Thermodynamics is the branch of physics that studies the transformation of energy. Many practical devices are designed to transform energy from one form, such as the heat from burning fuel, into another, such as work. Chapters 19 and 20 established two laws of thermodynamics that any such device must obey:
An important consequence of the second law is that heat energy is transferred spontaneously from a hotter system to a colder system but never from a colder system to a hotter system.
Our goal in this chapter is to discover what these two laws, especially the second law, imply about devices that turn heat into work. In particular:
How does a practical device transform heat into work?
What are the limitations and restrictions on these energy transformations?