Document 3NDMj9Rxz3vDeDZj199KBEy1J

594 CHAPTER 33 1965 Guide And Data Book Rg. 1 .... Interaction of Air. and Water in Evaporative Air Coding Apparatus wingfa hftnW to 10 gpm for double baulks-per.'1000 cfm. Pump ing heads will usually be in the range front 55 to 80 ft bf water 1 depehtling bn spray pressure, height bf apparatus, pressure 'lQ&sesin'pipe'and strainers,; etc. j Ul The !resisUaoe to air flow through an air Washer vkHes "with the':type and number bf baffles, eliminators, and wetted 'Surfaces; number of spray banks and their directibh; air "; velocityfsize Ahd type of other resistances slich as cboHhg 7aQd!-hfeatihg coils; and othef factors such as air density. "Re sistance may be as low as J in. or high as 1 in. water column. The'manufacturer'should be consulted as `to theresistance of ' ^ahy'^aJGcular' washer design cbmbinatiob. ;-'n(Sarig.'ah'd tank may be constructed1 of various materials, '`although galvanised steel is' the most common. Casings !are '-'usually ihade bf 18 gage steel reinforced with aiigtes. Sides 'rand top'are' bolted and gasketed for water-tightness.' Ohe or nhbredbbrs are commonly provided for mspection'andlhhebss. ' The5tank is normally hot lesa than 16 in. high with a l4-ih. "water level and may extend beyond the "casing on the inlet end to Vriftlfo the suction"strainer more accessible. The.~tA`nk -^rhay fee partitiohed by the installation bf a weir, nsuhlly in t&eT&terihg end, to permit .recirfculatibh of spftiy water for "'bbhirol purpbsbs'in dehumidificatioh work.The ekeess i%futiis 'bver the 'Weir to'the central water chilling machirfe. 1-i`/ '%A 'Elmunafcrs "consist of a series of vertical platesspheed `Wut'l to 2 ib. on centers in the leaving'end bf to&Wi&hdr. _iThe'plates,' usually 24 gage, are fonned'With a number.hf ' behds'tbdeflect the air and obtain iihpingement on thb wbtted ^Siirfsfces. Hbbks' are' Ordinarily provided On the edgeferthe plat^ibliipto've'ih'biatbre 'eiimiliatkm. Louvere'fhay be in- -'stalled 6ft'theinlet'ehd'of the washer to obtain more uniform iur'distribution through 'the rspiay ch&Triber`add 'to* prevent 1 of the spray. They consist of horizontal or vertical plates with one or more surfaces, spaced about 3 in. apart. These plates are-usually made up of 24 gage steel and are re movable individiiBiiy''tfr h"a` group. ;':!--.;Spiay ^rotates are designed to produce a finely-atomised "Spr&y And Bpsced to'give a uniform coverage through which rtoeair must'pass, -Pressures normally vary from -psig :tb'40psig,'depending onthe duty. Small orifices, at pre&ures -'up to.aboiit' 40 .psig,' produce a fine spray necessary for high : humidifying while the larger orifices, at pressures -around 25'psig> are common'for dehumidification. Nozaksof the self-deaning type have recently become available. Spray .'nozzle capacities vary:from'about T; gpm to 3^i gpnl:per nozzle, .-and spray' densities 'are ordinarily 1 gpm-to about 5 cgpm per, square foot of cross-sectional afea per bank. Spacing rvaries from about 0i75 to 2.5 nozzles per square foot per teak. For lower spray densities smaller orifices should be used'to avoid bypassingair because of a poor spray coverage. Flooding nozzles; for washing toe eliminators, discharge about one gpm iper'nosrfein'a-flatfstreamat 3 to 5 pagpressure. 'Strainers are us&illy tnade of .fine mesh copper oi- brass '^sdreen eitendlng. abrfedS ' tiie width of toe tank. They ire Jsometimes, placed in cylindrical shape over the' pump suction Air -Washers, Evaporative' Air-Copling Equipment and Humidifiers 595 eonnection.-within the tank. Stainers should be readily re* movable for inspection and cleaning. The openings in .the': screen should be.smaller than the spray, orifice to minimjgq flagging of nozzles. Belt type; automatic and other specially dcignftd strainers sue available for. use in textile mil^ and other industries where lint or heavy concentrations of dust are present. Accessories which should generally- be' included! are a.float valve to automatically maintain the minimum water level, a quick^fill connection, a. trapped overflow,, a., tank drain opening; a'suction connection;'ai^ a mrjne light' on toe'spray chamber. ' Cell-Type Washers4 :i "^These washers obtain intimate'air-Water contact'by passing^ tbVair through cells packed with glass, metal, or fiber screens.