The present invention relates to air samplers. More particularly, it relates to air samplers that strip a target material from the ambient air (the air mass being sampled), and concentrate it in a stripping liquid. The stripping liquid may then be delivered to any suitable detection apparatus for the target material.
One aspect of the present invention may be to provide a high efficiency wetted wall cyclonic air sampler that is so small, so light weight and so low in energy consumption that it may be battery powered and human-portable; and that is so efficient that it may be used to strip target material that is present in the ambient air in concentrations of only a few parts per trillion, or less.
The target material may comprise one or more solids, liquids and/or gasses. If the target material is a solid, it may comprise particulate matter such as dust, bacteria, or viruses, for example. If the target material is a liquid, the particulate matter may comprise liquid droplets, such as a mist or fog, for example. If the target material is a gas, it may comprise any gas-phase molecular species.
Another aspect of the present invention may be that the air flow through the air sampler""s main body and air inlet section may be provided by a fan, such as when the air sampler is stationary or is moving at a relatively low velocity with respect to the ambient air. Air flow through the air sampler may also be provided by movement of the air sampler through the ambient air.
A first embodiment of the air sampler may comprise an air inlet section, a main body and a fan. If a fan is used, it may urge air through the air inlet section and the main body during use of the air sampler.
The air sampler""s main body may comprise a cyclonic cup, a stripping column and a demister. Ambient air flows tangentially into the cyclonic cup""s perimeter from the air inlet section, creating a rapidly rotating air flow within the cyclonic cup and an upwardly rising air vortex that extends from the cyclonic cup, through the stripping column and into the demister.
The low pressure area created by the air vortex in the center of the cyclonic cup may be used to permit, or assist, the stripping liquid to be gravity fed into the cyclonic cup through an input port in the center of cyclonic cup""s base, with little or no external pump pressure for the stripping liquid being needed.
The shear forces generated by the upwardly rising air vortex within the cyclonic cup may urge the incoming stripping liquid to form around the cup""s input port a thin film that flows radially outwardly across the cyclonic cup""s base, that then flows in a spiral path up the inner surface of the cyclonic cup""s sidewalls, and that then flows onto the inner surface of the stripping column.
Similarly, the shear forces generated by the upwardly rising air vortex within the stripping column may urge the stripping liquid from the cyclonic cup to form a thin film that flows in a spiral path up the inner surface of the stripping column, and that then flows across the top edge of the stripping column; to fall into the demister""s reservoir under the force of gravity.
From the reservoir, the stripping liquid may be recycled one or more times by gravity feed back to the input port in the cyclonic cup, so that it may pass through the cyclonic cup, the stripping column and the demister again; to strip still more target material from the air passing through the air sampler. A liquid level control may be provided for the reservoir.
Thus, the cyclonic cup, the stripping column and the demister may be xe2x80x9cself-pumpingxe2x80x9d, in the sense that no external liquid pump may be needed to force the stripping liquid through them, since that job may be done by the action of the air/liquid shear forces generated by the upwardly rising air vortex within them; and since no external liquid pump may be needed to recirculate the stripping liquid from the demister""s reservoir back into the cyclonic cup, since that job may be done by gravity feed.
All along its journey from the cyclonic cup""s input port to the demister""s reservoir, the thin film of stripping liquid may strip the target material from the upwardly rising air vortex at high efficiencies. Such high efficiencies may be due to such factors as the high velocity of the circulating air and the upwardly rising air vortex; the very large surface area of the thin film; the very long path followed by the thin film as it flows across the cyclonic cup""s base and spirals up the inside of the inner surfaces of the sidewalls of the cyclonic cup and the stripping column; the very low volume of stripping liquid that resides in the air sampler""s main body and air inlet section at any one time; the very low flow rate of the stripping liquid through the air sampler""s main body and air inlet section; the very high volume of air flowing through the air sampler; and/or the evaporation of substantial amounts of the stripping liquid by the air flowing through the air sampler.
