Which cycle specifies heat addition occurs at constant pressure?

The Rankine cycle is the correct choice because it is defined by processes that include heat addition at constant pressure. In the Rankine cycle, water is typically used as the working fluid. The cycle consists of four main processes: isentropic compression, isobaric heat addition, isentropic expansion, and isobaric heat rejection.

During the isobaric heat addition process, the working fluid, which is in a liquid state, absorbs heat at constant pressure as it is converted into steam. This phase change occurs in a boiler, where the fluid is heated while maintaining a steady pressure.

This characteristic is critical for many thermal power plants that utilize the Rankine cycle because it allows for efficient steam generation and subsequent power production when the steam expands through a turbine. Understanding the pressure and temperature conditions at which heat is added allows engineers to design systems that maximize efficiency and optimize performance.

In contrast, the Carnot cycle operates between two temperature reservoirs and includes both isothermal and adiabatic processes, while the Brayton cycle involves heat addition at constant pressure but is more closely associated with gas turbines and its processes. The Otto cycle is associated with gasoline engines and features heat addition at constant volume, further distinguishing it from the Rankine cycle.