We have the following expression for the temperature of the latent heat of vaporisation:(adsbygoogle = window.adsbygoogle || []).push({});

d(L/T)/dT = (Cpv - Cpl)/T + [d(Vv - Vl)/dT] *dP/dT

Where Cpv is the heat capacity at constant pressure of the vapour and the liquid respectively, Vv and Vl are the volumes of the vapour and liquid respectively, and the d(Vv - Vl)/dT is a partial derivative at constant P.

We need to show that "when the saturated vapour of an incompressible liquid is expanded adiabatically, some liquid condenses out if Cpl + Td(L/T)/dT < 0"

I'm not sure about the meaning of "saturated vapour". Does this mean it is in equilibrium with the liquid (i.e we are on the phase boundary in the P-T plane), or does it mean supersaturated (i.e there is no liquid present)?

Also, what significance does "incompressible liquid" have?

thanks very much for your help.

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# Liquid condensing out in thermodynamics

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