29 January 2018

Brayton cycle

The Brayton cycle is a thermodynamic cycle that can be invented by George Brayton in 1872.

The Brayton cycle is a type of power cycle that utilizes and ideal gas to generate power from a type of fuel used to heat the air.

What is the Brayton cycle?

In the Brayton cycle, two reversible adiabatic processes and two constant pressure process are done in a heat engine. 

Brayton cycle

Process of Brayton cycle :

The Brayton cycle consist of four processes following below :
  • Adiabatic quasi-static process compression process: In this process compressor takes fresh ambient air and compressed it to a higher temperature and pressure. 
  • Constant pressure heat addition process: In this process, compressed air is sent to the combustion chamber where fuel is burnt at constant pressure. 
  • Adiabatic quasi-static expansion process: High-temperature gases expand to the ambient temperature in the turbine and produce the power.
  • Constant pressure heat rejection process: The exhaust gases leave the turbine and air back to its initial condition.

The efficiency of the Brayton cycle :

In general, the thermal efficiency of the Brayton cycle is defined as the ratio of the work output to the heat input at the high temperature.

ŋth = W / QH

For ideal gas can now we expressed in terms of temperature :

ŋth  = NetWork / Heat Input = WT – WC / Qin

      = cp [ (T3 – T4 ) – (T2 – T1) ] / cp (T3 – T2)

      = 1 – [ (T4 – T1) / (T3 – T2) ]


WT = Work is done by the gas in the turbine
WC = Work was done on the gas in the compressor
cp = Heat capacity ratio