Document rpbZym71Odz5R5npr15mz08pE

592- CHAPTER 32 1965 Guide And Data Book' all installation^ because they^operite dunng sleeping fours. . * Standard' Test Code for Air'-Moving Devices (Air Moving and Conditioning'Amoriation, A MCA Bulletin 210, 1962,ro. 7). Central units are'available' in 'sizes' from 3,000:to 30,000 Beeommended.Praetice'for.Sotsnd-Te^ng-cf AvMmng.D*-^. cfm, and window unite in dees up to.8,000 cfm` ' \'' \ .. Fans ForSpedaL Applications -id-.. ^ vices (Air Moving.and. Conditioning. Asswaataon, Budcttn.30^ February 1963). _ ... , ... , - 4`R. D. .Moyer: Fan' laws' simplify performance calculations (Petoer, August 1946).- '- i-'i 'J'l I Fans are used to, ,handle many gaaes1 other, than, air .at. F.-L. Busey: jThe. centrifugal fan {ASHVE Transactions, ; normal temperature..These range from,heated 4ur to many.; V'^82tlM^<?^S'siinth|'and Wl.R.' Foote^Biergy t^nsf: types of fumes,- vaporsj- and industrial^gases .which may.be., corrosive, explosive,. toxicJ,jradiqactiyeJJor. merely, noxious.,. .For baQdli^^wrrodre.gasra^fans.sbouU.be cpnstructed of a material suitable for,the :particular gas being.handled,. , although,at times it is .economical to plapon .replacing, a, unit of standard material at morerfrequent intervals.. Ext:: plosive combinationar.-usually .dictate a; npn-spar^mg .farC between attuid aad.a rotor forpump and tortme^piachiDery ^R^rjSoh^Kf'&^Ward, and-R. M,.Ptokerton:.r& Char- aderistics cf.78 Related Airfoil Sections from.Tats xn iht Variable Density Wmd Tiawl (Natidna^ Advisory:CorranjiUc far Aviation Peport-No.;460)rR;-M. Pinterton and Harry Greenberg: Aervd&rmic Charaderistiet.&f* Large#umber ^ Atrfotti Tested w the VorvdiU Densitg'WiniT.iamelXNatiimal Advisory Committee for, in.wjjicheither the entire fan, or only.those parts which;rpiig^t.; strike together if, not"; adjusted, ...is built:of..non-^parkmg , materials Noxious, .toxic, radioactive, ,or pure.or, valuable Aeronautics Beport No..678)., iVi-'.t,. \ J. ELMcDonald: Centnfu^U^andAxuU Fwu (Mks Me^^ iral Engineers Handbook, McGraw-Hill BookCo^ New York)._ hlC'^aart1 arid;J^B.-Luaki-'nieispecific characteristics.off g{^!^;for;si>E^;Mnstruction^to.preYent.leakage. This ] usually consists of.a-welded gas-tight housing, using.flanged; inlet andj0utlet, 'and some form.of shaft sail. . -; -,1a.most of these, speciaJ :appbcations, dnce it ia desirable - fans (ASHVE TBAMaaerioKa.^VoL 43tlw7,:p. 57)r,.: , i*.W:.R.,Heath and A: E. Cnqm; The axial flow, plaiTn ventilation (ASHVE-^TBaNSAcnoNS, VoL 60,1944). . . ^ O Wood: Technique* for ddsigrisng dud systems^{Atr Eng+- tp .keqj ^all bearings, drives'and'motors .outside the. gas stream,^centrifugal fans areusually,.used, in arrangement l,.2,,4rjor 8 (Fig., 9). The,exception;is in,the case of.farts , handling explosive. mixtures, where propeller or axial .fans, are permissible when built with explpaanrproof:motors and; non-ferrous wheels.,, j: ..Fans handling hot,dr or gasare generally;of:the centrif-,. ugal types and follow arrangements 1 or.8,so that bearings,;, 2Sb: B. Hetauih Mid G- H. . Tattle: Comfort. coolio6_witi attic ventilating fans (ASHVE TnANsacnoNS, VoL 40, 193*. R,, lS A. P. Krais and S. Konzo: ASHVE Rasnancs RBrowr Nck 979--Stucty of summer cooling in, the research resutenee of 1933 (ASHVE ThajNSactto^s^VoL- 4D, 1W4, p. 1W). wTmntonlnd A. P. Poor: ASHVE RasBaRCH Rbpobt No. drives,. and ^motor^ are. remote from;the heat.. 1/,o/fdoubleinUt'ctype, they/have inlet boxes and* long shafts to-.keep; the outside -the,stream. Propeller or axialytypea? 1198^-The effect of attic fan tun (ASHVE Transactions, iYoL .48, 1942, p. 145)..,W. Badgett: The-Installation and Ceflfcrr of Texas Bulletm No. 62, 1940). W.A. Hinton are-rare-..when the temperature exceeds J50 F.