11-1 Nomenclature Acfm = actual volumetric flow rate of air-vapor mixture, m3/h ahp = air power, kW AWB = ambient wet bulb temperature, °C B = combined water loss through blowdown a
Trang 1INTRODUCTION
The purpose of this section is to provide a basic
understand-ing of the design and operation of a coolunderstand-ing tower A coolunderstand-ing
tower allows water to be cooled by ambient air through
evapo-ration.
COOLING TOWER PSYCHROMETRICS
Psychrometry is the study of cooling by evaporation Maxi-mum evaporation takes place when water, in the form of tiny droplets, is exposed to the maximum air flow for the longest pos-sible time The process of evaporation through removal of latent
SECTION 11
Cooling Towers
FIG 11-1 Nomenclature
Acfm = actual volumetric flow rate of air-vapor mixture,
m3/h
ahp = air power, kW
AWB = ambient wet bulb temperature, °C
B = combined water loss through blowdown and
windage, % of circulating water or m3/h
CWT = cold water temperature, °C
DB = dry bulb temperature, °C
E = water evaporated, % of circulating water or m3/h
G = air rate, kg/(m2 • h)
ha = specific enthalpy of dry air, kJ/kg
has = hs – ha, kJ/kg
hs = enthalpy of moist air at saturation per kg of dry
air, kJ/kg
HWT = hot water temperature, °C
kgs = kilograms of dry air
kgw = kilograms of water
L = water rate, kg/(m2 • h) L/G = liquid to gas ratio, kg/kg
Q = m3/h
PF = performance factor, dimensionless
R = cooling tower range, °C
V = air velocity, m/h
va = specific volume of dry air, m3/kg
vas = vs – va, m3/kg
vs = volume of moist air at saturation per kg of dry air,
m3/kg
Ws = kgw/kgaa, humidity ratio at saturation
WB = wet bulb temperature, °C
DEFINITIONS OF WORDS AND
PHRASES USED IN COOLING TOWERS
Air inlet: Opening in a cooling tower through which air enters
Sometimes referred to as the louvered face on induced draft
towers.
Air power: The power output developed by a fan in moving a
given air rate against a given resistance
Air rate: Mass flow of dry air per square foot of cross-sectional
area in the tower’s heat transfer region per hour
Air velocity: Velocity of air-vapor mixture through a specific
region of the tower (i.e the fan).
Ambient wet-bulb temperature: The wet-bulb temperature
of the air encompassing a cooling tower, not including any
temperature contribution by the tower itself Generally
mea-sured upwind of a tower, in a number of locations sufficient
to account for all extraneous sources of heat
Approach: Difference between the cold water temperature and
the entering wet-bulb temperature.
Blowdown: Water discharged from the system to control
con-centrations of salt or other impurities in the circulating
wa-ter
Capacity: The amount of water that a cooling tower will cool
through a specified range, at a specified approach and wet-bulb temperature
Cell: Smallest tower subdivision which can function as an
inde-pendent unit with regard to air and water flow; it is bounded
by either exterior walls or partition walls Each cell may have one or more fans and one or more distribution systems.
Circulation rate: Actual water flow rate through a given
tower
Cold water temperature: Temperature of the water leaving
the collection basin, exclusive of any temperature effects incurred by the addition of makeup and/or the removal of blowdown
Collection basin: Chamber below and integral with the tower
where water is transiently collected and directed to the sump
or pump suction line.
Counterflow: Air flow direction through the fill is
countercur-rent to that of the falling water.
Crossflow: Air flow direction through the fill is essentially
per-pendicular to that of the falling water.
Distribution basin: Shallow pan-type elevated basin used to
distribute hot water over the tower fill by means of orifices in the basin floor Application is normally limited to crossflow towers.
Trang 2Double-flow: A crossflow cooling tower where two opposed fill
banks are served by a common air plenum.
Drift: Circulating water loss from the tower as liquid droplets
entrained in the exhaust air stream Units percent of
circu-lating water rate or gpm [For more precise work, an L/G
parameter is used, and drift becomes kilograms of water per
million kilograms of exhaust air (ppmw).]
Drift eliminators: An assembly of baffles or labyrinth
pas-sages through which the air passes prior to its exit from the
tower, for the purpose of removing entrained water droplets
from the exhaust air.
Dry-bulb temperature: The temperature of the entering or
ambient air adjacent to the cooling tower as measured with
a dry-bulb thermometer
Evaporation loss: Water evaporated from the circulating
wa-ter into the air stream in the cooling process
Fan cylinder: Cylindrical or venturi-shaped structure in
which a propeller fan operates Sometimes referred to as a
fan “stack” on larger towers.
Fan deck: Surface enclosing the top of an induced draft
cool-ing tower, exclusive of the distribution basins on a crossflow
tower.
Fan pitch: The angle which the blades of a propeller fan make
with the plane of rotation, measured at a prescribed point on
each blade
Fill: That portion of a cooling tower which constitutes its
pri-mary heat transfer surface Sometimes referred to as
“pack-ing.”
Forced draft: Refers to the movement of air under pressure
through a cooling tower Fans of forced draft towers are
lo-cated at the air inlets to “force” air through the tower.
Hot water temperature: Temperature of circulating water
entering the cooling tower’s distribution system
Induced draft: Refers to the movement of air through a
cool-ing tower by means of an induced partial vacuum Fans of
in-duced draft towers are located at the air discharges to “draw”
air through the tower.
