Patent Application: US-14066008-A

Abstract:
an aerodynamic sampler for sampling particles from a surface or a flowing gas stream is provided . the sampler can include an arcuate - shaped shroud having a first opening and a second opening , the first opening being directed in a first direction and the second opening oppositely disposed and spaced apart from the first opening . a gas nozzle having at least one gas outlet directed generally in the first direction can be included and may or may not be located at least partially within the shroud . the gas nozzle is operable to supply a gas jet to a surface that is proximate the first opening of the shroud . in addition , a suction device operable to pull or suck the gas proximate the first opening through the second opening and afford for the gas to enter a detector is provided . the arcuate - shaped shroud can be a bell - shaped shroud with the first opening located at a bottom of the bell - shape .

Description:
research experience at the penn state university gas dynamics laboratory and elsewhere has demonstrated that trace contaminants are effectively dislodged from a surface ( e . g . from people &# 39 ; s clothing ) by a brief turbulent jet impact [ 8 , 9 ]. it is known to those in the art that shear stress generated by the jet impact in a direction parallel to the surface being sampled is active in detaching trace - bearing particles from that surface . it is also known that the jet impact “ rolls out ” along the impacted surface in a “ starting vortex ” [ 10 ] and forms a “ wall jet ” that can be made to separate from the impacted surface . capturing the wall jet by suction through an appropriately designed “ shroud ” can thus afford for a particulate and / or a vapor signal dislodged from the surface to be examined . such an airborne sampling process can be quite brief ( e . g . milliseconds ) such that a volume of air sampled is small and can avoid the need for undue pre - concentration . it is thus possible to interrogate the volume of air sampled directly , e . g . using an ion mobility spectrometer ( ims ) detector , with appropriate concern for the desorption of trace chemicals from any particles that are captured . turning now to fig1 , a first embodiment of an aerodynamic sampler 10 according to the present invention is shown . this embodiment may be referred to as a jet - puff sniffer , the sniffer 10 including an outer , properly - shaped , duct or shroud 12 and an outlet nozzle 14 disposed inside the shroud . in the alternative , a second embodiment wherein an outlet nozzle 14 ′ is disposed outside the shroud 12 is shown in fig2 . furthermore , it is appreciated that the nozzle 14 shown in fig1 is positioned along a central axis of the shroud 12 , however this is not required . a source of compressed gas 18 , illustratively including compressed air , nitrogen , argon , oxygen and the like , is connected to the outlet nozzle 14 to provide a jet 19 , namely a pulse of gas , to a sampling surface s . in some instances , the jet 19 has a pressure up to 10 atmospheres . in other instances , the jet 19 has a pressure of between 1 and 10 atmospheres , while in still yet other instances the jet 19 has a pressure between 2 and 8 atmospheres . a standoff distance h defined as the distance from the shroud 12 to the sampling surface s is preferably small , typically comparable to or preferably less than the shroud diameter , for successful operation . in the alternative , the sampler 10 can be placed in a moving stream and used to sample a moving airstream and the like . a suction device 16 in the form of a fan , blower or the like draws a sample flow into the shroud 12 through a first opening , also known as a shroud inlet 11 , and through a second opening , also known as a shroud outlet 21 , as indicated by arrows 1 . it is appreciated that the sample flow or a portion thereof can be delivered to a detector for analysis , for example to optional chemical analyzer 100 , or to a pre - concentrator if so required . it is further appreciated that the jet 19 can be provided by a source of compressed gas , modern synthetic jet technology [ 11 ] or the like , the jet 19 providing an axisymmetric wall jet 13 that separates from the sample surface s as shown in fig1 due to the adverse pressure gradient imposed upon sample surface s by the shroud inlet 12 and associated airflow . in the alternative , a non - axisymmetric wall jet 13 ′ that also separates from the sample surface s is shown in fig2 . it is appreciated that the shroud 12 along with the outlet nozzle 14 and 14 ′ are directed generally in the same direction , which in this case is toward the sampling surface s . the supply of compressed gas to the nozzle 14 and 14 ′ can be controlled by solenoid valves known to those skilled in the art and can range from intermittent duration of a few milliseconds to continuous operation . in order to scour a surface and remove particles and / or vapor , a shear stress in the range of 10 - 30 pascals ( pa ) ( 0 . 0015 - 0 . 0045 pounds per square inch ( psi )) can be used . for example , and for illustrative purposes only , an outlet nozzle having an exit opening with an inside diameter of 1 millimeter ( mm ) ( 0 . 04 inch ( in .)) with a standoff distance of 25 mm ( 1 in .) and a nozzle - exit stagnation pressure of 14 kpa ( 2 psi ) above atmospheric pressure can provide such a shear stress . such a pressure would result in a mass flow rate through the nozzle of 0 . 00015 kilograms per sec ( kg / sec ), corresponding to a volume flow rate of 1 . 17 × 10 − 4 cubic meters per second ( m 3 / sec ) ( 0 . 