^With'.tem- and W. O. Wanamaker: Some effMto.of attic fan opmaUon on peratures above 600.F;:spedal heat-resistant.materials_may;. comfort (ASHVE ThaNSACTioSS, VoL SO, 1944, p. 37.1>. be required for. the. rotors. In addition,to,a remote.location,. for the bearings, external cooling is'1 frequently required.; when ;the temperature exceeds2Q0 to 230 F..,T^his is often obtained, by. use of airrcooled or;watw^<wle>i j^kets. ^ith.. anti-friction . bearings, a . head-radiating disc.;or7 a;:amallj circulating impeller.between the fan.and.the nearest bearing, is,6om^times: sufficient.rOii lubrication rather.than, grease; hibricatinn is commonly.reoo.nunpnded.;'; :: ,.. ... 1 1. RffERBKES . ; 1 Standard Test Codefor dir Moving Devices (Air Moving and< Conditioning Association, AAfCA-BuftrtHv210,-1962). ; BiBUGRAPHy - A.H. .Church: The. Centrifugal:Pumps ..and Blowers (John' WUey'A Soiai'.New York)!' ' ' " - t- -.. ' Pen Engineering (Buffalo Forge C6.)."r: - ' ',! Theodore Baum^ster, < Jr;: - Fan*. (McGraw-HHl ' Co., New' Y,oCrku)r:t . K.eller:- 7v7.ir Th.e;rory and ..Performance of .Axial . Plots , F<pi/adapted by' L. 8. Marks,'and J. R. ,Weke'(McGraw-' Hill Oi, Now YdA): - ' 7 ,s'- ' " - ' ' * - * C. H.'Beriy:'Plow and'Fan (The Industrial Press, New York,:; 19541..f - r,.. . -;(K'' - .io\ i. <_ ( OHAPTER 33 AIR WASHERS, EVAPORATIVE AIR-COOLING EQUIPMENT AND HUMIDIFIERS dir Washers: Humidification, Dehumid/ficol/on and CoolingsMaintenance; Evaporative Air Cooling: Wetted-Pad, Slinger, arid Hotary Packaged Air Coolers, Mo/nfenance; Residenf/af and^ Industriai Humidification: Sizing, Types of Equipment, Controls THIS chapter discusses: (1) the use of air washers for AIR WASHERS evaporative air cooling, humidification and dehumidification; (2) evaporative air-cooling equipment; and (3).red- Spray-Type Washers* ..... jantiai and industrial humidification: principles and equip- A spray-type, air washer consists essentially of a chamber . ment. ^ or casing containing a spray nozzle system, a tant'for.col; lecting the spray water as it falls, and an fiiminator section : EVAPORATIVE AIR COOUNG ;' ' ; at the discharge end for removal of entrained drops of water from the air. A pump recirculates water at a rate greatly, in - In-Its broadest soise, the evaporative cooling principle applies 'to all equipment that exchanges' sensible heat for - latent beat. Cooling towers, evaporative condensers, vacuum cooling apparatus, air washers, and packaged evaporative 'coolers utilize the principle. This equipment falls into two general categories: (1) apparatus -for air cooling and ; (2) apparatus-for heat rejection. This chapter- deals"' primarily with equipment for air cooling, but the use. of air washers for humidification and dehumidification also will be discussed. Evaporative air cooling applies the well known process-'of . evaporating'1water into an air stream, fig. 1 illustrates the - following thermodynamic changes' that can take place between. the air and water ` i 1! In'A, the water'ia constantly rearculated'so'that it 'soon reaches an equilibrium with the thermodynamic wetibulb-tem-. peratiire of the entering air,' both water- temperature and - wet7 bulb temperature of the air becoming ;the same. The constant . temperature water lowers the dry-bulb temperature of the enter- ' ing air so that it approaches the water temperature. This is &n ' adiabatic'heat transfer process in winch the wet-bulb-tempera ture of the air remains constant, but the dry-bulb temperature drops as the humidity rises. 