Patent Application
20070295207
The present invention is described in detail below with reference to the attached drawing figures, wherein:
Embodiments of the present invention relate to an electrostatic device that utilizes electrostatics to collect particles from gas, such as air. The particles are collected onto a collection surface such as walls or a collection post to concentrate the particles. The particles collected may be analyzed by visual inspection of the collection surface and/or heating the collection surface to vaporize the particles for subsequent detection by a downstream collector. Target particles collected may include, but are not limited to, biologicals, such micron and submicron bioaerosols, molds, pollen, fungi, bacteria, viruses and bacteriophages, chemicals such as low vapor pressure chemicals (LVPCs), explosives, toxins and other particles.
With reference to
With reference to
Multiple rows 19 of electrodes 24 may be used to help improve collection efficiency. Each additional row of electrodes 19 improves collection efficiency by increasing the plasma area of the corona charging zone 18. There are three rows 19 of electrodes 24 shown in
Exemplary collection post 22 is shown in
More than one post 22 may be located in the electrostatic device 10. The collection post 22, while shown as being round, may be polygonal, rectangular, square or any variety of other shapes. Round is preferred, however, to minimize the occurrence of reverse corona generation which can affect collection efficiency. The one or more collection posts 22 may be removable. It will be appreciated that the post 22 may be non-perforated or perforated.
To improve the particle collection, or enable the ability to collect vapors, on the surface of the collection post 22, a chemical adsorbent may be used to coat the surface of the collection post 22. Exemplary chemical adsorbents may include polymers such as polyether ether ketone and polytetrafluoroethylene.
Referring again to
Housing 12 encases the air passage 16, corona charging zone 18, collection post 22 and air mover 14. It will be appreciated that housing 12 may be any type including modular housing. Air mover 14 may be any variety of air movers, including fans. Exemplary air movers include commercial, of the shelf fan, such as small muffin fans like those generally used to aid in the cooling of computer processors.
Utilizing a muffin fan, the sampling flow rate for the collection device 10 can be varied from about 20 to 100 L/min with a collection efficiency about >90% for 1 μm particles at a flow rate of about 20 L/min.
A variety of power supplies may be utilized to power collection device 10. The power supplies include internal and external power supplies. The power supply may power the air mover 14, electrodes 24, heating of the collection post 22 and removal of the vaporized particles.
After collection is completed, particles collected on the collection post 22 may be analyzed by 1) visual inspection of the collection post 22 and/or 2) heating the collection post 22 to vaporize the collected particles for subsequent detection by a downstream collector.
For visual inspection, the particles are concentrated onto small collection surface, such as collection post 22, for visual inspection. The decreased size of the collection surface allows more collected particles to be viewed by visual inspection. Visual inspection may be aided by the use of microscopes, raman laser interrogation, UV spectroscopic techniques and the like.
The heating of the collection post 22 after collection converts collected particles into a vapor form usable by detectors, such as chemical detectors, mass spectrometry (such as a MEMS mass spectrometer), and ion mobility spectrometry. The detectors may be part of the collection device 10 or may be located separate from the collection device 10.
The heating method used to heat the collection post 22 may vary depending on the target particle(s) to be vaporized for collection. Different particles will vaporize at different temperatures and vapor pressure. For instance, the collection post 22 may be continuously heated to just below the vaporization temperature of the target material during and/or after collection. This is done to avoid concentration of “interferent” particles while still allowing the concentration of the target particles. Alternatively, the collection post 22 may be heated slowly after collection. For quick vaporization of collected particles, the collection post 22 may be rapidly heated after collection. The collection post 22 may be heated in stages at different temperatures to obtain the vapor from selected particles at varying time periods or to find out more information about the collected particles. The vaporization temperature of the particles depends on its chemical makeup, for instance readily available pesticides may vaporize between 160 and 250° C., while biological organisms may pyrolize at or above 400° C.
Heating of collection post 22 may be done in a variety of ways including, but not limited to, an internal cartridge heater, coil heating, contact heating, and laser ablation of particles on collection surface.
By way of example, and not by limitation, a COTS heating element is utilized to heat the collection post after the collection process is complete. Because of the small size and low mass of the collection post 22 as well as heating unit, the ramp rate is targeted to be 15° C,/second enabling the post to change from about 0° C. to 200° C. in less than 15 seconds. After the collection post 22 has met the targeted maximum temperature it dwells for a brief pre-determined period of time to ensure that all material has been vaporized.
Vaporization of particles can occur in fixed air volume contained or moved through the air passage 16. The concentration of vapor from the particles will depend on the airflow rate.
Once the particles have been vaporized, the resulting vapor is drawn through either an external port in the device 10 or through the existing outlet by the air mover 14, or through perforations in the collection post for subsequent detection. The transport of the vapor will be controlled either through a secondary port on the side of the device 10, or by the primary exit by re-activating the air mover 14.
