第八章第八章干燥干燥

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1、第八章第八章干燥干燥Chapter8Chapter8第一节第一节基本概念基本概念BasicConceptsBasicConcepts88——1Importanceand1ImportanceandPurposeofdryingPurposeofdrying（重要性和目的）•SignificanceofDryingProcessasanUnitOperation–Itiswidelyusedineverywalkoflife.E.g.Foodstuff,woodprocessing,plasticsindustry,papermakingetc.•I

2、tisoneoftheoldestmethodsofpreservingfood.–Primitivesocietiespracticedthedryingofmeatandfishinthesunlongbeforerecordedhistory.–Todaythedryingoffoodsisstillimportantasamethodofpreservation.Driedfoodscanbestoredforlongperiodswithoutdeteriorationoccurring.•Theprincipalreasonsforth

3、isarethat∑Themicroorganismswhichcausefoodspoilageanddecayareunabletogrowandmultiplyintheabsenceofsufficientwater.∑Manyoftheenzymeswhichpromoteundesiredchangesinthechemicalcompositionofthefoodcannotfunctionwithoutwater.(Withoutmoistureorwater,theenzymeactivityisinactivated)TheP

4、urposeofDryingThePurposeofDrying••EasyforpreservationorstoreEasyforpreservationorstore–Dryingmakesfoodorrawfoodmaterialshavelongshelflife.(intermsofmicroorganismandenzymeaction).–Needsmallspaceofstorehouse••ConvenientfortransportationConvenientfortransportation–Weightandvolume

5、aregreatlyreduced,improvessignificantlytheefficiencyoftransportationIntermsofloadingandunloading••ConvenientforconsumeruseConvenientforconsumeruse–E.g.milkpowder,driedvegetablesetc.88——2Classification,Definitionand2Classification,DefinitionandContainedProcessesforDryingContain

6、edProcessesforDrying8.2.1DehydrationandDrying8.2.1DehydrationandDryingDehydrationByMechanicalMethodDehydrationByPhysical-ChemicalMethodDehydrationByHeatingMethod（RemovingSolventfromsolidsbyheatingiscalleddrying—Thedefinitionofdrying）DehydrationbyDehydrationbyMechanicalMethodMe

7、chanicalMethod••Themoistureisremovedbyfiltration,Themoistureisremovedbyfiltration,Express,Suction,andCentrifugation.Express,Suction,andCentrifugation.ThesemethodsareusedonlyintheThesemethodsareusedonlyinthecasethatthemoisturedosenotneedcasethatthemoisturedosenotneedtobetotally

8、removed.tobetotallyremoved.••即通过过滤、压榨、抽吸即通过过滤、压榨、抽吸和和离心分离等方法除