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Author: Alireza Karbalaei Baba Publisher: ISBN: Category : Languages : en Pages : 106
Book Description
Passive and electrically active coalescence and mixing of pairs of trapped squeezed nanodroplets were studied in this work. PDMS-glass microfluidic devices were designed and fabricated using multilevel photolithography technique. Flow-focusing method was used to generate nanoliter droplets of died glycerol inside oleic acid. The effect of factors such as flow rates and their ratio, interfacial tension, and viscosities on the size and frequency of droplet generation was studied and concluded by demonstrating the capillary number effect. A passive droplet trapping technique based on minimizing the surface energy of the droplets was employed to minimize the shear flow effects and increase the accuracy of passive coalescence and mixing experiments. The theoretical platform was presented for the analysis of this multiphase problem and a numerical solver was developed based on the lattice Boltzmann method to simulate the passive and electro-coalescence of the droplet pairs. Mixing of nanodroplets was studied by discussing the contributing mixing time scales and passive mixing of glycerol nanodroplets was experimentally realized. The rate of passive mixing percentage was derived by performing image processing and its exponential asymptotical behavior was presented. This study provided physical perspectives for droplet coalescence and mixing and can be extended in several numerical and experimental aspects.
Author: Alireza Karbalaei Baba Publisher: ISBN: Category : Languages : en Pages : 106
Book Description
Passive and electrically active coalescence and mixing of pairs of trapped squeezed nanodroplets were studied in this work. PDMS-glass microfluidic devices were designed and fabricated using multilevel photolithography technique. Flow-focusing method was used to generate nanoliter droplets of died glycerol inside oleic acid. The effect of factors such as flow rates and their ratio, interfacial tension, and viscosities on the size and frequency of droplet generation was studied and concluded by demonstrating the capillary number effect. A passive droplet trapping technique based on minimizing the surface energy of the droplets was employed to minimize the shear flow effects and increase the accuracy of passive coalescence and mixing experiments. The theoretical platform was presented for the analysis of this multiphase problem and a numerical solver was developed based on the lattice Boltzmann method to simulate the passive and electro-coalescence of the droplet pairs. Mixing of nanodroplets was studied by discussing the contributing mixing time scales and passive mixing of glycerol nanodroplets was experimentally realized. The rate of passive mixing percentage was derived by performing image processing and its exponential asymptotical behavior was presented. This study provided physical perspectives for droplet coalescence and mixing and can be extended in several numerical and experimental aspects.
Author: Osameh Ghazian Publisher: ISBN: Category : Languages : en Pages :
Book Description
Electric field induced flows, or electrohydrodynamics (EHD), have been promising in many fast-growing technologies, where droplet movement and deformation can be controlled to enhance heat transfer and mass transport. Several complex EHD problems existing in many applications were investigated in this thesis. Firstly, this thesis presents the results of numerical simulations of the deformation, oscillation and breakup of a weakly conducting droplet suspended in an ambient medium with higher conductivity. It is the first time that the deformation of such a droplet was investigated numerically in a 3D configuration. We have determined three types of behavior for the droplets, which are less conducting than ambient fluid: 1) oblate deformation (which can be predicted from the small perturbation theory), 2) oscillatory oblate-prolate deformation and 3) breakup of the droplet. Secondly, a numerical study of droplet oscillation placed on different hydrophobic surfaces under the effect of applied AC voltage including the effect of ambient gas was investigated. The presented algorithm could reproduce droplet oscillations on a surface considering different contact angles. It has been found that the resonance frequency of the water droplet depends on the surface property of the hydrophobic materials and the electrostatic force. Thirdly, a new design of an electrowetting mixer using the rotating electric field was proposed which offers a new method to effectively mix two droplets over a different range of AC frequencies. Two regimes were observed for droplet coalescence: 1) coalescence due to the high droplet deformation, 2) coalescence due to the interaction of electrically induced dipoles. Fourthly, the spreading and retraction control of millimetric water droplets impacting on dry surfaces have been investigated to examine the effect of the surface charge density and electric field intensity. The effect of the surface charge on the spreading of droplets placed gently on surfaces was investigated in the first part. It was found that the maximum spreading diameter increases with an increasing charge. In the second part, the impact of a droplet on a ground electrode was considered. It was also found that in order to keep the maximum diameter after the impact, less charge is needed for surfaces with lower contact angle. Finally, the interaction between two identical charged droplets was investigated numerically. The effects of the impact velocity, drop size ratio and electric charge on the behavior of the combined droplet were investigated. It was shown that two conducting droplets carrying charges of the same polarity under some conditions may be electrically attracted. The formation of charged daughter droplets has been investigated and it was found that the number of the satellite droplets after collision appears to increase with an increase in the droplet charge.
