How to Calculate Work and Heat Transfer in a Polytropic Process of Nitrogen?

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Homework Help Overview

The discussion revolves around calculating work and heat transfer in a polytropic process involving nitrogen gas, with specific initial and final conditions provided. The problem is situated within the context of thermodynamics, particularly focusing on the behavior of gases under polytropic transformations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the use of the temperature ratio and pressure ratio to find the final temperature, as well as the application of equations related to work and internal energy. Questions arise regarding the correct interpretation of these equations and the need to find specific volumes to proceed.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the equations involved. Some guidance has been provided regarding the distinction between work and change in internal energy, and the necessity of integrating pressure with respect to volume to find work. There is an acknowledgment of the first law of thermodynamics in relation to heat transfer.

Contextual Notes

Participants are navigating the complexities of the polytropic process and the associated calculations, with some uncertainty regarding the initial and final volumes needed for further calculations. The original poster's approach has been questioned, leading to a deeper exploration of the problem's requirements.

ZLing
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Homework Statement


Nitrogen at 100°C and 600 kPa expands in such a way it can be approximated by a polytropic process with n=1.2. Calculate the work and the heat transfer if the final pressure is 100 kPa.

Homework Equations

The Attempt at a Solution


I used the equation T2/T1=(P2/P1)^[(n-1)/n] to find T2. Then i used W=nCv(T1-T2) to calculate work done. Is this correct? But i don't know how to calculate the heat transfer.
 
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ZLing said:

Homework Statement


Nitrogen at 100°C and 600 kPa expands in such a way it can be approximated by a polytropic process with n=1.2. Calculate the work and the heat transfer if the final pressure is 100 kPa.

Homework Equations

The Attempt at a Solution


I used the equation T2/T1=(P2/P1)^[(n-1)/n] to find T2. Then i used W=nCv(T1-T2) to calculate work done. Is this correct?
No. This is not the work. This is the change in internal energy. To get the work, you need to integrate PdV.
But i don't know how to calculate the heat transfer.
If you know the change in internal energy and the work, then you can use the first law to get the heat.

Chet
 
Chestermiller said:
No. This is not the work. This is the change in internal energy. To get the work, you need to integrate PdV.

If you know the change in internal energy and the work, then you can use the first law to get the heat.

Chet
Hi, does that mean I have to find V1 and V2 first?
 
ZLing said:
Hi, does that mean I have to find V1 and V2 first?
That's one way to start.

Chet
 

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