Question 5: [5 Marks] Cake (or surface) filtration involves the build-up of a be

Question

Question 5: [5 Marks] Cake (or surface) filtration involves the build-up of a bed or 'cake' of particles on the filter medium. In cake filtration, the pore size of the medium is less than the size of the particles to be filtered. This filtration process can be analysed in terms of the flow of fluid through a packed bed of particles, the depth of which is increasing with time. Which is the primary filtration medium, the cake buill-up on the filter or the filter itself? 11) a) b) How do you maintain a constant flow filtration with time through an incompressible cake? [2 c) How does the volumetric flow rate of filtrate change with time if you maintained constant pressure drop filtration through an incompressible cake?

Explanation / Answer

1) Filter Itself is primary filteration medium as it retain the particle of desire size to be remove from the solid from solid-liquid solution.

2) based on Poiseulle's law , filteration rate dv/ A dt= P/ / u alfa ( w/ A)

where alfa -- average specific cake resistance. For incompressible cake, alfa is constant.

P- Pressure across the medium

W- weight of cake

Hence, filteration rate for incompressible cake depend on pressure across the medium and weight of the cake-w (i.e cake thickness). So for constant filteration rate , pressure across the filter need to be varied or maintain the weight of cake -w ( i.e. cake thickness) constant.

3) based on equation mentioned in ans-2, filteration rate ( i.e volumetric flow rate) will decrease with time if pressure drop is constant. Approximately it will be shown as below

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