Method and apparatus for measuring size distribution of particles using a three-dimensional alternating current electric field

Claim 2

Apparatus for measuring the size distribution of particles including particulate matter in a gas sample comprising means for saturating a gas sample containing various particles including particulate matter with a condensible vapor, a duct having an input end in communication with an output of said vapor saturating means, means positioned in said duct intermediate the input and output ends thereof for electrically charging the particles in the gas sample, an expansion chamber having an input in communication with an output end of said duct, pump means in communication with an output of said expansion chamber for developing a flow of the gas sample from said vapor saturating means through said duct to said expansion chamber and therefrom, means positioned within said expansion chamber for generating a three-dimensional multipolar alternating current electric field which traps and confines charged particles in a particular range of charge-to-mass ratio and directs charged particles outside the particular range of charge-to-mass ratio to sides of said chamber and thereby accomplishes mass-selective sorting of the charged particles which is not sensitive to the gas flow rate through the apparatus, and is not dependent on the proximity of the particles to an electrode, means associated with said expansion chamber for causing expansion of the condensible vapor saturated gas sample therein to produce cooling and supersaturation thereof whereby droplets condense on the particles, and means in communication with a region within said expansion chamber containing the confined particles for detecting the relative number of the droplets which correspond to a like relative number of the charged particles in the particular range of charge-to-mass ratio occurring in the gas sample.

Claim 3

The apparatus set forth in claim 1 wherein said condensible vapor saturating means consists of a vessel partially filled with a relatively high vapor pressure liquid and having an input open to the gas sample being analyzed and an output connected to the input end of said duct.

Claim 4

The apparatus set forth in claim 1 wherein said three-dimensional Field generating means comprises three electrodes including a centrally oriented hollow cylindrical electrode and two substantially flat electrodes disposed along both open ends of said cylindrical center electrode in spaced apart relationship therefrom, and an alternating current power supply having an output connected to said center electrode whereby said center electrode is supplied with alternating current voltage and the three electrodes generate a three-dimensional quadrupole alternating current electrodynamic field.

Claim 5

The apparatus set forth in claim 3 wherein said three electrodes are formed of an electrically conductive mesh and are spaced apart from sides of said expansion chamber.

Claim 6

The apparatus set forth in claim 4 wherein said flat end electrodes are oriented parallel to each other and perpendicular to the longitudinal axis of the cylindrical center electrode.

Claim 7

The apparatus set forth in claim 5 wherein the diameter of said cylindrical electrode is in the range of 1/2 to 1 inch.

Claim 8

The apparatus set forth in claim 6 wherein the diameter of the conductors in the mesh is approximately 0.010 inch and the center-to-center spacing between adjacent conductors is approximately 0.100 inch.

Claim 9

The apparatus set forth in claim 3 wherein the alternating current power supply is controllably variable over a range of 0.5 to 5 kilovolts and a frequency range of 60 to 10,000 hertz.

Claim 10

The apparatus set forth in claim 3 and further comprising a direct current power supply, and first switch means for connecting said end electrodes to said direct current power supply whereby said end electrodes are maintained at a unidirectional potential slightly negative with respect to said cylindrical center electrode or at ground potential.

Claim 11

The apparatus set forth in claim 3 and further comprising a direct current power supply, and first switch means for connecting said center electrode to said direct current power supply whereby said center electrode is further supplied with direct current voltage of magnitude up to several hundred volts to thereby obtain a more narrow range of the charge-to-mass ratio of particles being analyzed.

Claim 12

The apparatus set forth in claim 3 and further comprising first switch means for connecting said alternating current power supply to said center electrode, a high voltage direct current power supply having a voltage output in a range up to 10 kilovolts, and second switch means for connecting said direct current power supply to said center electrode, an open state of said first switch means and closed state of said second switch means resulting in application of only a high direct current voltage to said center electrode for generating a high strength constant direct current field which effectively sweeps out all of the charged particles in the volume defined by the center and end electrodes and permits only the neutral particles in the gas sample to remain therein for determination of the neutral particle background.

Claim 13

The apparatus set forth in claim 1 wherein said gas sample expansion means comprises a first valve connected at the input of said expansion chamber, a second duct having an input end connected to the output of said expansion chamber, a second valve connected in said second duct at an output of said expansion chamber, and a third valve connected in said second duct adjacent an output end thereof, said pump means connected in said second duct downstream of said third valve, the second duct between said second and third valves forming a volume into which the gas sample in said expansion chamber is expanded.

