气相中的稳态分子扩散 (13).pdf

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1、Separation of Heterogeneous Mixture and solid fluidizationPrinciples of Chemical Engineering-CDUTBasic Equation of Filtration1.The flow characteristics of the filtrate through the cake layer.Characteristic 1:the process of filtration is unsteady.Characteristic 2:holding flowSimplify the actual flow

2、process Principles of Chemical Engineering-CDUTEquivalent Diameter of Particulate Bed The simplified model assumes that the length of the irregular channel in thebed is L,and the equivalent diameter of a group of parallel tubes isandstipulates that:(1)The total flow space of the tube is equal to the

3、 void volume of theparticulate bed；(2)the internal surface area of the tube is equal to the total surface area ofthe particulate bed.Principles of Chemical Engineering-CDUTBased on the 1m3 bed volume,the equivalent diameterof the tube can be expressed as：（3-49）Principles of Chemical Engineering-CDUT

4、The pressure drop of the fluid passing through the fixed bed mainly hastwo aspects:First,the pressure drop caused by the friction between the fluid and theparticulate surface.Second,sudden expansion and shrink of the cross-sectional area of thepore as well as the pressure drop caused by the impact o

5、f the fluid on theparticles.The pressure drop of the fluid passing through the solid particulate bed(fixed bed).Principles of Chemical Engineering-CDUTUsing the simplified model used to calculate the equivalent diameter of the bed,the fluid flow through the bed is regarded as the fluid flowing throu

6、gh a set of parallel thin tubes of equivalent diameter deb,and the pressure drop can be obtainedas：（3-52）Reynolds number of the bed Reb:The friction coefficient of the bed is a function of the Reynolds number of the bedPrinciples of Chemical Engineering-CDUTKozeny EquationErgun Equation（3-55）（3-58）P

7、rinciples of Chemical Engineering-CDUT2.Filtration Speed and Rate Filtraion SpeedFiltraion RateThe volume of filtrate that passes through the unit filtration area per unit time,and the unit is m/s.The filtrate volume obtained per unit time,the unit is m3/s.(3-59a)(3-59b)7.3.1 Material Balance and Op

8、eration Line Equation of the Absorbent TowerPrinciples of Chemical Engineering-CDUT3.Filtration ResistanceSpecific Resistance of the Filter CakeIt reflects the influence of the shape and size of the particles and thevoidage of the bed on the filtrate flow,and is the resistance of the bed perunit thi

9、ckness,which is measured in 1/m2.(3-60)Principles of Chemical Engineering-CDUTResistance of the Filter Cake the unit is 1/m.thus，(3-62)(3-61)Principles of Chemical Engineering-CDUT(3-62)The velocity equation of the filtrate passing through the layer of filter media can be written by imitating the eq

10、uation 3-61:Resistance of the filter medium 1/m.Resistance of the Filter Medium Principles of Chemical Engineering-CDUT4.Basic Filtration EquationAssuming that the resistance of the filter medium to the filtrate flow isequivalent to that of the cake layer with a thickness of Le,that is:Consider the

11、resistance and filter cake togetherEquivalent filter cake thickness,Virtual filter cake thicknessPrinciples of Chemical Engineering-CDUTThe equation goes:For a certain moment,the relation between the cake thickness and the filtrate volume obtained at that time is:The ratio of the cake volume to the

12、corresponding filtrate volume,m3/m3Principles of Chemical Engineering-CDUTAlso,we could figure out:The equivalent filtrate volume of the filter medium,Virtual filtrate volumeThus,（3-69）Principles of Chemical Engineering-CDUTIf:Then:The equivalent filtrate volume of the filter medium,Virtual filtrate

13、 volumeEquivalent filtrate volume per unit filtration areaPrinciples of Chemical Engineering-CDUTFor the compressible filter cake,the specific resistance r is no longer aconstant in the filtration process,but a function of the pressure differencebetween the two sides:（3-70）The compressibility index

14、of the filter cake，the dimension is 1In general,s=01.For incompressible filtercake,s=0.Principles of Chemical Engineering-CDUTMaterialDiatomiteCalcium CarbonateCalcium Carbonate(Flocculate)Kaolin TalcClayZnSO4Aluminum Hydroxides0.010.190.270.330.510.560.60.690.9The index values of compressibility of

15、 several typical materials are given in the following forms:Principles of Chemical Engineering-CDUTorFinally we could reach to:Basic Eqiation of Filtration（3-71）（3-71a）Principles of Chemical Engineering-CDUTThen for a certain suspension,K can be regarded as a constant.If：Basic Eqiation of Filtration（3-73）（3-73a）（3-72）