Fluid Drop Research Articles

Ultra-Hydrophobic Water

When a drop of a viscous fluid is deposited on a bath of the same fluid that is vibrating, it is shown that it coalesces with this substrate or lifts off when the vibration of the surface is larger than g, leading to a steady condition where a drop can be kept bouncing for any length of time, as shown in figure 1. The phenomena that will occur depends on various parameters, such as drop impact acceleration, liquid surface tension, density, dynamic viscosity, gravity, droplet radius and impact speed, bath vibration frequency and amplitude. The effect of different parameters will conclude to a set of conditions which results in a system, called “ultra-hydrophobic water” which plays important role in chemical micro fluidic applications.

Leukocyte Esterase as a Biomarker in the Diagnosis of Periprosthetic Joint Infection.

BackgroundTotal joint arthroplasty (TJA) has been one of the most rewarding interventions for treating patients suffering from joint disorders. However, periprosthetic joint infection (PJI) is a serious complication that frequently accompanies TJA. Our study aimed to investigate the application of the leukocyte esterase (LE) strip in the diagnosis of PJI.Material/MethodsFrom October 2014 to July 2015, 72 patients who had undergone joint puncture after arthroplasty in our hospital were enrolled in this trial. One drop of synovial fluid from each available patient was applied to the LE strip, and the results were observed after 1–3 min. If the color turned to dark purple, we recognized this as a positive result, while other colors were regarded as negative results. Centrifugation was used when the synovial fluid was mixed with blood. The Musculoskeletal Infection Society (MSIS) definition was used as the standard reference to identify whether PJI was found in patients or not. The results of diagnosis and LE strips test were compared, and indicators reflecting diagnostic value were calculated. Correlation of the LE data with erythrocyte sedimentation rate (ESR), elevated C-reactive protein (CRP), synovial white blood cell (WBC) counts, and polymorphonuclear neutrophil (PMN) percentage was calculated.ResultsBy MSIS criteria, 38 patients were diagnosed with PJI and 34 patients were not infected. Two types of LE strip presented the same results with sensitivity of 84.21% (95% confidence interval [CI]: 68.75~93.98%), specificity of 97.06% (95% CI: 84.67~99.93%), positive predictive value (PPV) of 96.97% (95% CI: 84.24~99.92%), and negative predictive value (NPV) of 84.62% (95% CI: 69.47~94.14%). There were one false-positive case and six false-negative cases in this trial. There is a strong correlation between LE strip and synovial fluid PMN percentage.ConclusionsThe sensitivity and specificity of the LE strip in the diagnosis of PJI are quite high, which means the LE strip might be used as an alternative to diagnose PJI in clinical practice.

Comparison of the hanging-drop technique and running-drip method for identifying the epidural space in dogs

ObjectiveTo compare the running-drip and hanging-drop techniques for locating the epidural space in dogs. Study designProspective, randomized, clinical trial. AnimalsForty-five healthy dogs requiring epidural anaesthesia. MethodsDogs were randomized into four groups and administered epidural anaesthesia in sternal (S) or lateral (L) recumbency. All blocks were performed by the same person using Tuohy needles with either a fluid-prefilled hub (HDo) or connected to a drip set attached to a fluid bag elevated 60 cm (RDi). The number of attempts, ‘pop’ sensation, clear drop aspiration or fluid dripping, time to locate the epidural space (TTLES) and presence of cerebrospinal fluid (CSF) were recorded. A morphine–bupivacaine combination was injected after positive identification. The success of the block was assessed by experienced observers based on perioperative usage of rescue analgesia. Data were checked for normality. Binomial variables were analysed with the chi-squared or Fisher’s exact test as appropriate. Non-parametric data were analysed using Kruskal–Wallis and Mann–Whitney tests. Normal data were studied with an anova followed by a Tukey's means comparison for groups of the same size. A p-value of < 0.05 was considered to indicate statistical significance. ResultsLateral recumbency HDo required more attempts (six of 11 dogs required more than one attempt) than SRDi (none of 11 dogs) (p = 0.0062). Drop aspiration was observed more often in SHDo (nine of 11 dogs) than in LHDo (two of 11 dogs) (p = 0.045). Mean (range) TTLES was longer in LHDo [47 (18–82) seconds] than in SHDo [20 (14–79) seconds] (p = 0.006) and SRDi [(34 (17–53) seconds] (p = 0.038). There were no differences in ‘pop’ sensation, presence of CSF, rescue analgesia or pain scores between the groups. Conclusion and clinical relevanceThe running-drip method is a useful and fast alternative technique for identifying the epidural space in dogs. The hanging-drop technique in lateral recumbency was more difficult to perform than the other methods, requiring more time and attempts.

