In this chapter, we devote our attention to vapor power and refrigeration cycles. The power cycle that we consider is the Rankine or steam power plant cycle, which accounts for most of the electric power generation worldwide, far outweighing the uses of hydroelectric, nuclear, and solar power. In the Rankine cycle, the working medium is usually water, which is alternately evaporated and condensed. This is in contrast to the gas power systems discussed in Chapter 8 where the working medium is a gas that never changes phase.