Gas Turbine Cycle with Reheat

A common method of increasing the mean temperature of heat reception is to reheat the gas after it has expanded in a part of the gas turbine. By doing so the mean temperature of heat rejection is also increased, resulting in a decrease in the thermal efficiency of the plant. However , the specific output of the plant increases due to reheat. A reheat cycle gas turbine plant is shown in Figure 5.1

The specific work output is given by,

The heat supplied to the cycle is

Thus, the cycle efficiency,

Therefore, a reheat cycle is used to increase the work output while a regenerative cycle is used to enhance the efficiency.

Gas Turbine Cycle with Inter-cooling

The cooling of air between two stages of compression is known as intercooling. This reduces the work of compression and increases the specific output of the plant with a decrease in the thermal efficiency. The loss in efficiency due to intercooling can be remedied by employing exhaust heat exchange as in the reheat cycle.

Specific work output	=

Heat supplied =

If is constant and not dependent on temperature, we can write:

Here heat supply and output both increases as compared to simple cycle. Because the increase in heat supply is proportionally more, decreases.

With multiple inter-cooling and multiple reheat, the compression and expansion processes tend to be isothermal as shown in Figure 5.3