Claim 14

The apparatus set forth in claim 12 wherein the second duct between said second and third valves is of elongated length for defining an appreciable volume.

Claim 15

The apparatus set forth in claim 12 wherein the second duct between said second and tHird valves is of foreshortened length but includes an enlarged portion for defining an appreciable volume.

Claim 16

The apparatus set forth in claim 8 wherein a particular value of the alternating current voltage and frequency determines a particular range of charge-to-mass ratio of particles to be trapped in the three-dimensional quadrupole alternating current electrodynamic field, and means for varying the voltage and, or, frequency of said alternating current power supply whereby a decrease in the voltage and, or, increase in the frequency results in a second particular range of charge-to-mass ratio of the charged particles being trapped and confined in the quadrupole field.

Claim 17

The apparatus set forth in claim 1 wherein said droplet detecting means comprises an intense light source for providing illumination of the droplets condensed on the confined particles, photocell means for detecting the illuminated droplets, and read-out means for establishing a count representing the relative number of particles detected by said photocell means.

Claim 18

The apparatus set forth in claim 16 wherein said photocell means is oriented at 90* relative to said intense light source for detecting the light scattered off the droplets.

Claim 19

The apparatus set forth in claim 16 wherein said intense light source and said photocell means are in alignment and disposed adjacent opposite sides of said expansion chamber for detecting the droplets by detecting the absorption of the light by the droplets.

Claim 20

The apparatus set forth in claim 3 wherein said three electrodes consist of three coatings of an electrically conductive material attached on inner surfaces of top, bottom and side walls of said expansion chamber, a first of the three coatings attached along the top wall of said chamber, a second coating attached along the bottom wall of said chamber, and a third of said coatings attached along the side walls of said chamber to form a generally cylindrical coating, said first and second coatings spaced from said third coating to provide electrical insulation therebetween.

Claim 21

Apparatus for measuring the size distribution of particles including particulate matter in a gas sample comprising means for saturating a gas sample containing various charged particles including particulate matter with a readily condensible vapor, said vapor saturating means having an input end open to the ambient containing the gas sample, a first duct having an input end in communication with an output of said vapor saturating means, a chamber having an input in communication with an output end of said first duct, a second duct having an input end in communication with an output of said chamber, pump means in communication with an output end of said second duct for developing a flow of the gas sample from said vapor saturating means through said first duct to said chamber and therefrom through said second duct, means positioned within said chamber for generating a three-dimensional quadrupole alternating current electrodynamic field which traps charged particles in a particular range of charge-to-mass ratio as determined by the particular voltage and frequency of an alternating current power supply associated with said quadrupole field generating means whereby the charged particles in the particular range of charge-ro-mass ratio remain confined within the quadrupole field and the charged particles outside the particular range of charge-to-mass ratio are swept to sides of said chamber to thereby accomplish mass-selective sorting of the charged particles, valve means connected in said first and second ducts for controlling the flow of the gas sample into and from said chamber, said chamber initially being evacuated to approximately 80 percent of the ambient pressure by said pump means and a first state of said valve means, the gas sample being introduced into said chamber in a second state of said valve means until the Pressure within said chamber reaches substantially ambient pressure at which time said valve means is operated into a third state to cause expansion of the gas sample to thereby produce cooling and supersaturation thereof resulting in formation of droplets condensing on the particles in said chamber, and means in optical communication with a selected region within said chamber containing the confined particles for detecting the relative number of the droplets therein which correspond to a like relative number of the charged particles in the particular range of charge-to-mass ratio occuring in the gas sample.

