Re: latent heat of evaporation

[Bernard Cleyet <anngeorg@PACBELL.NET>]

"...*some*dependence of L on temperature and pressure. BC suggested it
would depend mightily, but I say it depends only slightily."

There must be a misunderstanding here as L [enthalpy of evaporation] is
~ 2257 kJ/kg at 101.33 kN/m^2 [100 deg C] and 1730 at 4000 kN/m^2 [250
deg. C.]  (end of SI steam Saturation table)

using English table:

212 deg, F   (14.696 Lb/Sq. in.)  970.3 BTU/Lb and

705.4           (3206.2                 )   Zero

i.e. L goes from 970 to zero with a 73 % increase in temp. (absolute).

http://www.waudesign.com/steam_fundamentals.htm


bc


John Denker wrote:

> Ludwik Kowalski wrote:
>
>
> > Are you saying, John, that to accept two different values of L (one for
> > evaporation without boiling and another with boiling) would
> > automatically lead to the violation of conservation of energy?
>
> To zeroth order, yes.
> To first order in small quantities, there is *some*
> dependence of L on temperature and pressure.  BC
> suggested it would depend mightily, but I say it
> depends only slightily.  The molar entropy and molar
> enthalpy of the vapor are nice smooth continuous
> indeed differentiable functions in this regime.

cut