A piston-and-cylinder device contains 0.1 m3 of liquid water and 0.9 m3 of water vapor in equilibrium at 800 kPa. Heat is transferred at constant pressure until the temperature reaches 350°C.
a.) What is the initial temperature of the water?
b.) Determine the total mass of the water.
c.) Calculate the final volume.
d.) Show the process on a PV diagram with respect to saturation curves.
9 comments:
For part a, we just look this up in the saturated pressure part of the steam table to get the value. Can we then assume that the quality is 0.9 because 9/10 of the volume is in water vapor? Finally, for part C) is calculating the final volume going to be an interpolation from the saturation value @ 350 C and 16.5mPa to 350 C and 800kPa?
Answer to 10:17 PM comment:
You are correct about part (a).
No, the quality is NOT 0.9.
Quality is the fraction of the MASS in the vapor phase, not the volume.
The quality will be MUCH less than 0.9
part (c)
If you add heat to a sat'd mixture and eventually the temperature rises above Tsat, then the fluid is superheated.
You will need to interpolate on the 800 kPa superheateed steam table to determine the final volume.
I do not understand where you got the 16.5 MPa.
graham:
You know the volume of the liquid and you can look up the specific volume. Remember that V^ = V/m. Solve for m. Do the same thing for the vapor. Add the mass of liquid and the mass of vapor to get the total mass !
dr. b,
in part d, you ask for a PV diagram of an isobaric process, however, the in Thermo-CD I can only find isobaric diagrams that use a TV curve, is the TV curve what you actually meant to ask or are we supposed to use a PV diagram, and if so, how do we go about drawing it?
Anonymous @ 8:53 PM:
I meant a PV diagram. It looks like any other PV diagram with a 2-phase envelope. You need to add an isobaric path. What does isobaric mean ? What would such a path look like on a PV diagram ? If you did parts (a)-(c) you should know exactly what the PV diagram looks like because you have the data !
Just to clarify something...In the superheated Vapor tables, the temperature given in parenthesis is the critical temperature at that pressure, right? ex (pg 283) P=0.01 MPa (45.806 deg C)
jo:
No, the T givenin parentheses at the top of each table in the superheated vapor tables is the SATURATION temperature AT THAT PRESSURE.
There is ONLY ONE critical T for each substance.
When drawing the TV diagram, should our line start within the 2 phase part of the diagram since our initial conditions start us with a saturated mixture or should we draw tha entire process as if we had started with subcooled liquid in the cylinder
Squirrel @ 12:56 PM
This problem asks for a PV diagram.
Since the initial state for the system is a 2-phase mixture, the path for this process begins in the 2-phase envelope. You will need to calculate the quality to get a good idea of where in the 2-phase envelope the initial state lies.
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