Gas Turbine Power Augmentation: Parametric Study Relating to Fog Droplet Size and Its Influence on Evaporative Efficiency

Several gas turbine power augmentation techniques are available to counter the detrimental drop in power and thermal efficiency that occur at high ambient temperatures. Inlet fogging and wet compression are two common and relatively simple techniques. This paper addresses the influence and importance of droplet size on evaporative cooling performance and efficiency. Common spray nozzles used for inlet fogging and wet compression are the impaction pin, swirl jet, air assisted, and swirl flash nozzles. The atomization process from these nozzles and their performance depends on the droplet size, size distribution, and spray plume shape. Droplets size varies with nozzle types, configurations, operating conditions, and nozzle manifold location in the gas turbine inlet duct as they are affected by airflow velocity, residence time coalescence effects, evaporation efficiency, and water carryover. The proper selection of nozzle type and location and nozzle distribution are of importance to avoid large droplets and under/over saturated areas which would affect compressor mechanical and aerodynamic efficiency. Analytical and numerical studies are compared to experimental results available from installed systems, and treated in the literature. This paper provides a comprehensive treatment of parameters affecting droplet size and will be of value to gas turbine fog system designers and users.