Water evaporates in a cooling tower through direct contact with air, resulting in evaporative cooling.
Here's a breakdown of the process:
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Water Distribution: Hot water from an industrial process or HVAC system is pumped to the top of the cooling tower. It's then distributed through nozzles or sprayers, creating a large surface area.
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Airflow: Air is forced or drawn through the cooling tower, either by fans (forced draft or induced draft) or natural convection (natural draft).
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Direct Contact: The water and air come into direct contact, typically over a fill material (packing) designed to increase the contact time and surface area.
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Evaporation: A small portion of the water evaporates. This evaporation process absorbs heat from the remaining water, cooling it down. The driving force behind evaporation is the difference in vapor pressure between the water and the surrounding air. Warmer water has a higher vapor pressure, leading to a net transfer of water molecules into the air if the air is not saturated.
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Cooling Effect: The heat absorbed during evaporation lowers the temperature of the remaining water. This cooled water is then collected at the bottom of the tower and pumped back to the heat source (e.g., condenser in an HVAC system) to absorb more heat, continuing the cycle.
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Humid Air Exhaust: The now-humid air, containing the evaporated water, is discharged from the cooling tower.
In essence, the cooling tower facilitates the evaporation of a small amount of water, and this phase change extracts heat from the bulk water, thus cooling it. This cooled water is then reused in the system.
