[Phys-L] Re: Latent heat of evaporation

[betwys1 at SBCGLOBAL.NET (Brian Whatcott)]

At 03:33 PM 11/9/2005, Ludwik K.,  you wrote:

> Latent heat of water evaporation, L, is 2450 J/g at 20 C and 2260 J/g
> at 100 C. That is a decrease by about 10%. And what happens at higher
> temperatures? At high pressure water boils at higher temperatures and
> its many parameters have been measured, as shown at:
>
> http://engineeringtoolbox.com/water-thermal-properties-24_162.html
>
> 1) But the table does not say anything, at least explicitly, about L. I
> need L values for 200 C, 300 C etc. Please help, if you can. Thanks in
> advance.

A steam table calculator such as this one:
      http://www.connel.com/freeware/steam.shtml

will show the enthalpy of evaporation as 1938 kJ/kg at 200 C
                                                            1406 kJ/kg at 300 C
                                                   and    448 kJ/kg   at 370 C


> 2) Is it reasonable to assume that L is positively correlated with
> viscosity (L goes down when viscosity goes down, at higher
> temperatures). I suspect that these two parameters are correlated via
> inter-molecular forces. But I am not sure.
> Ludwik Kowalski

It is reasonable to suppose that enthalpy of evaporation
and viscosity are correlated because they are (!)
I imagine that any liquid not subject to cross-linking follows
  a similar rule.   Whether this is an intra-molecular effoct in water,
or an intermolecular effect, I have not checked.



Brian Whatcott    Altus OK    Eureka!