# Lecture 8-- CALM - PowerPoint PPT Presentation

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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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Lecture 8-- CALM

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### 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)

Chapter 3 problems (examples)

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).

273.16K

http://boomeria.org/chemlectures/textass2/fig17-9.jpg

### P340 Lecture 10“Practical Thermometry”

• International Temperature Scale (ITS-90)

• This is the accepted standard against which secondary thermometers are typically calibrated (it deviates from absolute temperature in certain regions by several mK).

• 0.65-5K (3He or 4He equil. vapor pressure over liquid)

• 3.0 to 24.5561 K (He gas thermometer calibrated at defined fixed points)

• 13.8033 to 1234.93 K (Pt resistance thermometer calibrated at defined fixed points with set interpolation scheme).

• Above 1234.93 K: Planck radiation law.