The Carnot cycle is an idealized thermodynamic cycle that operates between two temperature extremes, a high-temperature source (T_H) and a low-temperature sink (T_C). It is the most efficient thermodynamic cycle possible for a given temperature range. While the Carnot cycle is a useful theoretical construct, it is not suitable for practical steam power plants due to several reasons:
Irreversibilities: The Carnot cycle assumes that all processes within the cycle are reversible, meaning there are no energy losses or inefficiencies. However, real-world systems, including steam power plants, involve various irreversibilities such as friction, heat losses, and pressure drops. These irreversibilities result in energy losses and reduce the actual efficiency of the system.
Condensation and Evaporation: In a steam power plant, water is heated to generate high-pressure steam in a boiler, which is then expanded through a turbine to produce work. The Carnot cycle assumes that the heat transfer occurs isothermally (at constant temperature) during the heat addition and rejection processes. However, in practice, the heat transfer in a steam power plant involves condensation of steam in the condenser and subsequent evaporation in the boiler, which are not isothermal processes.
Non-ideal behavior of working fluids: The Carnot cycle assumes that the working fluid used in the cycle is an ideal gas, which does not experience any phase change or other non-ideal behavior. In steam power plants, water and steam exhibit non-ideal behavior due to their phase transitions, specific heat variations, and properties like wetness fractions. These non-ideal behaviors make it challenging to achieve the theoretical efficiency of the Carnot cycle.
Practical limitations: Steam power plants have practical considerations such as mechanical limitations, thermal stresses, material constraints, and cost considerations that need to be taken into account. These practical limitations further prevent the realization of the idealized Carnot cycle efficiency.
Despite the Carnot cycle not being suitable for steam power plants, engineers and designers aim to maximize the efficiency of these power plants through various improvements and innovations. Efforts are made to optimize the design, improve heat transfer, minimize irreversibilities, and incorporate advanced technologies to enhance the overall efficiency of steam power plants.