Effect of thermophoresis on sub-micron particle deposition from a laminar forced convection boundary layer flow onto an isothermal cylinder

Sub-micron deposition from a laminar forced convection boundary layer developing on a heated isothermal vertical cylinder has been investigated. Pseudo-similarity solutions, as proposed by Sparrow et al. (1970, AIAA J. 8, 1936), have been used to calculate the local cumulative particle deposition theoretically; with the thermophoretic velocity being that proposed by Talbot et al. (1980, J. Fluid Mech. 101, 737). It was demonstrated that the effect of thermophoresis can decrease particle transfer by about two orders of magnitude and that the effect increases with particle size and distance along the cylinder. Experiments were also conducted using mono-disperse fluorescent uranin particles with mean diameters of 0.05–0.25 μm. A calibrated fluorimeter was used to measure the mass of the particles deposited at different axial locations along the cylinder. Results showed similar trends to the theoretical model, but absolute values of the deposits were greater than theoretical predictions. On the other hand, good agreement was obtained for the percentage change in deposition relative to that obtained under isothermal conditions.