Lecture Notes: Rankine Cycle and Thermodynamics

Introduction

• Acknowledged current global tensions, historical context of drills in school.
• Homework: 5 problems from Chapter 10 due next Wednesday.
  • Reminder of modified problem 9-119.
  • Last day to show proof of prerequisites for one student.

Rankine Cycle Overview

• Models steam power plants, not gas power cycles.
• Uses water (H2O) transitioning through liquid and vapor phases.

Components of Rankine Cycle

• Pump: Moves liquid (water) from low to high pressure.
• Boiler: Heats water to vapor (steam).
• Turbine: Work is done as steam expands and pressure drops.
• Condenser: Removes heat, condenses vapor back to liquid.
• Heat rejection typically into a separate water supply, not directly into the atmosphere.
• Heat Inputs/Outputs:
  • Boiler (heat input)
  • Condenser (heat rejection)
  • Work input from pump
  • Work output from turbine.

Comparison to Brayton Cycle

• Similar in constant pressure heat transfer.
• Work done isentropically in ideal Rankine cycle.

Thermodynamic Process and Efficiency

• First Law of Thermodynamics applied to each component.
• Enthalpy changes:
  • Pump: Work input (H2 - H1)
  • Turbine: Work output (H3 - H4)
  • Boiler: Heat input (H3 - H2)
  • Condenser: Heat rejection (H4 - H1)
• Thermal Efficiency: Net work over heat input.
• Power Calculation: Based on mass flow rate and work/heat per unit mass.

Example Problem: Ideal Rankine Cycle

• Given pressures, temperatures, and mass flow rate to determine thermal efficiency and net power.
• Process involves using steam tables for properties and applying first law for calculations.

Non-Ideal Rankine Cycle

• Isentropic Efficiency: Accounts for real-world losses in pump and turbine.
• Modified equations for heat input, pump work, and turbine work.
• Example problem demonstrating these principles.

Improving Rankine Cycle Efficiency

• Reheat Cycle:
  • Expands steam in stages, reheating in between to increase efficiency.
  • Allows for lower material stress by avoiding extreme temperatures.
• Regeneration (not same as Brayton):
  • More complex due to temperature differences.

Practical Considerations

• Multiple pumps for maintenance.
• Real-world applications require balancing cost and efficiency.

Conclusion

• Looked at non-ideal cycles and methods to improve efficiency.
• Reminder: Homework and prerequisite proof due dates.

Next Steps:

• Explore more example problems and thermodynamic cycles in future sessions.