Abstract:
A compact electrostatic particulate collector for sampling contaminants has a collection chamber defined by a titanium inner surface of a wall. A potential inducer is disposed within the chamber to create a field potential between itself and the wall of the chamber. A blower is disposed to propel air to be sampled through the chamber. At least one rinse channel is disposed to wet the inner surface of the wall of the chamber substantially 100%. The rinse channel is angled to direct a rinse liquid in a spiral direction around the inner surface of the wall. Contaminants in the air being sampled are electro statically biased into the rinse liquid on the wall and rinsed out of the chamber for collection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is in the field of removing particulates from the air, particularly as applied to sampling contaminants. 
     2. Background 
     Removing particulate contaminants from the atmosphere may be achieved with several known technologies. One known device is an electrostatic particulate collector. Known electrostatic particulate collectors have traditionally been designed for continuous, high volume use, as for example, as antipollution devices. Prior art devices are disadvantageous in contaminant sampling situations for multiple reasons. 
     Electrostatic particulate collectors are typically designed with a metallic chamber through which a gas, typically air, is directed for removal of particulate matter such as contaminants. Disposed within the chamber is a current carrying element supplied with sufficient electrical voltage that the potential between itself and the metallic walls of the chamber creates a coronal discharge. The coronal discharge electrostatically charges particulates in the gas within the chamber, and these ionized particles are thereby electrostatically driven to adhere to the walls of the chamber. 
     Once collected on the chamber walls, the contaminants may be removed. Manual removal of collected contaminants requires frequent shutdown for a replacement and/or cleaning of the chamber walls. To avoid this, it is known to rinse the chamber walls with a liquid in order to collect the removed contaminants and also retard contaminant buildup on the chamber walls. Purified water is often used as a rinse liquid. 
     Some prior art designs fail to wet all of the chamber wall, allowing disadvantageous contaminant buildup on dry portions of the chamber wall. Prior art devices do not wet the chamber walls quickly, and require significant volumes of liquid in order to achieve adequate wetting of the chamber walls. Prior art designs typically use large cumbersome components, use larger volumes of rinse liquid and demand a high power draw for both rinse liquid distributors and blowers used to propel the atmosphere being treated through the treating chambers. 
     SUMMARY OF THE INVENTION 
     The present invention is an electrostatic particulate collector having a novel structure. One aspect of the present invention is to achieve 100% wetting of the inner surface of the chamber wall with a minimum volume of liquid. It is another aspect of the invention to achieve 100% wetting of the inner surface of the chamber wall quickly. In so doing, the structure of the present invention promotes greater efficiency, greater throughput of air to be sampled, greater portability and/or greater automation. Smaller volumes of the required purified water need to be transported or installed with the test unit. Power requirements may be reduced. Speed, water volume and volume of air throughput may be improved because impedance of air flow by the wetting structures is reduced. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an exploded view of the electrostatic particulate collector of the present invention. 
         FIG. 2  is a perspective and cutaway view of a prior art weir type fluid distributor and collection tube. 
         FIG. 3  is a perspective view of a collection tube and fluid distributor. 
         FIG. 4  is an exploded view of a collection tube and fluid distributor. 
         FIG. 5  is a cutaway view of the fluid distributor and collection tube. 
         FIG. 6  is a bottom view of the fluid distributor and collection tube. 
         FIG. 7  is a side view of the fluid distributor and collection tube. 
         FIG. 8  is a perspective view of the fluid distributor insert. 
         FIG. 9  is a side view of an alternative collection tube and fluid distributor 
         FIG. 10  is an exploded view of an alternative collection tube and fluid distributor in an open position. 
         FIG. 11  is a perspective view of an alternative fluid distributor insert. 
         FIG. 12  is an exploded view of alternative fluid distributor insert. 
         FIG. 13  is an exploded view of alternative fluid distributor insert. 
         FIG. 14  is a cutaway view of the collection chamber and blower. 
         FIG. 15  is a graph of wetting times and rinse liquid volumes. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings in which like reference numbers indicate like elements,  FIG. 1  is an exploded overall view of the electrostatic particulate collector of the present invention. Particulate collector  10  is a compact device to promote portability for mobile and rapid response testing of atmospheres such as may have been purposefully contaminated, as for example with a biological agent such as anthrax or other detrimental particulate matter suspended in the air. Accordingly, the compact unit  10  has a housing  12 . Alternatively, the unit may also be deployed for automatic testing in response to actuation by a sensor. This provides for installation of the unit for constant monitoring of certain facilities such as government buildings. 