By way of example, an not by limitation, in order to meet a target time of about two minutes for start to alarm for detection—the collection, concentration, and thermal desorption of target particles is less than about 1 minute and 30 seconds. To achieve this target, the projected maximum cycle time for each phase of the collection device is about 45 seconds for collection/concentration, about 30 seconds for thermal desorption, (heating of collection post 22) about 15 seconds for vapor transfer and about 30 seconds for the collection post 22 to cool-down. This exemplary cycle is shown in
The exemplary collection post 23 in
The charged particles are attracted by electrostatic forces and are collected on the perforated collection post 23 in the center of the device 10. The particles are collected on the perforated post 23 until the desorption cycle is initiated. After the post 23 is heated, vapors are drawn through the perforated post 23 and directly into a transfer tube connected at the base of the post and in communication with the inside of the post (not shown), rather than being allowed to fill the primary air passage 16 and device 10 volume before being drawn off. This allows for increased concentration of particles in the desorption vapor. The vapor may then be transferred to a vapor based detection system, or collected in standard available chemical sampling sorbent tubes for storage, transport, or later analysis.
The perforated post may be heated in a variety of ways including a coiled heater that allows the perforated collection post 23 to be heated quickly to convert the captured particles into vapor rapidly. The perforated collection post 23 may be heated after collection, continuously or in steps. Any number of rows of electrodes may be utilized, preferably, with a perforated post 23 two rows of electrodes are utilized to reduce costs and power consumption.
It will be appreciated that the electrostatic device 10 described typically uses lower power than other electrostatic applications, primarily due to a current control feedback method which maintains proper power to the array. Furthermore, the radial collector geometry of the electrostatic device 10 shown in
With reference to
The device 30 comprises an air passage 52, at least one corona charging zone 54, a collection surface 38, an air mover 50, shutters 34 and 36 and housing 56. The device 30 brings a gas, such as air, into primary air passage 52 utilizing air mover 50. Air mover 50 draws gas, such as air, through the air passing 52 with the shutters 34 and 36 open. The electrodes 48 create at least one corona 54 as shown in
With reference to
Air passage 52 is formed by an enclosure such as walls 58 or a duct. Air passage 52 may be any shape including, round, polygonal, square, rectangular and oval. The air passage 52 may be any size necessary for collection.
The walls 58 or the primary air passage 52 may also serve as a collection surface 38 as shown in
Housing 56 encases the primary air passage 52, one or more corona charging zones 48, collection surface 38 and air mover 50. It will be appreciated that housing 56 may be any type including modular housing. Air mover 50 may any variety of air movers, including fans. Exemplary air movers include a COTS fan.
Utilizing an air mover, the sampling flow rate for the collection device 30 can be varied depending on the efficiency needed. It will be appreciated that the flow rate, collection efficiency and target particle size may vary.
A variety of power supplies may be utilized to power the collection device 30. The power supplies include internal and external power supplies. Exemplary power supplies may power one or more of the air mover, electrodes, heating of the collection surface and removal of vaporized particles.
After collection is completed, particles collected on the collection surface 38 may be analyzed by 1) visual inspection of the collection surface and 2) heating the collection surface to vaporize the collected particles for subsequent detection by a collector.
For visual inspection, the particles are concentrated on the collection surface 38 for visual inspection. Visual inspection may be aided by the use of microscopes and the like.
The heating of the collection surface 38 after collection converts collected particles into a vapor form usable by detectors, such as chemical detectors, mass spectrometry, ion mobility spectrometry, and differential mobility spectrometry. The detectors may be part of the collection device or may be located separately from the collection device 30.
The heating method used to heat the collection surface 38 may vary depending on the target particle(s) to be vaporized for collection. Different particles will vaporize at different temperatures and vapor pressure. For instance, the collection surface 38 may be continuously heated during and/or after collection, just below the vaporization temp of the target material to avoid concentration of “interferent” particles while still allowing the concentration of target particles. The collection surface 38 may be heated slowly after collection. For quick vaporization of the collected particles, the collection surface 38 may be rapidly heated after collection. The collection surface 38 may also be heated in stages and at different temperatures to obtain the vapor from selected particles at varying time periods or to find out more information about the collected particles.
It will be appreciated that conversion of collected particles on collection surface 38 may occur continuously or after air mover 50 has stopped. When conversion of captured particles on collection surface 38 is desired after air mover 50 is stopped, collection surface 38 is heated to drive off the collected particles as a vapor with the shutters 34 and 36 closed to minimize escape of the desorbed vapor.
The heating of collection surface 38 may be done in a variety of ways, including, but not limited to, utilizing an internal cartridge heater and/or a coil heater, contact heating, laser ablation of particles on the collection surface.
Once the particles are driven off as vapor, the vapor 46 may be transferred via transfer port 40. The vapor 46 may be transferred to a variety of detectors or may be collected as a sample. Although transfer port 40 is shown as being centrally located in the collection device 30, it will be appreciated that the transfer port 40 may be located anywhere within the device 30, upstream of air mover 50. Device 30 allows for a high collection area and high capture and conversion efficiency.
From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent in the structure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
