Theoretical and experimental analysis of the core sampling method: Reducing diffusional losses in aerosol sampling line

摘要

Core sampling method (extracting a portion of a flow from the core of the flow) will reduce diffusional losses of highly diffusive species (e.g., aerosol nanoparticles, ions, and gases) when transporting them through a sampling tube. Revealing parameters governing the sampling efficiency of a core sampling system, eta(sam), helps to design the apparatus and to optimize its performance. In this study, we report an analytical solution for quantifying the eta(sam) by solving the convection diffusion equation of laminar flow field. The analytical results were experimentally evaluated using 1-5nm tungsten oxide nanoparticles. eta(sam) is governed by a dimensionless loss parameter and the transport-to-sample flow ratio. Theoretically predicted values for eta(sam) agree with experimental results, e.g., the relative deviation is within 5% when the value for the loss parameter is less than 0.1. The core sampling method is recommended to work at the loss parameter less than 0.1 such that eta(sam) is equal or close to the maximum value of unity and is also insensitive to variations in sampling conditions. In this study, how to apply the findings in designing and optimizing a core sampling system was discussed. A core sampling apparatus was then designed and experimentally evaluated. Its sampling efficiency was shown to be significantly higher than those of a tee, a cross fitting, and a Y fitting when the same sampling conditions were used.Copyright (c) 2019 American Association for Aerosol Research