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In a high-speed rotary bell-cup atomizer, which is mainly used in the automotive industry, atomization is achieved by disintegration of a thin liquid film at the bell-cup edge. To obtain the hydrodynamic behavior of the liquid film as it passes over the bell cup, the liquid-film formation was simulated using the volume of fluid method under various conditions of the rotational speed, flow rate, liquid viscosity, and surface tension coefficient, based on industrial painting conditions. The liquid supplied from the liquid supply nozzle to the bell-cup surface flowed radially upon rotation of the bell cup and formed a film, which reached steady-state. We clarified the flow field depended on the rotational speed, flow rate, and liquid viscosity, and was independent of the surface tension coefficient. Based on these results, an equation for the liquid film thickness was proposed. In addition, the unsteady behavior of film with flow fluctuation in liquid supply was also investigated; the fluctuations persisted at the edge of the bell-cup atomizer. The proposed equation can be applied to this case regardless of the normalized amplitude of the fluctuation up to 50%. Thus, in this condition, unsteady film flow may be described in the proposed equation, which assumes a steady flow. |
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