A suction air cooling by water spray has been used for inlet air of gas turbines. The cooling performance depends on spray characteristics and surrounding conditions. The aims of this study are to understand the spray characteristics under the various humidity conditions and to discuss influences of humidity on spray characteristics and cooling performance. A Phase Doppler Anemometry (PDA) provides spray characteristics. Air temperatures before cooling and after cooling are measured under various humidity conditions and the number of nozzles. Two types of nozzles, that is, an impaction PIN Jet nozzle and a Hole type nozzle, are tested. For both nozzles, evaporation of droplets becomes inactive with high humidity condition. For PIN Jet nozzles, spray droplets exist in large area and are smaller than those of Hole nozzle. For Hole nozzle, droplets size is larger at spray outer edge and spray area is smaller compared with PIN Jet nozzle. The cooling performance for PIN Jet nozzle is larger than that of Hole nozzle. The cooling performance becomes better when spray flow rate increases.

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Water spray is used for cooling intake air of gas turbine in thermal power plant. It is necessary to reduce the amount of residual droplets by optimizing the spray amount to keep the plant in good condition. In the actual thermal power plants, a phase Doppler anemometry (PDA), which can provide droplet velocity and diameter of spray, is difficult to apply because it requires precision setting. In this study, a new method for determining the residual droplet flow rate using the laser transmittance for the cooling water spray which can be used at thermal power plants is proposed. A laser transmission method system was applied to a scaledown model of an inlet duct at a laboratory in order to confirm the system reliability. The same types of weather louvers, eliminators, and nozzles installed in the actual thermal power plants were used in the experiment. The effects of optical path length, spatial distribution of spray, flow on conditions, etc. to the measurement accuracy were evaluated at the model case experiment in the laboratory. The residual droplet flow rate calculated by the laser transmission method and that of the PDA measurement are compared. The error of the residual droplet flow rate calculated by the proposed method was about 12.8%. The proposed system was applied to an actual thermal power plant. At the thermal power plant, the residual droplet flow rate was reduced to about 35% by the eliminator compared to the case without the eliminator. Since the residual droplet flow rate can be measured by the laser transmission method, it can be used for optimizing the spray amount in actual thermal power plants. Compared to other methods, the proposed method allows the experimental equipment to be also constructed relatively easily. It is easy to install in an actual thermal power plant. The experimental results demonstrate the effectiveness of the present apparatus as a relative evaluation method.

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