance, they certainly can effervesce. I associate the
effect with colder freezers, but I'm not sure why ... more rapid
freezing, less chance for gas to diffuse out of the solid, more
entrapped bubbles formed from the solid by nucleation after
solidification?

OYTOH ... don't drops of LN2 also dance on on countertops like water
on a hot skillet? Looks like all you need is rapid gas generation,
whatever the source.

In article ,
Ian Stirling wrote:
Gregory L. Hansen wrote:

When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

It's probably not just ice, but has oxygen and CO2 in it too.
Not to mention acetylene, and all other sorts of traces.

I wouldn't have thought it would be that cold. This is the boiloff from
the liquid nitrogen, and I just have a long hose attached to it to prevent
water vapor from backstreaming in, and to keep ice from building up at the
outlet -- the hose is long enough that the vapor is too warm to freeze
anything before it reaches the end.

I'm actually kind of disturbed that the LN2 boils off so quickly, I don't
think a good design should do that. But I have what I have.

--
"Let us learn to dream, gentlemen, then perhaps we shall find the
truth... But let us beware of publishing our dreams before they have been
put to the proof by the waking understanding." -- Friedrich August Kekulé

Gregory L. Hansen wrote:
In article ,
Ian Stirling wrote:
Gregory L. Hansen wrote:

When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

It's probably not just ice, but has oxygen and CO2 in it too.
Not to mention acetylene, and all other sorts of traces.

I wouldn't have thought it would be that cold. This is the boiloff from
the liquid nitrogen, and I just have a long hose attached to it to prevent

Hmm.
If you've got a cylinder of CO2 nearby, you could try wafting some over
the hose for a while, and see if it goes faster.
I'd still bet on this being the cause.
A thermometer would also do of course.

snip
I'm actually kind of disturbed that the LN2 boils off so quickly, I don't
think a good design should do that. But I have what I have.

Are you sure the vacuum (if any) is pumped down right?
Even a small leak will ruin a vacuum bottle.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
My inner child can beat up your inner child. - Alex Greenbank

Heat presure. The resistace of the conductor to take the heat away
,,the energy exchange is pushing against the resistor and cant go any
faster so it will hange directions.

Change veritables .
1 , use a copper table .
2 ,,place a gas over the ice and change the thermal conductive time of
surounding air.
3 ,,will resistance of thermal conductivity cause vibrations ?
4 ,,time of movment cycle ,,compa with same sise bubble going up in
water moves back and forth because it cant speed up .

In article ,
Ian Stirling wrote:
Gregory L. Hansen wrote:

snip
I'm actually kind of disturbed that the LN2 boils off so quickly, I don't
think a good design should do that. But I have what I have.

Are you sure the vacuum (if any) is pumped down right?
Even a small leak will ruin a vacuum bottle.

The liquid helium will last almost two weeks and the liquid nitrogen can
barely last until Monday morning if I fill it on Friday night, and it
holds more nitrogen than helium. So I don't know what the deal is.
--
"Let us learn to dream, gentlemen, then perhaps we shall find the
truth... But let us beware of publishing our dreams before they have been
put to the proof by the waking understanding." -- Friedrich August Kekulé

"tj Frazir" wrote in message
...
Change.. .. ..

BS Filter Activated.