droplet generation, a wide mismatch is observed between the experimental data obtained from cold model and hot model experiments. The reason for this large deviation has been investigated in the current study and a theoretical approach to estimate the droplet generation rate has been proposed. The suitability of the proposed model has been tested by numerically calculating the amount of metals in slag. The study shows that the weight of metals in emulsion falls in the range of 0 to 21 wt pct of hot metal weight when droplet generation rate has been calculated at ambient furnace temperature of 1873K (1600 °C).
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In the laser droplet generation process a metal wire is continuously fed into the focus of a pulsed annular laser beam that melts the wire-end and forms a growing pendant droplet that is then detached from the wire. The process is highly complex due to its non-stationarity, non- linearity, and the interplay of numerous physical phenomena. With the aim of describing the process, a low-dimensional, non-linear, dynamic force balance, mass-spring-damper model of the pendant droplet with time-dependent coefficients was formulated based on experimental observations of the process. A comparison between the modelled and experimental droplet centroid vertical position time series and their time- frequency maps showed that the model captures the essential pendant-droplet dynamics in the selected laser-pulse frequency range between 60 Hz and 190 Hz. It was also found that the modelled time of detachment and the detached-droplet diameter were in good agreement with the experimental results, including the bifurcation at the laser-pulse frequency of 120 Hz and the coexistence of two detached-droplet diameter values below that frequency. In addition, the pendent droplet’s lateral oscillation and the Rayleigh-Plateau instability were identified as having a significant influence on the process outcome in certain laser-pulse frequency ranges.
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Although flow physics of droplet generation at T-junctions has been extensively in- vestigated both experimentally and numerically, significant effort is required to under- stand droplet generation in a confined cross-junction. The droplet dynamics in a mi- crofluidic cross-junction is very complicated. Many coupled factors will affect the droplet formation process, e.g. interfacial tension, wetting properties and confinement of flow channels, fluid flow rates and viscosities. Cubaud et al.  investigated the liquid/gas flows in a cross-junction and found that the bubble breakup could be understood as the competition between the pressure drops in the liquid and gas phases. The bubble size could be predicted by the gas/liquid flow rate ratio. Garstecki et al.  investigated the mechanism for bubble breakup process in the cross-junction with a small orifice, and observed that the collapsing rate of the neck is quasi-stationary and proportional to the liquid flow rate. Tan et al.  studied the formation mechanism of plug flow in an oil/water microfluidic cross-junction. They found that the plug size depends on the flow rate ratio of both fluids and the capillary number. Recently, Fu et al.  found that the bubble (slug) breakup process in a cross-junction is mainly controlled by the collapse stage, during which the collapse rate of the thread neck and the collapse time were af- fected by the gas/liquid flow rate ratio and the viscosity of the liquid phase. Although the experimental studies have helped to understand the underlying physics, the current available data are sporadic. Various materials were used to fabricate the microchannels with a diverse range of dimensions, and the experiments are operated under a wide range of flow conditions with different fluids. Consequently, the information is fragmented, which leads to inconclusive and even incompatible findings. On the other hand, exper- iments at such small scale are still difficult. For example, it is challenging to accurately measure droplet size, pressure and velocity fields, and droplet deformation, breakup, and coalescence.
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For my master thesis at the BIOS-Lab-on-a-Chip group, and as a part of the Netherlands Centre for Multiscale Catalytic Energy Conversion (MCEC) program, I was tasked with the assignment of designing and testing a ‘Single Catalyst Particle Diagnostics: Droplet Microreactor platform’. This microreactor should be able to study single catalyst particles at high temperatures. As a report I have written a paper entitled ‘Design and characterization of a microreactor for monodisperse catalytic droplet generation at elevated temperatures and/or pressures’. In this paper I will explain all the results and findings obtained so far. The title is slightly different from the title chosen for my thesis, because the actual diagnostics within a droplet have not been achieved yet. However, as I will demonstrate, a microreactor with the potential of doing exactly that has been fabricated. The paper is accompanied by a supplementary information with more details about certain design aspects mentioned in the paper. As a small
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To take a good illustration we need to look at studies reported by Kumacheva and colleagues concerning consecutive flow-focussing droplet generators 79 (see Figure I- 2B). The layout consisted of three channels which are focused onto the fourth. In such devices the dispersed phase remains in the central channel, while the continuous phase flows through the side, dragging all flows into the fourth channel and forcing the droplet formation. In turn, the collection channel can be the central part of the second level of the channels, again allowing double emulsion droplet generation. 80 Retaining the general principle many variations of such devices were developed, for instance modular microfluidic reactors, 81 parallel droplet generators, 82-84 multiple emulsion droplet devices 85 and simplified devices. 86 Furthermore, additional modification allowed the splitting of droplets after generation and thereby doubling the total amount, 87 separating droplets by size and functionality, 88, 89 controlling the droplet composition 90 , and the monitoring of dispersity rate. 91 In addition, co-flow devices can be applied in conjunction with centrifugal force 92, 93 or electrospinning, 94, 95 increase the monodispersity and reduce the size respectively. As noted already, computational and experimental investigations are very important, and co-flow droplet generation using T- junctions were deeply studied. 16, 21, 96-103
