Thermodynamics: Cooling Superheated Water Vapor to Saturated Vapor

[afpskierx]

Superheated H20 at 400 kPa is slowly cooled in a sealed rigid vessel until the temperature is measured to be 115 centigrade, when condensation first occurs.

What is the Initial Temperature?

I know that the temperature and pressure at point two (saturated vapor) can be found in a standard saturated water vapor table. I found Tsat and Psat to be 115 Centigrade and 169.18 kPa respectively.

Is there enough information here to find the initial temperature of the superheated vapor? how do I proceed?

 

[afpskierx]

Is it a simple ratio of the Pressure and Temperature at each point?

i.e. P1/T1=P2/T2 ?

 

[Chestermiller]

Is it a simple ratio of the Pressure and Temperature at each point?

i.e. P1/T1=P2/T2 ?

Sure, but please check to make sure you are in the ideal gas region for water. The molar density is a constant in this problem (as is, of course, to mass density). You may be able to follow a constant density line for water on a published graph, or in the steam tables (I don't remember whether the steam tables give constant density data, although they probably don't). You can also use corresponding states info, virial equation parameters, or van der waals parameters to correct for non-ideal behavior, if that turns out to be significant.