     Within the housing  12  are the major components of the electrostatic particulate collector including a battery  16 , electronic control module  18 , high voltage power supply  20 , an air handling system having a blower  22 , fluid connector  24 , pump  26  and the test chamber  30 . A fluid reservoir  28  which may be separate, is provided to supply any rinse liquid for wetting the test chamber internally. 
     In the depicted embodiments the test chamber is a tube.  FIG. 2  depicts a prior art cylindrical test chamber  30 A comprised of a metal cylinder  32 A and a fluid distributor  34 A. The prior art device was a weir type fluid distributor which injects water into the chamber space within the tube  32 A by simply over topping the edge of the chamber cylinder  32 A. By force of gravity then the provided liquid descended onto the walls of the inner surface of the chamber  32 A, thereby wetting it. This design disadvantageously failed to wet 100% of the inner surface of the chamber wall, and left substantial vertical dry portions on the wall between the streams of the fluid provided. 
       FIG. 3  depicts the test chamber  30  of the present invention. In the depicted embodiment, the test chamber is a cylindrical tube  32 . At a top end a fluid distributor  34  is mounted. In the depicted embodiment the fluid distributor  34  is comprised of an outer shell or receiver  36  and an inner insert  38 . The female outer receiver has frustoconical internal surface  40  which is dimensioned to mate with a corresponding frustoconical outer surface  42  of the male fluid distributor insert  38 . The components of the fluid distributor  34  may be plastic. 
     The chamber is a cylindrical tube  32  in the depicted embodiment which may be made of metal. The metal may be steel, titanium, aluminum or otherwise. In the depicted embodiment the tube  32  is comprised of a cylindrical wall  44  having an inner surface  46 . The inner surface may be comprised of titanium. Providing a titanium inner surface may be achieved by constructing the entire tube wall  44  of titanium. Alternatively, the tube wall  44  may be aluminum, stainless steel, or other material, with a coating of titanium on its inner surface  46 . 
     As is known in the prior art, disposed within the collection chamber is a voltage potential inducer  50  (see  FIG. 4 ). In the depicted embodiment this may be a wire suspended along the axis of the cylinder  32 . A voltage is provided to the inducer  50  of sufficient potential, typically on the order of 5,000-30,000 volts, to induce a coronal discharge within the chamber. Hence a potential is established between the inducer  50  and the walls  44  of the chamber  32 . Contaminant particles entering into this field are electrostatically biased against the inner surface  46  of the chamber wall. 
     In operation, air flow is created through the chamber by a blower ( 22  in  FIG. 1 ,  196  in  FIG. 14 ) blowing contaminated air in the direction A (see  FIG. 3 ). 
       FIG. 4  and  FIG. 5  depict the internal structure of the spiral or swirl injection rinse liquid distributor  34 . Insert  38  includes grooves  60 . Insert  38  and receiver  36  are dimensioned such that when they are assembled together the grooves  60  are covered by the inner surface  40  of the receiver  36 , and rinse channels are thereby defined between them. These rinse channels are in fluid communication with a liquid intake port  82 . The fluid injection path is sealed by a recess 64 that serves as a seat for an O ring seal. 
     The grooves  60  and the rinse channels they form are oriented in a spiral configuration. Each rinse channel is at an angle therefore to the longitudinal axis of the cylinder  32 . As will be appreciated by those of skill in the art, this spiral orientation advantageously avoids the streaking and consequent dry portions of the inner surface  46  of the chamber that was typical of prior art devices. That is, injection of the rinse liquid in a spiral fashion, at an angle to the axis of the tube, promotes 100% wetting. 100% wetting, in the shortest amount of time and/or with the smallest volume of rinse liquid, is further promoted by the titanium surface  46  of the cylindrical chamber  32 . 
     As best seen in  FIG. 5 , the outer portion of the liquid distributor receiver  36  includes an annular seat  68  dimensioned to receive the cylindrical tube  32  comprising the collection chamber. The depth of the seat  68  is dimensioned to correspond to the thickness of the chamber wall  44 . The liquid distributor insert  38  has an inner diameter  66  dimensioned to substantially match the inside diameter of the cylindrical chamber  32 . Accordingly, upon assembly of the tube  32  with the outer liquid distributor receiver  36  and liquid distributor insert  38 , an overall collection chamber assembly  30  having a constant internal diameter is created. At the juncture of the liquid distributor insert  38  and the tube  32  the inner walls of each mate and multiple exit ports  70  for the liquid rinse channels  60  are defined. Rinse liquid exit ports  70  are flush with the constant internal diameter of the overall assembly. Accordingly, the rinse liquid injector assembly advantageously avoids any structure obstructing air flow from the liquid distributor air intake  72  and through the chamber. Therefore the flow of air over the rinse liquid exiting the multiple exit ports  70  further promotes the rapid and complete disbursal of rinse liquid over substantially 100% of the inner surface  46  of the chamber wall. 
