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1、Separation of Heterogeneous Mixture and solid fluidizationPrinciples of Chemical Engineering-CDUTFiltrationPrinciples of Chemical Engineering-CDUTCharacteristics of granular bedThe bed voidage()is calculated using thefollowing equation:率以表示，即1.Bed voidageWhere Vbis the volume of bed and Vpis the vol
2、ume ofparticles.率以表示，即Principles of Chemical Engineering-CDUT2.Free cross-sectional area of bedThere is no area occupied by particles and the fluidcan pass freely on the free cross-sectional area of bed.The specific surface area of bed is calculated using the following equation:Characteristics of gr
3、anular bed3.Specific surface area of bedWhereis the surface area of particles andis thevolume of bed.Principles of Chemical Engineering-CDUTThe specific surface area of the bed can also beestimated by the bulk density of particles,that is：Bulk density of particlesTrue density of particlesIf the cont
4、act area of overlapping particles in the bed is ignored,that is：Characteristics of Granular BedPrinciples of Chemical Engineering-CDUTPrinciples of FiltrationFiltration:to make use of gravity or man-made pressuredifference to make the suspension pass through the porousfilter medium,and the filtrate
5、flows out through the mediumwhen the solid particles in the suspension are intercepted.Principles of Chemical Engineering-CDUTFiltration MethodsCake Layer Filtration:It is the filter cake,not the filter medium,that reallyseparates the filter.is suitable for suspensions whose volume of solid phaseacc
6、ounts for more than 1%。Deep Filtration:The particles attach to the wall of the channel by the action ofstatic electricity or surface force,which is suitable for suspensions with solidvolume less than 0.1%.Principles of Chemical Engineering-CDUTFabric medium:natural fiber fabric,synthetic fiber fabri
7、c,glass fiber,metal,silk fabric and so on.Accumulation Media:sand,charcoal,asbestos,diatomiteand so on.Porous MediumPrinciples of Chemical Engineering-CDUTPorous Solid Media:porous ceramics,porous plastics,metalsintered plates and so on.Porous Filtration Membranes:microfiltration(MF),ultrafiltration
8、(UF),nanofiltration(NF)and reverse osmosis(RO)and so on.Principles of Chemical Engineering-CDUTThe particulate bed formed by the accumulation of intercepted solidparticles.Incompressible Filter Cake:the particles that constitute the filter cakeare not easy to deform and the gap of the filter cake do
9、es not change withthe increasing pressure difference.Compressible Filter Cake:the particles forming the filter cake are easilydeformed,the gap decreases with the increase of the operating pressuredifference,and the resistance of liquid flow increases.Poor filtrationperformance。CakePrinciples of Chem
10、ical Engineering-CDUTAnother kind of solid particles which are hard and not easy to deform are often added to thesurface of the filter medium(or filter slurry)to form a loose filter cake.This solid particle is calledfilter aid.The basic requirements for the selection of filter aids are as follows:(1
11、)goodpermeability and low flow resistance;(2)no chemical reaction with the filter slurry and insolublein the liquid phase;(3)incompressibility within the range of operating pressure difference.Asshown in the diagram,diatomite and toner are commonly-used filter aids.Filter AidPrinciples of Chemical Engineering-CDUT1.What are the ways of filtration?2.What really plays the role of filtration in the cake layer?