Design and Characterization of a New, Water-Based, High Sample-Flow Condensation Nucleus Counter

Abstract

We describe the development and performance of a new, continuous-flow, single-particle, condensation nucleus counter (CNC) that uses water as its working fluid. Supersaturation is generated both through mixing of the ambient temperature sample gas stream with a hot saturated gas stream and by cooling of this mixed gas stream. Nucleation and condensation upon the entrained particles occurs within a cooled growth tube and a laser-based optical counter detects the enlarged particles. This Modified-Mixing CNC (MMCNC) samples gas at 0.5 cfm (14.1 lpm), has a false count rate of 0.012/cf, and has a unity counting efficiency for NaCl particles larger than 12 nm in diameter.These attributes make it an ideal instrument for next-generation cleanroom monitoring, where it can be plumbed into an existing DI water line and run without the need for frequent maintenance. Its use of water and high flow rate may also give it a unique advantage for atmospheric and indoor air research applications. We characterize the MMCNC's performance by varying four critical variables affecting its operation. A simple model accounting for heat and mass transfer to the growth tube is successful at predicting the relative importance of each of these variables and in estimating the average supersaturation in the growth tube.