Thermodynamics-heating water in piston help

  • Thread starter Thread starter JGreen48
  • Start date Start date
  • Tags Tags
    Piston Water
AI Thread Summary
The discussion revolves around a thermodynamics problem involving a cylinder/piston system with water at 105°C and 85% quality. As the system is heated, the piston compresses a spring while the volume increases from 1L to 1.5L, and the pressure reaches 200 kPa. The force exerted on the spring is calculated to be approximately 3534.29N, leading to a spring displacement of about 35.34mm. Participants suggest using saturation tables to determine the final state of the water/vapor mix after the spring compression, emphasizing the importance of following a line of constant entropy to find the final temperature at the specified pressure. The conversation highlights the need for clarity on how to apply thermodynamic principles to solve for the final state of the system.
JGreen48
Messages
1
Reaction score
0

Homework Statement


A cylinder/piston arrangement contains water at 105 C, 85% quality with a volume of 1L.
The system is heated, causing the piston to rise and encounter a linear spring. At this
point, the volume is 1.5 L, piston diameter is 150 mm, and spring constant is 100 N/mm.
The heating continues, so the piston compresses the spring. What is the cylinder
temperature when the pressure reaches 200 kPa.


Homework Equations


F/A=pressure
F=K*d


The Attempt at a Solution


From what I stated with. I solved for the Force on the spring.
F/(pi/4)(.150^2)mm=200,000 Pa
F=3534.29N

Then I found out the displacement of the spring.
3534.39=100*d
d=35.3439mm

That is where I am stuck at. What I tough might work is to find the volume after the spring is compressed. That is just over 1.5L and comparing that to the saturation tables it is above the saturated vapor. So it would be a gas. But I don't think that is correct. If anyone can help straighten me out and point me in the right direction. Thanks.
 
Last edited:
Physics news on Phys.org
The expansion from 1 L to 1.5 L is done at constant pressure with heat input. So the final state (ie: quality) of the water/water vapor, can be found from the tables. Do you know how to do that?

Once the water/vapor mix begins pushing against the piston, it is doing work and follows a line of constant entropy. If you can find the state at 1.5L above, then you can find the entropy at that state from the tables. Follow the line of constant entropy up to the pressure specified to find the final state.
 
Thread 'Have I solved this structural engineering equation correctly?'
Hi all, I have a structural engineering book from 1979. I am trying to follow it as best as I can. I have come to a formula that calculates the rotations in radians at the rigid joint that requires an iterative procedure. This equation comes in the form of: $$ x_i = \frac {Q_ih_i + Q_{i+1}h_{i+1}}{4K} + \frac {C}{K}x_{i-1} + \frac {C}{K}x_{i+1} $$ Where: ## Q ## is the horizontal storey shear ## h ## is the storey height ## K = (6G_i + C_i + C_{i+1}) ## ## G = \frac {I_g}{h} ## ## C...
Back
Top