Abrasion
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The process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive.
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By reducing particle size.
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Advection
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A transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid's bulk motion in a particular direction. An example of advection is the transport of pollutants or silt in a river.
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Angle of Repose
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(or critical angle of repose) The minimum angle made by the inclined plane with the horizontal surface such that the body lying on the inclined plane is just at the verge of sliding down along the inclined plane. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material.
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For example, piles of granular material.
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Centrifugal Force
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An outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces (or inertial forces), so named because, unlike real forces, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act. Instead, centrifugal force originates in the rotation of the frame of reference within which observations are made.
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Cheerio Effect
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The tendency for small wettable floating objects to attract one another as a result of a combination of surface tension and buoyancy.
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Coanda Effect
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The tendency of a fluid jet to stay attached to an adjacent suitably shaped curved surface. Also applies to powdered solids.
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Coffee Ring Effect
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A pattern left by a puddle of particle-laden liquid after it evaporates. Named after the characteristic ring-like deposit along the perimeter of a spill of coffee. The pattern is due to capillary flow induced by the differential evaporation rates across the drop: liquid evaporating from the edge is replenished by liquid from the interior. The resulting edgeward flow can carry nearly all the dispersed material to the edge.
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Compression
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The result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is tension. In simple terms, compression is a pushing force.
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Convection
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The movement of molecules within fluids (i.e. liquids, gases) and rheids. One of the major modes of heat transfer and mass transfer. Convective heat and mass transfer take place through both diffusion (random Brownian motion) and by advection (transport by the larger-scale motion of currents). Note that a common use of the term convection refers specifically to heat transfer by convection, as opposed to convection in general.
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By first dispersing the divided solid in a fluid (liquid or gas).
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Crystallisation
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The (natural or artificial) process of formation of solid crystals precipitating from a identical solution or melt, or more rarely deposited directly from a gas. Crystallisation is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.
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Decomposition (biological)
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The break down of tissue of a formerly living organism into simpler forms of matter.
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Density Gradient
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Variation of density across an area or through a volume.
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Ekman layer
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The layer in a fluid where there is a force balance between pressure gradient force, Coriolis force and turbulent drag. In addition to enforcing the zero velocity condition at the wall, these Ekman layers can also control long-range properties of the flow. A classical illustration is given by the everyday experience of how a cup of tea returns to rest after stirring.
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Elastic Recovery
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The tendancy of a material that has been stretched to return to its original shape.
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Elasticity
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The physical property of a material when it deforms under stress (e.g. external forces), but returns to its original shape when the stress is removed. The amount of deformation is called the strain. The elastic regime is characterized by a linear relationship between stress and strain, denoted linear elasticity.
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Electret
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An Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.
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Electric Arc
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An electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air
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If the divided solid carries an electric charge.
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Electric Field
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The space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects.
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Electrohydrodynamics
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Includes the following types of particle and fluid transport mechanisms:Electrophoresis, electrokinesis, dielectrophoresis, electro-osmosis, and electrorotation. In general, the phenomena relate to the direct conversion of electrical energy into kinetic energy, and vice versa.
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Electromagnetic Induction
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The generation of electromotive force (EMF) in a current-carrying conductor exposed to a changing magnetic field
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Electrorheological Effect
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Electrorheological (ER) fluids are suspensions of extremely fine non-conducting particles (up to 50 micrometres diameter) in an electrically insulating fluid. The apparent viscosity of ER fluids changes reversibly by an order of up to 100,000 in response to an electric field. A typical ER fluid can go from the consistency of a liquid to that of a gel, and back, with response times of the order of ms. Sometimes called the Winslow Effect.
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Electrostatic Induction
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A redistribution of electrical charge in an object, caused by the influence of nearby charges. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Electrostatic induction should not be confused with electromagnetic induction; both are often referred to as 'induction'.
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Electrostatics
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The phenomena arising from stationary or slowly moving electric charges
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Electrostriction
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A property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. All dielectrics exhibit some electrostriction, but certain engineered ceramics, known as relaxor ferroelectrics, have extraordinarily high electrostrictive constants,e.g. Lead magnesium niobate (PMN), Lead magnesium niobate-lead titanate (PMN-PT), Lead lanthanum zirconate titanate (PLZT).
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Erosion
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The process of weathering and transport of solids (sediment, soil, rock and other particles) in the natural environment or their source and deposits them elsewhere. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals, in the case of bioerosion.
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Faraday Wave
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(or Faraday Ripples) Nonlinear standing waves that appear on liquids enclosed by a vibrating receptacle. When the vibration frequency exceeds a critical value, the flat hydrostatic surface becomes unstable. The waves can take the form of stripes, close-packed hexagons, or even squares or quasiperiodic patterns.
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Faraday waves are used as a liquid-based template for directed assembly of microscale materials including soft matter, rigid bodies and biological entities.
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Ferromagnetism
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The mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Responsible for commonly observed magnetism phenomena, e.g. 'fridge magnets. A material is 'ferromagnetic' only if all its magnetic ions add a positive contribution to the net magnetisation. If some of them subtract from the net magnetisation (i.e. are partially anti-aligned), then the material is 'ferrimagnetic'.
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Flocculation
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A process of contact and adhesion whereby the particles of a dispersion form larger-size clusters.
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Force
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That which can cause an object with mass to accelerate. Force has both magnitude & direction, i.e. it's a vector quantity. An object with constant mass will accelerate in proportion to the net force acting upon it and in inverse proportion to its mass (or the net force on an object is equal to the rate of change of momentum it experiences). Forces acting on objects may cause them to rotate or deform, or result in a change in pressure.