Liquid-to-gas ratio: A ratio of the total mass flows of
wa-ter and dry air in a cooling tower (See Air Rate and Wawa-ter
Rate)
Louvers: Blade or passage type assemblies installed at the air
inlet face of a cooling tower to control water splashout and/or promote uniform air flow through the fill In the case of film-type crossflow fill, they may be integrally molded to the fill sheets.
Makeup: Water added to the circulating water system to
re-place water lost by evaporation, drift, windage, blowdown, and leakage
Natural draft: Refers to the movement of air through a
cool-ing tower purely by natural means Typically, by the drivcool-ing force of a density differential.
Net effect volume: That portion of the total structural volume
within which the circulating water is in intimate contact with the flowing air
Performance factor: Variable used in determining
perfor-mance characteristics in cooling towers.
Psychrometer: An instrument incorporating both a dry-bulb
and a wet-bulb thermometer, by which simultaneous dry-bulb and wet-dry-bulb temperature readings can be taken.
Range: Difference between the hot water temperature and the
cold water temperature
Recirculation: Describes a condition in which a portion of the
tower’s discharge air re-enters the air inlets along with the fresh air Its effect is an elevation of the average entering wet-bulb temperatures compared to the ambient.
Water rate: Mass flow of water per square foot of fill plan area
of the cooling tower per hour
Wet-bulb temperature: the temperature of the entering or
ambient air adjacent to the cooling tower as measured with
a wet-bulb thermometer
Wet-Bulb thermometer: A thermometer whose bulb is
en-cased within a wetted wick.
Windage: Water lost from the tower because of the effects of
wind.
Wind load: The load imposed upon a structure by a wind
blow-ing against its surface.
heat allows the water to be cooled below the ambient dry-bulb
temperature The dry air enters the cooling tower and begins
to gain moisture and enthalpy in an effort to reach equilibrium
with the water The water may be cooled 8°C or more while the
air mass dry-bulb temperature may increase only slightly A
psychrometric chart ( Fig 11-2 ) may be used to illustrate the
relationships between wet- and dry-bulb temperatures All
no-menclature is indicated in Fig 11-1
Wet-bulb Temperature
The basis for thermal design of an evaporative type
cool-ing tower is the wet-bulb temperature of the air entercool-ing the
tower Water cannot be cooled below the wet-bulb temperature
by evaporation The air entering the tower at a temperature of 24°C and 100% relative humidity has a 24°C “wet-bulb” tem-perature The wet-bulb temperature is usually measured using
a sling psychrometer Wet bulb and dry bulb data for various locations around the world are shown in Figs 11-3a and 11-3b
Types of Cooling Systems
Cooling water is circulated through equipment to absorb and carry away heat The basic cooling systems are shown in
Fig 11-4 The open recirculating system is the most common for industrial plants.
Trang 3FIG 11-2 Psychrometric Chart
Trang 4U.S
State and Stations
Design
Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
ALABAMA
Alexander City 33 26
Anniston 33 26
Auburn 33 26
Birmingham 33 24
Decatur 33 24
Dothan 33 26
Florence 33 24
Gadsden 33 24
Huntsville 33 24
Mobile AP 33 26
Mobile CO 33 26
Montgomery 34 26
Selma-Craig 34 26
Talladega 33 26
Tuscaloosa 34 25
ALASKA
Anchorage 19 14
Barrow 9 8
Fairbanks 24 16
Juneau 19 14
Kodiak 17 13
Nome 15 13
ARIZONA
Douglas 34 20
Flagstaff 27 15
Fort Huachuca 32 19
Kingman 36 21
Nogales 34 21
Phoenix 41 24
Prescott 33 18
Tucson 38 22
Winslow 34 18
Yuma 42 25
ARKANSAS
Blytheville 33 26
Camden 34 26
El Dorado 34 26
Fayetteville 33 24
Fort Smith 35 26
Hot Springs 34 26
Jonesboro 33 26
Little Rock 34 26
Pine Bluff 35 27
Texarkana 34 26
CALIFORNIA
Bakersfield 37 21
