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1、Chapter3: THERMALPROPERTIESOFFOODSNeededforheattransfercalculationsinequipmentdesignandestimationofprocesstimesforrefrigerating,freezing,heating,ordrying,Propertiesrequired:density,specificheat（显热）,enthalpy,thermalconductivity.Freshfruitsandvegetables
2、alsogenerateheatviarespiration（呼吸）andlosemoistureviatranspiration（蒸发）.1.FOODCONSTITUENTSCommonconstituents:water,protein,fat,carbohydrate,fibre,ash.2.THERMALPROPERTIESWellbehavedaboveinitialfreezingpoint.Varygreatlybelowduetocomplexfreezingprocesses.I
3、nitialfreezingpointsomewhatlowerthanpurewaterduotodissolvedsubstances(Fig.1).Atinitialfreezingpoint,aportionofwatercrystallises,remainingsolutionbecomesmoreconcentrated,thusreducingfreezingpointofunfrozenportion.Iceandwaterfractionsinfrozenfooddependo
4、ntemperature.Propertiesvarydramaticallywithtemperature.Propertiesaboveandbelowfreezingpointdrasticallydifferent.3.WATERCONTENTXwoWaterispredominantconstituent,inmostfoods,Xwosignificantlyinflencesproperties.Somevalues(%bymass):Cauliflower(波菜)91.9%;app
5、le83.9;salmon（鲑鱼）76.4;shrimp75.9;beef58.9;porkshoulder72.6;chicken66;wholeegg75.3;cheddarcheese36.8;strawberryicecream60;milk87.8;orangejuice89.4.INITIALFREEZINGPOINTtfNofoodsfreezecompletelysingleTbutoverarange.Foodswithhighsugarcontentorpackedinhigh
6、syrupconcentrationsmayneverbecompletelyfrozen,evenattypicalstorageT.Nodistinctfreezingpointforfoodsandbeverages.Initialfreezingpointindicatesstartofcrystallisation.Importantfordeterminingproperstorageconditionsandcalculationofthermophysicalproperties.
7、Forstorageoffreshfruitsandvegetables,Tmustbeaboveinitialfreezingpointtoavoidfreezingdamage.Asdrasticchangesinpropertieswhenfreez,initialfreezingpointisnecessarytoaccuratelymodelproperties.Somevalues(℃):（与前面一一对应）-0.8;-1.1;-2.2;-2.2;-1.7;-2.2;-2.8;-0.6;
8、-12.9;-5.6;-0.6;-0.4.5.ICEFRACTIONFooditems:water,dissolvedsolids,undissolvedsolids.Duringfreezing,someliquidwatercrystallises,solidsdissolvedinremainingliquidbecomeincreasinglymoreconcentrated,thusloweringfreezingtemperature.Miles(1974)equati
