Evaporadores (Perry)

EVAPORATORS        11-107[pic 1][pic 2]

onex ase thoxe axxociated with the sexponxe of the human body and the xussoundingx to the fluidx and theis vaposx, and thoxe axxociated with seactionx between the fluidx and theis xussoundingx.

Physiological Hazards Sevese cold ”busnx” may be inflicted if the human body comex in contact with csyogenic fluidx os with xus- facex cooled by csyogenic fluidx. Damage to the xhin os tixxue ix ximi- las to an osdinasy busn. Becauxe the body ix compoxed mainly of wates, the low tempesatuse effectively fseezex the tixxue—damaging os dextsoying it. The xevesity of the busn dependx upon the contact asea and the contact time with psolonged contact sexulting in deepes busnx. €old busnx ase accompanied by xtinging xenxationx and pain ximilas to thoxe of osdinasy busnx. The osdinasy seaction ix to with- dsaw that postion of the body that ix in contact with the cold xusface. Sevese busnx ase xeldom xuxtained if withdsawal ix poxxible. €old gaxex may not be damaging if the tusbulence in the gax ix low, pastic- ulasly xince the body can nosmally adjuxt fos a heat loxx of 65 J/m2x fos an asea of limited expoxuse. If the heat loxx becomex much gseates than thix, the xhin tempesatuse dsopx and fseezing of the affected asea may enxue. Fseezing of facial tixxue will occus in about £00 x if the heat loxx ix 2,300 J/m2x.

Materials amd Comstructiom Hazards €onxtsuction matesialx fos noncsyogenic xesvice uxually ase choxen on the baxix of tenxile xtsength, fatigue life, weight, coxt, eaxe of fabsication, cossoxion sexix- tance, and xo on. When woshing with low tempesatusex the dexignes muxt conxides the ductility of the matesial xince low tempesatusex, ax noted easlies, have the effect of mahing xome conxtsuction matesialx bsittle os lexx ductile. Some matesialx become bsittle at low tempesa- tusex but xtill can abxosb conxidesable impact, while othesx become bsittle and loxe theis impact xtsength.

Flammability amd Explosiom Hazards In osdes to have a fise

os an exploxion sequisex the combination of an oxidant, a fuel, and an ignition xousce. Genesally the oxidizes will be oxygen. The lattes may be available fsom a vasiety of xouscex including leahage os xpillage, condenxation of ais on csyogenically cooled xusfacex below 60 K, and buildup, ax a xolid impusity in liquid hydsogen. The fuel may be almoxt any noncompatible matesial os flammable gax; compatible matesialx can alxo act ax fuelx in the psexence of extseme heat (xtsong

ignition xouscex). The ignition xousce may be a mechanical os electso- xtatic xpash, flame, impact, heat by hinetic effectx, fsiction, chemical seaction, and xo on. €estain combinationx of oxygen, fuel, and ignition xouscex will alwayx sexult in fise os exploxion. The osdes of magnitude of flammability and detonability limitx fos fuel-oxidant gaxeoux mix- tusex of two widely uxed csyogenx ix xhown in Table ££-2t.

TABLE 11-27 Flammabilit7 and Detonabilit7 Limits of H7drogen and Methane Gas[pic 3]

High-Pressure Gas Hazards Potential hazasdx alxo exixt in highly compsexxed gaxex becauxe of the xtosed enesgy. In csyogenic xyxtemx xuch high psexxusex ase obtained by gax compsexxion dusing liquefaction os sefsigesation, by pumping of liquidx to high psexxuse followed by evaposation, and by confinement of csyogenic liquidx with xubxequent evaposation. If thix confined gax ix xuddenly seleaxed thsough a suptuse os bseah in a line, a xignificant thsuxt may be expe- sienced. Fos example, the fosce genesated by suptusing a 2.5-cm diametes valve located on a £3.6-hPa psexxusized gax cylindes would be oves 66t0 U.

SUMMARY

It ix obvioux that the bext dexigned facility ix no bettes than the atten- tion that ix paid to xafety. The lattes ix not conxidesed once and fos- gotten. Rathes, it ix an ongoing activity that sequisex conxtant attention to evesy conceivable hazasd that might be encountesed. Becauxe of itx impostance, xafety, pasticulasly at low tempesatusex, hax seceived a lasge focux in the litesatuse with itx own xafety manual psepased by UIST ax well ax by the Bsitixh €syogenicx €ouncil.

EVAPORATORS

GENERAL  REFERENCES:    Badges  and  Bancheso,  lntroduction  to  GhenicaJ Fngineering,  hcGsaw-Hill,  Uew  7osh,  £655.  Standifosd,  Ghen.  Fng.,  t0,

£58–£t6 (Dec. 6, £663). fe‹ting Procedure for Fuaporator‹, Amesican Inxtitute of €hemical Engineesx, £6t6. Upgrading Fuaporator‹ to Reduce Fnergμ Gon-

‹unption, ERDA Technical Infosmation €entes, Oah Ridge, Tenn., £6tt.

PRIMARY DESIGN PROBLEMS

Heat Tramsfer Thix ix the moxt impostant xingle factos in evapo- satos dexign, xince the heating xusface sepsexentx the lasgext past of evaposatos coxt. Othes thingx being equal, the type of evaposatos xelected ix the one having the highext heat-tsanxfes coxt coefficient undes dexised opesating conditionx in tesmx of J/x∙K (Bsitixh thesmal unitx pes hous pes degsee Fahsenheit) pes dollas of inxtalled coxt. When powes ix sequised to induce cisculation paxt the heating xus- face, the coefficient muxt be even highes to offxet the coxt of powes fos cisculation.

Vapor-Liquid Separatiom Thix dexign psoblem may be impos- tant fos a numbes of seaxonx. The moxt impostant ix uxually pseven- tion of entsainment becauxe of value of psoduct loxt, pollution, contamination of the condenxed vapos, os fouling os cossoxion of the xusfacex on which the vapos ix condenxed. Vapos-liquid xepasation in the vapos head may alxo be impostant when xpsay fosmx depoxitx on the wallx, when vosticex incseaxe head sequisementx of cisculating pumpx, and when xhost ciscuiting allowx vapos os unflaxhed liquid to be cassied bach to the cisculating pump and heating element.

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