EFFECTS OF SODIUM HYPOCHLORITE ON THE PROTOSCOLICES OF ECHINOCOCCUS GRANULOSUS AND MEMBRANES OF HYDATID CYSTS

Aim . To assess sodium hypochlorite water solution anti-scolex activity against Echinococcus granulosus protoscolexies and effect on secondary echinococcus cysts envelopes. Material and methods. We preformed two in vitro trials of the sodium hypochlorite water solution 0.06%, 0.12%, 0.25%, 0.5%, 1%, 2% and 4%. Sodium hypochlorite water solution anti-scolex activity versus exposure and the concentration of the drug was assessed in the first trial. Two drops of sodium hypochlorite water solution of various concentrations were added to the drop of the echinococcal fluid with living protoscalexes. The morphological changes of the parasite were investigate with a light microscope with a 100X magnification. The death of protoscolexes occurred within the first minute after the addition of sodium hypochlorite water solution, irrespective of solution concentration. The effect of sodium hypochlorite water solution on the secondary Echinococcus granulosus cysts envelopes was evaluated in the second trial. Envelopes fragments of the secondary echinococcal cysts were placed in tubes with sodium hypochlorite water solution in different concentrations. The changes were evaluated macroscopically. The envelopes of the secondary echinococcal cysts were completely dissolved in all tubes with sodium hypochlorite water solution. Results . The experimental data have showed that sodium hypochlorite water solution is an effective anti-scolex medication enabling completely dissolution of the secondary echinococcal cysts envelops. Conclusions. Considering that sodium hypochlorite is thoroughly investigated and safe for human body, sodium hypochlorite could be “ultimate” anti-scolex medication, enabling extension of indications and ad value for less invasive percutaneous interventions under radiation control in echinococcosis.

The hydrodynamics of segmented two-phase flow in a circular tube with rapidly dissolving drops.

This article discusses boundary integral simulations of dissolving drops flowing through a cylindrical tube for large aspect ratio drops. The dynamics of drop dissolution is determined by three dimensionless parameters: λ, the viscosity of the drop fluid relative to the suspending fluid; Ca, the capillary number defining the ratio of the hydrodynamic force to the interfacial tension force; and k, a dissolution constant based on the velocity of dissolution. For a single dissolving drop, the velocity in the upstream region is greater than the downstream region, and for sufficiently large k, the downstream velocity can be completely reversed, particularly at low Ca. The upstream end of the drop travels faster and experiences greater deformation than the downstream end. The film thickness, δ, between the drop and the tube wall is governed by a delicate balance between dissolution and changes in the outer fluid velocity resulting from a fixed pressure drop across the tube and mass continuity. Therefore, δ, and consequently, the drop average velocity, can increase, decrease or be relatively invariant in time. For two drops flowing in succession, while low Ca drops maintain a nearly constant separation distance during dissolution, at sufficiently large Ca, for all values of k, dissolution increases the separation distance between drops. Under these conditions, the liquid segments between two adjacent drops can no longer be considered as constant volume stirred tanks. These results will guide the choices of geometry and operating parameters that will facilitate the characterization of fast gas-liquid reactions via two-phase segmented flows.

Interplay between viscosity and elasticity in freely expanding liquid sheets

We investigate the dynamics of freely expanding liquid sheets prepared with fluids with different rheological properties, (i) viscous fluids with a zero-shear viscosity $\eta_0$ in the range $(1-1000) \, \mathrm{mPa.s}$ and (ii) viscoelastic Maxwell fluids whose elastic modulus, $G_0$, characteristic relaxation time, $\tau$, and zero-shear viscosity, $\eta_0=G_0 \tau$, can be tuned over several orders of magnitude. The sheets are produced by impacting a drop of fluid on a small cylindrical solid target. For viscoelastic fluids, we show that, when $\tau$ is shorter than the typical lifetime of the sheet ($\sim 10$ ms), the dynamics of the sheet is similar to that of Newtonian viscous liquids with equal zero-shear viscosity. In that case, for little viscous samples ($\eta_0 <\sim 30$ mPa.s), the maximal expansion of the sheet, $d_{\rm{max}}$, is independent of $\eta_0$, whereas for more viscous samples, $d_{\rm{max}}$ decreases as $\eta_0$ increases. We provide a simple model to account for the dependence of the maximal expansion of the sheet with the viscosity that is based on an energy balance between inertia, surface tension and viscous shear dissipation on the solid target, and which accounts well for our experimental data. By contrast, when $\tau$ is longer than the typical lifetime of the sheet, the behavior drastically differs. The sheet expansion is strongly enhanced as compared to that of viscous samples with comparable zero-shear viscosity, but is heterogeneous with the occurrence of cracks, revealing the elastic nature of the viscoelastic fluid.

