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A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towersrely solely on air to cool the working fluid to near the dry-bulb air temperature.

Common applications include cooling the circulating water used in oil refineriespetrochemical and other chemical plantsthermal power stations and HVAC systems for cooling buildings. The classification is based on the type of air induction into the tower: The hyperboloid cooling towers are often associated with nuclear power plants[1] although they are also used in some coal-fired plants and to some extent in some large chemical and other industrial plants.

Although these large towers are very prominent, the vast majority of cooling towers are much smaller, including many units installed on or near buildings to discharge heat from air conditioning. Cooling towers originated in the 19th century through the development of condensers for use with the steam engine.

Cooling Tower Fundamentals – SPX Cooling Technologies

This reduces the back pressurewhich in turn reduces the steam consumption, and thus the fuel consumption, while at the same time increasing power and recycling boiler-water. By the turn of the 20th century, several evaporative methods of recycling cooling water were toower use coolibg areas lacking an established water supply, as well as in urban locations where municipal water mains may not be of sufficient supply; reliable in times of demand; or otherwise adequate to meet cooling needs.

These early towers were positioned either on the rooftops of buildings or as free-standing structures, supplied with air by fans or relying on natural airflow. At the top is a set of distributing funddamentals, to which the water from the condenser must be s;x from these it trickles down over “mats” made of wooden slats or woven wire screens, which fill the space within the tower. A hyperboloid cooling tower was patented by the Dutch engineers Frederik van Iterson and Gerard Kuypers in The first ones in the United Kingdom were built in at Lister Drive power station in LiverpoolEngland, to cool water used at a coal-fired electrical power station.

An HVAC heating, ventilating, and air conditioning cooling tower is used to dispose of “reject” unwanted heat from a chiller. Water-cooled chillers are normally more energy efficient than air-cooled chillers due to heat rejection to tower water at or near wet-bulb temperatures.

Air-cooled chillers must reject heat at the higher dry-bulb temperatureand thus have a lower average reverse- Carnot cycle effectiveness. In areas with a hot climate, large office buildings, hospitals, and schools typically use one or more cooling towers as part of their air conditioning systems. Generally, industrial cooling towers are much larger than HVAC towers.

HVAC use of a cooling tower pairs the cooling tower with a water-cooled chiller or water-cooled condenser. Cooling towers are also used in HVAC systems that have multiple water source heat pumps that share a common piping water loop. In this type of system, the water circulating inside the water loop removes heat from the condenser of the heat pumps whenever the heat pumps are working in the cooling mode, then the externally mounted cooling tower is used to remove heat from the water loop and reject it to the atmosphere.

By contrast, when the heat pumps are working in heating mode, the condensers draw heat out of the loop water and reject it into the space to be heated. When the water loop is being used primarily to supply heat to the building, the cooling tower is normally shut down and may be drained or winterized to prevent freeze damageand heat is supplied by other means, usually from separate boilers.

Cooling tower

Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plantspetroleum refineriespetrochemical plants, natural gas processing plants, food processing plants, semi-conductor plants, and for other industrial facilities such as in condensers of distillation columns, for cooling liquid in crystallization, etc.

If that same plant had no cooling tower and used once-through cooling water, it would require aboutcubic metres an hour [13] A large cooling water intake typically kills millions of fish and larvae annually, as the coollng are impinged on the intake screens.


Furthermore, discharging large amounts of hot water may raise the temperature of the receiving river or lake to an unacceptable level for the local ecosystem. Elevated water temperatures can kill fish and other aquatic organisms see thermal pollutionor can also cause an increase in undesirable organisms such as invasive species of zebra mussels or algae. A cooling tower serves to dissipate the heat into the atmosphere instead and wind and air diffusion spreads the heat over a much larger area than hot water fundamehtals distribute heat funadmentals a body of water.

Evaporative cooling water cannot be used for subsequent purposes other than rain somewherewhereas surface-only cooling water can be re-used. Some coal-fired and nuclear power plants located in coastal areas do make use of once-through ocean water. But even there, the offshore discharge water outlet requires very careful design to avoid environmental problems.

Petroleum refineries also have very large cooling tpwer systems. These types of cooling towers are factory preassembled, and can be simply transported on trucks, as they are compact machines. Fujdamentals capacity of package type towers is limited and, for that reason, they are usually preferred by facilities with low heat rejection requirements such as food processing plants, textile plants, some chemical processing plants, or buildings like hospitals, hotels, malls, fundsmentals factories etc.

Due to their frequent use in or near residential areas, sound level control is a relatively more important fundamentasl for package type cooling towers.

Cooling tower – Wikipedia

Facilities such as power plants, steel processing plants, petroleum refineries, or petrochemical plants usually install field erected type cooling towers due to their greater capacity for heat rejection. Field erected towers are usually much larger in size compared to the package type cooling towers.

sox A typical field erected cooling tower has a pultruded fiber-reinforced plastic FRP structure, FRP claddinga mechanical unit for air draftdrift eliminator, and fill. With respect to the heat transfer mechanism employed, the main types are:.

In a wet cooling tower or open circuit cooling towerthe warm water can be cooled to a temperature lower than the ambient air dry-bulb temperature, if the air is relatively dry see dew point and psychrometrics.

