ON THE PREDICTIONOFAN AVERAGE DROPLET SIZE EVOLUTION DURING TRANSPORT IN HOMOGENEOUSPOROUS MEDIA UNDERLAMINAR FLOW CONDITIONS

This study describes the dynamic behaviors of droplet formation in microfluidic cross-junction devices (MFCDs) based on a two-dimensional numerical model using the volume of fluid (VOF) method. The effects of the junction angle (ϕ = 30 to 90 deg) between the main and side channels and the viscosity ratios (β = 10−5 to 2.0) are considered. The numerical results indicate that the active area for droplet formation in the alternating digitized pattern formation (ADPF) generally increases with the decrease of ϕ at the same water fraction (wf). A junction angle of around 60 deg was predicted as the most efficient angle at which alternating droplets are still formed at lower capillary numbers (Ca). In addition, the droplet size in ADPF decreases as ϕ increases with the same flow conditions. When ϕ is less than 90 deg and prior to approaching the equilibrium state, there always exists a periodic deviation in the relative distance between droplets. The frequency of droplet generation in ADPF decreases as ϕ decreases, and it decreases more quickly when ϕ is less than 60 deg. In addition, the throughput of MFCDs can be controlled effectively as a function of ϕ, wf, and Ca. The droplet formation in MFCDs depends significantly on the viscosity ratio β, and the ADPF becomes a jetting formation (JF) when β is greater than unity. Furthermore, the droplet size in ADPF decreases with the increase of β. The understanding of droplet formation in MFCDs is very useful for many applications, such as nanoparticle synthesis with different concentrations, hydrogel bead generation, or cell transplantation in biomedical therapy.

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Description of the Droplet Size Evolution in Flowing Immiscible Polymer Blends

Polymers ◽

10.3390/polym11050761 ◽

2019 ◽

Vol 11 (5) ◽

pp. 761 ◽

Cited By ~ 9

Author(s):

Fortelný ◽

Jůza

Keyword(s):

Polymer Blends ◽

Droplet Size ◽

Phase Structure ◽

Droplet Breakup ◽

Structure Evolution ◽

Immiscible Polymer Blends ◽

Collision Efficiency ◽

Immiscible Polymer ◽

Size Evolution ◽

Analytic Expressions

Control of the phase structure evolution in flowing immiscible polymer blends during their mixing and processing is fundamental for tailoring of their performance. This review summarizes present state of understanding and predictability of the phase structure evolution in flowing immiscible polymer blends with dispersed structure. Results of the studies of the droplet breakup in flow, important for determination of the droplet breakup frequency and of the size distribution of the daughter droplets, are reviewed. Theories of the flow-induced coalescence providing equations for collision efficiency are discussed. Approximate analytic expressions reliably describing dependence of the collision efficiency on system parameters are presented. Available theories describing the competition between the droplet breakup and coalescence in flow are summarized and approximations used in their derivation are discussed. Problems with applicability of available theories on prediction of the droplet size evolution during mixing and processing of immiscible polymer blends, which have not been broadly discussed so far, are addressed.

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A Study on Diesel Fuel Drop Size Distribution

10.1115/imece2000-1653 ◽

2000 ◽

Author(s):

Badih A. Jawad

Keyword(s):

Droplet Size ◽

Drop Size ◽

Optical Measurement ◽

Optical Signal ◽

Diesel Fuels ◽

Intermittent Behavior ◽

Size Evolution ◽

Cylindrical Volume ◽

Droplet Size Distributions ◽

Collimated Beam

Abstract A pulsed Malvern drop-size analyzer, based on Fraunhofer diffraction, was utilized to determmine droplet size size ranges of diesel fuels under different conditions of injection. the effects of fuel properties, design and operating parameters on the formation of diesal spray are discussed. In these studies, the spray is formed by injecting a calibrated amount of fuel into air with the frequency of the intermittent behavior controlled by the speed of the fuel pump. In this study, an injection cycle was tailored so that it was divided into several increments which were injected sequentially. A two mm diammeter collimated beam illuminated a cylindrical volume perpendicular to the axis of the fuel spray, and its attenuation was recorded and stored on the oscilloscope. With the optical measurement being synchronized to the needle lift of the injector, the output of the needle lift transducer and the optical signal was recorded simultaneously. Thus, the arrival and the duration of the spray at various positions along its axis were measured. The droplet size distributions were obtained directly as penetration measurements were made. However, by applying a delay time through the synchronization feature of the sizer, information about droplet size evolution within the same spray was possible. Distribution widths are plotted as a function of time for different chamber pressures, injection pressures, different positions, and different fuels. Coagulation seems to be a dominant phenomenon in these studies.