Barstow 39 21
Blythe 42 23
Burbank 31 21
Chico 37 20
Concord 34 20
Covina 33 21
Crescent City 17 15
Downey 30 21
El Cajon 26 20
El Centro 42 26
Escondido 28 21
Eureka/Arcata 17 15
Fairfield-Travis AFB 33 19
Fresno 36 21
Hamilton 27 19
Laguna Beach 25 20
Livermore 34 20
Lompoc,
Vandenburg AFB 19 16
Long Beach 25 20
Los Angeles AP 25 20
Los Angeles CO 30 21
Merced-Castle AFB 36 21
Modesto 35 21
Monterey 20 16
Napa 33 20
Needles 42 23
Oakland 24 17
Oceanside 25 20
Ontario 36 22
Oxnard 25 19
Palmdale 37 19
Palm Springs 42 23
Pasadena 33 21
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Petaluma 31 20 Pomona 35 22 Redding 38 20 Redlands 36 22 Richmond 24 17 Riverside-March AFB 35 21 Sacramento 34 21 Salinas 19 15 San Bernardino,
Norton AFB 36 22 San Diego 26 20 San Fernando 31 21 San Francisco AP 23 17 San Francisco CO 21 16 San Jose 25 18 San Luis Obispo 29 21 Santa Ana 28 21 Santa Barbara 24 19 Santa Cruz 20 16 Santa Maria 23 17 Santa Monica 25 20 Santa Paula 29 20 Santa Rosa 33 19 Stockton 34 20 Ukiah 33 19 Visalia 36 21 Yreka 32 18 Yuba City 37 20 COLORADO
Alamosa 27 16 Boulder 32 17 Colorado Springs 30 16 Denver 32 17 Durango 29 17 Fort Collins 32 17 Grand Junction 33 17 Greeley 33 17
La Junta 35 21 Leadville 26 12 Pueblo 33 18 Sterling 32 18 Trinidad 32 18 CONNECTICUT
Bridgeport 27 23 Hartford,
Brainard Field 29 23 New Haven 28 23 New London 28 23 Norwalk 27 23 Norwich 28 23 Waterbury 28 22 Windsor Locks,
Bradley Field 29 23 DELAWARE
Dover AFB 31 24 Wilmington 31 24 DISTRICT OF
COLUMBIA Andrews AFB 31 24 Washington National 32 24 FLORIDA
Belle Glade 32 26 Cape Kennedy 31 26 Daytona Beach 31 26 Fort Lauderdale 32 26 Fort Myers 33 26 Fort Pierce 32 26 Gainesville 33 26 Jacksonville 33 26 Key West 32 26 Lakeland 32 26 Miami 32 26 Miami Beach 31 26 Ocala 33 26 Orlando 33 26 Panama City,
Tyndall AFB 32 26 Pensacola 33 26
St Augustine 31 26
St Petersburg 32 26 Sanford 33 26
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Sarasota 32 26 Tallahassee 32 26 Tampa 32 26 West Palm Beach 32 26 GEORGIA
Albany, Turner AFB 34 26 Americus 33 25 Athens 32 24 Atlanta 32 24 Augusta 34 26 Brunswick 31 26 Columbus,
Lawson AFB 33 25 Dalton 33 25 Dublin 33 25 Gainesville 32 24 Griffin 31 24
La Grange 32 24 Macon 33 25 Marietta,
Dobbins AFB 32 24 Moultrie 33 26 Rome 33 25 Savannah-Travis 33 26 Valdosta-Moody AFB 33 26 Waycross 33 26 HAWAII
Hilo 28 23 Honolulu 29 23 Kaneohe Bay 28 24 Wahiawa 29 23 IDAHO
Boise 33 18 Burley 33 16 Coeur d’Alene 28 16 Idaho Falls 29 16 Lewiston 32 18 Moscow 29 17 Mountain Home AFB 34 17 Pocatello 32 16 Twin Falls 33 16 ILLINOIS
Aurora 31 24 Belleville, Scott AFB 32 24 Bloomington 31 24 Carbondale 32 25 Champaign/Urbana 32 24 Chicago, Midway 31 23 Chicago, O’Hare 30 23 Chicago 31 24 Danville 31 24 Decatur 31 24 Dixon 31 24 Elgin 30 24 Freeport 31 23 Galesburg 31 24 Greenville 32 24 Joliet 31 24 Kankakee 31 24
La Salle/Peru 31 24 Macomb 32 24 Moline 31 24
Mt Vernon 32 24 Peoria 31 24 Quincy 32 25 Rantoul,
Chanute AFB 32 24 Rockford 31 23 Springfield 32 24 Waukegan 31 24 INDIANA
Anderson 32 24 Bedford 32 24 Bloomington 32 24 Columbus,
Bakalar AFB 32 24 Crawfordsville 31 24 Evansville 33 25 Fort Wayne 31 23 Goshen 30 23
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Hobart 29 23 Huntington 31 23 Indianapolis 31 24 Jeffersonville 32 24 Kokomo 31 23 Lafayette 31 24
La Porte 31 24 Marion 31 23 Muncie 31 24 Peru,
Bunker Hill AFB 30 23 Richmond 31 24 Shelbyville 31 24 South Bend 30 23 Terre Haute 32 24 Valparaiso 31 24 Vincennes 32 24 IOWA
Ames 31 24 Burlington 31 24 Cedar Rapids 30 24 Clinton 31 24 Council Bluffs 31 24 Des Moines 31 24 Dubuque 30 23 Fort Dodge 30 23 Iowa City 31 24 Keokuk 32 24 Marshalltown 31 24 Mason City 29 23 Newton 31 24 Ottumwa 31 24 Sioux City 32 24 Waterloo 30 24 KANSAS
Atchison 33 25 Chanute 34 24 Dodge City 35 22