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In inkjet printing, the ink jetting quality is closely related to the ejected droplets, including the droplet size, droplet consistency and satellite formation. The droplet generation process is empirical observation with operating parameters such as pulse shape, pulse amplitude and dwell time. The droplet generation processes are not only sensitive to waveform , nozzle structure  but also to ink properties . Since droplet formation process requires different viscosity, and operating parameters vary with materials properties [3,4], viscosity and surface tension of this suspension are identified as key parameters . To explore the relationship between viscosity and driving voltage in dispensing, Meixner et. al  compared polymer inks with variable viscosity and surface tension based on Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). The results showed that for the same surface tension, the higher viscosity liquid required larger voltage to produce droplets. The same conclusion was also drawn by Tsai et al., who observed that higher voltage was needed for silver suspension compared to DW. In this study, drop On demand (DOD) system of 80 micron diameter piezoelectric actuated nozzle, was utilized and the advantage of piezo actuation is that the pressure, pulse rise and fall time can be tailored to optimize monodisperse satellite free droplet production and dynamically alter the diameter the ejected drops. Furthermore, extensive investigation printhead variables and operation parameters is the key to obtaining stable droplet generation conditions. The research focus of this work is to characterize the 80 micron nozzle printhead and investigate the effects of viscosity, dwell time and pulse amplitude in droplet generation process for printing 3d structures with photoreactive polymer.
The present research study is intended to provide fundamental understanding of the dynamics and transport of aerosols from an e-cigarette in an idealized tubular G3 – G6 respiratory tract model. A computational model has been developed that includes the effects of hygroscopic growth as well as evaporation from multicomponent aerosol droplets. The aerosols investigated usually contain carrier solvents such as propylene glycol (PG) and glycerol, along with water, nicotine, and flavors. An experimentally validated computational fluid-particle dynamics (CF-PD) model is presented, which for the first time is capable of simultaneously simulating interactive, multicompo- nent droplet-vapor dynamics with evaporation and/or condensation. As a first step to accomplish such complex numerical simulations, an idealized G3–G6 triple bifurcating unit (TBU) has been selected. The results are compared with the conventional smoke particles (CSPs) as well as solid particles. Parametric analysis and comparisons of the evaporation/condensation dynamics for EC-droplets vs. cigarette smoke particles were performed, including the effects of different droplet initial diameter, composition, temperature, and ambient relative humidity. The results indicate that EC-droplets, being more hygroscopic than cigarette smoke particles, tend to grow larger in maximum size in a typically highly humid environment. Additionally, a correlation for the growth ratio of EC-droplets in TBUs is proposed.
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The corrosion rate of copper under a single droplet of NaCl has been investigated using electrochemical impedance spectroscopy technique. The changes in contact angle, volume loss and droplet height during the progress of corrosion process will be monitored. Corrosion rates were greatly accelerated as the droplet height decreases as a result of the decrease of the diffusion layer thickness and did not alter significantly for higher droplet height. The values of the contact angle, droplet height increase as the holding time progresses, while the volume loss increases. The decrease in contact angle with holding time is accompanied by a decrease in the wetting properties of the copper surface with time. A mechanism describing the successive stages of the corrosion process within a droplet is suggested.
Three different categories of fuels namely, alkanes, alcohols and biodiesels were selected to isolate the effects of various thermophysical properties on important combustion and emission characteristics. It was observed that dimensionless flame diameter is influenced primarily by the fuel boiling point. The same conclusion could be drawn for the variation of F D / ratio and flame standoff distance with time. Also, the F D / ratio was found to increase throughout the droplet burning period, suggesting transient burning. From versus time plot, it was observed that for steady state burning, droplet lifetime was highest for the fuel having smallest burning constant (from the relationship coming out from the 2
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In this paper, the droplet size distribution of the Tehran refinery crude oil/water emulsions is determined by analyzing the photomicrographs of model emulsions which were taken by microscope. The normal distribution function is fitted to the experimental data in order to reproduce the droplet size distribution (DSD) of the emulsions by using mean diameter and standard deviation. The effect of different parameters such as surfactant concentration, salinity, and the power of homogenizer on the droplet size distribution and mean droplet diameter of the emulsions are determined. The smaller droplet size was observed in high concentrations of surfactant and in the absence of salt, and also in emulsions which were prepared with lower power of homogenizer.
