Mechanical & Industrial Engineering

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The mission of the Mechanical & Industrial Engineering Department is to serve the State of Montana, the region, and the nation by providing outstanding leadership and contributions in knowledge discovery, student learning, innovation and entrepreneurship, and service to community and profession.

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Author: search.filters.author.Krisshna, VenkataSubject: search.filters.subject.NGA

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    Investigating atomization characteristics in an electrostatic rotary bell atomizer
    (Elsevier BV, 2024-05) Krisshna, Venkata; Owkes, Mark
    Electrostatic rotary bell atomizers are commonly used in several engineering applications, including the automobile industry. A high-speed rotating nozzle operating in a strong background electric field atomizes paint into charged droplets that range from a few micrometers to tens of micrometers in diameter. The atomization process directly determines the droplet size and droplet charge distributions which subsequently control the transfer efficiency and the surface finish quality. We have previously developed a tool to perform high fidelity simulations of near-bell atomization with electrohydrodynamic effects. In this work, we perform simulations employed with a droplet ancestry extraction tool to analyze previously inaccessible information and understand the physical processes driving atomization. We find that the electric field accelerates breakup processes and enhances secondary atomization. The total number of droplets, the ratio of secondary to primary droplets, and the ratio of coalescence to breakup activity are all much higher when operating in an electric field. We analyze the droplet velocity, local Weber number and charge density statistics to understand the complex physics in electrically assisted breakup. The results of the study have helped us gain insights into the physics of atomization in electrostatic rotary sprays.
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    High-fidelity simulations of a rotary bell atomizer with electrohydrodynamic effects
    (Elsevier BV, 2023-11) Krisshna, Venkata; Liu, Wanjiao; Owkes, Mark
    Electrostatic rotary bell atomizers are extensively used as paint applicators in the automobile industry. Paint undergoes atomization after exiting the edge of a high-speed rotating bell. In most setups, the paint is electrically charged and a background electric field is applied between the nozzle and the target surface to increase the transfer efficiency (TE). The atomization process directly determines the droplet size and droplet charge distributions which subsequently control TE and surface finish quality. Optimal spray parameters used in industry are often obtained from expensive trial-and-error methods. In this work, three-dimensional near-bell atomization is computationally simulated using a high-fidelity volume-of-fluid transport scheme that includes electrohydrodynamic (EHD) effects. We find that electrifying the setup results in the production of smaller droplets. Additionally, the electric field has a minor effect on primary atomization but a negligible effect on the size and stability of atomized droplets after secondary breakup. This cost-effective method of simulating EHD-assisted atomization allows for the understanding of the effect of the electric field and the extraction of droplet charge characteristics which is otherwise challenging to obtain experimentally.
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