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On the performance of a cascade of turbine rotor tip section blading in wet steam Part 2: Surface pressure distributions

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/0954406971521917 ◽

1997 ◽

Vol 211 (7) ◽

pp. 531-540 ◽

Cited By ~ 19

Author(s):

F Bakhtar ◽

H Mashmoushy ◽

O C Jadayel

Keyword(s):

Droplet Size ◽

Surface Pressure ◽

Turbine Rotor ◽

Pressure Measurements ◽

Wet Steam ◽

Flow Conditions ◽

Two Phase ◽

Blow Down ◽

Pressure Distributions ◽

Phase Mixture

In the course of expansion in turbines steam nucleates to become a two-phase mixture, the liquid consisting of a very large number of extremely small droplets carried by the vapour. Formation and subsequent behaviour of the liquid lowers the performance of turbine wet stages. To produce turbine nucleating and wet flow conditions realistically requires a supply of supercooled steam which can be achieved under blow-down conditions by the equipment employed. To obtain wet steam, the supercooled vapour generated is passed through a venturi before admission to the cascade. To evaluate the influence of droplet size two separate Venturis have been used in the investigation. The performance of a cascade of rotor tip section blading in wet steam has been studied. This paper is the second of a set and describes the results of the surface pressure measurements.

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Droplet Measurement in a Rod Bundle Geometry for a Reflood Heat Transfer Test

18th International Conference on Nuclear Engineering: Volume 4, Parts A and B ◽

10.1115/icone18-30286 ◽

2010 ◽

Author(s):

H. K. Cho ◽

K. Y. Choi ◽

S. Cho ◽

C.-H. Song

Keyword(s):

Heat Transfer ◽

Droplet Size ◽

Superheated Steam ◽

Image Processing Technique ◽

Test Facility ◽

Flow Conditions ◽

Spacer Grid ◽

Rod Bundle ◽

Droplet Behavior ◽

Break Up

During the reflood phase of a postulated loss of coolant accident in a nuclear reactor, the entrainment of liquid droplets can occur at a quench front of reflooding water. It is widely recognized that the behavior of the entrained droplet crucially affects the reflood heat transfer phenomena by decreasing the superheated steam temperature and interacting with a rod bundle and spacer grids. For this reason, various experimental and numerical studies have been performed to examine droplet behavior such as the droplet size, velocity and droplet fraction inside a rod array. In this study, an experiment on the droplet behavior inside a heated rod bundle has been performed. The experiment was focused on the break-up of droplets induced by a spacer grid in a rod bundle geometry, which results in the increase of the interfacial heat transfer between droplets and superheated steam. A 6×6 rod bundle test facility in Korea Atomic Energy Research Institute was used for the experiment. Steam was supplied by an external boiler into the bottom of the test channel, and a droplet injection nozzle was equipped instead of simulating a quench front of reflooding water. The major measuring parameters of the experiment were the droplet size and velocity, and these were measured by a high-speed camera and a digital image processing technique. A series of experiments were conducted with various flow conditions of a steam injection velocity, heater temperature, droplet size and droplet flow rate. The experiments provided the data on the change of the Sauter mean diameter of droplets after collision with a spacer grid depending on flow conditions. Moreover, the data was analyzed with a droplet break-up model by a spacer grid which was implemented into a thermal hydraulic analysis code, COBRA-TF.

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Influence of Cavitation and Mixing Conditions on Oil Droplet Size in Simultaneous Homogenization and Mixing (SHM)

ChemEngineering ◽

10.3390/chemengineering4040064 ◽

2020 ◽

Vol 4 (4) ◽

pp. 64

Author(s):

Vanessa Gall ◽

Heike P. Karbstein

Keyword(s):

High Pressure ◽

Droplet Size ◽

Flow Conditions ◽

Mixing Conditions ◽

Oil Droplet ◽

Application Range ◽

Emulsion Droplets ◽

Save Energy ◽

Level Of Understanding ◽

Oil Droplet Size

High-pressure homogenizers (HPH) equipped with a Simultaneous Homogenization and Mixing (SHM) orifice allow for inducing a mixing stream directly into the disruption unit. Previous studies show that by doing so, synergies between the unit operations “emulsification” and “mixing” can be used to save energy, e.g., in homogenization of dairy products, or to extend the application range of HPH. Up to now, process design has mainly been based on the trial and error principle due to incomplete understanding of flow conditions and droplet break-up in the SHM unit. This study aims at a higher level of understanding of cavitation and mixing effects on emulsion droplet size. Experimental data were obtained using a model emulsion of low disperse phase concentration in order to avoid coalescence effects. The different flow conditions are created by varying the process and geometric parameters of an SHM unit. The results show that the oil droplet size only depends on mixing conditions when the emulsion droplets are added in the mixing stream. Furthermore, a smaller oil droplet size can be achieved by reducing cavitation, especially for droplets fed in the high-pressure stream.