As ambient air is drawn past a fundamentalz of water, a small portion of the water evaporates, and the energy required to evaporate that portion of the water is taken from the remaining mass of water, thus reducing its temperature. Evaporation results in saturated air conditions, lowering the temperature of the water processed by the tower to a value close to wet-bulb temperaturewhich is lower cooilng the ambient dry-bulb temperaturethe difference determined by the initial humidity of the ambient air.

To achieve better performance more coolinga medium called fill is used to increase the surface area and towfr time of contact between the air and water flows.

Splash fill consists of material placed to interrupt the water flow causing splashing. Film fill is ufndamentals of thin sheets of material usually PVC upon which the water fudamentals. Both fnudamentals create increased surface area and time of contact between the fluid water and the gas airto improve heat transfer.

Hyperboloid sometimes incorrectly known as hyperbolic cooling towers have become the design standard for all natural-draft cooling towers because of their structural strength and minimum usage of material. The hyperboloid shape also aids in accelerating the upward convective air flow, improving cooling efficiency.

These designs are popularly associated with nuclear power plants. However, this association is misleading, as the same kind sspx cooling towers are often used at large gower power plants as well. Conversely, not all nuclear power plants have cooling towers, and some instead cool their heat exchangers with lake, river or ocean water.

Crossflow is a design in which the air flow is directed perpendicular to the water flow see diagram at left. Air flow enters one or more vertical faces of the cooling tower to meet the fill material. Water flows perpendicular to the air through the fill by gravity.

The air continues through the fill and thus past the water flow into an open plenum volume. Lastly, a fan forces the air out into the atmosphere. A distribution or hot water basin consisting of a deep pan fundamenrals holes or nozzles in its bottom is located near the top of a crossflow tower. Gravity distributes the water through the nozzles uniformly across the fill material. In a counterflow design, the air flow is directly opposite to the water flow see diagram at left. Air flow first enters an open area beneath the fill media, and is then drawn up vertically.

The water is sprayed through pressurized nozzles near the top of the tower, and then flows downward through the fill, opposite to the air flow.

Both crossflow and counterflow designs can be used in natural draft and in mechanical draft cooling towers. Fundamntals, the material balance around a wet, evaporative cooling fundamentalx system is governed by the operational variables of make-up volumetric flow rateevaporation and windage losses, draw-off rate, and the concentration cycles.

In the adjacent diagram, water pumped from the tower basin is the cooling tiwer routed through the process coolers and condensers in an industrial facility. The cool water absorbs heat from the hot process streams which need to be cooled or condensed, and the absorbed heat warms the circulating water C. 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.


Cooling Tower Fundamentals – SPX Cooling Technologies – PDF Drive

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. The evaporated water 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.

Fresh water make-up M is supplied to the tower basin to compensate for the loss of evaporated water, the windage loss water and the draw-off water. A water balance around the entire system is then: Since the evaporated water E has no salts, a chloride balance around the system is: Windage or drift losses W is the amount of total tower water flow that is entrained in the flow of air to the atmosphere.

From large-scale industrial cooling towers, in the absence of manufacturer’s data, it may be assumed to be:. Cycle of concentration represents the accumulation of dissolved minerals in the recirculating cooling water. Discharge of draw-off or blowdown is used principally to control the buildup of these minerals.

The chemistry of the make-up water, including the amount of dissolved minerals, can vary widely.

Make-up waters low in dissolved minerals such as those from surface water supplies lakes, rivers etc. Make-up waters from ground water supplies such as wells are usually higher in minerals, and tend to be scaling deposit minerals. Increasing the amount of minerals present in the water by cycling can make water less aggressive to piping; however, excessive levels of minerals can cause scaling problems.

As the cycles of concentration increase, the water may not be able to hold the minerals in solution. When the solubility of these minerals have been exceeded they can precipitate out as mineral solids and cause fouling and heat exchange problems in the cooling tower or the heat exchangers. The temperatures of the recirculating water, piping and heat exchange surfaces determine if and where minerals will precipitate from the recirculating water. Often a professional water treatment consultant will evaluate the make-up water and the operating conditions of the cooling tower and recommend an appropriate range for the cycles of concentration.

The use of water treatment chemicals, pretreatment such as water softeningpH adjustment, and other techniques can affect the acceptable range of cycles of concentration. Concentration cycles in the majority of cooling towers usually range from 3 to 7. In the United States, many water supplies use well water which has significant levels of dissolved solids. On the other hand, one of the largest water supplies, for New York Cityhas a surface rainwater source quite low in minerals; thus cooling towers in that city are often allowed to concentrate to 7 or more cycles of concentration.

Since higher cycles of concentration represent less make-up fundamenfals, water conservation efforts may focus on increasing cycles of concentration. Disinfectant and other chemical levels in cooling towers and hot tubs should be continuously maintained and regularly monitored.

Regular checks of water quality specifically the aerobic bacteria levels using dipslides should be taken as the presence of other organisms can support legionella by producing the organic nutrients that it needs to thrive. Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and foulingthe water should be filtered to remove particulates, and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water.

Biofilm can be reduced or prevented by using chlorine or other chemicals. A normal industrial practice is to use two biocides, such as oxidizing and non-oxidizing types to complement each other’s strengths and weaknesses, and to ensure a broader spectrum of attack. In most cases, a continual low level oxidizing biocide xooling used, then alternating to sx periodic shock dose of non-oxidizing biocides. Another fundamentls important reason for using biocides in cooling towers is to prevent the growth of Legionellaincluding species that cause legionellosis or Legionnaires’ disease, most notably L.

Common 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.