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In arid areas, natural draft dry cooling tower (NDDCT) has become the primary choice in concentrating solar thermal power plants due to its advantages of low water consumption, low maintenance cost and little parasite loss. However, NDDCT suffers from deteriorated cooling performance in hot summer days, causing net power loss for power plants. To solve this problem, we propose a pre-cooling technology by introducing a spray of controlled and small quantity of fine water droplets to cool the inlet air and thus improve the cooling tower performance when ambient temperature is high. The effective pre-cooling requires the careful arrangement of spray nozzles. Here the optimal injection for a hollow cone nozzle has been identified based on CFD study. This study shows that pre-cooling performance heavily depends on the injection direction of nozzle. For a single nozzle with the water flowrate of 5 g/s, the largest temperature drop is 1.27 degrees C, corresponding to the radiator temperature of 38.73 degrees C. It is found that the injection angle varies with the height of nozzle location to achieve full evaporation. (C) 2017 Elsevier Ltd. All rights reserved.