What is a (wet, atmospheric) cooling tower?
A cooling tower is a heat rejection machine, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The kind of heat rejection in a cooling tower is termed “evaporative” in that it permits a small portion of the water being cooled to evaporate into a moving air stream to offer vital cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air’s temperature and its relative humidity to 100%, and this air is discharged to the environment. Evaporative heat rejection devices corresponding to cooling towers are commonly used to supply significantly lower water temperatures than achievable with “air cooled” or “dry” heat rejection units, just like the radiator in a automotive, thereby achieving more value-efficient and power efficient operation of systems in need of cooling. Consider the occasions you’ve got seen one thing hot be rapidly cooled by placing water on it, which evaporates, cooling rapidly, akin to an overheated car radiator. The cooling potential of a wet floor is much better than a dry one.
Common purposes for cooling towers are providing cooled water for air-conditioning, manufacturing and electric energy era. The smallest cooling towers are designed to handle water streams of only a few gallons of water per minute provided in small pipes like these would possibly see in a residence, while the biggest cool hundreds of 1000’s of gallons per minute equipped in pipes as much as 15 feet (about 5 meters) in diameter on a large power plant.
The generic time period “cooling tower” is used to describe both direct (open circuit) and oblique (closed circuit) heat rejection gear. Whereas most think of a “cooling tower” as an open direct contact heat rejection device, the indirect cooling tower, generally referred to as a “closed circuit cooling tower” is nonetheless also a cooling tower.
A direct, or open circuit cooling tower is an enclosed structure with inner means to distribute the heat water fed to it over a labyrinth-like packing or “fill.” The fill supplies a vastly expanded air-water interface for heating of the air and evaporation to happen. The water is cooled as it descends by way of the fill by gravity while in direct contact with air that passes over it. The cooled water is then collected in a cold water basin under the fill from which it is pumped back by means of the process to absorb more heat. The heated and moisture laden air leaving the fill is discharged to the ambiance at a point distant sufficient from the air inlets to stop its being drawn again into the cooling tower.
The fill may consist of a number of, mainly vertical, wetted surfaces upon which a skinny movie of water spreads (movie fill), or several ranges of horizontal splash parts which create a cascade of many small droplets that have a large combined surface area (splash fill).
An indirect, or closed circuit cooling tower includes no direct contact of the air and the fluid, normally water or a glycol mixture, being cooled. Not like the open cooling tower, the indirect cooling tower has two separate fluid circuits. One is an exterior circuit during which water is recirculated on the surface of the second circuit, which is tube bundles (closed coils) that are connected to the method for the hot fluid being cooled and returned in a closed circuit. Air is drawn by the recirculating water cascading over the skin of the hot tubes, offering evaporative cooling much like an open cooling tower. In operation the heat flows from the interior fluid circuit, via the tube partitions of the coils, to the exterior circuit after which by heating of the air and evaporation of a number of the water, to the ambiance. Operation of the oblique cooling towers is subsequently very just like the open cooling tower with one exception. The process fluid being cooled is contained in a “closed” circuit and is circuitously uncovered to the atmosphere or the recirculated external water.
In a counter-move cooling tower air travels upward by way of the fill or tube bundles, opposite to the downward movement of the water. In a cross-flow cooling tower air moves horizontally by the fill because the water strikes downward.
Cooling towers are additionally characterized by the means by which air is moved. Mechanical-draft cooling towers depend on power-pushed fans to attract or force the air by the tower. Natural-draft cooling towers use the buoyancy of the exhaust air rising in a tall chimney to supply the draft. A fan-assisted natural-draft cooling tower employs mechanical draft to augment the buoyancy impact. Many early cooling towers relied only on prevailing wind to generate the draft of air.
If cooled water is returned from the cooling tower to be reused, some water have to be added to replace, or make-up, the portion of the circulation that evaporates. As a result of evaporation consists of pure water, the focus of dissolved minerals and different solids in circulating water will have a tendency to extend unless some means of dissolved-solids control, akin to blow-down, is supplied. Some water can be misplaced by droplets being carried out with the exhaust air (drift), but this is typically reduced to a very small quantity by installing baffle-like devices, referred to as drift eliminators, to collect the droplets. The make-up quantity must equal the entire of the evaporation, blow-down, drift, and different water losses similar to wind blowout and leakage, to maintain a steady water degree.
Some helpful phrases, generally utilized in the cooling tower industry:
Drift – Water droplets which are carried out of the cooling tower with the exhaust air. Drift droplets have the identical concentration of impurities as the water coming into the tower. The drift rate is often reduced by using baffle-like devices, called drift eliminators, via which the air should journey after leaving the fill and spray zones of the tower.
Blow-out – Water droplets blown out of the cooling tower by wind, typically on the air inlet openings. Water may even be misplaced, in the absence of wind, by way of splashing or misting. Devices such as wind screens, louvers, splash deflectors and water diverters are used to restrict these losses.
Plume – The stream of saturated exhaust air leaving the cooling tower. The plume is visible when water vapor it contains condenses involved with cooler ambient air, like the saturated air in a single’s breath fogs on a cold day. Below sure circumstances, a cooling tower plume may current fogging or icing hazards to its surroundings. Be aware that the water evaporated in the cooling process is “pure” water, in distinction to the very small share of drift droplets or water blown out of the air inlets.
Blow-down – The portion of the circulating water circulation that’s removed so as to maintain the quantity of dissolved solids and other impurities at a suitable level.
Leaching – The loss of wood preservative chemicals by the washing action of the water flowing by way of a wooden construction cooling tower.
Noise – Sound energy emitted by a cooling tower and heard (recorded) at a given distance and direction. The sound is generated by the impression of falling water, by the movement of air by fans, the fan blades transferring within the structure, and the motors, gearboxes or drive belts.