- See.Flg- 4..The.cells.are arranged in.tiersover,which water; ia disbibuted aiid are followed by conventional type or! glass mat elimihatom.' Most, cell-type',- washera are arranged for concurrent'air and water flow! They are also constructed! for special duty with counter-current flow characteristics or wmbiM^ans\ol both arrangernente. Cell washers ore made in .a raiige !of sizes in' either uninsulated or insulated con- stryction. Standard washers are available up to IQ cells high byl2 cells wide with a capacity of 130,000 cfm, They are also fei^t m uhitafy!apparatus up' to 33,000 cfm complete with fan, motor,.pump, and external spray piping. !... ^ Cell-type washers do not require atomization pf the spray, water, but good water distribution over toe face"of.the cells is essential.",The quantity <?f waiter required for hear saturation of the ah is very low. A saturation effectiveness' of 90 to 97 percent is typicaL Water requirements vary frora'2Ji,to 4 gpm.per 1000 cfm' with resistance to air fiowi ranging from 0.15 to 0.65 in. depending on the water circulated and the" air yeEdcity'through'the cells.' ; ' ' ' - J"- - ` Ehch washer consists of a number of cells, normally 20 & square, arranged to tiers. A .typical cell consists of a'metel frame packed with glass fiber strahds. Hie glass occupies only 3 to 6 percent of the volume of the cell but presente a total wetted area; when sprayed, of approximately.lOO to 125 sq ft. Wire mesh screens are employed at both faces of the cell frame! to retain toe glass pack. Each tier is independent of.the other and has its own spray header, drain sheet, and conduit to the tank below except for the lowest tier. . ' ' -. The tank is provided with either a flat or sloping bottom aa a reservoir for the circulating water and for dirt froqx the cells. The sprays consist of a pipe header with nozzles for, each tier of cells. These are usually manifolded, externally. - with a valve and pressure gage in .the connection .to. ewefe* header. Nozzles deliver approximately.2 gpm at 6 psig. Rifyiil' natora are provided downstream from the cells to remove en trained moisture from the air stream. They may be of a mcti$ blade type, providing 30 deg deflection of the air stream witt} hooks for ..trapping impinged droplets, or glass mat. type arranged in tiers similar to the cell arrangement. Hie glass mat type is 2 in. .deep, random packed with glass fiber to ,a metal frame. Connections are provided for internal, spray headers, drain, overflow, steam injector for clp-Aning toacells in place, pump suction, water quick fill, and make-up .water controlled .by a float valve. When dehumidi/ying, a weir and weir outlet for returning chilled water to the refrigeration system' is usually included. * High-Velocity Spray-Type Washer Recently a high-velocity type of air washer has come into, use which employs a rotating eliminator. The unit operates* on the same general principle as the conventional spray-type washer. However,-the easing is cylindrical and the eliminator consists of a revolving assembly of sheet metal blades extend ing radially from a.central hub. See Fig.-5. The higher air velocity permissible with the rotary design reduces the crosssectional area. of. toe unit, while high saturation efficiencies are maintained by. use of more nozzle hanW and a; deeper spray path. Velocities as high as 2400 fpm have been' applied; Higb-velocity washers, with axial flow fans designed for 1 in. external pressure, are presently built in sizes from 10,000 to 45,000 cfm. They are furnished with from' -1 to 6 spray., banks, making possible a saturation effectiveness ps high as 98 percent. Recommended spray pressure is 30 to $0 psig with a nominal water flow ranging from 80 to 400 gpinj depending on size of wisher. The high-velocity air drives the rotating eliminator which discharges moisture .by centrifugal force so that the water and its entrained material drain from the unit into a central storage tank. Return and outdoor air dampers are built into this unitary design of waslier.1 Opera tion with velocities 3 to 4 times those of conventional air wash-, ers substantially reduces space and weight requirements.,, ': " Humidification with Air Washers .- . ., - j`;r. Air humidification can be accomplished in three ways with an air washer. These are:.(I) use of recirculated spray wate? without prior treatment of the air; (2) preheating .the air and washing it with recirculated spray water; and (3) using Fig. 5 ,,.. High Velocity Spray-Type Washer . f