In their 1927 patent, Leo Szilard and Albert Einstein use butane as a refrigerant in their non-compressive refrigerator design. In the patent the authors begin the description of the principle of operation by stating:

A suitable refrigerant, for instance butane, in liquid form is contained within evaporator 1. An inert gas, for instance ammonia, is in troduced into evaporator 1 through conduit 30 and distributor head 31. The refrigerant evaporates in the evaporator in the presence of the inert gas due to the fact that the partial pressure of the refrigerant is reduced thereby and the resulting gaseous mixture passes through conduit 5 to within condenser 6. (Emphasis added)

Why would adding gaseous ammonia to the butane-ammonia mixture result in additional butane evaporating?

The quote refers to the parts of the diagram shown below. A full color-coded diagram of the refrigerator design can be found here. enter image description here

  • $\begingroup$ What is the driving force for evaporation? $\endgroup$ Feb 24, 2023 at 16:46
  • $\begingroup$ @ViníciusGodim evaporation is driven by the molar concentration (i.e. partial pressure) of gas molecules. Equilibrium occurs when the molar concentration is high enough that an equal number of gas molecules return to the liquid phase as leave the liquid phase. An change in average kinetic energy (i.e. temperature) will change the equilibrium point. $\endgroup$
    – cms
    Feb 25, 2023 at 16:47
  • $\begingroup$ I would say the driving force is the difference between the partial pressure at the interface, which is given by equilibrium considerations (in fact it's the saturation/vapor pressure), and the partial pressure of the bulk (distant from the interface). It's all about this difference. Diluting the gas phase will increase the diference (driving force), so more evaporates. $\endgroup$ Feb 25, 2023 at 21:57


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