The internal diameter of the stripping column may be less than that of the cyclonic cup, to cause the air vortex within the stripping column to rotate at a higher speed as compared to the air vortex in the cyclonic cup. The higher speed of rotation may help the stripping column to more effectively strip liquid and solid particulate target material from the air due to higher centrifugal forces; and may create a relatively lower pressure within the stripping column that may permit the relatively higher pressure within the cyclonic cup to urge the stripping liquid from the inner surface of the cyclonic cup to the inner surface of the stripping column.
The inner surface of the stripping column may be provided with spiral grooves for increasing its surface area; for providing a long spiral path for the thin film of stripping liquid to follow on its inner surface; and/or for helping to prevent air-entrainment of the stripping liquid on its inner surface by encouraging the air flow to follow a spiral path, by shielding the stripping liquid from the air flow""s axially-directed shear forces, by preventing the stripping liquid from forming large surface waves that may be captured and subsequently broken into droplets by the air flow, and by providing a partially-protected path by which the stripping liquid can spill into the demister.
A portion of the stripping column may extend into the demister, and the diameter of the demister may be greater than the diameter of the stripping column, to provide a space between the larger sidewall of the demister and the smaller sidewall of the stripping column that may serve as the demister reservoir, and to reduce the speed of rotation and upward velocity of the air vortex within the demister to the point that at least some of any air-entrained stripping liquid may be dropped by the air vortex in the demister.
The air sampler""s cyclonic cup may further comprise a passive (i.e., non-powered or non-moving) means for producing a fog of stripping liquid droplets that utilizes the low pressure area created in the center of the cyclonic cup by the cyclonic cup""s air vortex, and that utilizes the extremely high tangential air velocities that may be created by the cyclonic cup""s air vortex near the cyclonic cup""s longitudinal axis.
A first embodiment of the passive fog generating means may comprise a radially oriented slot centered in the cyclonic cup""s base that is fed by the cyclonic cup""s stripping liquid input port. A second embodiment of the passive fog generating means may comprise a spiral fog generating nozzle having an input port located over the cyclonic cup""s stripping liquid input port. With both embodiments of the passive fog generating means, the fog particles they produce may, during their passage through the cyclonic cup, the stripping column and the demister, strip the target material from the air and be deposited on the inner surfaces of the cyclonic cup, the stripping column and the demister. The fog particles that are deposited on the inner surfaces of the cyclonic cup and the stripping column may then become part of, and travel along with, the stripping liquid film on those surfaces. Any fog particles deposited on the inner surface of the demister""s sidewall may drain, under the force of gravity, into the demister""s reservoir. The extremely high efficiency with which the fog particles may strip the target material from the air may be due to such factors as their extremely small size, their extremely large numbers, and/or their extremely large cumulative surface area.
The air sampler""s air inlet section may comprise an air inlet tube and a fog generator for producing a fog of stripping liquid droplets in the air inlet tube and/or in the cyclonic cup. During their passage through the air inlet tube, the cyclonic cup, the stripping column and the demister, the fog particles may strip the target material from the air and be deposited on the inner surfaces of the cyclonic cup, the stripping column and the demister. Those fog particles deposited on the inner surfaces of the cyclonic cup and the stripping column may then become part of, and travel along with, the stripping liquid film on those surfaces. Those fog particles deposited on the inner surface of the demister""s sidewall may drain, under the force of gravity, into the demister""s reservoir.
From all of the forgoing, it may now be seen that the air sampler""s main body 11 and air inlet section 12 may provide a unique five-step stripping process for stripping the target material from the incoming air, namely, (a) the action of the fog of stripping liquid particles produced by the fog generator in the air inlet tube, (b) the action of the fog of stripping liquid particles produced by the fog generating means in the cyclonic cup, (c) the action of the film of stripping liquid on the inner surface of the cyclonic cup, (d) the action of the film of stripping liquid on the inner surface of the stripping column, and/or (e) the action of the film of stripping liquid on the inner surface of the demister.
A second embodiment of the cyclonic air sampler of the present invention may comprise a main body and/or an air inlet that may be formed as one integral piece, such as by blow-molding or roto-molding. The integrally formed main body and/or air inlet may have exceedingly smooth inner surfaces, and may have inner surfaces that intersect in smoothly curved fillets, for better flow of the air and/or thin water film over them, and to prevent the formation of undesirable water traps that may be hard to clean and that may cause the air sampler to produce erroneous readings regarding the target material under certain circumstances.