25 standard cubic feet per minute ( scfm )). taking for example a shroud that can collect 5 to 10 times the volume flow rate of the outlet nozzle , i . e . 5 . 85 × 10 − 4 - 1 . 17 × 10 − 3 m 3 / sec ( 1 . 25 - 2 . 5 scfm ), a diameter of such a shroud could be of the order of 12 centimeters ( cm ) ( 4 . 7 in .). larger diameter outlet nozzles could naturally result in higher mass flow rates out of the nozzle and thus larger shrouds . smaller devices may likewise be designed . in an alternate embodiment shown in fig3 , where like numerals represent like elements as referenced in previous figures , a sniffer 20 includes an ejector nozzle 22 directed away from the shroud inlet 11 and towards the shroud outlet 21 . the compressed - air source 18 can simultaneously power the jet 19 and provide a suction using the ejector 22 which induces a low - speed flow by way of a pressure drop created by entrainment into a small high - speed turbulent jet 17 . a dump - tube 24 may be provided proximate the shroud outlet 21 in order to collect jet 17 and discard it , thus increasing the concentration of a trace signal originating from the surface s and presented to a detector ( not shown ) via the airflow indicated by arrows 1 . in addition , optional valves 6 , 7 and 8 , can be included and used to direct compressed gas to the outlet nozzle 14 and / or ejector 22 . it is appreciated that the embodiment illustrated in fig3 can be modified in a similar fashion as the embodiment shown in fig2 with an outlet nozzle 14 ′ disposed outside the shroud 12 , or in a different non - axially - symmetric form . as noted in earlier discussion , the “ reach ” of heretofore inlets is quite limited . the flow into a bulbous - shaped shroud ( i . e ., shaped like an animal nose ) could be focused in a forward direction to improve the “ reach ” of sniffing if inlet walls were able to generate vorticity aimed towards a central suction opening . one method to generate such vorticity aimed towards the central suction opening is with moving walls . however , this method requires great mechanical complexity . in the alternative , the same effect can be accomplished with a coanda - inlet sampler 30 shown schematically in fig4 . it is appreciated that henri coanda proposed [ 5 ] an explanation of why a fluid flow clings to a curved surface . various inventions have put this principle to use , for example in kitchen ventilation [ 6 ], but not thus far to the type of aerodynamic sampling described in the present disclosure . the sampler 30 includes a shroud 32 with an outer portion 34 and an inner portion 36 . an outward “ step ” nozzle 38 is disposed between the outer portion 34 and the inner portion 36 and can be formed by a gap 39 therebetween . it is appreciated that the shroud 32 and / or step nozzle 38 can be axisymmetric in orientation and / or position , or in the alternative , not be axisymmetric . attached surface jets 35 , generated by compressed gas 37 flowing through the step nozzle 38 and aimed inward , entrain air in order to “ focus ” the flow . the sampler 30 functions in some sense similarly to the ejector 22 shown in fig3 and a capture or sample tube 40 captures only the incoming airstream 42 from the immediate forward direction . the remaining air flux can be discarded , in that it does not arise from the desired forward direction and is thus irrelevant to the desired sampling task . it is appreciated that the location of the step nozzle 38 in fig4 is for illustrative purposes only and in no way limits the embodiment . an inlet of this type typically requires compressed gas to power the coanda jets 35 . a suction can be applied to the capture tube 40 in order to extract the sampled air and subsequently present it to a detector . the sampler 30 may be used in conjunction with puffer jets , described earlier , in order to dislodge particles and / or vapor from surfaces before “ sniffing ” them . it is further appreciated that the sample tube 40 can provide the puffer jet , or in the alternative , an outlet nozzle 14 ′ as shown in fig5 can be provided to afford for a jet of compressed gas to impact a sample surface . for example , and in no way limiting the scope of the embodiment , the sampler 30 could have an inside diameter of shroud 36 of 51 mm ( 2 inches ( in )) with the sample tube 40 having an inside diameter of 13 mm ( 0 . 5 inch ). thus in operation , a centrifugal blower known to those in the art could supply the coanda jet flow 37 with a volume flow rate of 0 . 014 m 3 / sec ( 30 scfm ) that would be drawn into the sampler 30 through the inside diameter of shroud 36 . such a volume flow rate would produce a velocity of 7 meters per second ( m / sec ) and the sample tube 40 could draw in a volume flow rate of 9 . 