The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Electrostatic deposition and electrical mobility size separation of airborne particles are widely used techniques for the collection or analysis of airborne particles. These methods require that the particles to be collected or analyzed carry an electric charge. However, for very small particles with diameters less than about 50 nm, adding an electrical charge is difficult. In this size range exposure to a bipolar ion source provides singly charged particles, but the charging efficiency is low. For particles with diameters of 50 nm, just 17% of the particles will acquire a positive charge, with an approximately equal number acquiring a negative charge. At 10 nm the fraction of particles charged with a single polarity is .about.4%, and at 3 nm this drops to less than 2%. Unipolar charging can improve charging efficiencies for particles above about 10 nm, but it also becomes ineffective at smaller particle sizes.
"One technique that has been used to increase the charging efficiency of these small particles is condensation-enhanced particle charging, wherein the particles are grown through condensation, charged and re-evaporated. Some prior art techniques have used butanol condensation to prepare highly charged particles in the 10-30 nm size range. Others have used condensation of glycol to enhance the charging of sub-20 nm particles. Still others have explored this approach with water condensation, albeit for larger (80-130 nm) particles. Limitations of these existing methods are: (1) the contamination of the particle through the use of organic materials as the condensing vapor, (2) addition of multiple electrical charges to each particle, and (3) inability to charge particles below about 10 nm."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "A system and method to provide efficient, low-level electrical charging of particles in the sub-100 nm size range is disclosed. This method uses an ion source coupled to a laminar flow water condensation and evaporation cell. Ions are introduced together with a particle-laden flow into a water condensation and evaporation device. In the presence of the ions, particles grow through water condensation, collide with the ions to become charged, and then quickly evaporate to return the particle to near its original size. The dried particle retains the electrical charge acquired as a droplet, leaving a higher fraction of charged particles than entered the system. The time as a droplet can be short, less than 200 milliseconds. With this short residence time the opportunities for chemical artifacts are minimized. The process occurs in a laminar flow, wherein the saturation ratios can be controlled, and calculated.
"A particle charging method and apparatus are provided. An ion source is applied to a particle laden flow. The flow is introduced into a container in a laminar manner. The container has at least a first section, a second section and a third section. The first section includes wetted walls at a first temperature. A second section adjacent to the first section has wetted walls at a second temperature T2 greater than the first temperature T1. A third section adjacent to the second section has dry walls provided at a temperature T3 equal to or greater than T2. Additional water removal and temperature conditioning sections may be provided.
"This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 is a schematic of a nanoparticle condensation charger in accordance with the present technology.
"FIG. 2 is a graph of the calculated saturation ratio (top) and droplet diameter (bottom) as a function of axial position for a system operated to produce saturations sufficient to activate 3 nm particles.
"FIG. 3 shows a configuration of the nanoparticle condensation charger with two additional stages added for water vapor removal and temperature recovery.
"FIG. 4A illustrates a system condensation-evaporator for the nanoparticle charger.
"FIG. 4B is a cross sectional view of the system of FIG. 4A, showing two of the three parallel tubes used for particle growth and evaporation.
"FIG. 5A shows the typical wall temperatures used in the operation and testing of the system of FIG. 4A.
"FIG. 5B shows, for the scenario of FIG. 5A, the saturation ratios calculated for flow trajectories along the centerline.
"FIG. 5C shows, for the scenario of FIG. 5A, the dew point values calculated for flow trajectories along the centerline.
"FIG. 6 illustrates the experimental configuration used to measure the charging efficiency and charge distribution produced by a condensation-evaporator nanoparticle charger.
"FIG. 7A shows the mobility distribution output by the nanoparticle charger of the configuration shown in FIG. 1 using a bipolar ion source, when presented with a test aerosol is centered at 25 nm.
"FIG. 7B shows the mobility distribution obtained with the system of FIG. 7A for an input aerosol centered at 10 nm.
"FIG. 8A shows the mobility distribution output by the nanoparticle charger of the configuration shown in FIG. 4 using a bipolar ion source, when presented with a test aerosol is centered at 20 nm. Singly charged 20 nm particles appear at a mobility size of 20 nm, while multiply charged particles, being more mobile, appear at smaller mobility diameters. The mobility distribution for simple, bipolar charging is also shown.
"FIG. 8B shows the mobility distribution obtained with the system of FIG. 8A for an input aerosol centered at 10 nm."
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