in order to recover properly the stress jump condition in the sharp- interface limit. Here z is the spatial location normal to the interface. Although Eqs. (8) and (9) allow computing the velocity ﬁeld, an advection equation has to be additionally solved to cap- ture the evolution of interface in traditional multiphase solvers, e.g., the volume-of-ﬂuid (VOF) and level-set methods, where the sophisticated interface reconstruction algorithm or unphysical re- initialization process is often required. In order to avoid these issues, we use the lattice Boltzmann colour gradient model, ﬁrst proposed by Gunstensen et al.  and later improved by Halli- day and his coworkers , to simulate the dynamical behaviour of a droplet subjected to a simple shear ﬂow. The colour gradi- ent model possesses many advantages in simulating immiscible two-phase ﬂows, including the ability of capturing interface auto- matically, low spurious velocities, high numerical accuracy and strict mass conservation for each ﬂuid. In this model, two sets of distribution functions f R
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practical fuels fall within a narrow range o f 0.70 mm /s to 1.10 mm /s. Makino  stated the burning rate constant for conventional hydrocarbon fuels is about 1.00 mm2/s. They observed changes o f droplet diameter squared over time were linear which was confirmed from the results in Figure 6.14 and Figure 6.18. Fuels with higher molecular weight will tend to deviate from this pattern. This is due to enhanced radiant heat transfer caused by more intense soot formation for other fuels. A crucial factor affecting the burning rate is the convective gas flow around the burning droplet.
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Droplet impingement widely exists in many industries[1-4], like ink-jet printing, thermal/plasma spraying, spray cooling, engine combustion. Droplet impact on the substrate is a strong transient and nonlinear process with complex topology structure of phase interface, which attracts much effort for many years[5-7]. Despite many experiment and simulation investigations on dynamics of droplet impact on flat surface, the publications concerning droplet impact on small targets are quite limited. The small target has the size which can be comparable to droplet size. It is clear that droplet impact onto small targets is quite different from large substrate, especially like spheres and particles. Bakshi investigated the impact of droplets onto a spherical target by experimental and theoretical method. They observed the initial drop deformation phase, the inertia dominated phase, and the viscosity dominated phase of the ﬁlm dynamics. They also presented the effect of droplet Reynolds number and target-to-drop size ratio on the dynamics of the ﬁlm ﬂow on the surface of the target. Hardalupas conducted experiments to investigate the phenomenon of monodisperse water-ethanol- glycerol solution droplets (160-230 μm diameter) impinging at velocity of 6-13m/s upon a spherical surface (0.8-1.4mm diameter). They observed crown liquid jet with the effect of surface roughness, droplet kinetic energy and liquid properties. Rozhkov presented the results of the collision of water drops(2.8-4mm diameter) impact on a steel disk(3.9 mm diameter) at the impact velocity of 3.5m/s. They observed the effect of rupture wave on liquid jet disintegration. Mitra carried out research about droplet impact on a highly thermally conductive spherical surface. They also studied the effect of Weber number on droplets spreading. In fact, droplet impact on a small target has enormous applications in new areas on drop/spray impact.
cloud forests (e.g. Eugster et al., 2006; Holwerda et al., 2006; Beiderwieden, 2007; Beiderwieden et al., 2008; Schmid et al., 2010), in temperate ecosystems (Burkard et al., 2002; Thalmann, 2002; Burkard, 2003), and deposition fluxes in rather arid areas (Westbeld et al., 2009). It has also been used as a single instrument for microphysical studies of fog (Gonser et al., 2011; Liu et al., 2011) and compared to other devices (Holwerda et al., 2006; Schmid et al., 2010; Frumau et al., 2011). Most of the presented work used the channel configuration defined by the manufacturer in order to trans- late the voltage to a droplet size; while Niu et al. (2010) used the 20 channel configuration, which is the one that is used by the manufacturer to calibrate the instrument, some of the authors (Burkard et al., 2002; Eugster et al., 2006; Beider- wieden, 2007; Beiderwieden et al., 2008; Westbeld et al., 2009; Frumau et al., 2011) used the 40 channel configura- tion in order to obtain a better resolved size distribution. A different approach was taken by Gonser et al. (2011) – which is one of the most recent publications – who defined their own 23 channel sizes and widths by using Mie curves prior to sampling. Such a procedure has already been suggested earlier for the FSSP (Pinnick et al., 1981; Dye and Baum- gardner, 1984). Nevertheless, this has not been the standard procedure for the FM-100 so far. Here, we will propose a similar procedure that can be applied after sampling.