El Dorado 36 24 Emporia 34 24 Garden City 34 22 Goodland 34 20 Great Bend 35 24 Hutchinson 36 23 Liberal 34 22 Manhattan,
Fort Riley 33 24 Parsons 34 24 Russell 35 24 Salina 36 24 Topeka 34 24 Wichita 36 24 KENTUCKY
Ashland 32 24 Bowling Green 32 24 Corbin 32 24 Covington 31 23 Hopkinsville,
Campbell AFB 32 24 Lexington 31 24 Louisville 32 24 Madisonville 32 25 Owensboro 33 25 Paducah 33 25 LOUISIANA
Alexandria 33 26 Baton Rouge 33 26 Bogalusa 33 26 Houma 33 26 Lafayette 33 26 Lake Charles 33 26 Minden 34 26 Monroe 34 26 Natchitoches 34 26 New Orleans 32 26 Shreveport 34 26 MAINE
Augusta 28 21 Bangor, Dow AFB 27 21 Caribou 26 19 Lewiston 28 21
FIG 11-3a
Trang 5U.S
State and Stations
Design
Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Millinocket 27 20
Portland 27 21
Waterville 27 21
MARYLAND
Baltimore AP 32 24
Baltimore CO 31 24
Cumberland 31 24
Frederick 31 24
Hagerstown 32 24
Salisbury 31 24
MASSACHUSETTS
Boston 29 22
Clinton 29 22
Fall River 27 22
Framingham 28 22
Gloucester 28 22
Greenfield 28 22
Lawrence 29 23
Lowell 29 23
New Bedford 27 22
Pittsfield 27 21
Springfield,
Westover AFB 29 22
Taunton 28 23
Worcester 27 21
MICHIGAN
Adrian 29 23
Alpena 28 21
Battle Creek 29 23
Benton Harbor 29 22
Detroit 30 23
Escanaba 27 21
Flint 29 22
Grand Rapids 29 22
Holland 28 22
Jackson 29 23
Kalamazoo 29 23
Lansing 29 22
Marquette 25 20
Mt Pleasant 29 22
Muskegon 28 22
Pontiac 29 23
Port Huron 28 23
Saginaw 29 22
Sault St Marie 25 20
Traverse City 28 22
Ypsilanti 30 22
MINNESOTA
Albert Lea 29 23
Alexandria 29 22
Bemidji 27 21
Brainerd 29 22
Duluth 26 20
Fairbault 29 23
Fergus Falls 29 22
International Falls 27 20
Mankato 29 23
Minneapolis/St Paul 30 23
Rochester 29 23
St Cloud 29 22
Virginia 27 20
Willmar 29 22
Winona 29 23
MISSISSIPPI
Biloxi, Keesler AFB 32 27
Clarksdale 33 26
Columbus AFB 33 26
Greenville AFB 33 26
Greenwood 33 26
Hattiesburg 33 26
Jackson 34 26
Laurel 33 26
McComb 33 26
Meridian 34 26
Natchez 33 26
Tupelo 33 26
Vicksburg 34 26
MISSOURI
Cape Girardeau 33 25
Columbia 33 24
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Farmington 32 24 Hannibal 32 25 Jefferson City 33 24 Joplin 34 24 Kansas City 34 24 Kirksville 32 24 Mexico 33 24 Moberly 33 24 Poplar Bluff 33 26 Rolla 32 24
St Joseph 33 25
St Louis AP 33 24
St Louis CO 33 24 Sedalia,
Whiteman AFB 32 24 Sikeston 33 25 Springfield 33 24 MONTANA
Billings 31 18 Bozeman 29 16 Butte 27 14 Cut Bank 28 16 Glasgow 29 18 Glendive 32 18 Great Falls 29 16 Havre 31 18 Helena 29 16 Kalispell 29 17 Lewiston 28 17 Livingston 29 16 Miles City 33 19 Missoula 29 17 NEBRASKA
Beatrice 33 24 Chadron 33 20 Columbus 33 24 Fremont 33 24 Grand Island 33 23 Hastings 33 23 Kearney 32 22 Lincoln 33 24 McCook 33 22 Norfolk 32 24 North Platte 32 22 Omaha 31 24 Scottsbluff 32 19 Sidney 32 19 NEVADA
Carson City 32 16 Elko 32 16 Ely 29 14 Las Vegas 40 21 Lovelock 34 18 Reno AP 32 16 Reno CO 33 16 Tonopah 32 16 Winnemucca 33 16 NEW HAMPSHIRE
Berlin 27 21 Claremont 28 22 Concord 29 22 Keene 28 22 Laconia 28 22 Manchester,
Grenier AFB 29 22 Portsmouth,
Pease AFB 28 22 NEW JERSEY
Atlantic City 30 24 Long Branch 31 24 Newark 31 24 New Brunswick 30 24 Paterson 31 24 Phillipsburg 30 23 Trenton 29 24 Vineland 30 24 NEW MEXICO
Alamogordo, Holloman AFB 34 19 Albuquerque 33 18
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Artesia 36 21 Carlsbad 36 21 Clovis 33 19 Farmington 33 18 Gallup 30 16 Grants 29 16 Hobbs 36 21 Las Cruces 34 19 Los Alamos 29 16 Raton 31 17 Roswell,
Walker AFB 36 21 Santa Fe 30 16 Silver City 33 17 Socorro 34 18 Tucumcari 35 20 NEW YORK
Albany AP 29 22 Albany CO 29 22 Auburn 29 22 Batavia 29 22 Binghamton 27 21 Buffalo 28 22 Cortland 28 22 Dunkirk 28 22 Elmira 28 22 Geneva 29 22 Glen Falls 28 22 Gloversville 28 22 Hornell 28 22 Ithaca 28 22 Jamestown 28 22 Kingston 29 23 Lockport 29 23 Massena 27 21 Newburg-
