Abstract View
Numerical Modeling of the Transport and Fate of Ice Nucleating Particles Inside a Continuous Flow Diffusion Chamber
JORDAN SPENCER, Russell Perkins, Ezra Levin, Gavin McMeeking, Shantanu Jathar, Colorado State University
Abstract Number: 334
Working Group: Instrumentation and Methods
Abstract
Ice nucleating particles (INPs) are important for the formation of ice clouds and, hence, INPs affect climate systems through variations in cloud precipitation and radiation balance. Laboratory measurements of INPs can be made using a continuous flow diffusion chamber (CFDC). Previously, numerical calculations including those for particle residence times in the CFDC have not matched experimental observations. In this study, we used a computational fluid dynamics software package (ANSYS Fluent) to model the transport, loss, and spatiotemporal distribution of 1 μm particles during normal operation in a CFDC. Predictions of the pressure, temperature, velocity, and saturation ratio across the annular space were consistent with those derived from analytical expressions, although we did observe differences in these profiles along the length of the CFDC column. Surprisingly, baseline results showed that nearly two-thirds of the particles were lost via turbulent eddies to the inner cold wall and only a third of the remaining particles were exposed to the maximum supersaturation ratio. Simulations were run to examine the sensitivity in the model results to sample and sheath flow rates (5 to 20 L min-1), air and wall temperatures (237.15 to 300 K), particle size (0.3 to 30 μm), and modifications to the inlet geometry. We found that when the sample and sheath flows were cooled, changes were made to improve the inlet geometry, or flow was directed so as to push the particles away from the inner wall, the device performance improved. When compared to baseline results, loss rates were limited to a fifth of the total particles and three-quarters of those remaining were exposed to the maximum supersaturation ratio. Simulation results were found to be insensitive to the particle size range considered. Our findings are relevant to the future design and operation of CFDCs, providing new insights into how the device geometry and operating conditions relate to particle transport and fate.