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Thermodynamics Cycle of Processes

  • #1

Homework Statement


A certain fluid of mass 1kg undergoes a cycle of processes in a piston and cylinder device as follows:

Process A-B: 70kJ of work done on the fluid. 35kJ of heat rejected to surroundings

Process B-C: 50kJ of heat transferred to the fluid. No change in internal energy of system.

Process C-A: 100kJ of work done by the fluid, fluid returns to the initial state.

Calculate the heat transferred to or from the fluid in process C-A.


Homework Equations


I know that ΔU=Q-W is a relevant equation as I have been able to work out the other parts of this question that I have not written here with it, this part is actually the first part of the question but I am finding it the hardest to see what to do here :redface:

The Attempt at a Solution


I dont know whether you are supposed to use some of the values listed in Process A-B again or am I missing something?
 

Answers and Replies

  • #2
19,675
3,987

Homework Statement


A certain fluid of mass 1kg undergoes a cycle of processes in a piston and cylinder device as follows:

Process A-B: 70kJ of work done on the fluid. 35kJ of heat rejected to surroundings

Process B-C: 50kJ of heat transferred to the fluid. No change in internal energy of system.

Process C-A: 100kJ of work done by the fluid, fluid returns to the initial state.

Calculate the heat transferred to or from the fluid in process C-A.


Homework Equations


I know that ΔU=Q-W is a relevant equation as I have been able to work out the other parts of this question that I have not written here with it, this part is actually the first part of the question but I am finding it the hardest to see what to do here :redface:

The Attempt at a Solution


I dont know whether you are supposed to use some of the values listed in Process A-B again or am I missing something?
What you're missing is that, for a cyclic process, the sum of the three ΔU's has to be zero.

Chet
 
  • #3
Ah thank you very much for pointing that out! Much appreciated!
 

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