       FIGS. 9 ,  10 ,  11 ,  12  and  13  depict an alternative embodiment of the present invention. This alternate embodiment also avoids obstruction of air throughput by components of the liquid distributor, and also uses the air flow over the exit ports to spread, flatten and rapidly distribute the rinsing liquid over the interior wall of the chamber. The alternative embodiment is comprised of a chamber wall  132 , which is again a cylinder in the depicted embodiment. The wall  132  defines within itself a collection chamber having a first diameter. The liquid distributor  134  is assembled to be a single piece in this embodiment. It has an interior wall  166  that defines a second diameter that is smaller than the first diameter defined by the chamber wall  132 . The liquid distributor  134  has an annular extension  142  with an exterior wall  186  that has a diameter substantially corresponding to the interior diameter of the collection chamber wall  132 , so that the later receives the former in close cooperation upon assembly to establish a tight fit. The liquid distributor  134  is further comprised of a housing  180  having at least one liquid intake port(s)  182  that is in fluid communication with the spiral liquid distribution rinse channels  160  and ultimately with the liquid exit ports  170 . The rinse liquid channel is created in the housing  180  by assembling an upper housing portion  180 A with a lower housing portion  180 B, each of which has a trough,  190 A and  190 B respectively, that mate upon assembly and form the rinse channel  190  connecting intake port(s)  182  with spiral rinse channels  160 . Interior rinse channel  190  proceeds through multiple vertical channels  192 . 
     Upon assembly, the liquid exit ports  170  are disposed so that an outer side of the exit port  170  is substantially flush with the first diameter that is the inner wall of the collection chamber. The aperture of the exit ports  170  are on the step  184  that is the inner end of the liquid distribution extension  142 . 
       FIG. 14  is a cutaway view of the collector assembly showing the rinse liquid collection reservoir  194  and a blower  196 . 
     In one embodiment, the particulate collector may be a cylinder having an internal diameter of between about 0.25 inches and about 6.0 inches. The particulate collector may have a length of between about 1.0 inches and about 36 inches. In embodiments with Titanium coatings, the coatings may be from about 0.25 microns to about 6 microns thick. In the depicted embodiments, the cylinder has a diameter of about 2 inches. The rinse liquid ports in the depicted embodiment are spaced about ¾ of an inch apart and the ports have a complex cross section ranging from about 1/64 of an inch to about ¼ of an inch. 
     Test data confirm an unexpected, synergistic effect when combining both a swirl liquid distributor with a titanium collection chamber wall in the configuration disclosed herein, as compared to the effect of either component by itself. The time and liquid volume needed to attain substantially 100% wetting is only marginally increased by combining a swirl liquid distributor as depicted herein with a traditional steel or aluminum inner chamber surface, in a compact contaminant sampling device. At a flow rate of 528 mil/min, 100% wetting was obtained in a range of from 9 to 34 seconds, with an average of about 19 seconds. Little or no improvement is achieved by combining a titanium inner chamber surface with a prior art weir liquid distributor, as compared to a traditional aluminum inner chamber surface combined with a weir liquid distributor, in a compact contaminant sampling device. In fact, 100% wetting was not achieved in experimental apparatuses combining a Titanium coated cylinder with a weir distributor. 
     Surprisingly, combining the swirl liquid distributors depicted herein with a titanium inner chamber surface in a compact contaminant sampling device improves results more than the sum of the individual degrees of improvement attained by each component individually. In a compact sample collector having both a swirl injector and titanium inner surface, substantially 100% wetting was attained faster and with less liquid than the expected sum of the two features tested individually. Hence, test data confirms an unexpected synergy when combining both features. 
     The particulate collector of this invention may attain substantially 100% wetting of said inner surface of said chamber with a rinse liquid flow rate of no more than about 520 milliliters/minute. The particulate collector may attain substantially 100% wetting of said inner surface of said chamber within no more than about 26 seconds. The particulate collector having a collection chamber of titanium coated aluminum may attain substantially 100% wetting of said inner surface of said chamber within no more than about 11 seconds at a rinse liquid flow rate of about 290 milliliters/minute. 
     EXAMPLES 
     In each of the examples, De-ionized (DI) water was used as the rinse liquid. DI water was pumped from a reservoir into the Fluid Distributor. Depending on the flow rate required, one or two diaphragm pumps were used to deliver the DI water to the Fluid Distributor. The DI water was collected in a beaker placed under the test item. 
     Using the test set-up described above, the flow rate required to produce a fully wetted collection surface within approximately 30 seconds was determined for each device configuration. The actual flow rate was calculated by measuring the amount of fluid collected in the beaker per unit time. 
     Using these fluid pump settings, a repetitive series of tests was performed to determine the required time to fully wet the collection surface. The collection surface was air dried between every test using a small fan. 
     Example 1 
     Prior Art 
     Aluminum Chamber Surface with Weir Distributor 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration ID: 01 
               
