Lecture: Basics of heat engines

Contemporary Challenges 2021
This brief lecture covers the basics of heat engines.
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    • 2498/heat-engine-flow.svg
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This short lecture precedes osharmonicproj.

Let's apply the relationship of heat, entropy, and temperature to a contemporary challenge!

We'd like to maximize the efficiency of any process that is based on heat flow as an input.

Just a few examples of heat engines.

Energy flow diagram
Energy flow diagram

The efficiency of the machine is \begin{align} \text{efficiency} &= \frac{W}{Q_{\text{in}}} \\ \textit{e.g.} &=\frac{500\text{ J}}{1000\text{ J}} = 50\% \end{align} For a car engine, \(T_H\approx 600\text{ K}\) and \(T_C\approx 300\text{ K}\).

Remember that \(\Delta S=\frac{Q}{T}\), and \(\Delta S_{\text{tot}} \ge 0\).

Learning Outcomes