Radiation Heat Transfer and Soot Thermophoresis in Laminar Tube Flow

The transport of soot particles suspended in laminar hot gas, flowing in a tube, was numerically modeled and parametrically studied. The objective was to assess the coupled effects of radiation heat transfer and thermophoresis on the soot particle transport in hot-walled tubes. The wall material was assumed to be transparent to radiation for wavelengths shorter than a threshold wavelength at high temperatures, an essential property of high temperature resistive materials. The results indicated that, as a consequence of strongly-coupled thermal radiation transport and thermophoresis, a radially-nonuniform temperature profile develops as the distance from the tube inlet is increased. Furthermore, the soot particles move towards the tube centerline due to thermophoresis, leading to the development of a sharp radial soot concentration profile. The pace of the development of the nonuniform radial temperature and soot concentration profiles is sensitive to several parameters. Reduction in soot particle size, higher average soot concentration, and higher tube wall temperature all promote the development of sharp radial profiles.