Gas Turbine Handbook : Principles and Practices

Gas Turbine Inlet Treatment 125
As an example, assume that the ambient temperature is 100°F
and the relative humidity is 20%. Referring to the Psychometric
Chart 1 (Figure 8-5), the corresponding wet bulb temperature is 70°F.
For an 80% effective design cooler, the temperature drop through the
cooler should be:
∆T DB
= 0.8(T 1DB
– T 2WB
), or 24F. (8-2)
The actual cooler effectiveness can be determined by measuring
dry-bulb temperatures and either relative humidity or wet-bulb
temperatures before and after the evaporative cooler. This testing
determines if the design target is being met and if there is margin
for improving the evaporative cooler effectiveness. The exact increase
in available power attributable to inlet air cooling depends upon the
machine model, ambient pressure and temperature, and relative humidity.
Likewise, the decrease in heat rate attributable to inlet air
cooling depends upon the machine model, ambient pressure and temperature,
and relative humidity. Figure 8-6 1 can be used as a rough
Figure 8-5. Courtesy of General Electric Company. This psychrometric
chart shows the path taken by an evaporative cooling process
and an inlet air chilling process.