Method to determine precisely the size of small particles via vapor condensation

Abstract

Improvement are proposed to increase the size accuracy and resolving power with which variants of the variable saturation condensation particle sizer (VSCPS) of Gallar et al. (2006) may characterize particles suspended in a gas. One essential component of this invention is an efficient method to achieve saturation of the gas flow passing through a saturation chamber, independently from the value of the gas flow rate through that chamber. The resulting strict linearity between the maximum vapor saturation ratio achieved in the instrument and the finely controlled gas flow rate through the saturator facilitates the precise inference of particle size, as well as the possibility to determine size without lengthy calibrations. Also described is a novel approach to introduce the particles to be sized in the center of a stream of vapor laden sheath gas. The new sheathing method delays the flow instability in prior sheathing schemes, where the aerosol was injected from a centered capillary into the surrounding sheath gas/vapor mixture. In one embodiment of this invention, the centered aerosol flow is fed at the bottom of a cylindrical tube, while the gas/vapor mixture enters laterally through the porous walls of this tube. This mixing approach is intrinsically stable over a much wider range of flow rates of sheath and aerosol, allowing for improvements in sizing resolution. In another embodiment the flow in the mixing region is stabilized by accelerating the gas either in the missing region or after it. A method to infer a condensation size without the need of extensive calibration or complex numerical computations is also disclosed.

Dependencies are inferred from the claim text.