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Bed Surface Grain Size Evolution under Unsteady Flow Conditions in a Degrading Channel

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/304/2/022024 ◽

2019 ◽

Vol 304 ◽

pp. 022024

Author(s):

Zhijing Li ◽

QiuliLi ◽

Zhongwu Jin ◽

Shiming Yao ◽

YinjunZhou

Keyword(s):

Grain Size ◽

Unsteady Flow ◽

Flow Conditions ◽

Size Evolution

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Droplet size evolution during coalescence in semiconcentrated model blends

AIChE Journal ◽

10.1002/aic.690440421 ◽

1998 ◽

Vol 44 (4) ◽

pp. 951-958 ◽

Cited By ~ 74

Author(s):

I. Vinckier ◽

P. Moldenaers ◽

A. M. Terracciano ◽

N. Grizzuti

Keyword(s):

Droplet Size ◽

Size Evolution

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Investigation of irradiation-induced nucleation processes in silicon and germanium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100137495 ◽

1995 ◽

Vol 53 ◽

pp. 224-225

Author(s):

Harry A. Atwater ◽

C.M. Yang ◽

K.V. Shcheglov

Keyword(s):

Room Temperature ◽

Crystal Size ◽

Initial Distribution ◽

Engineering Control ◽

Size Evolution ◽

Silicon And Germanium ◽

Ge Quantum Dot ◽

And Control ◽

Germanium Quantum Dots ◽

Kinetics Of

Studies of the initial stages of nucleation of silicon and germanium have yielded insights that point the way to achievement of engineering control over crystal size evolution at the nanometer scale. In addition to their importance in understanding fundamental issues in nucleation, these studies are relevant to efforts to (i) control the size distributions of silicon and germanium “quantum dots𠇍, which will in turn enable control of the optical properties of these materials, (ii) and control the kinetics of crystallization of amorphous silicon and germanium films on amorphous insulating substrates so as to, e.g., produce crystalline grains of essentially arbitrary size.Ge quantum dot nanocrystals with average sizes between 2 nm and 9 nm were formed by room temperature ion implantation into SiO2, followed by precipitation during thermal anneals at temperatures between 30°C and 1200°C[1]. Surprisingly, it was found that Ge nanocrystal nucleation occurs at room temperature as shown in Fig. 1, and that subsequent microstructural evolution occurred via coarsening of the initial distribution.

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Thrombus formation on artificial surfaces: Correlative microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010016176x ◽

1990 ◽

Vol 48 (3) ◽

pp. 840-841

Author(s):

Quintin J. Lai ◽

Stuart L. Cooper ◽

Ralph M. Albrecht

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Low Voltage ◽

Thrombus Formation ◽

Blood Platelets ◽

Polymer Surfaces ◽

Flow Conditions ◽

Transmission Electron ◽

Adhesion Of Platelets ◽

Microscopic Techniques

Thrombus formation and embolization are significant problems for blood-contacting biomedical devices. Two major components of thrombi are blood platelets and the plasma protein, fibrinogen. Previous studies have examined interactions of platelets with polymer surfaces, fibrinogen with platelets, and platelets in suspension with spreading platelets attached to surfaces. Correlative microscopic techniques permit light microscopic observations of labeled living platelets, under static or flow conditions, followed by the observation of identical platelets by electron microscopy. Videoenhanced, differential interference contrast (DIC) light microscopy permits high-resolution, real-time imaging of live platelets and their interactions with surfaces. Interference reflection microscopy (IRM) provides information on the focal adhesion of platelets on surfaces. High voltage, transmission electron microscopy (HVEM) allows observation of platelet cytoskeletal structure of whole mount preparations. Low-voltage, high resolution, scanning electron microscopy allows observation of fine surface detail of platelets. Colloidal gold-labeled fibrinogen, used to identify the Gp Ilb/IIIa membrane receptor for fibrinogen, can be detected in all the above microscopies.

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