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How to Get Ultra-low Temperature Like -196 C

02/24/2017 3:46 AM

How to get Ultra-low temperature like -196C

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Anonymous Poster #1
#1

Re: How to get Ultra-low temperature like -196C

02/24/2017 3:53 AM

Try this.

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#2
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Re: How to get Ultra-low temperature like -196C

02/24/2017 8:28 AM

Liquid Nitrogen, it boils at -195.79C.

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#3
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Re: How to get Ultra-low temperature like -196C

02/24/2017 9:18 AM

That's good unless you need -196 C to make liquid nitrogen...

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#18
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Re: How to get Ultra-low temperature like -196C

02/24/2017 12:45 PM

You are right of course, but the OP doesn't state what he needs -196C for. For all I know, he trying to get a record for overclocking an old AMD cpu.

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#4

Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 9:30 AM

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The lowest temperature that has been achieved till now is by cooling of sodium gas to only half a billionth of a degree above absolute zero which corresponds to -273°C .
Now , the basic principle to consider is that temperature is the measure of energy content of the matter i.e, the cooler the molecules are , the smaller is their energy and their velocity.
Ultra low temperatures can be achieved by Laser cooling and Evaporative cooling methods .
LASER COOLING
It is based on the principle that when an atom absorbs and re-emits a photon , it's momentum changes. There are number of laser cooling methods out of which the common method is by Dopppler Cooling which is accompanied by Magneto-optical trap for trapping of cooled atoms.
The primary force used in laser cooling and trapping is the recoil when momentum is transferred from photons scattering off an atom. This radiation-pressure force is analogous to that applied to a bowling ball when it is bombarded by a stream of ping-
pong balls. The momentum kick that the atom receives from each scattered photon is quite small; a typical velocity change is about 1 cm/s. However, by exciting a strong
atomic transition, it is possible to scatter more than 10^7 photons per second and produce large accelerations (10^4 g). The radiation-pressure force is controlled in such
a way that it brings the atoms in a sample to a velocity near zero (cooling), and holds them at a particular point in space (trapping).
The cooling is achieved by making the photon scattering rate velocity-dependent using the Doppler effect.


If the laser frequency is below the atomic resonance frequency, the atom, as a result of this Doppler shift, will scatter photons at a higher rate if it is moving toward the laser beam , than if it is moving away. This leads to a larger force on the counter-propagating atoms. If laser beams
impinge on the atom from all six directions, the only remaining force on the atom is the velocity-dependent part, which opposes the motion of the atoms. This provides strong damping of any atomic motion and cools the
atomic vapor. This arrangement of laser fields is often known as "optical molasses”.
Although optical molasses will cool
atoms, the atoms will still diffuse out of the region if there is no position dependence to the optical force. Position dependence can be introduced by "Magneto-Optical Trap" (MOT).

​The position-dependent force is created by using appropriately polarized laser beams and by applying an inhomogeneous magnetic field to the trapping region. The magnetic field regulates the rate at which an atom in a particular position scatters photons from the various beams and thereby causes the atoms to be pushed to a particular point in space.
EVAPORATIVE COOLING
Further cooling is done by evaporative cooling, by selective removal of the most energetic atoms of the system. In a magnetic trap, the most energetic atoms can move further against the pull off the magnetic forces and can therefore reach regions with higher magnetic fields than the cooler atoms . At those high magnetic fields , they get into resonance with radio waves or microwaves which changes the magnetic moment in such a way that the atoms fly away and escape from the trap.
MEASUREMENT OF ULTRA LOW TEMPERATURE :
The ultra low temperatures achieved can be measured by calculating the extension of the cloud . The larger the cloud is, the more energetic are the atoms because they can move further against the magnetic forces.
The size of the atomic clouds is determined by illuminating the cloud with laser light which is strongly absorbed by the atoms and they cast a shadow. Since the magnetic fields are precisely known, the size of the cloud is an absolute measure of the atom's energy and temperature. The density distribution of the atom reflects the distribution of potential energy.
Another method to determine temperature is to measure the kinetic energy of the atom. For that, the magnetic trap is suddenly switched off by switching off the current through the magnetic coils. In the absence is magnetic forces, the atoms simply fly away and the clouds expands ballastically. For a fixed time of ballistic expansion, the size of the shadow is a measure of the temperature which is proportional to the square of the size of the shadow

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#5

Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 10:06 AM
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#6
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 10:42 AM

Very interesting. I have a wafer of "high" temperature superconductor that I've always wanted to play with but have never located a supply of liquid N2 and I have wondered about making it.

