Understanding Freeze-Drying: IR Radiations, Sublimation & Phase Transitions

[Himanshu_6174]

Well! the material to be freeze-dried is irradiated with IR radiations before, why??
Also I am confused as to how can ice sublime at atmospheric pressure?? Isn't the triple point of water much lower? is the vacuum around the material created for this reason? ( to lower the pressure I mean)

Also stupid it may sound, but why does the phase diagram of H₂0 show that at atmospheric pressure water will undergo phase transition at a perticular temperature ?? (100°C) when evaporation occurs all the time i.e at all temperatures!

thanks in advance!

 

[collinsmark]

Also I am confused as to how can ice sublime at atmospheric pressure?? Isn't the triple point of water much lower? is the vacuum around the material created for this reason? ( to lower the pressure I mean)

Also stupid it may sound, but why does the phase diagram of H₂0 show that at atmospheric pressure water will undergo phase transition at a perticular temperature ?? (100°C) when evaporation occurs all the time i.e at all temperatures!

thanks in advance!

You may wish to research the concept of vapor pressure.

In a closed (i.e., sealed, isolated) system, vapor pressure can be calculated (or looked up from a reference table) and is approximately a function of temperature alone (for a given liquid or solid [such as ice] also in the container).

But what happens in an open system, where the vapor pressure cannot be maintained because perhaps the atmosphere (if there even is an atmosphere) might wisk away the vapor molecules? What happens to remaining liquid (or solid, such as ice) if its container is not closed and thus cannot maintain its otherwise stable vapor pressure?

[As far as the IR irradiating is concerned, I think that's a separate issue.]