Finite stopping times for freely oscillating drop of a yield stress fluid

The paper addresses the question if there exists a finite stopping time for an unforced motion of a yield stress fluid with free surface. A variational inequality formulation is deduced for the problem of yield stress fluid dynamics with a free surface. The free surface is assumed to evolve with a normal velocity of the flow. We also consider capillary forces acting along the free surface. Based on the variational inequality formulation an energy equality is obtained, where kinetic and free energy rate of change is in a balance with the internal energy viscoplastic dissipation and the work of external forces. Further, the paper considers free small-amplitude oscillations of a droplet of Herschel-Bulkley fluid under the action of surface tension forces. Under certain assumptions it is shown that the finite stopping time Tf of oscillations exists once the yield stress parameter is positive and the flow index α satisfies α ≥ 1. Results of several numerical experiments illustrate the analysis, reveal the dependence of Tf on problem parameters and suggest an instantaneous transition of the whole drop from yielding state to the rigid one.

Hydrodynamics of Highly Viscous Flow past a Compound Particle: Analytical Solution

To investigate the translation of a compound particle in a highly viscous, incompressible fluid, we carry out an analytic study on flow past a fixed spherical compound particle. The spherical object is considered to have a rigid kernel covered with a fluid coating. The fluid within the coating has a different viscosity from that of the surrounding fluid and is immiscible with the surrounding fluid. The inertia effect is negligible for flows both inside the coating and outside the object. Thus, flows are in the Stokes regime. Taking advantage of the symmetry properties, we reduce the problem in two dimensions and derive the explicit formulae of the stream function in the polar coordinates. The no-slip boundary condition for the rigid kernel and the no interfacial mass transfer and force equilibrium conditions at fluid interfaces are considered. Two extreme cases: the uniform flow past a sphere and the uniform flow past a fluid drop, are reviewed. Then, for the fluid coating the spherical object, we derive the stream functions and investigate the flow field by the contour plots of stream functions. Contours of stream functions show circulation within the fluid coating. Additionally, we compare the drag and the terminal velocity of the object with a rigid sphere or a fluid droplet. Moreover, the extended results regarding the analytical solution for a compound particle with a rigid kernel and multiple layers of fluid coating are reported.

Absorption of picoliter droplets by thin porous substrates

Absorption of picoliter (pL) droplets into porous substrates is studied experimentally and numerically. In the case of pL droplets, major phenomena involved in the interaction between droplet and porous media develop at different time scales: spreading and wetting at microseconds, absorption and wicking at milliseconds, and evaporation at seconds. Therefore, one can decouple these processes to minimize the complexity of the study. A high‐speed imaging system capable of 1 million frames per second is used to visualize individual droplets impacting, spreading, and imbibing on substrates. To simulate droplet dynamics, the governing equations for flow outside and inside porous media are proposed and solved using an in‐house developed computational fluid dynamics solver. The simulation results are in good agreement with the experimental data. The effect of drop impact velocity and fluid properties on final dot shape in the porous substrates is investigated through a series of parametric numerical studies. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1690–1703, 2017

Puddle jumping: Spontaneous ejection of large liquid droplets from hydrophobic surfaces during drop tower tests

Large droplets and puddles jump spontaneously from sufficiently hydrophobic surfaces during routine drop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamic droplet phenomena for drops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed in drop tower tests including relationships to predict droplet ejection durations and velocities as functions of drop volume, surface texture, surface contour, wettability pattern, and fluid properties including contact angle. The latter is determined via profile image comparisons with numerical equilibrium interface computations. Water drop volumes of 0.04–400 ml at ejection speeds of −0.007–0.12 m/s are demonstrated herein. A sample application of the drop jump method is made to the classic problem of low-gravity phase change heat transfer for large impinging drops. Many other candidate problems might be identified by the reader.

