Surface filtration can be performed with perforated plate, sieve plate, wire mesh, filter cloth, felt or filter paper. The primary function of the filter plate is therefore not full filtering, but enabling the formation of a filter cake by providing a suitable sustaining surface for the depositing mass of particles and withstanding the strain of vacuum or pressure. In case of (e.g. activated carbon filtration) the particles finer than the pore size of the filter filtration medium enter the pores and channels of the grainy or fibrous filter medium and deposit there. Particles accumulate in the cavities of pores and capillaries due to direction breaksand changes in channel cross section, depositing due to inertial and surface forces. The cake forming on the surface is insignificant. Extremely fine particles are adsorptively bound by surface and capillary forces. In the course of filtration the permeable cross section and porosity of pores decreases and the resistance of the filter medium increases. Fig. filtration The above mechanisms are often intermingled in real-life filtration processes, with the filter initially retaining only larger particles, acting as a surface filter, producing a cloudy filtrate. Later, with the formation and buildup of the filter cake the depth filtering mechanism prevails and subsequently the filtrate gradually clears up. The is described by the (the amount of filtrate flowing through in a unit of filter’s performance filtration rate time, V/t). in correlation with unit filter surface (A) is: Filtration rate (1.) The law is applicable in case of laminar, frictional and temporally constant flow. According Hagen Poiseuille – to this, filtration can be considered a flow flowing through parallel capillaries and average rate is one half of maximum rate: (2.) radius of capillary, r viscosity of liquid, h length of capillary. h studied the flow of liquids through granular media at constant pressure and established that filtration rate Darcy is : (3.) volume of filtrate, V duration of filtration, t permeability constant of the filter bed, B filter surface, A
Surface filtration can be performed with perforated plate, sieve plate, wire mesh, filter cloth, felt or filter paper. The primary function of the filter plate is therefore not full filtering, but enabling the formation of a filter cake by providing a suitable sustaining surface for the depositing mass of particles and withstanding the strain of vacuum or pressure. In case of filtration (e.g. activated carbon filtration) the particles finer than the pore size of the filter medium enter the pores and channels of the grainy or fibrous filter medium and deposit there. Particles accumulate in the cavities of pores and capillaries due to direction breaksand changes in channel cross section, depositing due to inertial and surface forces. The cake forming on the surface is insignificant. Extremely fine particles are adsorptively bound by surface and capillary forces. In the course of filtration the permeable cross section and porosity of pores decreases and the resistance of the filter medium increases. Fig. filtration The above mechanisms are often intermingled in real-life filtration processes, with the filter initially retaining only larger particles, acting as a surface filter, producing a cloudy filtrate. Later, with the formation and buildup of the filter cake the depth filtering mechanism prevails and subsequently the filtrate gradually clears up. The filter’s performance is described by the filtration rate (the amount of filtrate flowing through in a unit of time, V/t). Filtration rate in correlation with unit filter surface (A) is: (1.) The Hagen – Poiseuille law is applicable in case of laminar, frictional and temporally constant flow. According to this, filtration can be considered a flow flowing through parallel capillaries and average rate is one half of maximum rate: (2.) r radius of capillary, h viscosity of liquid, h length of capillary. Darcy studied the flow of liquids through granular media at constant pressure and established that filtration rate is : (3.) V volume of filtrate, t duration of filtration, B permeability constant of the filter bed, A filter surface,
2011-0016_01_the_theory_and_practise_of_pharmaceutical_technology.docx