Increasing the Performance
Image Source: Thermodynamics : an Engineering Approach, C Engle
Methods Of Increasing Efficiency:
1) Increase Turbine inlet temperatures: This follows basic logic; An increase in temperature is related to an increased pressure ratio (by the ideal gas law). This leads to an increased efficiency according to the ideal Brayton efficiency equation. The upper limit of this temperature is related to the material properties of the turbine blades.
2) Increase Turbine and Compressor Efficiency: As sub-components of the cycle, an increased efficiency with these components directly relates to greater cycle efficiency. The major improvement in turbine and compressor efficiency is mostly due to advancements in aerodynamic simulations.
3) Modifications to the Simple Brayton Cycle: These fall into several categories:
a) Regeneration: This step creates a closed heat exchanger between the turbine exhaust and the compressor outlet. This step heats the air prior to the combustion chamber recapturing heat that would normally be discharged to the environment.
b) Multiple stage compression with intercooling: The theory here follows basic thermodynamic principle; if we can maintain a near constant temperature, less work will be required for compression. This is done by compressing in multiple stages, and removing heat between devices.
c) Multiple stage expansion with reheating: The idea here is the same as compression with intercooling but in reverse: the high pressure, high temperature air is expanded in a turbine, reheated back to the high pressure and temperature, and then expanded again in another turbine, these processes create the work out of the cycle.
Text reference (Thermodynamics 5th Ed., Cengle, Y. p 517-519)
1) Increase Turbine inlet temperatures: This follows basic logic; An increase in temperature is related to an increased pressure ratio (by the ideal gas law). This leads to an increased efficiency according to the ideal Brayton efficiency equation. The upper limit of this temperature is related to the material properties of the turbine blades.
2) Increase Turbine and Compressor Efficiency: As sub-components of the cycle, an increased efficiency with these components directly relates to greater cycle efficiency. The major improvement in turbine and compressor efficiency is mostly due to advancements in aerodynamic simulations.
3) Modifications to the Simple Brayton Cycle: These fall into several categories:
a) Regeneration: This step creates a closed heat exchanger between the turbine exhaust and the compressor outlet. This step heats the air prior to the combustion chamber recapturing heat that would normally be discharged to the environment.
b) Multiple stage compression with intercooling: The theory here follows basic thermodynamic principle; if we can maintain a near constant temperature, less work will be required for compression. This is done by compressing in multiple stages, and removing heat between devices.
c) Multiple stage expansion with reheating: The idea here is the same as compression with intercooling but in reverse: the high pressure, high temperature air is expanded in a turbine, reheated back to the high pressure and temperature, and then expanded again in another turbine, these processes create the work out of the cycle.
Text reference (Thermodynamics 5th Ed., Cengle, Y. p 517-519)