Claim 22

Apparatus for measuring the size distribution of particles including particulate matter in a gas sample comprising means for saturating a gas sample containing various charged particles including particulate matter with a readily condensible vapor, said vapor saturating means having an input end open to the ambient containing the gas sample, a first duct having an input end in communication with an output of said vapor saturating means, a chamber having an input in communication with an output end of said first duct, a second duct having an input end in communication with an output of said chamber, pump means in communication with an output end of said second duct for developing a flow of the gas sample from said vapor saturating means through said first duct to said chamber and therefrom through said second duct, means positioned within said chamber for generating a three-dimensional quadrupole alternating current electrodynamic field which traps charged particles in a particular range of charge-to-mass ratio as determined by the particular voltage and frequency of an alternating current power supply associated with said quadrupole field generating means whereby the charged particles in the particular range of charge-ro-mass ratio remain confined within the quadrupole field and the charged particles outside the particular range of charge-to-mass ratio are swept to sides of said chamber to thereby accomplish mass-selective sorting of the charged particles, valve means connected in said first and second ducts for controlling the flow of the gas sample into and from said chamber, said chamber initially being evacuated to approximately 80 percent of the ambient pressure by said pump means and a first state of said valve means, the gas sample being introduced into said chamber in a second state of said valve means until the Pressure within said chamber reaches substantially ambient pressure at which time said valve means is operated into a third state to cause expansion of the gas sample to thereby produce cooling and supersaturation thereof resulting in formation of droplets condensing on the particles in said chamber, and means in optical communication with a selected region within said chamber containing the confined particles for detecting the relative number of the droplets therein which correspond to a like relative number of the charged particles in the particular range of charge-to-mass ratio occuring in the gas sample.

Claim 25

The method set forth in claim 21 wherein the step of generating the three-dimensional multipolar alternating current electric field consists of applying an alternating current voltage having a predetermined first amplitude and frequency to the centrally oriented of three electrodes positioned within the expansion chamber to thereby generate a three-dimensional quadrupole alternating current electrodynamic field which traps and confines charged particles in the first particular range of charge-to-mass ratio as determined by the particular voltage and frequency values of the alternating current voltage.

Claim 26

The method set forth in claim 22 and further comprising the steps of repeating the steps of evacuating the expansion chamber to approximately 80 percent of the ambient pressure and saturating the gas sample with the readily condensible vapor and electrically charging the particles and developing the gas sample flow through the duct into the expansion chamber, adjusting the alternating current voltage source to provide a second set of particular voltage and frequency values of the alternating current voltage corresponding to a particular second range of charge-to-mass ratio of particles to be trapped and confined in the quadrupole field, applying the second set of values of alternating current voltage to the center electrode to thereby repeat the step of generating a three-dimensional quadrupole field within the expansion chamber for trapping and confining charged particles in the particular second range of charge-to-mass ratio, repeating the steps of expanding the gas sample in the expansion chamber and detecting the relative number of confined droplets in the particular second range of charge-to-mass ratio to thereby determine the size distribution of the charged particles in the gas sample over two ranges of charge-to-mass ratio.

Claim 27

The method set forth in claim 21 wherein the step of expanding thE gas sample consists of closing a first valve at the entrance to the expansion chamber and opening a second valve at the exit of the chamber while maintaining a third valve located downstream of the second valve in a second duct in a closed position whereby the gas sample expands into the second duct between the second and third valves.

Claim 28

The method set forth in claim 21 and further comprising the steps of removing the alternating current voltage applied to the center electrode, applying a high direct current voltage to the center electrode in the order of several thousand volts to thereby generate a high strength constant direct current electric field which effectively sweeps out all of the charged particles and confines only neutral particles in the gas sample, expanding the gas sample in the expansion chamber to thereby cause formation of droplets on the particles including the neutral particles confined in the volume defined by the electrodes, and detecting the relative number of confined droplets which correspond to a like relative number of neutral particles in the gas sample to thereby determine the neutral particle background which is generally present in each of the particular ranges of charge-to-mass particle count measurements.

Claim 29

The method set forth in claim 21 wherein the step of detecting the relative number of confined droplets in the expansion chamber consists of directing a high intensity light into a particular region of the expansion chamber containing the confined droplets, detecting the scattered light reflected by the confined droplets in the particular region of the expansion chamber, and obtaining a count corresponding to the relative number of confined droplets detected in the particular region of the expansion chamber.

Claim 30

The method set forth in claim 21 wherein the step of detecting the relative number of confined droplets in the expansion chamber consists of directing a high intensity light into a particular region of the expansion chamber containing the confined droplets, detecting the light absorbed by the confined droplets in the particular region of the expansion chamber, and obtaining a count corresponding to the relative number of confined droplets detected in the particular region of the expansion chamber.