Thermophoresis deposition studies for NaCl and diesel exhaust particulate matter under laminar flow

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Deposition of fine particles is acknowledged as a concern in various processes. Previous studies have investigated thermophoretic transport for various flow regimes (~30 < Re < 1400), particle sizes (0.01 to 8 µm), and temperature ranges of 25 to 145 °C and 425 to 580 °C. An experimental setup was developed to study thermophoretic deposition for particles near ~1 µm size, in the 170 < Tgas < 360 °C temperature range, similar to the conditions of exhaust from the diesel engine used in the present study. NaCl test aerosols (Mass mean diameter (MMD) 0.32 and 0.61 µm), and diesel exhaust particles (MMD 0.44, 0.35 and 0.29 µm) were used at gas inlet temperatures of 170, 260 and 360 °C, and 400 < Re < 2000. A model was developed to predict thermophoretic deposition under laminar flow in a pipe with an axially decreasing wall temperature. Use of a thermal conductivity (kp) value of 0.5 W m-1 K-1 for engine exhaust particles in the model, was found to best match with the experimental observations. For both kinds of particles, the model developed in the present work performed as well as other existing models in the literature.

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