ANS:A - 10-15

A natural draft cooling tower typically has wooden grids or other types of fill material installed inside the tower to increase the contact surface area between the air and the water being cooled. This fill material aids in the heat exchange process by promoting greater air-water interaction. The wooden grids or fill material usually cover a significant portion of the tower height to maximize the cooling efficiency. Typically, these fill materials cover about: 70-80 percent of the tower height. This range allows for effective heat transfer between the warm water entering the tower and the cooler air moving upward through the tower due to natural convection. The large surface area provided by the fill material facilitates the transfer of heat from the water to the air, thereby promoting efficient cooling of the water.