               
                 Collection Surface Treatment: Bead blasted Al 6061 
               
               
                 Fluid Distributor: Weir 
               
               
                 Serial Number: 01 
               
             
          
           
               
                 Test 
                 Flow Rate 
                 Time to coat 100% 
               
               
                 number 
                 (ml/min) 
                 (sec) 
               
               
                   
               
             
          
           
               
                 1 
                 1750 
                 9 
               
               
                 2 
                 1750 
                 25 
               
               
                 3 
                 1750 
                 13 
               
               
                 4 
                 1750 
                 33 
               
               
                 5 
                 1750 
                 34 
               
               
                 6 
                 1750 
                 26 
               
               
                 7 
                 1750 
                 59 
               
               
                 8 
                 1750 
                 18 
               
               
                 9 
                 1750 
                 20 
               
               
                 10 
                 1750 
                 5 
               
               
                 11 
                 1750 
                 6 
               
               
                 12 
                 1750 
                 13 
               
               
                 13 
                 1750 
                 7 
               
               
                 14 
                 1750 
                 4 
               
               
                 15 
                 1750 
                 30 
               
               
                 16 
                 1750 
                 4 
               
               
                 17 
                 1750 
                 4 
               
               
                 18 
                 1750 
                 35 
               
               
                 19 
                 1750 
                 11 
               
               
                 20 
                 1750 
                 6 
               
               
                 21 
                 1750 
                 4 
               
               
                 22 
                 1750 
                 4 
               
               
                 23 
                 1750 
                 5 
               
               
                 24 
                 1750 
                 6 
               
               
                 25 
                 1750 
                 5 
               
               
                 26 
                 1750 
                 5 
               
               
                 27 
                 1750 
                 4 
               
               
                 28 
                 1750 
                 6 
               
               
                 29 
                 1750 
                 6 
               
               
                 30 
                 1750 
                 11 
               
               
                   
