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Numerical estimation of film thickness with an air-assisted spray gun

Baytok Yusuf Mert, Erek Aytunc, Saf Orcun

Engineering Transactions

2023

Vol. 71, iss. 2

241--263

The main goal of this study is to present the effects of spraying parameters on the numerical evaluations of the fundamental behaviors of an air-assisted spray gun during the formation of child droplets in the spray flow field and material deposition on the target surface. For this purpose, first of all, the air-assisted spray gun geometry was created using the Solidworks software. Then, a computational domain with a 3D, unstructured grid structure was generated using the ANSYS-Workbench meshing tool. Numerical calculations were conducted using ANSYS-Fluent 2020-R2 commercial software. Different breakup models and their effects on the child droplet size were investigated. By coupling the Taylor analogy breakup (TAB) model and discrete phase model (DPM), the droplet size, trajectory, and coating thickness calculations were made under different atomizing air pressures. Also, the effects of spraying distance and droplet size on coating thickness and the critical Weber (We) number on the atomized particle diameter and particle speed were investigated. The results show that with the increase in atomizing air pressure, droplet sizes decrease and the film thickness on the center of the target surface and droplet speeds increases. Also, increasing the critical Weber number makes it more difficult to atomize the droplets.

Modelling particle deagglomeration in a batch homogenizer using full CFD and mechanistic models

Krzosa Radosław, Wojtas Krzysztof, Golec Jakub, Makowski Łukasz, Orciuch Wojciech, Adamek Radosław

Chemical and Process Engineering

2021

Vol. 42, nr 2

105–-118

Modelling of titanium dioxide deagglomeration in the mixing tank equipped with a high shear impeller is presented in this study. A combination of computational fluid dynamics with population balance was applied for prediction of the final particle size. Two approaches are presented to solve population balance equations. In the first one, a complete population balance breakage kinetics were implemented in the CFD code to simulate size changes in every numerical cell in the computational domain. The second approach uses flow field and properties of turbulence to construct a mechanistic model of suspension flow in the system. Such approach can be considered as an attractive alternative to CFD simulations, because it allows to greatly reduce time required to obtain the results, i.e., the final particle size distribution of the product. Based on experiments shattering breakage mechanism was identified. A comparison of the mechanistic model and full CFD does not deviate from each other. Therefore the application of a much faster mechanistic model has comparable accuracy with full CFD. The model of particle deagglomeration does not predict a very fast initial drop of particle size, observed in the experiment, but it can predict, with acceptable accuracy, the final particle size of the product.

Jet and droplet breakup modelling approaches

Kapusta Ł. J., Jaworski P., Kowalski J.

Journal of KONES

2015

Vol. 22, No. 3

83--90

Three-dimensional computational fluid dynamics (CFD) plays important role in engines development. The mixture formation in a direct-injection piston engines poses a huge challenge in successful simulations of the engine processes. It is due to the fact that the spray as a two-phase flow complicates the computational process. Moreover, this multiphase flow is not uniform. Three main zones, depending on the distance from the nozzle exit are visible when a liquid is injected. Very dense so called “thick” in a direct vicinity of the injector hole, than “thin” as a result of pri-mary breakup downstream the injector and finally in the certain distance from the injector appears “very thin” region as a result of secondary breakup. It is important to take into account that the liquid phase in various regimes behaves differently and is under influence of different phenomena. The modelling approach needs to take in to consideration all those elements. This paper focuses on presentation of the theory and numerical models for primary and secondary breakup phenomena. The primary breakup is a process that results from a combination of three mechanisms: turbu-lence within liquid phase, implosion of cavitation’s bubbles and aerodynamic forces acting on a liquid jet. Secondary breakup regime occurs mainly due to the aerodynamic interactions between the liquid and the gaseous phase.