Natural Draft Cooling Towers is a collection or cold water basin is used to collect and contain the cooled water after its interaction with the air flow.Both crossflow and counterflow designs can be used in natural draft and in mechanical draft cooling towers.The warm water returns to the top of the cooling tower and trickles downward over the fill material inside the tower. As it trickles down, it contacts ambient air rising up through the tower either by natural draft or by forced draft using large fans in the tower. That contact causes a small amount of the water to be lost as windage and some of the water to evaporate. The heat required to evaporate the water is derived from the water itself, which cools the water back to the original basin water temperature and the water is then ready to recirculate.
Natural Draft Cooling Towers leaves its dissolved salts behind in the bulk of the water which has not been evaporated, thus raising the salt concentration in the circulating cooling water.The salt concentration of the water from becoming too high, a portion of the water is drawn off for disposal. Fresh water makeup is supplied to the tower basin to compensate for the loss of evaporated water, the windage loss water and the draw-off water and sources of Legionella include cooling towers used in open recirculating evaporative cooling water systems, domestic hot water systems, fountains, and similar disseminators that tap into a public water supply. Natural sources include freshwater ponds and creeks.
Natural Draft Cooling Towers constructed in whole or in part of combustible materials can support internal fire propagation. Such fires can become very intense, due to the high surface-volume ratio of the towers. The resulting damage can be sufficiently severe to require the replacement of the entire cell or tower structure. some codes and standards recommend that combustible cooling towers be provided with an automatic fire sprinkler system. Fires can propagate internally within the tower structure when the cell is not in operation and even while the tower is in operation, especially those of the induced-draft type, because of the existence of relatively dry areas within the towers.