               
             
          
         
       
     
     Example 2A and 2B 
     Swirl Injector with Titanium Coated Aluminum Chamber 
     
       
         
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                   
               
               
                   
                 Flow Rate 
                 Time to coat 100% 
               
               
                 Test number 
                 (ml/min) 
                 (sec) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Configuration ID: 02A 
               
               
                 Collection Surface Treatment: Al with Ti coating 
               
               
                 Fluid Distributor: Swirl injector 
               
             
          
           
               
                 1 
                 285 
                 4 
               
               
                 2 
                 285 
                 4 
               
               
                 3 
                 285 
                 10 
               
               
                 4 
                 285 
                 6 
               
               
                 5 
                 285 
                 4 
               
               
                 6 
                 285 
                 5 
               
               
                 7 
                 285 
                 11 
               
               
                 8 
                 285 
                 5 
               
               
                 9 
                 285 
                 4 
               
               
                 10 
                 285 
                 5 
               
             
          
           
               
                 Configuration ID: 02B 
               
               
                 Collection Surface Treatment: Al with Ti coating 
               
               
                 Fluid Distributor: Swirl injector 
               
             
          
           
               
                 1 
                 290 
                 3 
               
               
                 2 
                 290 
                 3 
               
               
                 3 
                 290 
                 3 
               
               
                 4 
                 290 
                 3 
               
               
                 5 
                 290 
                 3 
               
               
                 6 
                 290 
                 3 
               
               
                 7 
                 290 
                 3 
               
               
                 8 
                 290 
                 3 
               
               
                 9 
                 290 
                 3 
               
               
                 10 
                 290 
                 3 
               
               
                   
               
             
          
         
       
     
     Example 3 
     Swirl Distributor with Polished Titanium Chamber 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration ID: 03 
               
               
                 Collection Surface Treatment: Polished Ti tube 
               
               
                 Fluid Distributor: Swirl injector 
               
             
          
           
               
                   
                 Flow Rate 
                 Time to coat 100% 
               
               
                 Test number 
                 (ml/min) 
                 (sec) 
               
               
                   
               
             
          
           
               
                 1 
                 520 
                 21 
               
               
                 2 
                 520 
                 26 
               
               
                 3 
                 520 
                 19 
               
               
                 4 
                 520 
                 19 
               
               
                 5 
                 520 
                 17 
               
               
                 6 
                 520 
                 23 
               
               
                 7 
                 520 
                 19 
               
               
                 8 
                 520 
                 19 
               
               
                 9 
                 520 
                 16 
               
               
                 10 
                 520 
                 19 
               
               
                   
               
             
          
         
       
     
     Example 4 
     Swirl Distributor with Titanium Coated Steel 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration ID: 04 
               
               
                 Collection Surface Treatment: SST with Ti coating 
               
               
                 Fluid Distributor: Swirl injector 
               
             
          
           
               
                   
                 Flow Rate 
                 Time to coat 100% 
               
               
                 Test number 
                 (ml/min) 
                 (sec) 
               
               
                   
               
             
          
           
