The Implementation of Poisson Field Analysis Within FLUENT to Model Electrostatic Liquid Spraying
Univ. of Western Ontario, LondonDOI: 10.1109/CCECE.2007.395 Conference: Electrical and Computer Engineering, 2007. CCECE 2007. Canadian Conference on
Source: IEEE Xplore
The process of electrostatic liquid spraying involves a combination of hydrodynamics, aerodynamics and electrostatics. Many parameters affect the process such as atomizing air pressure, liquid flow rate, nozzle-to-target distance, droplet size, charge-to-mass ratio, etc. The mechanical portion can be directly modeled with the computational fluid dynamics software, FLUENT. Although this software does not provide a direct solution for the electrostatic field, its user-defined functions can be used to solve the Poisson field by incorporating it into the general scalar transport equations within FLUENT. This enables the calculation of the electrostatic force on the charged droplets. The key to this technique is to find the space charge density for different charging models. An air-assisted electrostatic induction charging spray nozzle was modeled for both flat and spherical targets. Coupling between the airflow phase, the droplet discrete phase and the electrostatic field yields the trajectories of the charged droplets. Parameters such as droplet size, charge-to-mass ratio and nozzle-to-target distance were varied to demonstrate their effects on the motion of the charged droplets. The results show that the spray cloud expands with increased droplet charge-to-mass ratio and nozzle-to-target distance due to increased space charge. Thus they need to be independently controlled in order to increase the transfer efficiency and reduce drift.
- [Show abstract] [Hide abstract]
ABSTRACT: Electrohydrodynamic atomization (EHDA) is a promising method for the fabrication of micro- and nano-sized particles with narrow size distribution and better morphologies than a few conventional methods of particle fabrication such as spray drying. Further enhancement in monodispersity and morphology of particles can also be achieved using an enclosed shuttle chamber with controlled solvent evaporation rate during the fabrication process. The objective of this study is to simulate the fluid and particle dynamics in the EHDA chamber, thereby providing a means of predicting collection efficiency prior to experimental verification. The first part of the simulations focuses on identifying the effects of the charge-to-mass ratio of particles on their collection efficiency. This is necessary because usage of the chamber restricts measurements of the actual charge-to-mass ratio. In the second part of the study, the Poisson equation is solved for the prediction of electrical force due to charge repulsion in the simulation of particle trajectories. For particles moving in a fluid, buoyancy, gravitation and drag are the three major mechanical forces that influence their trajectories. Two dominant classes of entities contribute to the determination of electrical potential profiles in the EHDA chamber. The first type of objects is the stationary surfaces which are charged conductors. These comprise of the nozzle, ring and collection plate. The electrical potential due to such entities can be predicted by the Laplace equation with the appropriate boundary conditions. The second type of entities is the moving charged particles. With the addition of such entities, the Poisson equation is solved for the overall electrical potential profiles. All the forces acting on a particle are combined to determine its acceleration and trajectory based on the Lagrangian approach. Since organic solvent has occupied more than 90% of volume of each droplet at the outlet of the EHDA nozzle, organic solvent is evaporated from the droplets during the flight process. This evaporation results in the shrinkage of the droplets during the flight, decreasing their weight and size and finally converting them into particles. Therefore, droplet shrinkage has a considerable effect on droplet motion and collection in the chamber. A set of dimensionless partial differential equations are solved to investigate the effect of the evaporation of a liquid droplet accompanying a nitrogen stream in the EHDA process. A better geometry for EHDA shuttle chamber with enhanced particle collection efficiency can be designed using the results of this simulation study. Key words: Electrohydrodynamic atomization; particle collection efficiency; particle trajectory; simulation.2009 AIChE Annual Meeting; 11/2009
- [Show abstract] [Hide abstract]
ABSTRACT: Charge to mass ratio is a crucial parameter that governs the behavior of particle trajectories in a charged cloud of particles. The complex nature of the charging process limits our ability to accurately determine the charging level when particles of varying size are present. Using a numerical approach, it is possible, however, to take into account predefined values for this parameter. In this paper, the average charge to mass ratio and the distribution of the charge to mass ratio in the coating of a flat target were systematically varied to demonstrate their effect on the motion of the charged particles. The results show that the transfer efficiency increases as the average charge to mass ratio increases. It was found that the transfer efficiency is a weak function of the average particle size in the range tested and that it increases as the width of the size distribution increases.Journal of Electrostatics 06/2011; 69(3):189-194. DOI:10.1016/j.elstat.2011.03.008 · 0.86 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Due to the presence of a high voltage and the specific geometry configuration, corona discharge is an inevitable part of many electrostatic coating processes. A full mathematical model of the corona discharge is practically impossible to implement due to the complexity of the problem. In this paper, a new, simplified and efficient method for incorporation of the corona current into the numerical model of the electrostatic coating process is presented. The objective of the paper is to describe the novel procedure and fit it into the existing numerical frameworks. A software package FLUENT is used to solve a transport equation for a new, user-defined scalar function. The gradient of this function corresponds to the corona current density. The numerical simulation is performed for the full three-dimensional model of the problem and the sample results of the simulations are presented.Particulate Science And Technology 09/2012; 30(5). DOI:10.1080/02726351.2011.598627 · 0.52 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.