Finding the work done by a Stirling Cycle

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Homework Help Overview

The discussion revolves around determining the theoretical work and heat transfer values in an ideal Stirling Cycle, as represented in a p-V diagram. Participants are exploring concepts from thermodynamics, particularly focusing on the relationships between pressure, volume, and temperature in the context of the Stirling engine.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of work using the integral of pressure with respect to volume and question how to apply the ideal gas law to express pressure in terms of other variables. There is also an exploration of the four distinct processes in the Stirling cycle and their corresponding formulas.

Discussion Status

Some participants have provided guidance on identifying the processes in the Stirling cycle and suggested relevant formulas. There is an ongoing exploration of how to derive the theoretical values for work and heat transfer, with no explicit consensus reached yet.

Contextual Notes

One participant notes their limited understanding of thermodynamics, indicating a potential gap in foundational knowledge that may affect their ability to engage with the problem fully. There is also mention of a desire to compare theoretical results with actual values to assess efficiency.

TheBigDig
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1. Given the following p-V diagram of an ideal Stirling Cycle, determine the theoretical values of W12, Q12, W34 and Q34 in terms of T1, T2, V1, V2, n (the number of moles) and R (the universal gas constant). Determine the total theoretical p-V work W12341 for the full cycle.2. dU = dQ-Pdv3. I've only just started thermodynamics recently, so my grasp on it is still very weak. I've tried finding W12 using W = -∫pdV but I'm not really sure how that gives me theoretical work. I think I'm supposed to end up with some sort of numerical answer for the final part to compare it with an actual p-V work value and find the efficiency of the Stirling Engine.
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TheBigDig said:
I've tried finding W12 using W = -∫pdV but I'm not really sure how that gives me theoretical work.
When you write W12 = - ∫p dV, both p and V are changing from 1 to 2. How about replacing p with something else using the ideal gas law?
 
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The working fluid in an ideal Stirling cycle engine goes through four processes :

Compression at constant temperature .
Heat addition at constant volume .
Expansion at constant temperature .
Heat removal at constant volume .

Can you identify the four processes on your diagrams ?

What formulas apply to each process ?

Reading material :

Stirling Cycle
Constant temperature process
Constant volume process
 
Last edited:
Nidum said:
The working fluid in an ideal Stirling cycle engine goes through four processes :

Compression at constant temperature .
Heat addition at constant volume .
Expansion at constant temperature .
Heat removal at constant volume .

Can you identify the four processes on your diagrams ?

What formulas apply to each process ?

Reading material :

Stirling Cycle
Constant temperature process
Constant volume process
Oh thank you! Your response was very illuminating. I hope you don't mind but I'd just like to check I've got this right:
For Isothermal Expansion : W = nRTln[Vf/Vi]
For Isothermal Compression: W = - nRTln[Vf/Vi]
For Heat Addition: Q = nCvΔT
For Heat Removal: Q = - nCvΔT
 

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