Boundary conditions for three-dimensional DSMC simulations. Side view of a typical simulation domain. The domain consists of a parallelepiped of size 7.5 mm × 7.5 mm × L, where L is the dust-layer thickness. A gas temperature T_i and pressure P₀ are imposed at the inlet surface (z = 0). For gas-solid interactions, a diffuse reflection of the gas particles is considered, where the dust temperature is T_d(z). At the side walls, a specular reflection condition is considered. Finally, at the outlet surface (z = L), a vacuum condition is imposed.