Numerical analysis on the effects of water spraying on cooling tower evaporation and drift

Abstract

Evaporation and drift of a wet cooling tower were studied to reduce water loss by changing the makeup water model of the cooling tower. The tower interior had a sprayed makeup water area of 600 m2, which accounted for 30% of the water drenching area. Accurately measuring the water level of the collecting basin with a U-type liquidometer resulted in a test accuracy of 1.38 m3 mm-1. And the accurate data of water loss of cooling tower were obtained by using the liquid level of collecting basin and the water loss law of cooling tower. On the basis of the analysis of water and heat balance, the total water content of unit discharge air and the air humidity ratio of tower outlet were compared. In other words, the air humidity ratio method was used to verify the correctness of Merkel's assumption of 'the air saturation in the cooling tower'. And the formation process of drift is explained by the accurate analysis of evaporation loss. This process provided a new research model for the analysis of water loss and air state in cooling towers. The heat and water loss of circulating water before and after the spraying makeup water were compared and analyzed, respectively, according to the accurate water loss data and the droplet calculation model. The best water loss reduction effect was 7.9 m3 h-1, and the drift recovery law is established; the drift recovery rate in the water spraying area was 65.5-96.8%. Furthermore, the optimum working conditions of the drift recovery project were explained. This law guided the operation of the spraying makeup water system. Results showed that the spray water was more favorable to the operation of the cooling tower than the original makeup water and the expected water saving was achieved. The established theories were widely used in the study on water loss of cooling tower and the drift recovery project.