Search

In this work, we present a two-phase electro-magneto-fluid dynamics (EMFD) model that merges electromagnetics and fluid dynamics. The model is suitable for use in computational fluid dynamics (CFD) software and was incorporated into OpenFOAM® after deriving appropriate equations that bypassed certain limitations of the software. Currently, there is lack of even single-phase EMFD models that can be incorporated into CFD software; however, simpler models from electrohydrodynamics (EHD) and magnetohydrodynamics (MHD) are being implemented although they have certain approximations that can limit their applicability. We conclude that the derived EMFD model is applicable, and show its quality by implementing it and analyzing the results. We use cases with a droplet and the electrospinning process for verification. The drop deformations obtained were closer to analytical predictions than in the literature for two EHD models, but some oscillations were observed. We compared one simulation to the prediction of an analytical equation from MHD, and good agreement was shown. Finally, we simulate the electrospinning process, and the results were very close to the analytical predictions. We conclude that the implementation can be used for both EHD and MHD cases.

A perfect dielectric model was incorporated into the OpenFOAM® software and used for investigation and, possibly, improvements of electrohydrodynamic calculations. Two different sets of numerical simulations were analyzed, in which two different fluids were present. The first set was one-dimensional, while in the second, a drop of one fluid was surrounded by the other fluid. It is shown that oscillations and possibly artificial generation of a curl of the electric field strength can be observed at applying certain expressions or calculation strategies, which can be thus abandoned. Usage of dynamic meshes, at least those present in the used software, and of limiters for the gradient of the electric field strength can lead to large numerical errors. It is also shown that usage of certain cell face values could improve the results. An electric Courant number was derived by dimensional analysis, and it could be suggested for future calculations. Conclusions made in this paper are expected to be transferable to other more complicated models., Model idealnog dielektrika je uključen u programski paket OpenFOAM® (OpenFOAM Foundation, UK) i korišćen za ispitivanje i moguće poboljšavanje elektrohidrodinamičkih proračuna. Analizirana su dva različita seta numeričkih simulacija, u kojima su bila modelovana dva različita fluida. Prvi set je bio jednodimenzionalan dok je u drugom setu kap jednog fluida bila okružena drugim fluidom. U radu je pokazano da se određeni izrazi ili strategije izračunavanja mogu odbaciti usled pojave oscilacija i mogućeg veštačkog stvaranja rotora jačine električnog polja. Korišćenje pokretnih mreža, barem onih prisutnih u programskom paketu OpenFOAM®, i limitera za gradijent jačine električnog polja mogu dovesti do velikih numeričkih grešaka. Takođe je pokazano da bi korišćenje određenih vrednosti sa površi ćelija moglo poboljšati rezultate. Izraz za električni Kuronov broj je izveden dimenzionom analizom i mogao bi se preporučiti za buduće proračune. Očekuje se da su zaključci iz ovog rada prenosivi na druge, komplikovanije modele.

The electrohydrodynamics' (EHD) perfect dielectric model was added into computational fluid dynamics (CFD) software OpenFOAM® in order to improve its usability for the EHD field and specifically for the mentioned model. Based on the investigated literature, it can be said that this is the most complete implementation of the said model. Two sets of numerical simulations with two different fluids are presented and analyzed. One set is one-dimensional. The other set is with a drop of one fluid surrounded by other fluid. Oscillations can be observed with certain expressions or calculation strategies for the electrostrictive force, and used for disregarding them. Results that are closer to analytical predictions can be obtained by using appropriate expression for the dielectric force. The electrostrictive force was implemented not only for nonpolar, but also for polar fluids, and it is shown that it might significantly influence the drop deformation. Calculated and analytically predicted drop deformations were close or comparable even up to around 0.25, what is significantly higher and different from a previous study made by other authors. Different expressions for the electric permittivity and usage of limiters for volume fractions were investigated. Conclusions from this paper can be transferred to more complicated models.

In this study liposomes were investigated regarding the ability to encapsulate vitamins, vitamin E and folic acid. Liposomes were prepared using commercial mixture based on the soybean lecithin (Phospholipon 90 G) by the proliposome technique. High entrapment efficiency (85-90%) was achieved for both types of vitamins, while the size was dependent on the vitamin type (350 and 630 nm for vitamin E- and folic acid-containing liposomes). Physical stability expressed via changes of the size, polydispersity and zeta potential during storage was confirmed for the period of one month in case liposomes with folic acid and two months for the liposomes with vitamin E. The release study, done using Franc diffusion cell, under skin conditions (pH=5.5), showed that the release rate was determined by solubility of the vitamins.

The electrospray process is a process that uses an electric field to influence the liquid dripping out of a capillary tube in order to obtain a reduction in the mean droplet diameter. The theory regarding this process is called electrohydrodynamics. Based on the previous experimental results and on the published theories, important variables are listed. Some of those variables have a significant influence on the droplet diameter, while others should be controlled in order to check the applicability of the mentioned theories. Since theoretical equations have a simple power-type form, that form was used for obtaining a correlation of particle diameters when alginate solutions are used. Previous experimental data and a Generalized Reduced Gradient (GRG) nonlinear solver were used for calculating the coefficients present in the correlation. Interesting results were obtained because certain variables were eliminated during the calculation. Based on the presented analysis, future experiments should monitor more variables and computational fluid dynamics (CFD) should also be used.

While a liquid is dripping out of a capillary tube, there is a possibility to affect the characteristics of the exiting flow in certain ways. One of the ways already used is by introducing an electric field that can be used to change the average droplet diameter and the droplet size distribution. This process is called electrospraying, while the theory behind it is sometimes called electrohydrodynamics (EHD). This phenomenon has been investigated for more than a hundred years both empirically and theoretically. In this paper, a review of the available literature and the empirical and theoretical findings is presented. A new classification of the electrospray modes had to be given to include all the different modes mentioned by different authors. The necessary pieces of the equipment and their different types are also given.