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Forced Convection
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Heat advection by a fluid which is not due to the natural forces of buoyancy induced by heating. In forced heat convection, transfer of heat is due to movement in the fluid which results from many other forces, such as (for example) a fan or pump.
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Fractal Forms
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A fractal is generally 'a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole,' a property called self-similarity. A mathematical fractal is based on an equation that undergoes iteration, a form of feedback based on recursion.
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Free Convection
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Movement of molecules of fluids (or gases) dues to density differences in the fluid (or gas) occurring due to temperature gradients.
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Gravitation
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A natural phenomenon by which objects with mass attract one another. In everyday life, gravitation is most commonly thought of as the agency which lends weight to objects with mass.
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Holes
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A hole is a confined lack of structure in some part of an object.
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Impact Force
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A high force or shock applied over a short time period. Such a force or acceleration can sometimes have a greater effect than a lower force applied over a proportionally longer time period.
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Lorentz Force
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The force on a point charge due to electromagnetic fields. When a wire carrying an electrical current is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force).
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Magnetic Field
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A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
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Magnetism
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One of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field.
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Magnetostriction
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A property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetisation. The variation of material's magnetisation due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value. This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
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Melting
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A process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased (typically by the absorbtion of heat) to a specific temperature (called the melting point) at which it changes to the liquid phase.
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Ostwald Ripening
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An observed phenomenon in solid solutions or liquid sols that describes the change of an inhomogeneous structure over time, i.e., small crystals or sol particles dissolve, and redeposit onto larger crystals or sol particles. Occurs because larger particles are more energetically favored than smaller particles. This stems from the fact that molecules on the surface of a particle are energetically less stable than the ones in the interior. Ostwald ripening is also observed in liquid-liquid systems, causing diffusion of monomers (i.e. individual molecules or atoms) from smaller droplets to larger droplets due to greater solubility of the single monomer molecules in the larger monomer droplets.
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Example: the re-crystallization of water within ice cream which gives old ice cream a gritty, crunchy texture. Larger ice crystals grow at the expense of smaller ones within the ice cream, creating a coarser texture.
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Photophoresis
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The phenomenon that small particles suspended in gas (aerosols) or liquids (hydrocolloids) starts to migrate when illuminated by a sufficiently intense beam of light. The existence of this phenomenon is owed to a non-uniform distribution of temperature of an illuminated particle in a fluid medium.
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Physical Containment
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Partial or complete enclosure of an object or substance by some physical medium, typically for the purpose of protection or restriction of movement.
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Pressure Gradient
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A fluid (gas or liquid) subject to a pressure gradient results in a net force that is directed from high to low pressure (the 'pressure gradient force').
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In the case of a divided solid dispersed in a fluid.
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Pressure Increase
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Pressure is an effect which occurs when a force is applied on a surface. Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
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Rayleigh-Bénard Convection
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Convection cells that appear spontaneously in a liquid layer when heat is applied from below.
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For a divided solid dispersed in a fluid.
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Reaction (physics)
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In classical mechanics, Newton's third law states that forces occur in pairs: the Action and the Reaction. Both forces are equal in magnitude and opposite in direction. The distinction between action and reaction is purely arbitrary: any one of the two forces can be considered an action, in which case the other (corresponding) force automatically becomes its associated reaction.
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Saltation (geology)
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A specific type of particle transport by fluids such as wind, or the denser fluid water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields, or even snow drift over smooth surfaces such as those in the Arctic or Canadian Prairies.
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Sedimentation
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The motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal acceleration or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides.
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Settling
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The process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming a slurry at the vessel base.
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Sorption
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The action of both absorption and adsorption taking place simultaneously, i.e. the effect of gases or liquids being incorporated into a material of a different state and adhering to the surface of another molecule. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids absorbed by solid or gas absorbed by liquid). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule.
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Supersaturation
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A solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. It can also refer to a vapour of a compound that has a higher (partial) pressure than the vapour pressure of that compound.
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Suspension
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A heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase (solid) is dispersed throughout the external phase (fluid - which may be liquid or gas) through mechanical agitation, with the use of certain excipients or suspending agents.
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Thermal Contraction
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The tendency of matter to reduce in volume (contract) in response to a change in temperature or when a substance is cooled.
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Thermophoresis
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(also called thermodiffusion or Soret Effect) The effect of temperature gradient on multicomponent (or isotopic) mixtures of particles (i.e. particle movement from hotter to colder regions or vice versa). Regarded as 'positive' when molecules move from hot to cold and 'negative' when the reverse is true. Typically the heavier/larger species in a mixture exhibits positive behavior while the lighter/smaller species exhibit negative.
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A thermal precipitator is an instrument that collects aerosol particles using thermophoresis to deposit the particles onto a surface. It employs a heated element, such as a wire, and a collection surface. Aerosol passing between the heated element and the cooler surface will be driven to deposit on the surface.
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Triboelectric Effect
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A type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
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Ultrasonic Vibration
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Vibration at ultrasonic frequencies.
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Through settling.
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Ultrasound
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Cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person, 20 kHz serves as a useful lower limit in describing ultrasound.
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Vibration
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Mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.
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Through settling.
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Vortex Ring
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A torus shaped vortex in a fluid i.e. a region where the fluid mostly spins around an imaginary axis line that forms a closed loop. The dominant flow in a vortex ring is said to be toroidal, more precisely poloidal. Within a stationary body of fluid, a vortex ring can travel for relatively long distance, carrying the spinning fluid with it.
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In the case of a divided solid dispersed in a fluid, e.g. a smoke ring.
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Wear
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The erosion of material from a solid surface by the action of another surface.
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Through closer packing of finder particles.
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