  The effect of thermophoresis on the impaction of particles on a cylinder is
investigated for different particle sizes, particle conductivities, temperature
gradients and for Reynolds numbers between 100 and 1600. Simulations are
performed using the Pencil Code, a high-order finite difference code. An
overset-grid method is used to precisely simulate the flow around the cylinder.
The ratio of particles impacting the cylinder and the number of particles
inserted upstream of the cylinder is used to calculate an impaction efficiency.
It is found that both the particle conductivity and the temperature gradient
have a close to linear influence on the particle impaction efficiency for small
particles. Higher Reynolds numbers result in higher impaction efficiency for
middle-sized particles, while the impaction efficiency is smaller for smaller
particles. In general, it is found that thermophoresis only has an effect on
the small particles, while for larger particles the impaction efficiency is
controlled by inertial impaction.
  Finally, an algebraic model, developed based on fundamental principles, which
describes the effect of thermophoresis is presented. The model is found to
accurately predict the DNS results. As such, this model can be used to
understand the mechanisms behind particle deposition due to the thermophoretic
force, and, more importantly, to identify means by which the deposition rate
can be reduced.