Influence of fully miscible lubricating oil on the pressure drop during flow boiling of CO2 inside an enhanced tube

The total static pressure drop in both adiabatic and diabatic two-phase flow conditions during flow boiling of CO2-oil mixtures inside a horizontal enhanced tube of 8.62mm inner diameter were investigated, yielding interesting insights and supporting the design process of evaporators. The nominal mass fraction of fully miscible POE lubricating oil (1.3–3%), saturation pressure (10–39bar), mass flux (75–500kgm−2s−1), inlet vapor quality (0.1–0.9), and heat flux (0–120kWm−2) were varied over a wide range of parameters. An isothermal peripheral boundary condition was realized for the electrically heated tube. Experimentally determined pressure drops are discussed with respect to operating conditions as well as observed flow patterns. The findings are compared to experimental results for pure CO2 obtained in the same test facility under similar conditions. The pressure drop of both pure fluid and a mixture with an oil mass fraction of 1.3% can be predicted satisfactorily by using established correlations including the hydraulic diameter of the enhanced tube. A significant influence of oil on the pressure drop is observed especially for high oil mass fractions, high vapor qualities, and high heat fluxes.

Topological instability of a semi-bounded magnetic fluid drop under influence of magnetic and ultrasound fields

Theoretical and experimental results on deformation and disintegration on parts (topological instability) of semi-bounded magnetic fluid drop placed on horizontal plate in the presence of gravity and vertical external uniform magnetic field, and the influence of acoustic wave on these processes, as well as an experimental results of acoustic fountain on free surface of magnetic fluid are presented. The role of individual mechanisms leading to disintegration is analyzed, and analytical relationships and experimental dependences for critical parameters are established.

Global (weak) solution of the chemotaxis-Navier–Stokes equations with non-homogeneous boundary conditions and logistic growth

In biology, the behaviour of a bacterial suspension in an incompressible fluid drop is modelled by the chemotaxis-Navier–Stokes equations. This paper introduces an exchange of oxygen between the drop and its environment and an additionally logistic growth of the bacteria population. A prototype system is given by{nt+u⋅∇n=Δn−∇⋅(n∇c)+n−n2,x∈Ω,t>0,ct+u⋅∇c=Δc−nc,x∈Ω,t>0,ut=Δu+u⋅∇u+∇P−n∇φ,x∈Ω,t>0,∇⋅u=0,x∈Ω,t>0 in conjunction with the initial data (n,c,u)(⋅,0)=(n0,c0,u0) and the boundary conditions∂c∂ν=1−c,∂n∂ν=n∂c∂ν,u=0,x∈∂Ω,t>0. Here, the fluid drop is described by Ω⊂RN being a bounded convex domain with smooth boundary. Moreover, φ is a given smooth gravitational potential.Requiring sufficiently smooth initial data, the existence of a unique global classical solution for N=2 is proved, where ‖n‖Lp(Ω) is bounded in time for all p<∞, as well as the existence of a global weak solution for N=3.

Mathematical Modelling of Silica Scaling Deposition in Geothermal Wells

Silica scaling is widely encountered in geothermal wells in which produce two-phase geothermal fluid. Silica scaling could be formed due to chemical reacting by mixing a geothermal fluid with other geothermal fluid in different compositions, or also can be caused by changes in fluid properties due to changes pressure and temperature. One of method to overcome silica scaling which is occurred around geothermal well is by workover operation. Modelling of silica deposition in porous medium has been modeled in previously. However, the growth of silica scaling deposition in geothermal wells has never been modeled. Modelling of silica deposition through geothermal is important aspects to determine depth of silica scaling growth and best placing for workover device to clean silica scaling. This study is attempted to develop mathematical models for predicting silica scaling through geothermal wells. The mathematical model is developed by integrating the solubility-temperature correlation and two-phase pressure drop coupled wellbore fluid temperature correlation in a production well. The coupled model of two-phase pressure drop and wellbore fluid temperature correlation which is used in this paper is Hasan-Kabir correlation. This modelling is divided into two categories: single and two phase fluid model. Modelling of silica deposition is constrained in temperature distribution effect through geothermal wells by solubility correlation for silica. The results of this study are visualizing the growth of silica scaling thickness through geothermal wells in each segment of depth. Sensitivity analysis is applied in several parameters, such as: bottom-hole pressure, temperature, and silica concentrations. Temperature is most impact factor for silica scaling through geothermal wellbore and depth of flash point. In flash point, silica scaling thickness has reached maximum because reducing of mole in liquid portion.

Scaling crossover in thin-film drag dynamics of fluid drops in the Hele-Shaw cell.

