What Happens When Water Vapor Cools at Constant Pressure?

AI Thread Summary
When water vapor cools at constant pressure, the transition from state d to state 2 involves a decrease in temperature and an increase in volume, which keeps the fluid in a saturated vapor state. The process from point 1 to d maintains constant pressure, but the cooling from d to 2 does not, as it requires a simultaneous volume increase. After reaching point 2, further volume reduction occurs by compressing the piston, leading to point 3, where the fluid becomes a saturated liquid. Throughout this compression, pressure and temperature remain constant. Understanding these transitions is crucial for analyzing thermodynamic processes in moist air systems.
princejan7
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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

 
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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.
 
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