Low-Temp Liquid Helium System: Evaporation Heat & Temperature

[yamata1]

We consider a system composed of liquid helium in equilibrium with its vapor at very low temperature T, each phase being considered extensive. We neglect the mass of the gas compared to that of the liquid, as well as the heat capacities of the gas and the walls compared to that of the liquid.
On what condition can we consider that the amount of heat necessary for the evaporation of the liquid is taken internally in the system, reducing its temperature?

 

[dRic2]

I don't really understand the question. If you fix T by saying that the system is already at equilibrium then nothing happens. It is equilibrium. You need to provide some further input.

 

[yamata1]

I don't really understand the question. If you fix T by saying that the system is already at equilibrium than nothing happens. It is equilibrium. You need to provide some further input.

Perhaps it's an unstable equilibrium.I guess T is close to the evaporation temperature.

 

[dRic2]

I don't think you are very familiar with the concept of liquid-vapor equilibrium. I think there are some basic concepts that you should master first (like equilibrium concentration, temperature, heat of vaporization ecc...). One you understand those concept (which are covered in every book on thermodynamics) then understanding the process you asked for is not hard at all. Writing all those stuff here might take a while though (at least for me, maybe some more expert member could give you a quicker explanation).

BTW given the generalities of the topic I assume that if you ask in particular for Helium at low temperature you might be interested in the so called "quantum cooling" (that is, the way you can reach astonishing low temperatures in labs/quantum computers). If it is so, check out this video:

 

[yamata1]

I don't think you are very familiar with the concept of liquid-vapor equilibrium. I think there are some basic concepts that you should master first (like equilibrium concentration, temperature, heat of vaporization ecc...). One you understand those concept (which are covered in every book on thermodynamics) then understanding the process you asked for is not hard at all. Writing all those stuff here might take a while though (at least for me, maybe some more expert member could give you a quicker explanation).

BTW given the generalities of the topic I assume that if you ask in particular for Helium at low temperature you might be interested in the so called "quantum cooling" (that is, the way you can reach astonishing low temperatures in labs/quantum computers). If it is so, check out this video:

If we change the pressure condition below a certain pressure some of the liquid will turn into gas no ?

 

[dRic2]

If you are at equilibrium and you lower the pressure then some of the liquid will turn into gas and the liquid temperature decreases (if you are talking about an isolated system).