Two tanks are connected by a valve and line

Click For Summary

Homework Help Overview

The discussion revolves around a problem involving two tanks connected by a valve, focusing on the conservation of mass and the calculation of internal energy based on final states of the tanks. The subject area includes thermodynamics and fluid mechanics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the implications of constant total mass in the tanks and how this affects the mass fraction of vapor. There are attempts to clarify the relationship between final states, including temperature, pressure, and volume, and how these relate to internal energy calculations. Some participants express confusion regarding the reasoning and calculations presented.

Discussion Status

The discussion is ongoing, with participants providing insights into the relationships between variables and calculations. There is an exchange of ideas regarding the final quality and internal energy, but no consensus has been reached on the correct approach or interpretation of the problem.

Contextual Notes

Participants are working under the constraint of not having an answer key and are attempting to verify their calculations and reasoning based on the information provided in the problem statement.

joejoe121
Messages
17
Reaction score
2
Homework Statement
Two tanks are connected by a valve and line. The volumes are both 1 cubic meter with R-134a at 20 C, quality 15% in tank A and tank b is evacuated. The valve is opened and saturated vapor flows from A into B until the pressures become equal. The process occurs slowly enough that all temperatures stay at 20 C during the process.
a) Initial specific internal energy in A is......kj/kg
b) Initial mass in A is.......kg
c) Final specific internal energy of R-134 is..........kj/kg
d) Total work during process is.......kj
e) Total heat transfer during the process is.......kg
Relevant Equations
u = u_f + x(u_g-u_f)
v= = v_f +x(v_g-v_f)
mass = V/specific volume
I've attached all my work and data table I used to answer the questions but there isn't an answer key so I would like a second opinion.
1729777630818.png

1729781738954.png
 

Attachments

  • 1729777719669.png
    1729777719669.png
    54.1 KB · Views: 87
Last edited:
Physics news on Phys.org
In parts c, d, and e, the total mass is constant. This tells you the mass fraction vapor in the final state (assuming equal final mass in the two tanks).
 
Chestermiller said:
In parts c, d, and e, the total mass is constant. This tells you the mass fraction vapor in the final state (assuming equal final mass in the two tanks).
I'm sorry, I don't follow.
 
The total final mass in each tank is half the initial mass in the first tank. You know the final temperature, pressure, and volume of each tank, so this tells you the final quality. Once you know this information, you can calculate the final internal energy in each tank.
 
  • Like
Likes   Reactions: joejoe121
Chestermiller said:
The total final mass in each tank is half the initial mass in the first tank. You know the final temperature, pressure, and volume of each tank, so this tells you the final quality. Once you know this information, you can calculate the final internal energy in each tank.
I found my internal energy for Tank B by finding my values at state 2.
u = u_f + x(u_g - u_f)
but I need x so I solve quality in state 2 by using saturated volume values at 20 F and solved for specific volume by using V2 = V_a + V_b = 2 meter cubed. I used the mass of the initial tank and since mass is constant, I used it with specific volume = 2m^3/m.
Next, I plugged in my quality, and values given at 20 F for saturated vapor and liquid to get the specific internal energy at 20F using the final quality.
Lastly, I used Q = m(u_2 - u1) u_2 being the specific internal energy I solved for in the previous step and u_1 is from Part a.

I hope my writing gets my point across concisely.
 
  • Like
Likes   Reactions: Chestermiller

Similar threads

Replies
11
Views
1K
Replies
2
Views
2K
  • · Replies 13 ·
Replies
13
Views
1K
Replies
2
Views
2K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
Replies
60
Views
7K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 21 ·
Replies
21
Views
1K
  • · Replies 17 ·
Replies
17
Views
2K