What Happens When Water Vapor Cools at Constant Pressure?

[princejan7]

Homework Statement

This is a diagram T-v diagram for a closed system consisting of a sample of moist air that is cooled at constant pressure
can someone explain what happens for the state of the water vapor to move from d to 2? if its cooling at constant pressure, why does it not stay on the pv1<pg1 curve

Homework Equations

http://postimg.org/image/93qb4figj/

The Attempt at a Solution

 

[rude man]

Going from d to 2 is not at constant pressure. It's constant pressure from 1 to d. From the graph it looks like temperature is further dropped while the volume is simultaneously increased, always so as to keep the fluid at saturated vapor. That would get you to point 2. After that, you reduce the volume (by pressing on the piston) until you reach point 3 which is saturated liquid. In this last stage pressure (and temperature) stay constant even though you're pushing on the piston to reduce the volume.