Cryogenic Temperature

Because somebody else chose the terms before you did....

[My brief search for the etymology came up blank, so I wonder if there is really a better explanation. Maybe "cryo" is ancient Greek for "colder than hell"?]

Yeah, it's bound to be Greek or Latin.
Or maybe Irish from a Mr O'Genic who got tearful in cold weather?
Del

Consult your local Code or dictionary. Partisans can probably be found for <100°C, <100°F, and a host of other arbitrary choices.

Apparently you have a computer. You need to learn how to use the resources it provides!

http://en.wikipedia.org/wiki/Cryogenics

http://en.wikipedia.org/wiki/Cryonics

Ultra low is a relative term which if used with temperature describes temperatures below normal. This temperature may not necessarily be low enough to be considered cryogenic.

I have already checked these sites, could not get answer of OP.

You should read what has been posted already, without marking it as Off Topic. As mentioned already, there probably is no definite answer for this.

Dear guru Tornado, one more OT respectfully for you. Why you need to to comment on every question comes before you, particularly if you do not have proper answer. One should not expect that everyone know about every thing. Please see three consecutive comments after you, which are really GA's. Thank a lot for comments # 7,8 &9.

The first sentence of the first link (below -150° C, -238° F or 123 K)

Second link (from Greek kryos- meaning icy cold)

The etymology (per Wikipedia):

• The word cryogenics stems from Greek and means "the production of freezing cold"; however the term is used today as a synonym for the low-temperature state. It is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins, but most scientists^[1] assume it starts at or below -150 °C or 123 K (about -240 °F). The National Institute of Standards and Technology at Boulder, Colorado has chosen to consider the field of cryogenics as that involving temperatures below −180 °C (93.15 K). This is a logical dividing line, since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and normal air) lie below −180 °C while the Freon refrigerants, hydrogen sulfide, and other common refrigerants have boiling points above −180 °C.

In layman's terms, cryogenics is the study of how you make things like liquid helium. (Cryo = freeze genic = make) As you can see from the Wiki paragraph, it is a little more specific than "low temperature" or "ultra low temperature". It includes the study of how things react at very low temperatures (rubber balls shattering, etc). A lot of articles appeared in the late 50's and early 60's on the subject. Space exploration was probably the thing driving interest, although food processing might have had something to do with it too.

The discussion about what constitutes cryogenic and what doesn't is an endless one amongst academics that has many proponents for different temperatures. It has been discussed at the International Conference on Cryogenics and most recently in a publication called Low Temperature News where an article by Professor Scurlock who has many years experience in the field has proposed an upper limit of 250K or -23C and sets out some very good arguments why this should be the case.

The important thing is to define the relevant temperature to the application you are working on. My own area of engineering concentrates almost exclusively on 77K or -196C which by any definition is cryogenic but the superconductor community are searching for elusive High Temperature Superconductors by which they mean superconductors that operate at my temperature scale (-196C), high is releative to the temperatures they work at.

Liquid CO2 would be warm compared to my area but still cold enough to do you serious harm if you come into contact with it.

Hope this helps, doubt it does.