Lecture 35: Plate and frame press filter, Rotary filter
Principles of Filtration (cake)
(Fig. 35c)
Pressure–drop is applied across the filter:
Assuming that the flow of filtrate is under laminar conditions (low Re and viscous flow), one can apply the Ergun's equation, neglecting the inertial forms:
Consider a differential thickness of cake = at a distance of from the filter-medium.
where, viscosity of the filtrate
bed-porosity or porosity of the cake
surface area and volume of the cake-particles (solids of the slurry), respectively
(Important to note is the time–change of pressure and cake–thickness)
at a distance of 
from the filter-medium. 
viscosity of the filtrate 
bed-porosity or porosity of the cake 
surface area and volume of the cake-particles (solids of the slurry), respectively 
superficial velocity of filtrate 
