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أريد عن كل مايخص أبراج التبريد

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    Exclamation أريد عن كل مايخص أبراج التبريد

    يا أخوان لاتنسونا من الرسمات عن البرج واجزاءة


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  2. #2
    عضو فعال

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    Thumbs up Categorization by air-to-water flow

    Categorization by air-to-water flow

    Crossflow

    Crossflow is a design in which the air flow is directed perpendicular to the water flow (see diagram below). 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 area. A distribution or hot water basin consisting of a deep pan with holes or nozzles in the bottom is utilized in a crossflow tower. Gravity distributes the water through the nozzles uniformly across the fill material.



    Counterflow

    In a counterflow design the air flow is directly opposite of the water flow (see diagram below). Air flow first enters an open area beneath the fill media and is then drawn up vertically. The water is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air flow.



    Common to both designs:

    The interaction of the air and water flow allow a partial equalization and evaporation of water.
    The air, now saturated with water vapor, is discharged from the cooling tower.
    A collection or cold water basin is used to contain the water after its interaction with the air flow.
    Both crossflow and counterflow designs can be used in natural draft and mechanical draft cooling towers.


    [edit] Cooling tower as a flue gas stack (industrial chimney)
    At some modern power stations, equipped with flue gas purification like the Power Station Staudinger Grosskrotzenburg and the Power Station Rostock, the cooling tower is also used as a flue gas stack (industrial chimney). At plants without flue gas purification, this causes problems with corrosion.


    Wet cooling tower material balance

    Main article: Cooling tower system
    Quantitatively, the material balance around a wet, evaporative cooling tower system is governed by the operational variables of makeup flow rate, evaporation and windage losses, draw-off rate, and the concentration cycles:[3]



    M = Make-up water in m³/hr
    C = Circulating water in m³/hr
    D = Draw-off water in m³/hr
    E = Evaporated water in m³/hr
    W = Windage loss of water in m³/hr
    X = Concentration in ppmw (of any completely soluble salts … usually chlorides)
    XM = Concentration of chlorides in make-up water (M), in ppmw
    XC = Concentration of chlorides in circulating water (C), in ppmw
    Cycles = Cycles of concentration = XC / XM (dimensionless)
    ppmw = parts per million by weight

    In the above sketch, water pumped from the tower basin is the cooling water 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. That contact causes a small amount of the water to be lost as windage (W) and some of the water (E) to evaporate. 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. To prevent the salt concentration of the water from becoming too high, a portion of the water is drawn off (D) for disposal. Fresh water makeup (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:

    M = E + D + W
    Since the evaporated water (E) has no salts, a chloride balance around the system is:

    M (XM) = D (XC) + W (XC) = XC (D + W)
    and, therefore:

    XC / XM = Cycles of concentration = M ÷ (D + W) = M ÷ (M – E) = 1 + [E ÷ (D + W)]
    From a simplified heat balance around the cooling tower:

    E = C · ΔT · cp ÷ HV
    where:
    HV = latent heat of vaporization of water = ca. 2260 kJ / kg
    ΔT = water temperature difference from tower top to tower bottom, in °C
    cp = specific heat of water = ca. 4.184 kJ / (kg°C)

    Windage (or drift) losses (W) from large-scale industrial cooling towers, in the absence of manufacturer's data, may be assumed to be:

    W = 0.3 to 1.0 percent of C for a natural draft cooling tower without windage drift eliminators
    W = 0.1 to 0.3 percent of C for an induced draft cooling tower without windage drift eliminators
    W = about 0.005 percent of C (or less) if the cooling tower has windage drift eliminators
    Cycles of concentration represents the accumulation of dissolved minerals in the recirculating cooling water. Draw-off (or blowdown) is used principally to control the buildup of these minerals.

    The chemistry of the makeup water including the amount of dissolved minerals can vary widely. Makeup waters low in dissolved minerals such as those from surface water supplies (lakes, rivers etc.) tend to be aggressive to metals (corrosive). Makeup waters from ground water supplies (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 makeup 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 softening, pH 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 the majority of water supplies are well waters and have significant levels of dissolved solids. On the other hand one of the largest water supplies, New York City, has a surface supply quite low in minerals and cooling towers in that city are often allowed to concentrate to 7 or more cycles of concentration.

    Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and fouling, the water should be filtered and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water.[3] For closed loop evaporative towers, corrosion inhibitors may be used, but caution should be taken to meet local environmental regulations as some inhibitors use chromates.

    (Note: Draw-off and blowdown are synonymous. Windage and drift are also synonymous.)


    [edit] Cooling towers and Legionnaires' disease
    Further information: Legionella
    Another very important reason for using biocides in cooling towers is to prevent the growth of Legionella which is a Gram negative bacterium, including species that cause legionellosis or Legionnaires' disease, most notably L. pneumophilia[4]. The various Legionella species are the cause of Legionnaires' disease in humans and transmission is via exposure to aerosols—the inhalation of mist droplets containing the bacteria. 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.

    French researchers found that Legionella spread through the air up to 6 kilometres from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. That outbreak killed 21 of the 86 people that had a laboratory-confirmed infection.[5]

    Drift (or windage)is the term for water droplets of the process flow allowed to escape in the cooling tower discharge. Drift eliminators are used hold drift rates typically to 0.001%-0.005% of the circulating flow rate. A typical drift eliminator provides multiple directional changes of airflow while preventing the escape of water droplets. A well-designed and well-fitted drift eliminator can greatly reduce water loss and potential for Legionella or other chemical exposure.

    Many governmental agencies, cooling tower manufacturers and industrial trade organizations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers. Below is a list of sources for such guidelines:

    Centers for Disease Control and Prevention - Procedure for Cleaning Cooling Towers and Related Equipment (pages 239 and 240 of 249)
    Cooling Technology Institute - Best Practices for Control of Legionella
    Association of Water Technologies - Legionella 2003
    California Energy Commission - Cooling Water Management Program Guidelines For Wet and Hybrid Cooling Towers at Power Plants
    Marley Cooling Technologies - Cooling Towers Maintenance Procedures
    Marley Cooling Technologies - ASHRAE Guideline 12-2000 - Minimizing the Risk of Legionellosis
    Marley Cooling Technologies - Cooling Tower Inspection Tips {especially page 3 of 7}
    Tower Tech Modular Cooling Towers - Legionella Control
    GE Infrastructure Water & Process Technologies Betz Dearborn - Chemical Water Treatment Recommendations For Reduction of Risks Associated with Legionella in Open Recirculating Cooling Water Systems

    [edit] Cooling Tower Operation In Freezing Weather
    Do not operate the tower unattended.[6]
    Do not operate the tower without a heat load.
    Maintain design water flow rate over the fill.
    Manipulate airflow to maintain water temperature above freezing point.[7]
    Cooling towers with malfunctions can freeze. Failures that let smaller amounts of water go the top of a cooling tower can cause a tower to freeze (especially if the fans are running at high speeds). If a roof-mounted cooling tower is allowed to freeze and build up ice, the ice can grow to massive sizes and can result in the tower falling through the roof (note: this assumes that the ice 'grows' beyond the typical liquid volume).

    Typical methods to circumvent freezing are: air flow through the tower is reduced, a basin heater is installed, a heater is intalled indoors on the water loop, a drain system or remote basin design is used, and in some cases where evaportive closed loop towers are used the tower spray water is drained completely.



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  3. #3
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    Thumbs up ابراج تبريد

    فائدة ابراج تبريد هو يقوم بتبريد الماء الراجع من المكثف حتي لا يقوم المكثف بضغط والانفجارات فاستخدمو برج التبريد


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