We study both experimentally and theoretically the descending motion due to gravity of a fluid drop surrounded by another immiscible fluid in a confined space between two parallel plates, i.e., in the Hele-Shaw cell. As a result, we show a new scaling regime of a nonlinear drag friction in viscous liquid that replaces the well-known Stokes’ drag friction through a clear collapse of experimental data thanks to the scaling law. In the novel regime, the dissipation in the liquid thin film formed between the drop and cell walls governs the dynamics. The crossover of this scaling regime to another scaling regime in which the dissipation inside the droplet is dominant is clearly demonstrated and a phase diagram separating these scaling regimes is presented.

A comparison of three different needles used for spinal anesthesia in terms of squamous epithelial cell transport risk

Background and objectivesTo investigate the differences in the number of squamous epithelial cells carried to the spinal canal by three different types of spinal needle tip of the same size. MethodsPatients were allocated into three groups (Group I, Group II, Group III). Spinal anesthesia was administered to Group I (n=50) using a 25G Quincke needle, to Group II (n=50) using a 25G pencil point spinal needle, and to Group III (n=50) using a non-cutting atraumatic needle with special bending. The first and third drops of cerebral spinal fluid (CSF) samples were taken from each patient and each drop was placed on a slide for cytological examination. Nucleated and non-nucleated squamous epithelial cells on the smear preparations were counted. ResultsThere was statistically significant difference between the groups in respect to the number of squamous epithelial cells in the first drop (p<0.05). Group III had lower number of squamous epithelial cells in the first drop compared to that of Group I and Group II. Mean while Group I had higher number of squamous epithelial cells in the third drop compared to the other groups. The number of squamous epithelial cells in the first and third drops was statistically similar in each group respectively (p>0.05 for each group). ConclusionsIn this study of different needle tips, it was seen that with atraumatic needle with special bending a significantly smaller number of cells were transported when compared to the Quincke tip needles, and with pencil point needles.

Energy dissipation in a finite volume of magnetic fluid

This study is devoted to investigation of energy dissipation processes which happen in a magnetic fluid drop with compound magnet during its motion in cylindrical non magnetic container. The possibility of energy dissipation control by means of electromagnetic field is examined. It's found that a change of magnetic field of compound magnet can lead to both increase and decrease of oscillation decay time and relative damping factor can be varied in a range of ±35%.

Effect of Surface Roughness on Contact Angle Measurement of Nanofluid on Surface of Stainless Steel 304 by Sessile Drop Method

Contact angles play an important role in the mass and heat transfer. Stainless steel 304 has been used for nuclear power plan structure material until now. An experiment to measure contact angle of demineralized aqua and nanofluid containing nano particle of zirconia on metal surface of stainless steel 304 with sessile drop method was conducted. The measurement to measure the static contact angle and drop of nano fluid containing nano particle zirconia on stainless steel with different surface roughness was carried out. It was observed that stainless steel 304 was good hydrophylic properties with decreasing surface roughness of stainless steel during drop of aqua demineralized and nano fluid respectively. As a result the contact angle of demineralized aqua is decreased from 97.39 to 78.42 and contact angle of nano fluid from 94.3 to 67.50, respectively with decreasing surface roughness of stainless stee 304. Wettability of nanofluid on surface stainless steel 304 is better than aqua demineralized.

Acoustic microfluidics: Capillary waves and vortex currents in a spherical fluid drop

We calculate the radiation forces in a spherical drop lying on a solid substrate. The forces form as a result of the action of a capillary wave on a fluid as it propagates along the free spherical surface. We study the structure of acoustic currents excited by the radiation forces.

Dielectrophoretic- and electrohydrodynamic-driven translational motion of a liquid column in transverse electric fields

Computer simulations are performed to study translational motion and deformation of a liquid column or jet, in a plane perpendicular to its axis, due to a transverse electric field. A front tracking/finite difference scheme is used in conjunction with the Taylor-Melcher leaky dielectric theory to solve the governing equations. The column is confined within a rectangular channel, wall-bounded in the vertical direction and periodic in the horizontal direction. It is shown that perfect dielectric columns move toward electrode wall of shorter initial distance, but the leaky dielectric columns may move toward or away from it, depending on the relative importance of the ratios (drop fluid to suspending fluid) of their electric permittivity and conductivity. Furthermore, the degree of interface deformation might increase or decrease with the initial separation distance from the shorter electrode wall due to the same factor. Scaling arguments are used to discern the correlation between the translational velocity and the initial separation distance from the electrodes.