               
                 1 
                 365 
                 14 
               
               
                 2 
                 365 
                 32 
               
               
                 3 
                 365 
                 23 
               
               
                 4 
                 365 
                 29 
               
               
                 5 
                 365 
                 24 
               
               
                 6 
                 365 
                 21 
               
               
                 7 
                 365 
                 17 
               
               
                 8 
                 365 
                 21 
               
               
                 9 
                 365 
                 21 
               
               
                 10 
                 365 
                 22 
               
               
                 11 
                 365 
                 27 
               
               
                 12 
                 365 
                 30 
               
               
                 13 
                 365 
                 35 
               
               
                 14 
                 365 
                 35 
               
               
                 15 
                 365 
                 14 
               
               
                 16 
                 365 
                 31 
               
               
                 17 
                 365 
                 30 
               
               
                 18 
                 365 
                 21 
               
               
                 19 
                 365 
                 31 
               
               
                 20 
                 365 
                 23 
               
               
                 21 
                 365 
                 29 
               
               
                 22 
                 365 
                 31 
               
               
                 23 
                 365 
                 21 
               
               
                 24 
                 365 
                 49 
               
               
                 25 
                 365 
                 28 
               
               
                 26 
                 365 
                 30 
               
               
                 27 
                 365 
                 23 
               
               
                 28 
                 365 
                 35 
               
               
                 29 
                 365 
                 36 
               
               
                 30 
                 365 
                 27 
               
               
                   
               
             
          
         
       
     
     Example 5 
     Swirl Distributor with Aluminum Chamber 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration ID: 05 
               
               
                 Collection Surface Treatment: Bead blasted Al 6061 
               
               
                 Fluid Distributor: Swirl Injector 
               
               
                 Serial Number: 01 
               
             
          
           
               
                   
                 Flow Rate 
                 Time to coat 100% 
               
               
                 Test number 
                 (ml/min) 
                 (sec) 
               
               
                   
               
             
          
           
               
                 1 
                 528 
                 11 
               
               
                 2 
                 528 
                 22 
               
               
                 3 
                 528 
                 23 
               
               
                 4 
                 528 
                 17 
               
               
                 5 
                 528 
                 11 
               
               
                 6 
                 528 
                 28 
               
               
                 7 
                 528 
                 32 
               
               
                 8 
                 528 
                 22 
               
               
                 9 
                 528 
                 26 
               
               
                 10 
                 528 
                 22 
               
               
                 11 
                 528 
                 20 
               
               
                 12 
                 528 
                 27 
               
               
                 13 
                 528 
                 34 
               
               
                 14 
                 528 
                 15 
               
               
                 15 
                 528 
                 13 
               
               
                 16 
                 528 
                 16 
               
               
                 17 
                 528 
                 23 
               
               
                 18 
                 528 
                 21 
               
               
                 19 
                 528 
                 25 
               
               
                 20 
                 528 
                 17 
               
               
                 21 
                 528 
                 28 
               
               
                 22 
                 528 
                 11 
               
               
                 23 
                 528 
                 16 
               
               
                 24 
                 528 
                 16 
               
               
                 25 
                 528 
                 11 
               
               
                 26 
                 528 
                 15 
               
               
                 27 
                 528 
                 16 
               
               
                 28 
                 528 
                 9 
               
               
                 29 
                 528 
                 11 
               
               
                 30 
                 528 
                 12 
               
               
                   
               
             
          
         
       
     
     In  FIG. 15 , the y-axis left hand scale illustrates the time needed to achieve 100% wetting for each of the different versions from the examples, which are along the x-axis. The vertical bar extends from the fastest time to the slowest time for individual test runs, and a numerical average for each example version is given within the vertical bar at the oval. As can be seen, the lowest times achieved with any reliable consistency are with Example 2, a swirl distributor combined with titanium coated aluminum. 
       FIG. 15  also depicts the rinse liquid volume required to achieve 100% wetting with each of the different versions with the right hand scale of the y-axis. An oval with an X marks rinse liquid volumes. As can be seen, the prior art device having a Weir distributor and no titanium surface requires the most liquid by far, a disadvantage. All of the titanium coated examples have been proven to require a smaller volume of rinse liquid to achieve 100% wetting. 
       FIG. 15  combines the data for time results and rinse liquid volume results to illustrate the performance of all versions combining swirl injection with titanium chamber walls. As can be seen, Example 2, the combination of the swirl injector with titanium coated aluminum, surprisingly achieves advantageous results in both reduced time and reduced liquid volume required for 100% wetting, as compared to the other examples. 
     As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.