Sensitivity Analysis on the Effect of D32 and Dv90 on the Evaporation Efficiency of Gas Turbine Inlet Fogging for Power Augmentation

Gas turbine output is strongly dependent on the ambient air temperature. This decrease usually occurs in the hot afternoon during the peak demand for power. One way to counter this drop in output is to cool the inlet air using one of the available cooling technologies such as the inlet fog cooling of gas turbine engines for power augmentation. This technology is well established with over 1000 fogging systems installed all around the world on gas turbines of various makes and sizes ranging from 5 MW to 250 MW. Two types of statistical droplet diameters are used to characterize the droplet sizes from nozzles used in the fogging systems, namely D32 (Sauter mean diameter) (SMD) and Dv90 (diameter for which 90% of the water volume in the spray is less than or equal to). This paper will show the importance of each diameter on the performance of fogging systems. For this purpose, a heat and mass transfer theoretical model is developed to analyze the dynamics of evaporation of fog droplets. The model will quantify the evaporative efficiency of fog droplets for different D32 and Dv90 values derived from experimentally measured droplet size distributions at two typical ambient psychrometric conditions: hot and dry, and cold and humid.