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Filtration Terminology
Absorb
To intercept and retain, or drink in. To suck in, as a sponge sucks in water.
Activated Alumina
A highly porous and
granular form of aluminium oxide having preferential adsorptive capacity for moisture
from gases, vapours and some liquids. May be regenerated for extended use
under specified conditions.
Activated Carbon
Any form of carbon
characterised by high adsorptive capacity for gases, vapours or colloidal
solids. The carbon or charcoal is produced by destructive distillation of
wood, peat, lignite, nut, shells, bones, vegetable or other carbonaceous
matter, but must be activated by high temperature steam or carbon dioxide
which creates a porous particle structure.
Adsorption
The natural phenomenon of a gas, vapour or liquid being attracted to and held
on the surface of a solid. To some extent adsorption takes place on any solid
surface but certain materials have sufficient adsorbent capacity because of
the finely divided material to make them useful in such industrial
applications as the purification and separation of gases and liquids.
Aerosol
Ambient Surrounding.
For example, the ambient operating temperature of a vessel is the temperature
essentially the same as that surrounding the vessel.
ASME
American Society of
Mechanical Engineers. Publish code which governs the design of pressure
vessels.
Atmospheric Pressure
The presssure of approximately 14.7 pounds per square inch exerted at sea
level in all directions by the atmosphere.
Attrition
Wear caused by
rubbing or friction. Produces fine particles that usually contaminate liquid
that surrounds the point of attrition. Sometimes referred to as scouring or
scoring.
Autoclave
A pressure vessel into which steam is introduced and held at a predetermined
pressure and temperature for a period of time sufficient to ensure absolute
sterility of implements and dressings associated with aseptic techniques
practiced in all surgical operations and nursing care. Modern autoclaves are
fully automatic and go through five separate stages during the sterilisation
and drying of implements and/or dressings.
Blinding
Where filtered-out particles fill the openings in the filter medium to the
extent of shutting off the flow of product; loading up of the medium so as to
reduce capacity. Also referred to as blocking or plugging.
Boyle's Law
If the temperature of
a given kind of gas is held constant, the volume of a sample gas varies
inversely with the pressure. See also Charles Law.
Charles' Law
If the pressure of a given kind of gas is held constant, its density is
inversely proportional to its absolute temperature. See also Boyle's Law.
Coalescer
A mechanical device
which unites discreet droplets of one phase of one phase prior to being
separated from a second phase. Can be accomplished only when both phases are
immiscible. Requires a tight media which is preferentially wettable and, by
its nature of being tight, the filter is also a good filtering material. Good
coalescing may only be accomplished by a coalescer cartridge when the
specific gravities of the two phases are widely separate. As the gravities'
difference becomes less, the two stage principle is generally required where
finely coalesced discontinuous droplets are repelled by the second stage
separator cartridges.
Condensation
The process of cooling a vapour below its boiling point in order to liquify
it.
Contaminate
The foreign matter in a fluid which has accumulated from various sources such
as dirt, residue from wear of moving parts, atmospheric solids which can
settle in a open system. Contaminates tend to discolour a liquid, cause
additional wear on moving parts, cause system upsets in process streams or
reduce the efficiency of a fluid. Water as well as a solid may be considered
a contaminate when the presence of water causes adverse results. The presence
of contaminates, whether liquid or solid, is the basis on which the use of
filters or separator/filters is sought.
Corrosion
The conversion of metals into oxides, hydrated oxides, carbonates or other
compounds due to the action of air or water, or both. Salts and sulphur are
also important sources of corrosion. Removal of the solids and water reduces
the effect or speed of corrosion in many cases.
 P
Symbol designating pressure drop. The difference of pressure between two
points, generally measured at the inlet and outlet of a filter,
separator/filter etc. Normally measured in pounds per square inch (psi),
inches of mercury (In.Hg.) or bar.
Density
Compactness or thickness; ratio of weight of a medium to the weight of an
equal volume of fibre. In general, mass per unit volume usually expressed in
grams per cubic centimetre or pounds per cubic foot.
Depth Type Filtration
Filtration accomplished by flowing a fluid through a mass filter medium
providing a tortuous path with many entrapments to stop the contaminates.
