Gas turbine:

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. Gas turbine may also refer to just the turbine component. Energy is added to the gas stream in the combustor, where fuel is mixed with air and ignited. In the high pressure environment of the combustor, combustion of the fuel increases the temperature. The products of the combustion are forced into the turbine section. There, the high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades, spinning the turbine which powers the compressor and, for some turbines, drives their mechanical output. The energy given up to the turbine comes from the reduction in the temperature of the exhaust gas.

                                                Figure: Gas turbine chamber.

Gas turbine works on the basis of Bray ton cycle. Brayton cycle is called the backbone of the gas turbine. Here the T-S and P-V diagram is shown in below:

All four processes of the Brayton cycle are executed in steady flow devices so they should be analyzed as steady-flow processes.

When the changes in kinetic and potential energies are neglected, the energy balance for a steady-flow process can be express, on a unit-mass basis, as −

                       

                                                                                               

           Figure: 1^st stage blade of GT

                                        Figure: T-S and P-V diagram of Brayton cycle.

(Q _in –Q _out) + (W_in –W _out) = H _exit – H _inlet

Therefore, heat transfers to and form the working fluid are

                        Q _in = H₃ – H₂ = C_p (T₃- T₂)

            And, Q _out = H₄ – H₁ = C_p (T₄ – T₁)

Then the thermal efficiency of the ideal Brayton cycle is-

 Brayton efficiency = 1 – (Q _out / Q _in).