THERMODYNAMIC PRINCIPLES

The ambient conditions around a gas turbine vary with time and location.1 ^,2 Standard conditions are required for comparative purposes. The gas turbine industry uses these standard conditions: 59 F (14 C), 14.7 psia (1.013 bar), and 60 percent relative humidity. These conditions are established by the International Organization for Standardization (ISO) and are generally referred to as ISO Standards.

Figure 18.1 illustrates a simple-cycle gas turbine. Ambient air enters the compressor of the gas turbine. The pressure increase across the compressor is from 12- to 45-fold. The temperature also increases across the compressor as a result of the compression process. The discharge temperature from the compressor is between 650 and 900 F (345 and 480 C). The air leaving the compressor enters the combustors. The combustion process occurs at almost a constant pressure. In reality, there is a slight decrease in pressure across the combustors. There is significant increase in temperature in the combustors to between 2200 and 3000 F (1200 and 1650 C). The turbine converts the energy in the hot gases to mechanical work. This conversion occurs in two steps. First, the velocity of the hot gases increases in the stationary blades (nozzles) of the turbine. A portion of the thermal energy is converted into kinetic energy (first law of thermodynamics). Second, the rotating blades of the turbine (buckets) convert the kinetic energy to work. The work developed by the turbine drives the compressor and the load. The compressor normally requires from 55 to 67 percent of the total work...