Closed Cycle Gas Turbine

A closed cycle gas turbine, in its simplest form, as shown in Fig 5.14, consists of a compressor, heating chamber, gas turbine which drives the generator and compressor and a cooling chamber. In this turbine, the air is compressed adiabatically (generally in rotary compressor) and then passed into the heating chamber. The compressed air is heated at constant pressure with the help of some external source, and made to flow over the turbine blades (generally reaction type). The gas, while flowing over the blades, gets expanded. From the turbine, the gas is passed through the cooling chamber where it is cooled at constant pressure with the help of circulating water, to its original temperature. Now the air is made to flow into the compressor again. It is thus obvious, that in a closed cycle gas turbine, the air is continuously circulated within the turbine.

Since the heating and cooling of air takes place at constant pressure, therefore this turbine is also called a constant pressure closed cycle gas turbine. It works on Joule's cycle as shown by p-v and T - s diagram in. Fig. 5.15 (a) and (b) respectively.

The process 1-2 shows heating of the air in heating chamber at constant pressure. The process 2-3 shows isentropic expansion of air in the turbine. Similarly, the process 3-4 shows cooling of the air at constant pressure in cooling chamber. Finally, the process 4-1 shows isentropic compression of the air in the compressor.