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the electrokinetic potential of a particle and it is measured by evaluating its ability when interacting with a liquid surface. The determination of ζ-potential can be affected by the interaction between the particle surface and the dispersing medium by means of ionically charged functional groups present at the interface or through the adsorption of ionic species present in the medium. Values of ζ-potential higher than 30 mV (positive or negative) are usually indicators of a good system stability . Primary emulsions presented values of ζ-potential that indicate stable systems, in particular it was of − 53 ± 11 mV for A-T-LEO L and − 24 ± 1 mV for A-T-LEO H. The negative electrical charge observed can be mainly attributed to the anionic residues of sodium alginate that characterize the continuous phase . Both, the suspension with only alginate and with alginate plus Tween 80, showed a higher negative value of ζ-potential ( − 71 ± 5 mV and − 45 ± 3 mV, respectively). This indicates that the surface electrical charge of the emulsion particles was affected by the partition of polymer chains between the continuous phase and the particle surface that are affected by the droplet size and volume fraction of dispersed phase determining the total interfacial area.
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Microemulsions have a variety of applications in agrochemical industry, of which pesticide- containing systems are relatively old. The ease of handling and lower requirement of smelly solvents go in favour of the use of micro emulsions. Microemulsions formulated with a hydrotope solubilizing the herbicide can be promising.The much finer droplet size of the microemulsion leads to higher penetrability, much larger contact area of the active substance to the treated surface and a much more even distribution during application. Microemulsions in analytical applications : Applications of microemulsions in the field of analytical techniques, are chromatography, laser- excited photoionization spectroscopy, etc. The characterization of solute hydrophobicity by microemulsion electrokinetic chromatography (MEEKC) has been attempted , which provides a quick and reproducible method to obtain hydrophobic parameters for solvents.
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The system used in this work represents a benchtop apparatus that is highly adaptable to other benchtop pip- etting system due to the simplicity of wire-guided drop- let manipulation. Because the method employed is not highly-complex, it alludes to the ability for further miniaturization, making a potentially portable device for performing a nearly limitless number of protocols, in- cluding all of their variations. Future works includes the development of a handheld device for use in the field using an encapsulated silicone oil bath system cartridge. A one-time use cartridge makes contamination a non- issue, and the closed system prevents messy operation and ensures droplet stability while submerged. The de- sign includes a circular chamber, as opposed to an or- thogonal chamber, reducing the number of step motors to just two for complete operation. The encapsulated cartridge, circular design and reduced number of step motors will make the final device substantially smaller. Thus, this work demonstrates the reconfigurability of the system to replace many common laboratory tasks on a single platform (through reprogrammability), in rapid succession (using droplets), and with a high level of
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Following the pioneering works of Godsave  and Spalding , is developed a theoretical model which de- scribes the process of evaporation of a drop in the subcritical condition. This model, which is termed “Quasi-Steady Model” and also called -law, predicts that during the evaporation process, the droplet surface area, represented by the drop-squared diameter (the droplet being spherical), decreases linearly during its lifetime. Although this model is very successful in describing the vaporization process of fuel drop, the assumptions upon which the model has been developed are subjected to several experimental and nu-
Qian and Law (1997) presented the results of a comprehensive experimen- tal investigation of binary droplet collision dynamics with emphasis on the transition between different collision outcomes. They carried out numerous experiments involving different liquids, different environments and different gas pressures, and they also produced photographic images of the processes under examination. According to their experimental results, the ambient gas pressure affects the location of the boundary curves. If the gas pressure is low, then droplet bounce occurs only for large impact parameters, i.e. the tran- sition curves C and D intersect each other in certain cases of B > 0, while the regions of coalescence after minor and substantial deformation are not distinct. On the other hand, if the gas pressure is high, then transition curve C moves toward higher Weber numbers, while the transition curve D moves in the opposite direction. Thus, if the gas pressure increases, then the region of slow coalescence tends to shrink or even disappear. All the experimental results revealed in Qian and Law (1997) show good qualitative agreement with the regimes of outcomes and the transition between them obtained by the con- ditions presented in this section. Their results for water droplets in a nitrogen environment at a gas pressure of around 2 · 10 5 Pa coincide entirely with our
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The details of experimental procedure can be found in ref 89. The hair tresses were secured in a special frame to provide as much hair alignment as possible for wetting measurements. The thickness of the tresses was su ﬃ cient to avoid contact of the investigated liquid with the frame material. There was some expected variation in the arrangement of individual hair ﬁ bers on the frame in the repeat experiments, leading to the increased standard error in the measurements. Measurements of the contact angle were performed on dry hair tresses. The contact angle, θ , the droplet volume, V, and the droplet base diameter, 2L, were monitored as functions of time, t. The processing time was de ﬁ ned as the time during which the droplet remains on the hair tress. The initial contact angle was measured right after droplet deposition. The ﬁ nal (static advancing) contact angle was measured at the end of spreading when 2L reached a plateau. All measurements were made at 20 ° C and 40% relative humidity, and the droplet volume was 2 − 3 μ L. At least 10 repeat mea- surements were performed on hair tresses, and the error was in the range of 10 − 20% due to variations in the tress arrangement on the frame, as mentioned above.
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