Introduction to GAS Turbine

To discussion Gas Turbine we must Know thermo dynamic 

1.1   Introduction for thermodynamic cycles:-

Brayton cycle & Rankine cycle

   Ø  Brayton cycle

The Brayton cycle is a thermodynamic cycle that describes the workings of a constant pressure heat engine. Gas turbine engines and air breathing jet engines use the Brayton Cycle. Although the Brayton cycle is usually run as an open system (and indeed must be run as such if internal combustion is used), it is conventionally assumed for the purposes of thermodynamic analysis that the exhaust gases are reused in the intake, enabling analysis as a closed system.

-        A Brayton-type engine consists of three components:

         ·         Gas compressor

         ·         Burner (or combustion chamber)

         ·         An expansion turbine

-       Ideal Brayton cycle:

 Ambient air is drawn into the compressor, where it is pressurized, the compressed air then runs through a combustion chamber, where fuel is burned, heating that air—a constant-pressure process, since the chamber is open to flow in and out.

The heated, pressurized air then gives up its energy, expanding through a turbine (or series of turbines). Some of the work extracted by the turbine is used to drive the compressor, heat rejection (in the atmosphere).

-        

       ·         Adiabatic process - compression.

       ·         Isobaric process - heat addition.

       ·         Adiabatic process - expansion.

       ·         Isobaric process - heat rejection.

    Since neither the compression nor the expansion can be truly isentropic, losses through the compressor and the expander represent sources of inescapable working inefficiencies. In general, increasing the compression ratio is the most direct way to increase the overall power output of a Brayton system.