4.1SystemsforHeatingandCoolingFoodProducts（食品加热和冷却系统）4.1.1PlateHeatExchanger（板式换热器）StructureofPlateHeatexchangersPictureofPlateheatexchangerThemaintenanceissimpleHaveasanitarydesignforfoodapplications.TheircapacitycaneasilybeincreasedbyaddingmoreplatestotheframeHighUstrongturbulentflow，Ucanachieve3000～8000W/m2.K.Smallendtemperaturedifference,about1℃becauseofthecountercurrent.Heatefficiency≥98%,heatisolationmaynotbeneeded.Lowequipmentcostbecauseoflightweight*Lowflowratebecauseofitsstructure*Lowoperationpressureusually<2MPa*Lowtemperaturebecauseofthegasketmaterial.Usuallylowerthan250℃.ApplicationofPlateHeatexchanger—grapejuicepasteurization4.1.2TubularHeatExchanger（管式换热器）套管换热器动画Triple-tubeHeatExchanger列管式换热器动画列管换热器列管换热器清扫Floatingheadtubularheat-exchanger浮头式换热器4.1.3Scraped-SurfaceHeatExchanger（刮板式换热器）ApplicationofScrapedSurfaceHeatExchanger4.1.4SteamInfusionHeatExchanger（蒸汽注入式换热器）CharacteristicsofSteaminfusionHeatExchanger4.1.5Epilogue（结语）4.2ThermalPropertiesofFoods（食品的热力特性）4.2.1SpecificHeat（比热，热容量）SpecificHeatforCompoundsExample4.14.2.2ThermalConductivity（导热系数）ThermalConductivity,k4.2.3Thermaldiffusivity（热扩散系数）ThermalDiffusivity,aExample4.24.3ModesofHeatTransfer（传热方式）4.3ModesofHeatTransfer-Definition4.3.1ConductiveHeatTransfer（热传导）TheMechanismsofHeatConductionindifferentphaseofasubstanceFourier’sLawofHeatConductionExample4.34.3.2ConvectiveHeatTransfer（对流传热）CharacteristicsofconvectionNewton’sLawofCoolingExample4.44.3.3RadiativeHeatTransfer（辐射传热）ActualBody---Stefan-BoltzmannLawTheNetRateofRadiationHeatTransferbetweentwoSurfacesHeatLossfromapersonConsiderapersonstandinginabreezyroomat20℃.Determinethetotalrateofheattransferfromthispersoniftheexposedsurfaceareaandtheaverageoutersurfacetemperatureofthepersonare1.6m2and29℃,respectively,andtheconvectionheattransfercoefficientis6W/m2℃.Assumetheemissivityofapersonise=0.95.Example4.54.4Steady-StateHeatTransfer（稳定传热）4.4.1ConductiveHeatTransferinaRectangularSlab（穿过矩形板的热传导）ConductiveHeattransferthrough3-layeredslabExample4