A review on the performance evaluation of natural draft dry cooling towers and possible improvements via inlet air spray cooling

Concentrating solar power (CSP) plants make use of the renewable and inexhaustible solar energy to produce electricity. Limited by the scarce water resources, CSP plants built in arid areas choose Natural Draft Dry Cooling Tower (NDDCT) to remove waste heat. However, NDDCT suffers from low efficiency in hot summer days. To resolve this problem, inlet air spray-cooling is introduced to improve the performance of NDDCT. In the first part of this paper, the research progress focused on both the theoretical and experimental studies on NDDCT are summarized. Then, in the second part, the spray cooling system consisting of various kinds of spray nozzles are described. Various nozzles produce different spray patterns such as flat-fan, hollow cone, full cone and solid jet. These spray patterns are characterized by flow rate, pressure, mean droplet size and droplet size distribution. Furthermore, the mathematical models correlating the cooling tower performance with the droplet evaporation process are used to predict the spray cooling performance and are summarized here. Finally, predictive results are presented to evaluate the performance of the pre-cooling system. The results illustrate that the inlet air pre-cooling would improve the efficiency of NDDCT and thus reduce power generation loss under high-ambient air temperature conditions. More research should be conducted to develop a practical NDDCT-based spray cooling system for industrial applications.