Stewart AFB 29 23 NYC-Central Park 31 23 NYC-Kennedy AP 29 23 NYC-LaGuardia AP 31 23 Niagara Falls 29 23 Olean 27 22 Oneonta 27 21 Oswego 27 22 Plattsburg AFB 27 21 Poughkeepsie 30 23 Rochester 29 22 Rome-Griffiss AFB 28 22 Schenectady 29 22 Suffolk County AFB 27 23 Syracuse 29 22 Utica 28 22 Watertown 27 22 NORTH CAROLINA
Asheville 29 22 Charlotte 33 24 Durham 32 24 Elizabeth City 32 26 Fayetteville,
Pope AFB 32 25 Goldsboro, Seymour-
Johnson AFB 32 25 Greensboro 32 24 Greenville 32 25 Henderson 32 25 Hickory 31 23 Jacksonville 31 26 Lumberton 32 25 New Bern 31 26 Raleigh/Durham 32 24 Rocky Mount 32 25 Wilmington 32 26 Winston-Salem 32 23 NORTH DAKOTA
Bismark 31 21 Devil’s Lake 29 21 Dickinson 31 20 Fargo 29 22 Grand Forks 29 21 Jamestown 31 22
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Minot 30 20 Williston 29 20 OHIO
Akron-Canton 29 22 Ashtabula 28 22 Athens 32 23 Bowling Green 30 23 Cambridge 31 24 Chillicothe 32 23 Cincinnati 31 23 Cleveland 30 23 Columbus 31 23 Dayton 30 23 Defiance 31 23 Findlay 31 23 Fremont 29 23 Hamilton 31 23 Lancaster 31 23 Lima 31 23 Mansfield 29 23 Marion 31 23 Middletown 31 23 Newark 32 23 Norwalk 29 23 Portsmouth 32 24 Sandusky 31 23 Springfield 31 23 Steubenville 29 22 Toledo 29 23 Warren 29 22 Wooster 29 22 Youngstown 29 22 Zanesville 31 24 OKLAHOMA
Ada 35 24 Altus AFB 37 24 Ardmore 35 24 Bartlesville 35 24 Chickasha 35 24 Enid-Vance AFB 36 24 Lawton 36 24 McAlester 34 24 Muskogee 35 25 Norman 34 24 Oklahoma City 35 24 Ponca City 34 24 Seminole 34 24 Stillwater 34 24 Tulsa 35 25 Woodward 34 24 OREGON
Albany 30 19 Astoria 20 17 Baker 30 16 Bend 29 16 Corvallis 30 19 Eugene 30 19 Grants Pass 34 20 Klamath Falls 29 16 Medford 33 19 Pendleton 32 17 Portland AP 27 19 Portland CO 28 19 Roseburg 31 19 Salem 29 19 The Dalles 29 19 PENNSYLVANIA
Allentown 30 23 Altoona 29 22 Butler 29 23 Chambersburg 31 24 Erie 28 22 Harrisburg 31 24 Johnstown 27 21 Lancaster 31 24 Meadville 28 22 New Castle 30 23 Philadelphia 31 24 Pittsburgh AP 29 22 Pittsburgh CO 30 22
FIG 11-3a (Cont’d)
Trang 6FIG 11-3a (Cont’d)
U.S
State and Stations
Design
Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Reading 30 23
Scranton/Wilkes-Barre 29 22
State College 29 22
Sunbury 30 23
Uniontown 29 23
Warren 28 22
West Chester 30 24
Williamsport 30 23
York 31 24
RHODE ISLAND
Newport 28 23
Providence 28 23
SOUTH CAROLINA
Anderson 32 24
Charleston AFB 32 26
Charleston 32 26
Columbia 34 25
Florence 32 26
Georgetown 31 26
Greenville 32 24
Greenwood 33 24
Orangeburg 34 25
Rock Hill 33 24
Spartanburg 32 24
Sumter-Shaw AFB 32 25
SOUTH DAKOTA
Aberdeen 31 23
Brookings 32 23
Huron 32 23
Mitchel 32 23
Pierre 33 22
Rapid City 32 19
Sioux Falls 31 23
Watertown 31 23
Yankton 31 23
TENNESSEE
Athens 32 24
Bristol-Tri City 31 23
Chattanooga 33 24
Clarksville 32 24
Columbia 33 24
Dyersburg 33 26
Greenville 31 23
Jackson 33 25
Knoxville 32 24
Memphis 34 26
Murfreesboro 33 24
Nashville 33 24
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Tullahoma 33 24 TEXAS
Abilene 36 23 Alice 35 26 Amarillo 34 21 Austin 36 25 Bay City 33 26 Beaumont 33 27 Beeville 35 26 Big Springs 35 22 Brownsville 33 26 Brownwood 36 24 Bryan 34 26 Corpus Christi 33 26 Corsicana 36 25 Dallas 36 25 Del Rio,
Laughlin AFB 36 24 Denton 36 24 Eagle Pass 37 25
El Paso 36 20 Fort Worth 36 24 Galveston 31 27 Greenville 36 24 Harlingen 34 26 Houston AP 33 26 Houston CO 34 26 Huntsville 36 25 Killeen-Gray AFB 35 24 Lamesa 34 22 Laredo 37 25 Longview 35 26 Lubbock 34 22 Lufkin 34 26 McAllen 34 26 Midland 36 22 Mineral Wells 36 24 Palestine 36 26 Pampa 34 21 Pecos 36 22 Plainview 34 21 Port Arthur 33 27 San Angelo,
Goodfellow AFB 36 23 San Antonio 36 24 Sherman Perrin AFB 35 24 Snyder 36 22 Temple 36 25
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Tyler 35 26 Vernon 36 24 Victoria 34 26 Waco 36 25 Wichita Falls 37 24 UTAH
Cedar City 32 17 Logan 31 17 Moab 36 17 Ogden 31 18 Price 32 17 Provo 34 18 Richfield 32 17
St George 37 19 Salt Lake City 33 18 Vernal 30 17 VERMONT
