Intro: Carnot Efficiency & the Quality of Energy

Ch 6, Lesson G, Page 1 - Intro: Carnot Efficiency & the Quality of Energy

• In the previous lesson, we saw that the ratio of the amount of heat rejected to the cold reservoir by a heat engine to the amount of heat absorbed from the hot reservoir was equal to the ratio of the cold reservoir temperature to the hot reservoir temperature.
• This is a consequence of the 2nd Law and Lord Kelvin’s Temperature scale.  This equation also holds for the Rankine temperature scale, but not for the Fahrenheit or Celsius scales.
• All we need to know to determine the efficiency of a reversible heat engine is the temperature of the two reservoirs with which the HE interacts.
• Cool.  So, what is this lesson about ?
• In this lesson, we will look at the way that the efficiency of HE changes as the temperatures of the reservoirs change.
• This will lead us to the startling conclusion that some Joules are better or more valuable than others.
• This is sometimes called the “quality” of the energy.
• Joules that are stored at a higher temperature can do more work, so they are more valuable or have a higher quality.
• But Joules of work are already pure work, so they have the highest value or quality.
• That gives you a road-map of what this lesson is about.  So, now, let’s get started.