Fluid flow and heat transfer of a gas stream in various ducts have been studied thoroughly before. However, in real applications, a gas stream usually contains dust particles, whose effects have typically been neglected. In this study, the effects of the dust particles on the flow and heat transfer characteristics in a parallel-plates duct were numerically investigated in detail. A lattice Boltzmann method combined with a modified immersed boundary approach was employed to calculate the velocity and temperature distribution in the duct. The effects of the particles on the development of the hydrodynamic and thermal boundary layers in the duct were predicted. The product of friction factor and Reynolds number (fRe) and local Nusselt number (NuL) along the flow direction were obtained for a particle-laden flow and compared with those for a pure gas flow. The results indicated that for particle-laden flows, the “fully-developed” flow was just an approximation. Both the flow and thermal boundary layers were disrupted by the accompanying particles. The particles would form a stable and dense particulate fouling layer at the walls; this could increase the local (fRe) and reduce the NuL in “fully developed” regions. Moreover, ducts with superhydrophobic properties would be less influenced by the particles due to decreased particle deposition because of the anti-dust property of the surface.