However, 3500 psi sounds like it should be treated with respect!

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#7
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:09 AM

Praxair sells LN. I don't know if you can rent a cryostat but you probably can for a nominal fee and a deposit. I used to bring my LN home years ago in a good vacuum-bottle-type Thermos, for my high-temp superconductor. Just make damn sure you don't tighten the cap.

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#8
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:18 AM

note to self: don't tighten cap on boiling liquid! whew, I feel we've dodged a bullet there....

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#9
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:29 AM

This is a public forum which any visitor can read. You know as well I do a lot of people come here who have no common sense and wouldn't know not to do this, some of whom may have access to LN on the job and may want to bring some home for whatever reason. To you it may seem I am unnecessarily pointing-out the obvious, but to someone else this may not be obvious at all, they tighten the lid - and end up with shrapnel in their guts.

Are we now clear on this, Mr. Snarky, seeing as this aspect wasn't obvious to you at all?

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#10
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:43 AM

note to self: Andrew has no sense of humor....and a thin skin

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#12
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:49 AM

Justify your comments however you like. I couldn't care less.

What I do care about are readers maiming themselves because they don't know to take certain precautions when dealing with materials of this sort.

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#15
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:55 AM

You definitely need some more precautions if you feel your suggestion of obtaining through Praxair gives you liability (moral or legal).

It would be good to advise against swallowing.

It would be good to caution about frostbite.

It is very important to note suffocation hazard in spaces not well vented.... if they just loosen the cap, they might die sooner than had the thermos exploded.

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#17
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:57 AM

Reader take note ⇑

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#22
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Re: How to Get Ultra-Low Temperature Like -196 C

02/25/2017 1:11 PM

..not so ridiculous after all..

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#23
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Re: How to Get Ultra-Low Temperature Like -196 C

02/25/2017 1:44 PM

I wasn't going for ridiculous, just thinking of accidents. There was an instructor who was going to demonstrate Leidenfrost effect by holding ln in his mouth. He got confused and swallowed some which landed him blacked out in the ER in short order.

Can't find that particular 1st person essay, but here is indication of at least two more.

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#25
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Re: How to Get Ultra-Low Temperature Like -196 C

02/26/2017 8:28 AM

A professor? That's ridiculous in and of itself.

Perhaps he should have been honest and said he was doing a demonstration of how to be a contender for the Darwin award.

Maybe he was trying to demonstrate how to make ice cream in the stomach.

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#20
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 2:48 PM

Nothing like a near death experience to motivate one to educate one's self about the materials one is dealing with....

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#26
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Re: How to Get Ultra-Low Temperature Like -196 C

02/27/2017 11:15 AM

I do appreciate your concern, but given some of the questions I have seen asked on this forum...

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#11
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:45 AM

I think he was being ultraliteral....as in dodging shrapnel....or bullets from an exploding sealed container.

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#19
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 1:23 PM

Rixter, how long have you had your HT superconductor? I'm asking because I noticed that mine began to crumble some years after I bought it. You may wish to vacuum-seal yours until you're ready to use it. Also to dry it thoroughly (by baking at a low temperature) after use as it will quickly become covered in frost.

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#21
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 9:41 PM

I've had it for a long time. I'm not sure where it is right now, but the last time I saw it, it seemed OK. (I believe it's YBCO, Yttrium Barium Copper Oxide.)

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#13

Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:50 AM

To reduce the temperature below n2 boiling point at atmospheric pressure, the boiling point of n2 can be reduced with a decrease in pressure via vacuum pump.

The heat removed by evaporation of n2 at reduced pressure can bring the temp low enough to freeze n2 solid.....somewhere around -210° C.

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#14
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:54 AM

I tried this with a Styrofoam cup filled with LN, which I placed inside a vacuum desiccator (whose lid I replaced with a 1"-inch-thick slab of Plexiglas so I could see what was going on). About 2/5 of the LN boiled away before the rest froze.

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#16
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Re: How to Get Ultra-Low Temperature Like -196 C

02/24/2017 11:56 AM

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#24
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Re: How to Get Ultra-Low Temperature Like -196 C

02/26/2017 1:12 AM

You can also do it with liquid helium.

Several years ago one job I had involved inspection of two MRI installations.

LN2 was used to cool down the magnet windings to about 77 deg K, then LHe introduced and run through the whole assembly until no N2 was detected in outlet stream.

when I asked the installer if the the LHe would freeze the LN2 solid, he xplained that that's exactly what could happen.

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