Abstract
Electric charging of spray droplets is a common method of improving various (industrial) spraying processes. The mutual repulsion of charged droplets results in better dispersion, and the movement of charged droplets can be controlled through electric fields to increase deposition efficiency. In this thesis, the behaviour and formation of charged sprays, in the context of a spray chilling system, is studied through numerical simulation and experimental measurements.
Three chapters of this thesis are dedicated to numerical studies. In the first of these, a general framework for the simulation of charged sprays is presented and validated. It consists of a Finite Volume method solver to resolve the gas flow surrounding the spray and the electrostatic field, coupled to a Lagrangian Particle Tracking method that computes the trajectories of spray droplets.
The following chapter describes a method to compute the charge imparted on droplets of a charged spray, thereby addressing one of the existing knowledge gaps in charged spray simulation. The developed method makes use of the linear nature of electric fields, separating the field induced by the sprayer nozzle, the charged spray itself, and any other sources such as induction electrodes. The model needs no tuning input based on experimental results, and shows good accuracy in validation.
The final exploratory chapter investigates the possibility of using numerical methods to simulate spray formation in a pneumatic atomiser. A volume of fluid method is used to simulate the spray liquid, in combination with an algorithm that detects stable droplets and converts those to Lagrangian particles to reduce computational complexity.
The same pneumatic atomiser is also studied experimentally, and the influence of electric charge and liquid and gas flow rate on the spray properties is determined. A shadowgraphy method is used to determine the sizes and velocities of spray droplets. The resulting data serves to validate the numerical simulations. It is found that, for pneumatic atomisers, the spray properties strongly correlate to the liquid and gas supply rates, but are mostly unaffected by electric charge.
Three chapters of this thesis are dedicated to numerical studies. In the first of these, a general framework for the simulation of charged sprays is presented and validated. It consists of a Finite Volume method solver to resolve the gas flow surrounding the spray and the electrostatic field, coupled to a Lagrangian Particle Tracking method that computes the trajectories of spray droplets.
The following chapter describes a method to compute the charge imparted on droplets of a charged spray, thereby addressing one of the existing knowledge gaps in charged spray simulation. The developed method makes use of the linear nature of electric fields, separating the field induced by the sprayer nozzle, the charged spray itself, and any other sources such as induction electrodes. The model needs no tuning input based on experimental results, and shows good accuracy in validation.
The final exploratory chapter investigates the possibility of using numerical methods to simulate spray formation in a pneumatic atomiser. A volume of fluid method is used to simulate the spray liquid, in combination with an algorithm that detects stable droplets and converts those to Lagrangian particles to reduce computational complexity.
The same pneumatic atomiser is also studied experimentally, and the influence of electric charge and liquid and gas flow rate on the spray properties is determined. A shadowgraphy method is used to determine the sizes and velocities of spray droplets. The resulting data serves to validate the numerical simulations. It is found that, for pneumatic atomisers, the spray properties strongly correlate to the liquid and gas supply rates, but are mostly unaffected by electric charge.
| Original language | English |
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| Qualification | Doctor of Philosophy |
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| Supervisors/Advisors |
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| Award date | 26 Jan 2023 |
| Place of Publication | Enschede |
| Publisher | |
| Print ISBNs | 978-90-365-5523-4 |
| DOIs | |
| Publication status | Published - 26 Jan 2023 |