⚙️ Appendix 2: Turbines

Everything You Need to Know About Steam and Gas Turbines

• Operating Principles:
  • Axial stages: Nozzle acceleration → rotor energy conversion.
• Key Phenomena:
  • Choked flow: Sonic limit in nozzles (expansion ratio > 2).
  • Degree of reaction: Impulse vs. reaction turbines.
• Fundamental Laws:
  • Stodola’s Law: Flow vs. inlet/outlet conditions.
  • Baumann’s Rule: Efficiency degradation with steam quality.
• Gas Turbines Comparison:

Abstract

This appendix provides details on turbines used in steam and gas power plants, focusing on design principles, performance characteristics, and operational considerations. Turbines are introduced through analysis of velocity and pressure profiles in axial turbine stages, where fluid expansion occurs in two steps: stator nozzles accelerate the flow while rotors convert available enthalpy into mechanical energy. Performance maps demonstrate the choked flow phenomenon occurring when expansion ratios exceed approximately 2, establishing a corrected mass flow rate limit at sonic conditions in nozzle throats. The degree of reaction concept is explained, distinguishing impulse turbines from reaction turbines. The concepts of isentropic and polytropic efficiency are presented. The Stodola law relating turbine flow to inlet-outlet conditions is reviewed in multiple forms, from simple to complex formulation accounting for wet zone flows. Baumann’s rule quantifies expansion efficiency degradation with steam quality, showing approximately one percentage point reduction per quality point decrease below saturation. Gas turbines section contrasts closed-cycle systems using inert working fluids (helium, CO₂) at high pressures with combustion turbines operating on flue gases at lower pressures, highlighting differences in materials, cooling requirements, blade design, maintenance needs, and operational stability.