A New Horizontal Gradient, Continuous Flow, Ice Thermal Diffusion Chamber

Abstract

A continuous-flow, horizontal gradient, ice thermal diffusion chamber has been developed and tested for heterogeneous ice nucleation of aerosol particles under accurately controlled supersaturations and supercooling in the absence of a substrate. The chamber consists of preprocessing, main, and crystal settling sections. In the preprocessing and main sections, top and bottom plates are coated with clear, smooth ice by a new method. The main section maintains a range of supersaturations across the sample flow. Sample air is sandwiched with filtered and predried air to avoid wall effects and transient supersaturations. Nucleated crystals are received on Mylar copy film in the settling section and processed for analysis based on their temperatures and supersaturations at nucleation. Two numerical models are developed and used to evaluate transient supersaturation development in the shear flow and wall effects in the vertical plane across the flow. Stability of sample flow is confirmed with smoke tests.