Joule Cycle – Components and Processes

Joule Cycle is thermodynamic cycle using constant pressure heat addition and rejection. Fuel and compressor are used to heat and increase the pressure of the gas, the gas expands and spins the blade of the turbine which produces electricity.
Joule Cycle is a thermodynamic cycle which represents the operation of constant pressure heat engine. It is also known as Brayton Cycle. It is named after George Brayton who invented it.
The engine which uses this cycle is known as Brayton engine. It was a 2 stroke engine and produces power as every revolution.
This engine uses a seperate piston comressor and piston expander with compresssed air heated by internal fire as it enters the expander cylinder.
Brayton cycles engines were some of the first internal combustion engine used for motive power.

The joule cycle consist of 4 processses as shown in the diagram below. Out of these four processes, two processes are isobaric i.e at constant pressure and other two processes are isentropic processes.

Brayton cycle are mainly used for gas turbines. Main components of this gas turbines are :-
1) Compressor
2) Combustion Chamber
3) Turbine
4) Heat Exchange

Above figure shows different components used in a Joule Cycle. In this cycle, the process carried by copmressor and turbine are isentropic process and process carried by combustion chamber and heat exhange are constant pressure process i.e isobaric process.

PV and TS diagram of Joule Cycle

Above diagram shows different processes of a Joule Cycle that are isentropic compression, constant pressure heat addition, isentropic expansion and constant pressure heat rejection.

There are four steps in Joule Cycle :-

1) Isentropic Compression :-
This is the first process of Joule cycle. This process is an isentropic process. This process will take place in first component of joule cycle i.e compressor. In this process the volume of the gas will decrease as the gas is compressed. Due to compression, pressure will increase and as this process is isentropic process and the gas is compressed, the temperature will also increase and the entropy will remain same .

2) Heat additon at constant pressure :-
This process will take place inside the combustion chamber. In this process hot air from compressor is further heated in the combustion chamber. This process is isobaric process. In this process, temperature will increase as the gas is heated, volume will increase as the temperature increases and entropy will also increase as heat is added in this process. As this process is an isobaric process, pressure will remain constant.

3) Isentropic Expansion :-
This process will take place in the turbine. The volume will increase due to expansion. As the gas is expanded, the pressure of the gas will decrease and temperature will also decrease. Since this is an isentropic process, therefore the entropy will remain constant.

4) Heat rejection at constant pressure :-
This process will take place in heat exchanger. In this process, heat will be taken out of the gas. It is an isobaric process i.e this process will be carried at constant pressure. In this process, as the heat is taken out, entropy will decrease and the temperature will also decrease. Due to decrease in temperature the volume will also decrease and the pressure will remain constant as it is an isobaric process.


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