Barre 26 21 Burlington 28 22 Rutland 27 22 VIRGINIA
Charlottesville 31 24 Danville 32 24 Fredericksburg 32 24 Harrisonburg 31 23 Lynchburg 31 24 Norfolk 32 25 Petersburg 32 25 Richmond 32 25 Roanoke 31 23 Staunton 31 23 Winchester 31 24 WASHINGTON
Aberdeen 23 17 Bellingham 23 17 Bremerton 24 17 Ellensburg 31 17 Everett-Paine AFB 23 17 Kennewick 33 19 Longview 27 19 Moses Lake,
Larson AFB 32 18 Olympia 26 18 Port Angeles 19 16 Seattle-Boeing Fld 25 18 Seattle CO 26 18 Seattle-Tacoma AP 24 17 Spokane 31 17
U.S
State and Stations
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Tacoma- McChord AFB 26 18 Walla Walla 32 19 Wenatchee 33 18 Yakima 32 18 WEST VIRGINIA
Beckley 26 21 Bluefield 26 21 Charleston 31 23 Clarksburg 31 23 Elkins 28 22 Huntington 32 24 Martinsburg 31 24 Morgantown 29 23 Parkersburg 31 24 Wheeling 29 22 WISCONSIN
Appleton 28 22 Ashland 26 20 Beloit 31 24 Eau Claire 30 23 Fond du Lac 29 22 Green Bay 28 22
La Crosse 29 23 Madison 29 23 Manitowoc 28 22 Marinette 28 22 Milwaukee 29 23 Racine 29 23 Sheboygan 28 23 Stevens Point 30 23 Waukesha 29 23 Wausau 29 22 WYOMING
Casper 31 16 Cheyenne 29 16 Cody 28 16 Evanston 28 14 Lander 29 16 Laramie 26 15 Newcastle 29 19 Rawlins 27 16 Rock Springs 28 14 Sheridan 31 17 Torrington 31 17
The dry bulb and wet bulb temperatures represent values which have been equalled or exceeded by 5% of the total hours during the months of June through Sep-tember in the northern hemisphere and the months December through March in the southern hemisphere
The data for Canadian stations are based on the month of July only
AP = airport AFB = air force base CO = urban offices
Adapted to SI with permission of the American Society of Heating, Refrigerating and Air-Conditioning
Engineers, Atlanta, Georgia, from the 1993 ASHRAE Handbook—Fundamentals.
Trang 7Country and
Station
Design
Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
ADEN
Aden 37 28
AFGHANISTAN
Kabul 34 18
ALGERIA
Algiers 32 24
ARGENTINA
Buenos Aires 30 24
Córdoba 34 23
Tucuman 36 23
AUSTRALIA
Adelaide 33 20
Alice Springs 38 22
Brisbane 30 24
Darwin 33 27
Melbourne 30 20
Perth 34 23
Sydney 27 22
AUSTRIA
Vienna 28 19
AZORES
Lajes (Terceira) 25 22
BAHAMAS
Nassau 31 26
BELGIUM
Brussels 25 19
BELIZE
Belize 32 27
BERMUDA
Kindley AFB 29 26
BOLIVIA
La Paz 20 13
BRAZIL
Belem 31 26
Belo Horizonte 28 24
Brazilia 30 24
Curitiba 28 23
Fortaleza 32 26
Porto Alegre 32 24
Recife 30 25
Rio de Janeiro 32 26
Salvador 30 26
São Paulo 28 23
BULGARIA
Sofia 29 21
BURMA
Mandalay 38 27
Rangoon 35 28
CAMBODIA
Phnom Penh 34 28
CANADA (Alberta)
Calgary 26 17
Edmonton 26 18
Grande Prairie 26 17
Jasper 25 17
Lethbridge 29 18
McMurray 26 18
Medicine Hat 31 19
Red Deer 26 18
CANADA (British
Columbia)
Dawson Creek 24 17
Fort Nelson 26 18
Kamloops 31 18
Nanaimo 25 18
New Westminster 26 19
Penticton 31 19
Prince George 25 17
Prince Rupert 16 14
Trail 30 18
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
Vancouver 23 19 Victoria 21 16 CANADA (Manitoba)
Brandon 28 21 Churchill 23 17 Dauphin 27 21 Flin Flon 26 19 Portage la Prairie 28 22 The Pas 26 20 Winnepeg 29 22 CANADA (New
Brunswick) Campbellton 26 20 Chatham 28 21 Edmundston 27 21 Fredericton 28 21 Moncton 26 21 Saint John 24 19 CANADA
(Newfound-land) Corner Brook 22 18 Gander 25 19 Goose Bay 25 18
St John’s 23 19 Stephenville 22 18 CANADA (Northwest
Terr.) Fort Smith 26 18 Frobisher 15 11 Inuvik 24 16 Resolute 11 8 Yellowknife 23 17 CANADA (Nova
Scotia) Amherst 26 20 Halifax 23 19 Kentville 27 21 New Glasgow 25 21 Sydney 25 20 Truro 26 21 Yarmouth 21 18 CANADA (Ontario)
Belleville 28 23 Chatham 29 23 Cornwall 29 22 Hamilton 28 23 Kapuskasing 27 21 Kenora 27 21 Kingston 28 23 Kitchener 28 22 London 28 23 North Bay 26 20 Oshawa 29 23 Ottawa 29 22 Owen Sound 27 21 Peterborough 28 22
St Catharines 28 23 Sarnia 29 23 Sault Ste Marie 26 21 Sudbury 27 20 Thunder Bay 27 20 Timmins 27 20 Toronto 29 23 Windsor 30 23 CANADA (Prince
