Importance of Nozzles

Role of Nozzles in Performance Evaluation

• Water Distribution :

The impact of a nozzle is determined on the basis of how well is gets the hot water to the fill. The nozzles are located and sized in a manner that they provide uniform pattern of water over the fill with no gaps between their spray areas. The expense involved in placing a fill into the cooling tower is fully justified if the fill is totally wetted out and all its sections receive a constant amount of water.

Should some sections of the fill remain dry, these dry sections will naturally offer lower resistance to airflow resulting in the airflow being stolen from the wet fill sections which means decrease in the cooling effect of the hot water. Morever these gaps in spray coverage tend to pulse and shift around, the reason being that both air and water are fluids. These alternating cycles of dry and wet spells gives rise to scale formation within the fill. As the build up continues there is an adverse effect on the
thermal performance capability. The extreme occurs when the scale build up on the fill is to an extent that the airflow from the fill is totally blocked thus causing structural damage to the cooling tower.

• Spray Zone :

The cooling that happens as soon as the water exits the nozzle and falls to the fill is what we refer to as the spray zone. This cooling effect in the spray zone can vary from 5-15% of the total cooling provided by the tower. To get the best results in cooling one needs to ensure that the interaction between the hottest water and the coldest air is maximised. Hence a nozzle that generates very small droplets will deliver a performance far more superior to the one that generates big fat droplets.

• Drift Eliminators :

The fine spray of very small droplets from the nozzles maybe beneficial from a cooling point of view, but it creates a more difficult challenge in preventing the very same small droplets from exiting the cooling tower as drift.

As the surface tension of the water decreases, It causes smaller and smaller droplets to be formed. Combine this with a pressurized water distribution system, especially if there is a higher than expected pressure at the nozzles (due to over pumping), a mist is generated. Mist droplets typically being smaller than drift droplets, the drift eliminators lose their efficiency in removal thus necessitating mist eliminators which are designed differently from drift eliminators because of the greater difficulty in droplet removal.