Low-Temp Liquid Helium System: Evaporation Heat & Temperature

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Discussion Overview

The discussion revolves around the conditions under which the heat necessary for the evaporation of liquid helium can be considered as being taken internally from the system, thereby reducing its temperature. The context includes concepts of liquid-vapor equilibrium, particularly at very low temperatures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the premise of the original question, suggesting that if the system is at equilibrium, no changes occur without external input.
  • Another participant speculates that the equilibrium might be unstable, implying that the temperature is near the evaporation point.
  • Several participants emphasize the need for a solid understanding of basic thermodynamic concepts such as equilibrium concentration, temperature, and heat of vaporization to address the question effectively.
  • There is a suggestion that the discussion may relate to "quantum cooling," which is relevant for achieving low temperatures in laboratories and quantum computing.
  • One participant asserts that lowering the pressure in an equilibrium system will lead to some liquid turning into gas, which would result in a decrease in liquid temperature, assuming the system is isolated.

Areas of Agreement / Disagreement

Participants express differing views on the implications of equilibrium and the conditions necessary for evaporation to affect temperature. There is no consensus on the original question or the underlying concepts.

Contextual Notes

Participants highlight the importance of foundational thermodynamic principles, suggesting that the discussion may be limited by varying levels of understanding among contributors.

yamata1
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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?
 
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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.
 
Last edited:
dRic2 said:
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.
 
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:
 
dRic2 said:
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 ?
 
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).
 

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