Desiccant
A drying agent or
medium used in dehydration of air, gas and liquids. Examples silica gel,
activated alumina, molecular sieve.
Dewpoint
Temperature at which
air is saturated with moisture, or in general the temperature at which a gas
is saturated with respect to a considerable component.
Diffusion or Brownian
Motion
A natural phenomenon.
The random movement of very small particles (below 0.1 micron) caused by
bombardment of those particles by gas molecules. As a result of this random
or spiral movement, the particles describe paths much greater than their
actual size and are, therefore easier to trap.
Direct Interception
The collection of
relatively large particles (1.0 micron and over) on or near the surface of
the filter medium. The particles collide with the fibres or structure of the
filter medium, without deviating from streamline flow.
Dirt Holding Capacity
The volume of contaminate an element can hold before reaching the maximum
allowable pressure drop.
D.O.P. Test
A cloud of mono-dispersed dioctylphtalate liquid droplets of 0.3 micron diameter
is passed towards the filter under test. Efficiency is calculated by taking
readings of upstream and downstream contamination levels with a particle
counter.
Downstream
Portion of the product stream which has already passed through the system or
the portion of a system located after a filter, separator/filter etc.
Entrainment
Mist, fog or droplets transported by a fluid.
Filter
A term generally
applied to a device used to remove solid contaminate from a liquid or as, or
separate one liquid from another liquid or gas. A filter, as referred to in
the industry, is limited to a device which removes solid contaminates only.
If a device is used to remove solid and liquid contaminates, it is referred
to in general terms as a separator, separator/filter or entrainment
separator. A filter may be one of a number of such types as replaceable
cartridge, cyclone edge, leaf, baffle, plate and frame, precoat, centrifuge.
The term filter is sometimes erroneously used to describe the media used
inside the vessel or filter case, but the correct use should be filter
element, cartridge etc.
Flash Point
The lowest temperature at which a combustible liquid will give of a flammable
vapour which will burn momentarily.
Fluid
Term used in filtration and separation to include liquids, air or gas as a
general term.
Glass Fibre
The proper reference to fibrous material made from glass that is commonly
used as a filter and separator medium. Glass fibres may be used in blanket or
tube form and, due to the random dispersal of the fibres, the material makes
a good filter medium. Glass fibres are hydropholic (water wettable) and, as
such, perform the function of coalescing immiscible liquids for separation.
May be used effectively on compressed air, gas or liquids which are acidic or
only slightly caustic.
Heat of Adsorption
The heat when a
substance is adsorbed. It is the heat equivalent to the energy which the
adsorbate must give up in going from its normal energy state to the lower
energy state it has when adsorbed. The heat depends on the adsorbate and
adsorbent.
Hydrocarbon
Any one of a large number of compounds composed primarily of the elements
carbon and hydrogen. As they increase in molecular weight and boiling point
they may be respectively gases, liquids or solids.
Hydrostatic Test
A test conducted with
either air, water or other fluids at a given value over design pressure, to
prove the structural integrity of a pressure vessel.
Inert
Inactive-chemically
inactive.
Inertial Impaction
The capture of
particles (over 0.5 micron), within filter medium, as they fail to stay
within the flow path of the fluid being filtered.
Intersices
The spaces or openings in a medium. Also referred to as pores or voids.
Usually refers to those voids contained in adsorptive medium such as carbon,
fullers' earth etc. The available area for adsorbtion on or within a particle
then must take into account not only the surface area but also that area
within the particle due to the interstices, or voids.
Life Expectancy
The amount of use
which may be expected from an element before it must be replaced; will vary
according to the elements characteristics, the operating conditions, and the
degree of contamination of the fluid being filtered.
Micron
A short unit of
length in the metric system. One millionth of a metre, 10-4
centimetre, 10-3 millimetre or 0.000039 of one inch.
Mist
Visible water or
hydrocarbon vapour, floating or falling in fine drops.
Molecular Sieve
Zeolite, natural or synthetic, or similar materials whose atoms are arranged in
a crystal lattice in such a way that there are a large number of small
cavities interconnected by smaller openings or pores of precisely uniform
size. Used as drying agents for some liquids or gases as well as for some
adsorbtive applications. May be regenerated for extended use under special
conditions.
