Experimental and numerical study of fogging cooling performance through a cylindrical duct for a micro gas turbine

Abstract

Fogging cooling is one of the most effective methods for cooling gas turbine inlet air in hot areas. Most of the previous studies focused only on the influence of the fogging cooling effect on the gas turbine performance. Nevertheless, due to the limited space available for installing a system, the fogging system requires special attention, notably in micro gas turbines, to avoid the thermal stress and blade erosion risks at a compressor intake. Hence, in the current paper, the performance of the fogging cooling system for micro gas turbines has been investigated experimentally and numerically to enhance the cooling efficiency, temperature stability and accomplish complete droplets evaporation. An experimental setup has been designed and installed to study the fogging cooling effect through a cylindrical duct. Eulerian-Lagrangian CFD model was also adopted to simulate the trajectories of the injected droplets and to predict the evaporation cooling process through the spray duct. The CFD model was validated with the current experiments, and there is good agreement between the experimental data and simulation results with an average deviation of less than 6.4%. The droplets' size and injected mass flow were measured at different nozzles orifice diameters and injection pressures to select the appropriate spray nozzles at various test conditions. The fogging performance has been tested under various operating conditions, including nozzle arrangement and flow directions, to identify the crucial factors for obtaining fully saturated air and stable temperature from the spray duct. The results reveal that employing a single nozzle to achieve full saturation is ineffective. On the other hand, increasing the number of nozzles with the same input water flow rate improves droplets distribution across the duct and enhances the evaporation rate. It was found that the temperature drop can be reduced by 1.5 °C due to dividing the required water mass flow on four nozzles instead of one. Furthermore, it was observed that the cooling performance of the counter-current flow case could be improved by 3.4% compared to the co-flow one with a high uniform temperature profile through the duct. Finally, a counter-current spray design with four nozzles is proposed for micro gas turbines since it meets the design constraints best compared to other operating scenarios.