- #1
slashrulez
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Homework Statement
A mass of 5 kg of saturated liquid -vapour mixture is contained in a piston-cylinder
device at 100 kPa (see Figure 1). Initially 2 kg of water is in the liquid phase and the
rest is in the vapour phase (State 1). Heat is transferred to the water and the piston,
which is resting on a set of stops, starts moving when the pressure inside reaches 200
kPa (State 2). Heat transfer continues until the total volume is increased by 25% (State
3).
(2) (a) Find the temperature in State 1.
(4) (b) Determine the volume in State 1.
(4) (c) What is the temperature in State 3?
(3) (d) Is State 2 in the 2-phase region or in the superheated vapour region?
(4) (e) Show the process on a P-v diagram with respect to the saturation lines; points
1-3 must be labeled and the direction of the process indicated.
(3) (f) What is the work done during this process?
(5) (g) Calculate the total heat transferred to the system.
No need to include the figure, it's pretty much a piston sitting on some stops.
Homework Equations
Errmm...none I think
The Attempt at a Solution
My question is in regards to part c, and then part e. I know that in state 2 it's a superheated vapour because I know the pressure, so I can compare specific volumes and whatnot. My problem is that I don't really know how to find anything about state 3 with the info given. All I know is that the volume goes up, so I can find the new specific volume, but past that I don't know. I don't have any info about the pressure, and all I know is that the temperature is probably more than it is in state 2. I want to assume the pressure stays constant between 2 and 3, since I could work with the specific volume and pressure to figure out the temperature pretty easily, but I don't know if I can assume that without the question stating it. As for part e, I can't really calculate boundary work without knowing the pressure, so figuring out c will probably make it straightforward.
So pretty much I'm thinking that I can assume the pressure stays constant during the expansion. Other than that, I have no idea