Cooling Tower - Wikipedia, The Free Encyclopedia

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Natural draft wet cooling hyperboloid towers at

Didcot Power Station (UK)

Forced draft wet cooling towers (height: 34

meters) and natural draft wet cooling tower

(height: 122 meters)

"Camouflaged" natural draft wet cooling tower

near Dresden (Germany)

Cooling towerFrom Wikipedia, the free encyclopedia

A cooling tower is a heat rejection device which extracts 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 towers, rely 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 refineries, petrochemical and other chemical plants, thermal power

stations and HVAC systems for cooling buildings. The classification is based on the type of air induction into the tower: the main types of

cooling towers are natural draft and induced draft cooling towers.

Cooling towers vary in size from small roof-top units to very large hyperboloid structures (as in the adjacent image) that can be up to 200 metres

(660 ft) tall and 100 metres (330 ft) in diameter, or rectangular structures that can be over 40 metres (130 ft) tall and 80 metres (260 ft) long. The

hyperboloid cooling towers are often associated with nuclear power plants, [1] although they are also used 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, includingmany units installed on or near buildings to discharge heat from air conditioning.

Contents

1 History

2 Classification by use

2.1 Heating, ventilation and air conditioning (HVAC)2.2 Industrial cooling towers

3 Classification by build

3.1 Package type

3.2 Field erected type

4 Heat transfer methods

5 Air flow generation methods

6 Categorization by air-to-water flow6.1 Crossflow

6.2 Counterflow

6.3 Common aspects

7 Wet cooling tower material balance

7.1 Cycles of concentration

7.2 Water treatment

8 Legionnaires' disease9 Terminology

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Fan-induced draft, counter-flow cooling

tower

W = Windage loss of water in m³/h

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

A water balance around the entire system is then: [14]

M = E + D + W

Since the evaporated water (E) has no salts, a chloride balance around the system is: [14]

and, therefore:[14]

From a simplified heat balance around the cooling tower:

where:

HV = latent heat of vaporization of water = 2260 kJ / kg

∆T = water temperature difference from tower top to tower bottom, in °C

cp = specific heat of water = 4.184 kJ / (kg°C)

Windage (or drift) losses (W) is the amount of total tower water flow that is evaporated into the atmosphere. From large-scale industrial cooling towers, in the absence of manufacturer's data, it

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

W = about 0.0005 percent of C (or less) if the cooling tower has windage drift eliminators and uses sea water as make-up water.

Cycles of concentration

Cycles 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

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Cooling Tower - Wikipedia, The Free Encyclopedia

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