Benjamin Y. H. Liu’s research while affiliated with University of Minnesota, Duluth and other places

A method and apparatus are disclosed for exposing particles in a gas in order to cause the charge on the particles to change, the apparatus comprising a chamber having a conductive wall with a gas inlet and a gas outlet. An electrode with an exposed tip is in the chamber, the electrode being held at a different potential from the ground potential. The electrode is connected to a source of voltage sufficient to cause a corona discharge to occur forming ions in the chamber, and creating a region with a high electric field intensity and another region in which the electric field intensity is lower. The inlet and outlet define a gas flow path from the inlet to the outlet such that the gas flow path passes mainly through the region with the lower electric field intensity.

An apparatus and method for sampling and measuring air born particulate matter includes an inlet for the particulate containing gas to enter. A mechanism then removes coarse particles larger than a selected size while permitting filtered particles of less than the selected size to pass through. A chamber containing a quartz crystal sensor permits the filtered particles that have passed through to deposit to create an output signal in response to the deposited particle mass.

A novel water-based condensation particle counter has been developed using a patented, single-flow mixing (SFM) condenser that permits a conventional thermal approach of using a hot saturator followed by a cold condenser to activate and grow particles for counting with an optical detector. A computational fluid dynamics (CFD) model of the internal flow, temperature, and vapor profiles was used to predict the effectiveness of the SFM condenser. Using the results from the CFD model, the counting efficiency was numerically calculated for pure water droplets, and the CPC cut-point (i.e., 50% counting efficiency) was predicted to be 8.3 nm. The experimental performance of the new CPC was measured with differential mobility analyzer-classified, monodisperse particles. The measured cut-points were 8.2 nm for Ag particles and 3.9 nm for NaCl particles. The reduction in the cut-point for NaCl is the result of a compound effect: water uptake by NaCl particles, which increases their size before entering into the growth section (condenser), and the reduction of the equilibrium vapor pressure of water over NaCl-water droplets, resulting in a decrease of the activation diameter. Copyright © 2016 American Association for Aerosol Research

A novel instrument has been developed for generating highly monodisperse aerosol particles with a geometrical standard deviation of 1.05 or less. This aerosol generator applies a periodic mechanical excitation to a micro-liquid jet obtained by aerodynamic flow-focusing. The jet diameter and its fastest growth wavelength have been optimized as a function of the flow-focusing pressure drop and the liquid flow rate. The monodisperse aerosol generated by this instrument is also charge neutralized with bipolar ions produced by a non-radioactive, corona discharge device. Monodisperse droplet generation in the 15- to 72-μm diameter range from a single 100-micron nozzle has been demonstrated. Both liquid and solid monodisperse particles can be generated from 0.7- to 15-μm diameter by varying solution concentration, liquid flow rate, and excitation frequency. The calculated monodisperse particle diameter agrees well with independent measurements. The operation of this new monodisperse aerosol generator is stable and reliable without nozzle clogging, typical of other aerosol generators at the lower end of the operating particle size ranges.Copyright © 2016 American Association for Aerosol Research

Methods and apparatus for recovery of precursor vapor from a gas and precursor vapor mixture used in a deposition process. The gas and precursor vapor mixture is passed through a multitude of heat transfer surfaces in a heat conducting housing causing the precursor vapor to condense. The precursor vapor in liquid form is then collected after condensation.

The present disclosure describes a method and apparatus for detecting particles in a gas by saturating the gas with vapor and causing the gas to flow through a chamber with walls that are at a temperature different than the temperature of the entering gas creating a gas turbulence within the chamber resulting in the gas becoming super-saturated with vapor and causing said super-saturated vapor to condense on said particles and form droplets, which are then detected and counted by an optical light-scattering detector.

The present disclosure describes a method and apparatus for detecting particles in a gas by saturating the gas with vapor and causing the gas to flow through a chamber with walls that are at a temperature different than the temperature of the entering gas creating a gas turbulence within the chamber resulting in the gas becoming super-saturated with vapor and causing said super-saturated vapor to condense on said particles and form droplets, which are then detected and counted by an optical light-scattering detector.

The present disclosure relates to an apparatus and a method for vaporizing a liquid to form vapor preferably in a gas stream. The apparatus includes a composite metal structure, the structure comprising a plurality of passageways for providing heat to vaporize the liquid in the gas stream to form a gas/vapor mixture. A non-corrosive interface lies between the metal structure and the gas/vapor mixture, the interface being chemically inert to the gas/vapor mixture and the structure permitting heat to be conducted rapidly therethrough to vaporize the liquid. The apparatus further includes an inlet for the gas and an inlet for the liquid to be vaporized to flow into the plurality of passageways and an exit through which the gas/vapor mixture exits the apparatus.