2. If the air is heated, as in B, the warm water entering the apparatus will be cooled as the wet-bulb temperature of the air is increased. In such a beating process, the final water tempera ture approaches the final wet-bulb temperature of the air. 3. If the iur is cooled, as in C, the cold water entering the apparatus will be warmed as the wet-bulb temperature of the air is lowered. In such a cooling process, the final wet-bulb tempera ture of the air will always be higher than the final water temper ature. excess of the evaporation rate. Intimate contact between the . spray water and the flowing air causes heat and mass transfer between the air and the water. Air washers vary in length from.4;.to 10 ft, depending largely on the number of spray banks. The cross-sectional area is determined by the design velocity of. the air through . the spray chamber. Washers are commonly available, from . 2000 to 250,000 cfm capacity; however, there is no practical - limit to sizes specially constructed. There is no standardiza tion in washers. Instead, each manufacturer publishes .tables giving physical data and ratings for his own sizes. Hence,: air velocity, water spray density, spray pressure, and other.de-* .rign factors must be considered for each application...; , , The simplest design has a single bank of spray nozzles ndth a casing usually 4 to 7 ft long. This type is applied primarily . as an evaporative cooler, humidifier, and air cleaner. An in crease in cleaning efficiency may be expected by the addition - of flooding nozzles for washing the eliminator, plates. Two or more.spray.banks are usually used where a very high degree -of saturation 13.necessary, and for cooling and dehumidifica tion applications requiring chilled water. Two-stage washers are used for dehumidification when the quantity of chilled water is limited or when the temperature of water is above that necessary for the single stage design. Arranging the two stages for bounterflow of the water permits the use of smaller quantity of.water with a higher temperature rise. - Figs. 2 and 3 show the construction features of conventional spray-type air washers. Essential'requirements in the air Evaporative, air.cooling equipment may be placed in two general classes, direct and indirect The first of these uses pri mary wet surfaces which evaporate water directly into the air supplied to the space being' cooled. This may be done with a series of sprays as in an air washer or by use of an extended wetted-surface material as in packaged air coolers. The second class of evaporative air cooling is termed in direct. The indirect cooler uses the evaporative principle to washer operation are: uniform distribution of the air across ' the spray chamber, air velocities of from 300 to 700 fpm in the ^ washer chamber, an adequate amount of spray water broken up into fine droplets at pressures of from 15 to 30 psig, good spray distribution across the air stream, sufficient length of travel through the spray and wetted surfaces, and the elimi nation of free moisture from the outlet cur. Washers of nearly equal height and-width are desirable cool air or water in-a device such as a cooling tower. The resultant cool air or water is then used by means of a second ary heat exchanger to cool the air.in the1occupied space.1 More complex arrangements of-this principle have been from an air flow and economic standpoint, although these proportions are not necessary. The length of washers varies conriderably. A space of approximately 2} to 4| ft between spray banks is used, and the first and last banks of sprays are Use^- By applying recirculating, regenerating principles, tem peratures below the initial wet-bulb may be produced.* The complexity and cost of these devices has made them rare. located about' l to 1$ ft from the entering or leaving end of the washer. In addition,' air washers may be.,furnished with heating or cooling coils within the washer chamber. These coils may affect the overall length of the washer. Coolm *eCet*^ ^possibilitytot thi chapterU migraid toTC 9j.Erportire Spray water requirements for-spray-type air washers used for washing or evaporative cooling vary from 4 gpm with a 593