Edward Island) Charlottetown 24 20 Summerside 25 20
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
CANADA (Quebec) Bagotville 27 20 Chicoutimi 27 20 Drummondville 28 22 Granby 28 22 Hull 29 22 Mégantic 27 22 Montréal 28 22 Québec 27 21 Rimouski 24 19
St Jean 29 22
St Jéirome 28 22 Sept Iles 21 17 Shawnigan 28 22 Sherbrooke 27 22 Thetford Mines 27 22 Trois Riviéres 28 22 Val d’Or 27 20 Valleyfield 29 22 CANADA
(Saskatch-ewan) Estevan 30 21 Moose Jaw 30 20 North Battleford 28 19 Prince Albert 27 19 Regina 29 20 Saskatoon 28 19 Swift Current 31 19 Yorkton 27 20 CANADA (Yukon
Territory) Whitehorse 23 14 CEYLON
Colombo 31 27 CHILE
Punta Arenas 18 12 Santiago 31 21 Valparaiso 25 18 CHINA
Chungking 35 26 Shanghai 32 27 COLOMBIA
Baranquilla 34 28 Bogotá 21 14 Cali 26 20 Medellin 29 22 CONGO
Brazzaville 33 27 Kinshasa
(Leopoldville) 32 27 Stanleyville 32 27 CUBA
Guantanamo Bay 33 27 Havana 32 27 CZECHOSLOVAKIA
Prague 28 18 DENMARK
Copenhagen 23 18 DOMINICAN
REPUBLIC Santo Domingo 31 27 ECUADOR
Guayacil 32 26 Quito 22 17
EL SALVADOR San Salvador 35 24 ETHIOPIA
Addis Ababa 27 18 Asmara 27 17 FINLAND
Helsinki 22 17
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
FRANCE Lyon 30 21 Marseilles 29 21 Nantes 27 19 Nice 28 22 Paris 28 19 Strasbourg 27 19 FRENCH GUIANA
Cayenne 32 28 GERMANY
Berlin 26 19 Hamburg 23 18 Hannover 24 18 Mannheim 28 20 Munich 27 18 GHANA
Accra 32 26 GIBRALTER
Gibralter 30 23 GREECE
Athens 33 22 Thessaloniki 33 24 GREENLAND
Narssarssuaq 16 11 GUATEMALA
Guatemala City 27 19 GUYANA
Georgetown 31 26 HAITI
Port au Prince 34 27 HONDURAS
Tegucigalpa 29 22 HONG KONG
Hong Kong 32 27 HUNGARY
Budapest 29 21 ICELAND
Reykjavik 13 12 INDIA
Ahmenabad 41 26 Bangalore 34 23 Bombay 33 27 Calcutta 36 28 Madras 38 28 Nagpur 42 26 New Delhi 41 28 INDONESIA
Djakarta 31 26 Kupang 33 27 Makassar 31 26 Medan 32 26 Palembang 32 26 Surabaya 32 26 IRAN
Abadan 43 27 Meshed 34 19 Tehran 37 23 IRAQ
Baghdad 42 22 Mosul 43 22 IRELAND
Dublin 21 17 Shannon 22 17 ISRAEL
Jerusalem 33 21 Tel Aviv 33 22 ITALY
Milan 29 23 Naples 30 22 Rome 32 22 IVORY COAST
Abidjan 31 27
FIG 11-3b
Trang 8Country and
Station
Design
Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
JAPAN
Fukuoka 32 26
Sapporo 27 22
Tokyo 31 26
JORDAN
Amman 33 20
KENYA
Nairobi 26 18
KOREA
Pyongyang 29 24
Seoul 31 26
LEBANON
Beirut 32 24
LIBERIA
Monrovia 31 27
LIBYA
Bengasi 33 24
MADAGASCAR
Tananarive 28 22
MALAYSIA
Kuala Lumpur 33 27
Penang 33 27
Singapore 32 27
MARTINIQUE
Fort de France 31 27
MEXICO
Guadalajara 32 19
Mérida 34 25
Mexico City 26 15
Monterrey 34 25
Vera Cruz 31 28
MOROCCO
Casablanca 30 21
NEPAL
Katmandu 30 24
NETHERLANDS
Amsterdam 23 17
NEW GUINEA
Manokwari 31 27
Point Moresby 32 26
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
NEW ZEALAND Auckland 24 18 Christ Church 24 19 Wellington 22 18 NICARAGUA
Managua 33 26 NIGERIA
Lagos 32 27 NORWAY
Bergen 23 18 Oslo 23 18 PAKISTAN
Chittagong 32 27 Karachi 35 27 Lahore 41 27 Peshwar 39 26 PANAMA & CANAL
ZONE Panama City 33 27 PARAGUAY
Asunción 36 27 PERU
Lima 29 23 PHILIPPINES
Manila 33 27 POLAND
Kraków 26 19 Warsaw 26 20 PORTUGAL
Lisbon 28 19 PUERTO RICO
San Juan 31 26 RUMANIA
Bucharest 32 21 SAUDI ARABIA
Dhahran 42 29 Jedda 38 28 Riyadh 41 24 SENEGAL
Dakar 33 27
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
SOMALIA Mogadiscio 32 27 SOUTH AFRICA
Capetown 30 21 Johannesburg 27 21 Pretoria 29 20 SOVIET UNION
Alma Ata 28 19 Archangel 20 14 Kaliningrad 25 18 Krasnoyarsk 24 16 Kiev 27 19 Kharkov 28 19 Kuibyshev 27 19 Leningrad 22 17 Minsk 23 18 Moscow 26 18 Odessa 28 20 Petropavlovsk 18 13 Rostov on Don 29 20 Sverdlovsk 22 16 Tashkent 32 21 Tblisi 28 19 Vladivostok 23 20 Volgograd 30 21 SPAIN
Barcelona 29 23 Madrid 32 19 Valencia 31 23 SUDAN
Khartoum 40 24 SURINAM
Paramaribo 32 27 SWEDEN
Stockholm 22 16 SWITZERLAND
