On Feb 8, 2:09 pm, "RCE" wrote:
"JoeSpareBedroom" wrote in message

...

"RCE" wrote in message
m...

to reduce the pressure and it will suddenly freeze again and begin to

sublimate (goes from solid to vapor without becoming a solid).
All of this happens at what range of temperatures? When you're reducing
the air pressure, the temp is remaining fairly constant?

As the pressure is reduced, the only temperature left is that remaining in
the water, (aside from any radiant energy). As pressure is reduced, the
vapor pressure changes. Often, high intensity quartz lamps or UV emitters
are used to add energy to the remaining water molecules to excite them to a
state where they can be removed or captured by the vacuum pumps. Otherwise
they cling to the vacuum chamber walls and will slowly sublimate for hours
or days.

Think of your car's radiator. The pressure cap allows the cooling system to
operate at a higher barometric pressure than at atmosphere, raising the
boiling point of water. The opposite happens in the vacuum chambers. To a
less obvious degree, the normal barometric pressure variations at atmosphere
affects dew points, etc. for a given temperature.

BTW ... in my partial sentence quoted above about sublimation ... I meant to
say "goes from solid to vapor without becoming a liquid".

Water at altitude boils at a lower temperature - makes sense to me.