![]() Crossflow towers usually have a gravity feed system-a distribution deck with evenly spaced metering orifices to distribute the water. The crossflow design provides an easier path for the air, thus increasing the airflow for a given fan horsepower. In crossflow towers, air flows horizontally across the downward flow of water. Headers and spray nozzles are usually used to distribute the water in counterflow towers.Ĭrossflow Towers. This design provides good heat exchange because the coolest air contacts the coolest water. In counterflow towers, air moves upward, directly opposed to the downward flow of water. These towers can use either crossflow or counterflow air currents and tend to be larger than forced draft towers.Ĭounterflow Towers. Induced draft towers have a fan at the top to draw air through the tower. Almost all forced draft towers are counterflow designs. In a forced draft design, fans push air into the bottom of the tower. Mechanical draft towers use fans to move air through the tower. In both models, the empty chimney accounts for most of the tower height. In a counterflow model, the fill is inside the shell. The fill is external to the shell forming a ring around the base. Natural draft towers can be either counterflow or crossflow designs. The tall (up to 500 ft) chimney is necessary to induce adequate airflow. The warm, moist air inside the tower has a lower density, so it rises as denser, cool air is drawn in at the base of the tower. They are designed to take advantage of the density difference between the air entering the tower and the warmer air inside the tower. Sometimes called "hyperbolic" towers due to the distinctive shape and function of their chimneys, natural draft towers do not require fans. Mechanical draft towers are further subdivided into forced or induced draft towers. Some sensible heat loss (direct cooling of the water by the air) also occurs, but it is only a minor portion of the total heat rejection.Ĭooling towers are classified by the type of draft (natural or mechanical) and the direction of airflow (crossflow or counterflow). Heat rejection is primarily by evaporation of part of the cooling water. They are designed to provide intimate air/water contact. microorganisms, nutrients, and potential foulants can also be absorbed into the water across the towerĬooling towers are the most common method used to dissipate heat in open recirculating cooling systems.airborne gases such as sulfur dioxide, ammonia or hydrogen sulfide can be absorbed from the air, causing higher corrosion rates.the longer retention time and warmer water in an open recirculating system increase the tendency for biological growth.the relatively higher temperatures significantly increase corrosion potential.cooling by evaporation increases the dissolved solids concentration in the water, raising corrosion and deposition tendencies.However, open recirculating cooling systems are inherently subject to more treatment-related problems than once-through systems: The quantity of water discharged to waste is greatly reduced in the open recirculating method, and chemical treatment is more economical. Open recirculating cooling systems save a tremendous amount of fresh water compared to the alternative method, once-through cooling. Cooling towers, spray ponds, and evaporative condensers are used for this purpose. Heat absorbed from the process must be dissipated to allow reuse of the water. Monitoring and Control of Cooling Water EquipmentĪn open recirculating cooling system uses the same water repeatedly to cool process equipment.
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