Stirling efficiency and practice

  • Context: High School 
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Discussion Overview

The discussion revolves around the efficiency of Stirling engines, particularly in comparison to Carnot efficiency, and the practical implications of using pumps in Stirling generators. Participants explore the relationship between temperature differences, compression ratios, and the effects of internal pressure on mechanical work and efficiency.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that Stirling efficiency ideally matches Carnot efficiency, depending on the temperature difference (Th and Tc) and the compression ratio (V2/V1).
  • One participant questions the necessity of a pump in a Stirling generator, suggesting it does not alter the compression ratio or temperature difference.
  • Another participant proposes that increasing the internal pressure of the working fluid enhances the heat carrying capacity, potentially increasing system power without changing efficiency.
  • A comparison is made between Stirling engines and Otto or Diesel engines, noting that while turbo engines can produce more power at the same compression ratio, they also consume more fuel, implying that efficiency does not necessarily increase.
  • It is suggested that the use of a pump in a Stirling generator is analogous to using a turbine in an Otto engine, with the implication that it does not lead to increased efficiency.

Areas of Agreement / Disagreement

Participants express differing views on the impact of internal pressure and the role of pumps in Stirling engines, indicating that multiple competing perspectives remain without consensus on the relationship between power, efficiency, and the use of additional components.

Contextual Notes

Participants do not fully resolve the implications of increased internal pressure on efficiency versus power output, nor do they clarify the assumptions underlying their comparisons with Otto and Diesel engines.

Pisica
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https://www.physicsforums.com/threa...-is-it-the-same-as-the-carnot-engine.1066209/

Not to disturb these discussions, I think we should open the discussion about Stirling efficiency and practice.

The majority say that the Stirling efficiency is ideally the Carnot efficiency. That is, it would depend only on Th and Tc through eff=1-Tc/Th

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From this formula we deduce that the efficiency increases with the Th-Tc temperature difference and with the compression ratio V2/V1
 
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And then, if so, why does this man uses a pump at Stirling generator? That it does not change either the compression ratio or the temperature difference?
 
Quite simply more atoms per unit volume of the working fluid thus delivering greater heat carrying capacity. This leads to an increase in system power.
 
kazaly said:
Quite simply more atoms per unit volume of the working fluid thus delivering greater heat carrying capacity. This leads to an increase in system power.
Are you saying that a higher internal air pressure leads to a higher mechanical work obtained, but without changing the efficiency of the engine?
That is, higher pressure of the working gas, leads to a higher mechanical work obtained but with proportionally higher heat consumption?
 
Let's make a comparison: the Otto or Diesel engine with or without the turbine.
The turbo engine has more power at the same compression ratio, but also consumes proportionally more fuel.
Practically, the efficiency does not increase.

The Diesel engine can have a higher compression ratio than the Otto engine, so the Diesel engine has a higher efficiency,
This verifies the formula that the efficiency depends on the compression ratio.

I want to say that the man who uses the pump to increase the amount of air in the cylinder of the Stirling generator does the same thing as the turbine for the Otto engine and still does not increase its efficiency.
 

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