difference in Evaporation and vaporisation

Basic-Principles-Application-of-evaporators-and-Differences-between-Vaporisation-and-Evaporation

1. Dr. J. Badshah, HOD, D. E. Dept.
S.G. Institute of Dairy Technology
(Bihar Animal SciencesUniversity, Patna)
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2. Basic Principles of Evaporators
EvaporationandVapourisationprocessessimaltaneouslytakes
placeonapplicationofheatforremovalofwaterfromsurfaceof
liquidinclosedsystemwhichisfollowedbyremovalofwater
vapourfromtheclosedspacetocontroltheboilingpointwith
respecttopressureinthespacepreferablyvacuumforheat
sensitivefeedproductlikemilk.Therateofescapeofthesurface
moleculesdependsprimarilyuponthetemperatureoftheliquid,
thetemperatureofthesurroundings,thepressureabovetheliquid,
surfaceareaandrateofheatpropagationtoproduct.
Theboilingpointofsolutionduetodissolvedsolutesishigher
thanthatofpurewateranddependsonthemolecularweightof
the solute.
Inthedairyindustryevaporationmeanstheconcentrationof
liquidmilkproductscontainingdissolved,emulsifiedor
suspendedconstituentsundervacuumtomanufactureevaporated
milk,condensedmilk,wheyproteinconcentratesetc.
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2

3. Principles of evaporators…contd.
Importantpropertiescontrollingtheprinciplesofoperationare:
Boilingoffeed/milk:Concentrationofsolute,Pressureaboveor
surroundingtheliquidsurfaceandHydrostaticpressureabovethepoint
ofboilingorbulkvapourisationprocessarethefactorsaffectingboiling
process.Whentemperatureoftheliquidisequaltoorgreaterthan
vapourpressureabovetheliquid,thephasechange/boilingatconstant
temperaturetakesplace.Thetemperatureistermedassaturation
temperatureandthethecorrespondingpressureissaturationpressure.
Lowerpressureorvacuumabove/surroundingtheliquid:Designof
entrainmentseparators,designofcondensersforcondensing
condensablevapoursandproperremovalofnoncondensablegases
usingncgline,vacuumpump/steamjetejectorscontrolsthevacuum.
Higherthevacuummeanslowertheevaporationtemperatureand
highertherateofevaporation.
Concentrationofsolute/molecularweightofsolute:Lowerthe
molecularweightandhighertheconcentrationincreasestheboiling
pointofmilkanditdecreasesthetemperaturegradient.
Class ppt 3

4. Application of Evaporators
Thisprocessisusedinthedairyindustryformanufacture
ofevaporatedmilk,condensedmilkandtraditional
IndianDairyproducts.Moderndairyplantsuse
evaporatorstoremovepartofwaterfrommilkbyboiling
itunderlowpressureusingsaturatedsteaminthe
jackets.Theprocessofevaporationtakesplaceata
maximumtemperatureofabout70
0
Ccorrespondingto
anabsolutepressureof230mm(9.0inch)ofmercury
(Hg).Asthemilkboils,watervapourisformed.This
vapourisutilizedforheatingthemilkfurtherinthenext
stagewhichisatahighervacuum.
Theapplicationofevaporatorswiththermocompressorandmultiple
effectevaporationalongwithmultistagesteamjetejectorsarevery
commoninFood,Beverageanddairyindustriesapartfromchemical
industries.MVRorTVRareusedasperconvenience.
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5. SGIDT, BASU, Patna 5