The second embodiment of the cyclonic air sampler may include external capacitive or optical liquid level controls that may inherently avoid any cleaning or clogging problems, since they may never be in direct contact with the liquids passing through the air sampler.
A third embodiment of the cyclonic air sampler of the present invention may comprise an air inlet section, a main body and an air outlet section. Its main body may comprise a cyclonic cup having an internal, high speed, radial flow air impeller. Stripping liquid fed into the air inlet section may be urged by the spinning impeller to form a thin film on the impeller""s inner surfaces. The spinning impeller may then urge the thin film to move across the impeller""s inner surfaces to the impeller""s peripheral air outlet, where it may then be flung onto the cyclonic cup""s end wall to form a thin film on the cyclonic cup""s end wall. The air flow from the impeller through the cyclonic cup""s air chamber may then urge the thin film on the cyclonic cup""s end wall to enter a reservoir in the air outlet section. The thin film on the impeller""s inner surfaces and the cyclonic cup""s end wall may strip the target material from the air. The liquid from the reservoir may be recycled back into the air inlet section to strip more target material from the air.
The third embodiment""s air inlet section may comprise an air inlet tube and a fog generating means for producing a fog of stripping liquid particles in the air inlet tube. During their passage through the air inlet tube, the air chambers within the impeller, and the cyclonic cup""s air chamber, the fog particles may strip the target material from the air and be deposited on the inner surfaces of the air impeller and the cyclonic cup""s end wall. Those fog particles deposited on the inner surfaces of the air impeller and the cyclonic cup""s end wall may then become part of, and travel along with, the stripping liquid film on those surfaces.
The cyclonic cup""s end wall may be enlarged and/or may have a concave cross-sectional configuration, to increase its surface area, and to thus increase the surface area of the thin film of stripping liquid that it may carry.
The third embodiment may be highly efficient at stripping the target material from the air for reasons which are at least similar to, if not the same as, those set forth above regarding the first and second embodiments of the air sampler.
The inner surfaces of any of the embodiments of the air sampler that are wetted by the stripping liquid may be made from a hydrophilic material, may be coated with a hydrophilic material and/or may be treated to become hydrophilic, to improve their wettability and the thinness of the film of stripping liquid they may carry.
As used herein, the terms xe2x80x9cwettedxe2x80x9d, xe2x80x9cwettablexe2x80x9d, xe2x80x9cwettabilityxe2x80x9d, xe2x80x9chydrophilicxe2x80x9d, xe2x80x9chydrophobicxe2x80x9d, and the like, are to be interpreted as having meanings with respect to non-aqueous stripping liquids that correspond to their meanings when used with aqueous stripping liquids.
Air entering any of the embodiments of the air sampler may comprise air that is received directly from the ambient air; and/or it may comprise the output of a preconcentrator that receives the ambient air and provides a steady or pulsatile output stream of air that is already enriched with the target material. A suitable preconcentrator may also comprise means for removing large, non-target material debris from the air passing through it, such as a dry air cyclone or a canister with an absorbent material.
Any of the embodiments of the air sampler may further comprise fluidic circuitry that may be designed for multiple functions such as, for example, supplying the air sampler""s main body and/or air inlet section with stripping liquid and/or cleaning liquid; removing waste liquid from the air sampler""s main body and/or air outlet section; removing samples of the stripping liquid (which may contain stripped target material) from the air sampler""s main body and/or air outlet section; and/or detecting the presence, amount and/or identity of the target material in the samples of the stripping liquid.
The fluidic circuitry may further comprise a novel dual roller peristaltic sample and/or waste pump. The peristaltic pump may act as a normally-closed valve when shut off, may consume a very small amount of electric power due to its innovative design, and may be long-lived, self-priming, easily cleaned, light-weight, insensitive to shock, and/or computer-controllable.
It should be understood that the foregoing summary of the present invention does not set forth all of its features, advantages, characteristics, structures, methods and/or processes; since these and further features, advantages, characteristics, structures, methods and/or processes of the present invention will be directly or inherently disclosed to those skilled in the art to which it pertains by all of the disclosures herein.