Wetting Behavior between Droplets and Dust

The wetting behavior of dust by droplets is investigated by experiments and numerical simulation methods. Experimental observation reveals that the surface of a coal slice is hydrophilic in nature, while surfaces of coal dust stacks are hydrophobic. We show that water droplets settle on these surfaces following the Cassie–Baxter wetting model, as supported by theoretical, numerical analyses and experimental observations, i.e. water droplets only wet the first layer of coal dust. Our numerical simulation results also show that a water droplet could not enclose any coal dust inside it and many coal dust particles are adhered with a hexagonal close packing on a large water droplet. Based on these results, we conclude that the surface area of water droplets is an important factor on their wetting and capturing coal dust, and producing smaller water droplets can improve the efficiency of settling dust.