As a fundamental study of enhancing the efficiency of the current desulphurization process, water model experiments were carried out to understand the behavior of refining agents entering a molten iron bath. The agents such as CaO particles are usually poorly wetted by molten iron and carried into the bath together with a carrier gas. The penetration depth and residence time of the agents in the bath is strongly responsible for the efficiency. The main objective of this water model study is to make clear the wettability effect of the agents on their entry in the bath. A pair of spheres of different wettability and different diameters was simultaneously introduced into a water bath. An air cavity was formed under every experimental condition. Its scale was mainly dependent on the larger sphere. The penetration depth of larger sphere was favorably compared with an analytical solution for a single sphere penetrating into a water bath.