Zurich 26 19 SYRIA
Damascus 37 21
Country and Station
Design Dry-Bulb
°C 5%
Design Wet-Bulb
°C 5%
TAIWAN Tainan 32 28 Taipei 32 27 TANZANIA
Dar es Salaam 31 27 THAILAND
Bangkok 34 27 TRINIDAD
Port of Spain 32 26 TUNISIA
Tunis 36 23 TURKEY
Adana 35 25 Ankara 32 19 Istanbul 30 23 Izmir 34 23 UNITED ARAB
REPUBLIC Cairo 37 23 UNITED KINGDOM
Belfast 21 17 Birmingham 23 17 Cardiff 23 17 Edinburgh 20 16 Glasgow 20 16 London 24 18 URUGUAY
Montevideo 29 22 VENEZUELA
Caracas 27 21 Maracaibo 35 28 VIET NAM
Da Nang 34 29 Hanoi 35 29 Saigon 32 28 YUGOSLAVIA
Belgrade 30 22
FIG 11-3b (Cont’d)
The dry bulb and wet bulb temperatures represent values which have been equalled or exceeded by 5% of the total hours during the months of June through Sep-tember in the northern hemisphere and the months December through March in the southern hemisphere
The data for Canadian stations are based on the month of July only
AP = airport AFB = air force base CO = urban offices
Adapted to SI with permission of the American Society of Heating, Refrigerating and Air-Conditioning
Engineers, Atlanta, Georgia, from the 1993 ASHRAE Handbook—Fundamentals.
Trang 9The open recirculating system routes cooled water through
the heat-exchange equipment Effluent warm water then is
cooled by contact with air in a cooling tower The cooling
ef-fect is produced by evaporation of a portion of the circulating
water, and this evaporation causes the dissolved solids in the
water to become concentrated Water lost by evaporation must
be replaced by makeup water But water lost through
entrain-ment of droplets in the circulating air (windage or drift) tends
to limit the degree of concentration since the entrained droplets
also contain dissolved solids Windage loss varies with the type
of tower.
Typical windage losses, expressed as percentages of the
total system water circulation rate, for different evaporative
equipment are as follows:
Tower Location
Local heat sources upwind of the cooling tower can elevate the wet-bulb temperature of the air entering the tower Inter-ference occurs when a portion of the saturated air upwind of the tower contaminates the ambient air of a downwind tower Drift and condensed water can cause corrosion problems with downwind equipment.
PERFORMANCE CHARACTERISTICS
The performance characteristics of various types of tow-ers will vary with height, fill configuration, and flow arrange-ment — crossflow or counterflow; however, these factors have been taken into consideration in preparation of the Performance Characteristic Nomograph Fig 11-5 When accurate character-istics of a specific tower are required, the cooling tower manu-facturer should be consulted.
FIG 11-4 Cooling System Characteristics
Trang 10Example 11-1 — Effect of Varying WB Temperature on Cold Water
Tempera-ture (CWT).
What is new CWT when WB changes from 25° to 15° with m3/h and range
remaining constant?
Enter Nomograph at 30° CWT, go horizontally to 25° WB, then vertically
down to 15° WB, read new CWT of 24°.
Tempera-ture.
What is new CWT when cooling range is changed from 10° to 15° (50% increase in heat load) with m3/h and WB held constant?
Enter Nomograph at 30° CWT, go horizontally to 25° WB, vertically to 10° R, horizontally to 15° R, vertically downward to 25° WB, read new CWT 31.8°.
Example 11-3 — Effect of Varying Water Circulating Rate and Heat Load on
Cold Water Temperature.
What is new CWT when water circulation is changed from 200 m3/h to
300 m3/h (50% change in heat load at constant Range) Varying water rate,
particularly over wide ranges, may require modifications to the distribution
system Enter Nomograph at 30° CWT, go horizontally to 25° WB, vertically
to 10° R, horizontally to Performance Factor of 1.8 Obtain new PF by
multi-plying (1.8) (300/200) = 2.7, then enter Nomograph at PF of 2.7, go
horizon-tally to 10° R, vertically down to 25° WB, read new CWT 33.2°.