4 × 10 − 4 m 3 / sec ( 2 scfm ). it is appreciated that the gas flow could be drawn from a region 42 that can be of similar diameter as the inside diameter of the shroud 36 and located as much as , or more than one diameter away from the sampler 30 . another embodiment of a sampler or sniffer according to the present invention is shown generally at reference numeral 50 in fig6 and 7 . this design may be referred to as a radial - jet reattachment sniffer , and works in a manner logically opposite to that of the jet - puff sniffer taught above in that radial jet 53 is produced from a nozzle 52 combined with a flare 54 or 54 ′. near a surface s , the radial jet 53 attaches to the surface s and produces an internal toroidal vortex 55 between the nozzle flare 54 and the surface s . the vortex 55 sweeps air across the surface s , inward radially from a jet reattachment line 57 , and upward along a centerline where a sample tube 56 withdraws some of the trace - laden air for the chemical detection step . it is appreciated that if the nozzle shroud 52 and flare 54 are angled sharply downward toward the surface s as shown in fig6 , then a local surface area of small diameter is sampled . in the alternative , the nozzle flare 54 ′ and corresponding radial slot angle 59 can be parallel to the sampling surface s or even inclined up to 30 degrees away from it , and thereby result in a larger - sized radial jet reattachment circular “ footprint ” on the surface s , as shown in fig7 . as such , the embodiment affords for large semi - flat surfaces to be sampled , such as suitcases , the door panels of automobiles , etc . it is further appreciated that the samplers resulting in the flow patterns shown in fig6 and 7 can be made to be simply interchangeable on the front - end of a trace chemical detection system and / or that many different designs of the nozzle - flare combination 52 - 54 , 52 - 54 ′ and the like are possible with approximately the airflow effect shown in these figures afforded . in this manner , the sampling surface area for a trace chemical detection system can be varied and thereby provide a single detection system with multiple interchangeable samplers that afford for different - sized surfaces to be tested . another embodiment of a sampler or sniffer is shown in fig8 wherein an aerodynamically - assisted sniffer 70 may be integrated with a parabolic “ dish ” antenna 60 . vehicles and robotic devices often incorporate parabolic dish antennas for communications and / or for electromagnetic interrogation of a target . sophisticated actuators are required to aim the dish antenna for these purposes . the same equipment may serve the dual purpose of directional “ sniffing ” in close proximity to objects , given the antenna modifications illustrated in fig8 . the electromagnetically - active components of the antenna 60 are the parabolic reflector dish 61 and a signal “ pickup ” stalk 62 positioned at a parabola focus of the dish 61 . the sniffer 70 includes a sampling tube 73 , plenum 74 and radial nozzle 75 as shown in fig8 . in addition , compressed air from plenum 74 can be used to generate a radially - outward - flowing turbulent boundary layer 66 along an inner surface of the parabolic reflector dish 61 and thereby afford by entrainment a bulk airflow motion indicated by streamlines 67 . in the alternative , an optional outlet nozzle 14 ′ can be provided as shown in fig9 , the outlet nozzle 14 ′ affording for compressed gas to impact a sample surface as taught above . in this manner , a narrow stream - tube 68 may be sampled from a direction in which the dish antenna 60 is aimed , and may thus provide a small directional airflow 69 to a chemical detector mounted aft of the antenna 60 and not shown in fig8 and 9 . thus , with the modifications described above , a parabolic dish antenna can also serve a second purpose of directional sniffing for the aerodynamic interrogation of a suspected explosive device , an automobile , a person , etc . for trace chemical species . in fig8 and 9 the electromagnetic pickup on the stalk 62 may produce some interference with the aerodynamic sampling function of stream 68 , but such interference can be negligible . stated differently , any interference of the antenna &# 39 ; s electromagnetic function by the airflow is likewise appreciated to be negligible . in some instances , compressed air is first ejected through sampling tube 73 in a direction towards the stalk 62 and produces a turbulent jet that can impinge upon a surface to be sampled ( to the left in fig8 and 9 , not shown ) and dislodge particles and / or vapor via induced surface shear stress . after a brief interval , suction through sampling tube 73 , discussed above and shown in fig8 and 9 , can “ inhale ” particles and / or vapor from a sample surface and thence present them to a detection device . such a parabolic dish antenna 61 for a mobile electromagnetic communication device could have a diameter of 46 cm ( 18 in .) with a collection tube 73 having an inner diameter of 2 . 5 cm ( 1 in .) and a slot nozzle 75 having a width of 5 mm ( 0 . 2 in .) and a circumference of 23 cm ( 9 in .). such dimensions would allow for a gas flow rate of 0 . 36 m 3 / sec ( 77 scfm ) out of the slot nozzle 75 and a suction flow of 0 . 005 m 3 / sec ( 11 scfm ) through the capture tube 73 , thereby affording for a “ reach ” of the captured stream - tube 68 to extend from the end of the capture tube 73 to a distance ahead of the parabolic dish antenna 61 equal to , if not greater than the diameter of the dish antenna 61 . as will be clear to those of skill in the art , the embodiments of the present invention described and illustrated herein may be altered in various ways without departing from the scope or teaching of the present invention . for example , all of the embodiments can be used to sample a moving airstream as well as a surface and heated air can be used in the puffer jets in order to better desorb volatile chemicals from a surface . as such , the invention is not restricted to the illustrative examples and / or embodiments described above and the scope of the invention is defined by the scope of the claims . settles , g . s ., “ sniffers — fluid - dynamic sampling for olfactory trace detection in nature and homeland security ,” j . fluids engrg . vol . 127 , no . 2 , pp . 189 - 218 , march 2005 . 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