Molecular Weight
The sum of atomic
weights of all atoms in a molecule. Sometimes referred to as the mole weight
or mol weight.
Nm3/hr
Normal cubic metres per hour.
Pleated
Describes a physical
form of a cartridge made into a convoluted form to resemble the folds in an
accordian.
Plugging
Where filtered out
particles fill the openings in the medium to the extent off shutting off the
flow of product; the loading up of the medium so as to reduce capacity. Also
referred to as blinding or blocking.
Pores
The openings in a medium. Also referred to as intertices.
Porosity
The ratio of voids volume to total volume.
Prefilter
Filter for removing gross contamination before the liquid enters the main
separator/filter.
Pressure, Absolute
Gauge pressure plus 14.7 psi (1 bar)
Pressure, Atmospheric
The force exerted by the atmosphere at sea level which is equivalent to 14.7
psi (1 bar).
PSI
Pounds per square inch.
PSIA
Pounds per square
inch absolute.
PSID
Pounds per square inch differential.
PSIG
Pounds per square
inch gauge.
Regenerated
Cleaned of impurities and made reusable.
Relative Humidity
The percentage relation that the actual amount of water vapour present in a given
volume of air at a definite temperature bears to the maximum amount of water
vapour that would be present if the air were saturated with water vapour at
that temperature.
SCFM
Standard cubic feet per minute.
Separation
Vessel which removes solids and entrained liquid from another liquid or gas.
Uses a baffle and/or coalescer, or separator element. May be single stage,
two stage or single or two stage with prefilter section for gross solids
removal. Common application is the removal of water from gas. General
reference to term implies the equipment is capable of both separation and
filtration to specific degrees of efficiencies.
Sintered Medium
Filter medium manufactured by the fusion of powdered, granular materials.
Sintering produces greater strength and density.
Solids
A mass or matter, contained in a fluid stream which is considered undesirable
and should be removed; that part of the discontinuous phase which is removed
from liquid or gas by filtration.
Sodium Flame Test
Developed by the Chemical Defence Establishment at Porton Down and adapted as
a British standard for high efficiency filters-BS 3928 or BS4400. A dry salt
particle cloud, 0.02 micron to 2.0 micron, is introduced into the air stream
passing toward the filter under test. A sample of the filtered air is passed
through a hydrogen flame which changes colour should salt particles be
present. The change in colour of the flame is detected by a sensitive
photo-multiplier which transmits a signal to micro-ammeter. Prior calibration
of the micro-ammeter with known concentrations of sodium chloride in the
hydrogen flame, enables very rapid tests to be carried out on high efficiency
filters.
Specific Gravity
The ratio of weight of any volume of a substance to the weight of an equal
volume of another substance. (Water for solids and liquids, and air or
hydrogen for gases).
Spectrophotometer
A laboratory instrument which measures the wave length and intensity of a
light emitted by most chemical elements.
Stoke's Law
A physical law which approximates the velocity of a particle falling under
the action of gravity through a fluid. The particle will accelerate until the
frictional drag of the fluid just balances the gravitational acceleration,
after which it will continue to fall at a constant velocity known as the
terminal or free-settling velocity.
Sterile
No viable or living organisms present.
Temperature, Absolute
Temperature measures from absolute zero which is minus 273°C, or minus 460°F.
Toxic
Harmful, poisonous, injurious to life.
Ultrafiltration
A semi permeable membrane capable of the separation of colloidal solids from
liquids. Used in the process of reverse osmosis.
Vapour
A substance in the gaseous form which under normal conditions of pressure and
temperature would be liquid or solid.
Viscosity
A liquid has a viscosity of one poise if a force one dyne per square
centimetre causes two parallel liquid surfaces one square centimetre in area
and one centimetre apart to move past one another at a rate of one centimetre
per second. There are a great many crude and empirical methods for measuring
viscosity which generally involve measurement of the time of the flow or
movement of a ball, ring, or other object in a specially shaped or sized
apparatus.
Voids
The openings in the
medium. Also referred to as interstices or pores.
Volumetric Flow Rate
Fluid flow expressed as a volume flowing per unit of time-cubic feet/min. or
cubic metres/hr.
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