Lecture 8-- CALM

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# Lecture 8-- CALM - PowerPoint PPT Presentation

Lecture 8-- CALM. Explain as succinctly as you can, and in your own words, why, of all possible heat engines acting between two reservoirs of fixed temperature , a Carnot cycle has the greatest possible thermodynamic efficiency??

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Presentation Transcript
Lecture 8-- CALM
• Explain as succinctly as you can, and in your own words, why, of all possible heat engines acting between two reservoirs of fixed temperature , a Carnot cycle has the greatest possible thermodynamic efficiency??
• Several answers focused on aspects that the Carnot cycle shares with others e.g.
• The Carnot is the most eficient because it uses a temperature cycle which brings the system back to where it started in the beginning.
• A heat engine with only two reservoirs does not lose any thermal energy
• The decrease in entropy of the HOT reservoir is exactly equal in magnitude to the increase in entropy of COLD reservoir. Thus the net increase in entropy of the system is zero. (i.e. it is reversible! 12 answers)

Lecture 8– Otto Cycle (simplified)

Isochoric (constant volume) heating and cooling, connected by adiabatic expansions and compressions.

The Internal combustion engine (ICE) is approximated by the Otto Cycle (not really closely, since in the ICE, the working fluid is not contained)

Definition of the Kelvin Scale
• The TRIPLE POINT OF WATER (the only point in Density-Pressure,-Temperature space where solid, liquid, and gaseous H2O can coexist in equilibrium) is defined to be at 273.16 K. Since 0K is defined to be absolute zero, this defines the Kelvin scale completely.
• The normal melting point of water (0oC) occurs at a higher pressure (101.3 kPa rather than 612 Pa) and slightly lower temperature (273.15 K).