4th October 2008 - 04:25 PM
"One of the more important recent applications of vacuum technology is in large-scale industrial refrigeration. The rate of evaporation of water is accelerated in vacuum conditions and the process is used for freeze-drying foods (see Food Processing and Preservation). The water in the food is removed by sublimation into ice that, at the same time, freezes the food. "
When we freeze dry goods we keep the temperature near 273K (0.Celcius) and apply a strong vacuum. At that temperature the water gives of about 4mm Hg of pressure. What they do is to use a vacuum to turn ice directly into a vapor without having to go through the liquid stage. "If the temperature drops to 190K (-83.15C), the vapor pressure will go down to 0.0002mm Hg -or a drop of 4 orders of magnitude"
It seems that the temperature of deep space is around around 5K(-268.15C) which stops the sublimation process.
"The liquid phase, by the way, can exist only under a narrow range of conditions. For example, one can easily conceive of a situation in which the pressure is so low that liquid water cannot exist: at very low pressure, only at temperatures low enough to freeze will water have a vapor pressure low enough to remain condensed. This is, in fact, the situation in outer space; liquid water vented into space will boil and freeze simultaneously!"
You can take a look at this phase diagram
to see what that water pressure will be at different temperatures. " The mean surface conditions on Earth, Mars and Venus are indicated."
And if you find it as confusing as I did you can check this first
and then this
( which hopefully gave me a rudimentary understanding of it :)
Ps: In Sweden the funeral directors are planning to to use this instead of burning as it will be environmentally friendly :)
(It's Done by dry freezing the body and then shake it into a powder)
Kind of creepy if you ask me, humans as 'replaceable parts' sort of.