Ideal rankine cycle

Definition

The ideal Rankine cycle is a thermodynamic cycle that converts heat into mechanical energy, using water as the working fluid, and is characterized by four key processes: isentropic expansion, isobaric heat addition, isentropic compression, and isobaric heat rejection. This cycle serves as a foundational model for steam power plants and helps to evaluate and improve thermal efficiencies in energy conversion systems.

5 Must Know Facts For Your Next Test

1. The ideal Rankine cycle consists of two isentropic processes (expansion and compression) and two isobaric processes (heat addition and rejection).
2. The thermal efficiency of the ideal Rankine cycle can be improved by increasing the temperature at which heat is added and decreasing the temperature at which heat is rejected.
3. In an ideal Rankine cycle, water is vaporized in the boiler to produce steam, which then expands in the turbine to do work before being condensed back to liquid in the condenser.
4. This cycle assumes no friction losses, perfect insulation, and that all processes occur reversibly, making it an idealized version of real-world cycles.
5. The ideal Rankine cycle serves as a benchmark against which real cycles can be compared, allowing engineers to identify areas for modifications and improvements.

Review Questions

• How does the ideal Rankine cycle differ from real-world thermodynamic cycles, and what implications does this have for thermal efficiency?
  • The ideal Rankine cycle assumes perfect conditions with no irreversibilities such as friction or heat losses. In contrast, real-world cycles experience inefficiencies due to these factors, leading to lower thermal efficiencies. Understanding these differences allows engineers to analyze performance gaps and develop modifications aimed at improving efficiency in practical applications.
• Evaluate how increasing the temperature at which heat is added affects the efficiency of the ideal Rankine cycle.
  • Increasing the temperature at which heat is added raises the thermal efficiency of the ideal Rankine cycle according to Carnot's theorem. This is because higher temperatures lead to a greater temperature difference between the heat source and the working fluid, resulting in more energy converted to work. However, this improvement must be balanced against material limitations and costs associated with high-temperature operations.
• Propose modifications to the ideal Rankine cycle that could enhance its practical application in power generation.
  • To enhance the practical application of the ideal Rankine cycle in power generation, one could introduce reheat systems where steam is expanded partially in a turbine, then reheated before further expansion. Another modification could involve employing feedwater heaters to preheat water entering the boiler using extracted steam from various stages. These changes not only improve overall thermal efficiency but also help in minimizing water consumption and maximizing output.

Related terms

Isentropic Process: A process in which entropy remains constant, meaning no heat is transferred into or out of the system, often idealized for turbines and compressors.

Thermal Efficiency: A measure of the effectiveness of a thermodynamic cycle in converting heat energy into work output, typically expressed as a percentage.

Heat Exchanger: A device that facilitates the transfer of heat between two or more fluids without mixing them, commonly used in various stages of the Rankine cycle.