Theses and Dissertations at Montana State University (MSU)
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Item High-fidelity simulations of a rotary bell atomizer with electrohydrodynamic effects(Montana State University - Bozeman, College of Engineering, 2023) Pydakula Narayanan, Venkata Krisshna; Chairperson, Graduate Committee: Mark OwkesAtomizing flows involve the breakup of a liquid into a spray of droplets. These flows play a vital role in various industrial applications such as spray painting and fuel injection. In particular, these processes can have severe impacts especially in automotive paint shops - which can account for up to 50% of the total costs and 80% of the environmental concerns in an automobile manufacturing facility. A device commonly used for painting vehicles is called an electrostatic rotary bell atomizer (ERBA). ERBAs rotate at high speeds while electrically charging the liquid and operating in a background electric field to direct atomized charged droplets towards the target surface. The atomization process directly influences the transfer efficiency (TE) and surface finish quality. Optimal spray parameters used in industry are often obtained from expensive trial-and-error methods. To overcome these limitations, a computational tool has been developed to simulate three-dimensional near-bell ERBA atomization using a high-fidelity volume-of-fluid transport scheme. Additionally, the solver is equipped with physics modules including centrifugal, Coriolis, electrohydrodynamic (EHD), and shear-thinning viscous force models. The primary objective of this research is to investigate the influence of EHD parameters on near-bell atomization of paint and subsequently improve TE in ERBAs in a cost-effective manner. Using the tools developed, numerical simulations are performed to understand the physics of electrically assisted atomization. The influence of various operating parameters, such as liquid flow rate, bell rotation rate, liquid charge density, and bell electric potential, on atomization is examined. Results from a comparative study indicate that the electric field accelerates breakup processes and enhances secondary atomization. The droplet velocity, local Weber number and charge density statistics are also analyzed to understand the complex physics in electrically assisted breakup. Additionally, the effect of shear-thinning behavior of the liquid on atomization is also explored. High-fidelity simulations allow for the extraction of breakup statistics which are otherwise challenging to obtain experimentally. These findings have the potential to drive improvements in the design and operation of ERBAs, leading to enhanced TE and surface finish quality while reducing costs and environmental concerns in automotive paint shops.Item Numerical study of electric Reynolds number on electrohydrodynamic (EHD) assisted atomization(Montana State University - Bozeman, College of Engineering, 2016) Sheehy, Patrick John Harper; Chairperson, Graduate Committee: Mark OwkesIn today's modern world, nearly all industries utilize the benefits of fast, long distance transportation that burning fossil fuels deliver. However, fluctuating fuel prices has created interest in researching alternatives to fossil fuels. Bio-fuels are one of these alternatives, but they generally have a higher viscosity and water content than diesel. This means high pressures are required to atomize the fuel in the combustion chamber, thus bio-fuels are limited to larger or less efficient engines. A potential method to reduce the pressure requirements is to use Electrohydrodynamic (EHD) assisted atomization. EHD assisted atomization injects electrical charges into the liquid fuel before spraying, meaning the fuel has an electrical charge distribution before and after atomization. For many relevant engineering flows, including liquid fuel injection, the charge mobility timescale (time it takes the charges to relax to the fluid-gas boundary) is similar in magnitude to the charge convection timescale (relevant flow time), which leads to a non-trivial electric charge distribution. This distribution within the liquid fuel may enhance atomization, the extent to which is dependent on the ratios of the timescales which are known as the electric Reynolds number (Re subscript e). In this work, a computational approach for simulating two-phase EHD flows is used to investigate the amount Re subscript e influences the resulting atomization quality. The computational approach is second-order, conservative, and is used to consistently transport the phase interface along with the discontinuous electric charge density and momentum. The scheme sharply handles the discontinuous electric charge density, allowing robust and accurate simulations. In addition, this method is modified by a work distribution scheme to improve processor utilization on High Performance Computing (HPC) clusters. Using these methods, multiple three-dimensional test cases are simulated with varying Re subscript e values which highlight the effect of Re subscript e on the atomization efficiency of a liquid jet. Comparison of these cases shows the importance of Re subscript e on atomization and suggests that decreasing Re subscript e (increasing charge mobility) leads to larger concentrations of electric charge density, increased Coulomb force, and ultimately improved break-up during the atomization process.