Author: Zev Levin Publisher: ISBN: Category : Languages : en Pages : 110
Book Description
This report summarises results of the coalscence efficiency of colliding drops which were obtained from laboratory experiments and a theoretical model. Both theory and experiment suggest that the coalescence efficiency is a function of both drop radii and drop size ratio. Even though no clear dependence of coalescence efficiency on impact speed was observed experimentally, the theory does predict some dependence on velocity. Generally it is observed that the coalescence efficiency decreases with increase in the size of the large drop, R(L), and the drop size ratio, p. However, for small R(L) a decrease in the efficiency was also shown. Both theory and experiment demonstrate the strong dependence of coalescence on impact angle. From the experiments two empirical equations were obtained which relate the coalescence efficiencies and partial coalescence efficiencies with p and R(L). These could be used in numerical models of cloud and rain development. (Author).
Author: Núria Romero Herreros Publisher: ISBN: Category : Languages : en Pages :
Book Description
The electrowetting effect has emerged as an important research topic in recent years. Manipulation of droplets by electric fields has been extensively studied employing different setups, the most common being the configuration in which the electric field is created inside the droplet. However, such a configuration has been mostly employed using conductive liquids, whereas non-conductive droplets have been barely tested under the effect of an electric field using this setup. On the other hand, the influence of an electric field on the shape of a droplet has also been of considerable interest using an alternative configuration in which the electric field is applied between two electrodes with no contact with the drop – the Taylor cone configuration. However, the effects observed employing this last setup are rather different to those obtained using the aforementioned design. While the most important effect in those experiments in which the electric field is created inside the drop is the reduction of the contact angle, the main effect found using the second configuration is the droplet elongation in the electric field direction. In order to demonstrate if dielectric and almost perfectly wetting liquid droplets are affected in the same way as other fluids already tested, the effect of an electric field on the shape of an HFE-7500 droplet has been examined under two different experimental setups by means of interferometric techniques. For the setup where the internal electric field is created, no statistically relevant reduction was measured. Nevertheless, shape deviations have been found at a certain distance of the wire through which the electric field is applied. Moreover, the existence of such deviations depends strongly on the AC frequency. Regarding the second design, it should be mentioned that the initial parallel plate design was working correctly for water+salt droplets. However, no remarkable effects were observed applying strong electric fields of up to 10 kV/cm on HFE-7500 droplets. With the goal of increasing the field strength, two improvised configurations of a metal ring and a needle as a counter-electrodes have also been implemented. In these cases, a strong non-uniform electric field was created which did lead to shape changes of the droplets.
Author: Oliver C. Mullins Publisher: Springer Science & Business Media ISBN: 1489916156 Category : Science Languages : en Pages : 441
Book Description
The investigative assault upon the enigmatic asphaltenes has recently resulted in sig nificant advances in many varied disciplines. Taken individually, each discipline exposes certain facets of asphaltenes, but each, alone, can never reveal asphaltenes from all van tages. Even seemingly narrowly focused issues such as the molecular structures of asphal tenes, or the colloidal structures of asphaltenes require a confluence of many lines of investigation to yield an understanding which differs from truth by diminishing uncer tainty. An holistic treatment of the asphaltenes is a powerful approach to evolve further their understanding. For example, examination of asphaltenes at the highest resolution yields molecular structure. A slight increase in scale probes asphaltene colloidal structure. Weaving together asphaltene studies performed at different length scales results in a fabric which envelops an encompassing vision of asphaltenes. At the same time, the interfaces of these hierarchical studies provide additional constraints on imagination, more than investi gations at individual length scales alone. These considerations shaped the timing, format, and the content of our book. The editors are very appreciative of the diligence and hard work manifest in each of the contributed chapters herein. We thank the contributing authors for making this project a success. Oliver C. Mullins Eric Y. Sheu vii CONTENTS I. Asphaltenes: Types and Sources ...................................... .
Author: Alireza Karbalaei Baba
Author: Alireza Karbalaei Baba
Author: Richard Gerard Semonin
Author: Osameh Ghazian
Author: C. H. Hendricks
Author: Frederick Allen Pettersen
Author: 
Author: Zev Levin
Author: Mehran Mohammadi Farhangi
Author: Núria Romero Herreros
Author: Oliver C. Mullins