The effects of water droplet diameter distribution in the rain zone on the cooling capacity and water-splashing noise for natural draft wet cooling towers

Abstract

To reveal the impact mechanism of water droplet diameter distribution in the rain zone on the cooling capacity and water-splashing noise for natural draft wet cooling towers (NDWCTs), a 3 D numerical model of thermal performance and a theoretical calculation model of water-splashing noise were established and validated, respectively. Using these two models, the influences of different diameter distributions on the ventilation, thermal performance, and the sound pressure level (SPL) of water-splashing noise were analyzed to an NDWCT used for 1000 MW unit. The diameter distribution is described by the number ratios, which is the ratio of the number of water droplets with the same diameter to the total number of all the water droplets in the rain zone. The results revealed that, as the number ratio of the water droplet with a diameter of 1 mm or 2 mm increases, the SPL decreases and the cooling capacity worsens. Conversely, when the number ratio of the water droplet with the diameter of 4 mm increases, the SPL also increases, and the cooling capacity is enhanced. In addition, an increase in the number ratio of the water droplet with a diameter of 3 mm acts to improve the ventilation and thermal performance, while the SPL demonstrates a slight reduction. Therefore, when considering the simultaneous optimization of cooling capacity and water-splashing noise, it is recommended that the number ratio of the water droplet with a diameter of 3 mm is increased. When the number ratio of the water droplet with the diameter of 3 mm reaches 45%, compared with the working condition of the actual measured water droplet diameter distribution, the outlet water temperature reduces by 0.22 °C, the ventilation rate increases by 4.72%, while there is no significant change in the SPL.