The previous part of this Section covered processes that dealt with filtration in a minor way, but which were not primarily intended for the separation of particles from fluids. The majority of the Section is now concerned with those materials intended for filtration and will describe them in sufficient detail to explain how they are […]
First to be considered in this review of filter media are three types of material whose prime function is not the separation of solid particles from fluids, but in whose use such separation does occur. They operate by different physical processes from filtration (and from each other), and are used for different purposes. Absorbent media […]
The industrial context within which filter media are made and supplied to their endusers is of more than passing interest. The great variety in which media are made leads to a corresponding variety in the types of company involved with the supply of media. Some are devoted to its manufacture, while for others it may […]
A filter medium is any material that, under the operating conditions of the fi lter, is permeable to one or more components of a mixture, solution or suspension, and is impermeable to the remaining components. The retained components, the ones to which the medium is impermeable, may be particles of solid, droplets of liquid, colloidal […]
All gas phase filter tests are of the single-pass format using a particle challenge, but the methods differ widely, as do the particle formulations used in the challenge and the means of analysis to demonstrate performance. The materials used include natural sand/quartz mixtures, alumina dusts, methylene blue aerosols and di-octyl phthalate. A sand-quartz mix is […]
The test circuit used for fatigue tests subjects the filter to start-stop cycles (for evaluating fatigue behaviour under otherwise steady flow conditions), or to cycles of pressure fluctuation (for evaluation of fatigue under pulsating flow conditions). A bubble point test applied to the filter element before the fatigue test, and again after it, will demonstrate […]
A range of methods exists for testing various aspects of a filter ’ s performance. These will be briefly discussed here, although a more complete review of test methods and standards is given in Handbook of Filter Media (Derek B. Purchas and Ken Sutherland, 2002, 2nd Edition, Elsevier Advanced Technology, Oxford). Bead challenge test The […]
A steady flow of fluid through a filter will cause correspondingly steady accumulation of solids and rise in pressure drop. The effect of pulsating flow is to loosen the finer particles held in the filter cake, and so to allow them to pass through the filter and on into the filtrate. This effect is illustrated […]
The permeability is the reciprocal of the resistance to flow offered by the filter – thus, high permeability represents a low resistance and vice versa. Permeability is usually expressed in terms of a permeability coefficient, which is directly proportional to the product of flow rate, fluid viscosity and filter medium thickness, and inversely proportional to […]
One especially important case of purification concerns the removal of microbial contaminants so as to produce a sterile fluid. The use of membranes of 0.2 um rating is generally regarded in critical industries as a satisfactory means of achieving sterility, demonstrated by a bacterial challenge test (NB this is referring to sterility from bacteria, not from […]
