Single Liquid Drop Research Articles

Dynamic behaviors during a single liquid drop impact on a static drop located on spheres

Experimental observations during a single liquid drop impinging onto a static hemispherical drop on steel spheres are performed using a high speed digital camera at 10,000 frames per second. The sphere-drop curvature ratio ranges in 0.139–0.558 and the 30vol.% glycerol/water solution and water are selected as experimental fluids. By increasing the Weber number, experimental observations present outcomes of rebound, coalescence, and the circular liquid sheet successively. The circular liquid sheet diameter increases with the Weber number and Reynolds number. With the decrement in the curvature ratio, the liquid sheet diameter varies less at the initial stage, while after the maximum value, the smaller curvature ratio will lead to the larger liquid sheet diameter.

Air–water mass transfer mechanism due to the impingement of a single liquid drop on the air–water interface

The mass transfer mechanism across the air–water interface due to the impingement of a single liquid drop was investigated through laboratory experiments using particle imaging velocimetry (PIV) and planar laser-induced fluorescence technique (PLIF). Velocity and CO2 concentration fields in the liquid after the impingement were visualized. The results show that the impingement of a single liquid drop on the water surface generates several vortex rings near the water surface. The vortex rings renew the water surface and also convect the CO2 gas dissolved near the water surface downward. The vortical motion clearly shows that the vortex rings work as surface-renewal eddies. The radius, center velocity and presence time of surface-renewal eddies increase with increasing momentum of the impinging drop. This suggests that surface-renewal eddies with larger radius and faster center velocity are induced by the impingement of a single drop with larger vertical momentum, and air–water mass transfer is promoted by such eddies. Based on the surface-renewal concept including the area and time fractions, a model for the air–water mass transfer due to multiple impingements of drops is also proposed.

Lattice Boltzmann simulations of drop deformation and breakup in shear flow

The behavior of a single liquid drop suspended in another liquid and subjected to simple shear flow is studied numerically using a diffuse interface free energy lattice Boltzmann method. The system is fully defined by three physical, and two numerical dimensionless numbers: a Reynolds number Re, a capillary number Ca, the viscosity ratio λ, an interface-related Peclet number Pe, and the ratio of interface thickness and drop size (the Cahn number Ch). The influence of Pe,Ch and mesh resolution on accuracy and stability of the simulations is investigated. Drops of moderate resolution (radius less than 30 lattice units) require smaller interface thickness, while a thicker interface should be used for highly resolved drops. The Peclet number is controlled by the mobility coefficient Γ. Based on the results, the simulations are stable when Γ is in the range 1–15. In addition, the numerical tool is verified and validated in a wide range of physical conditions: Re=0.0625-50,λ=1,2,3 and a capillary number range over which drops deform and break. Good agreement with literature data is observed.

Hollow-Channel Paper Analytical Devices

We present a microfluidic paper analytical device (μPAD) that relies on flow in hollow channels, rather than through a cellulose network, to transport fluids. The flow rate in hollow channels is 7 times higher than in regular paper channels and can be conveniently controlled from 0 to several mm/s by balancing capillary and pressure forces. More importantly, the pressure of a single drop of liquid (~0.2 mbar) is sufficient to induce fast pressure-driven flow, making hollow channels suitable for point of care diagnostics. We demonstrate their utility for simple colorimetric glucose and BSA assays in which the time for liquid transport is reduced by a factor of 4 compared to normal cellulose channels.

Crown behavior and bubble entrainment during a drop impact on a liquid film

Physical and mathematical models are established to simulate a single liquid drop impinging onto a liquid film using the coupled level set and volume of fluid method. The crown liquid sheet after impact is obtained, which coincides well with the experimental results in literatures. Influence of Weber number, Reynolds number and the dimensionless film thickness on the crown diameter and height is discussed quantitatively. Results indicate that the crown diameter is independent of the two non-dimensional numbers, while it can be increased by reducing the dimensionless film thickness. The crown height increases with the increasing of Weber number, but Reynolds number has small effect on it. Mechanism of the jet formation process is revealed by analyzing pressure distribution and velocity field in the liquid. It is found that both pressure difference in the neck region and velocity discontinuity can greatly affect the jet formation. Besides, the bubble entrainment phenomenon during a liquid drop impact on a liquid film is successfully captured with this numerical method. It is found that the increase in both impact Weber number and the drop diameter contributes to the emerging of bubble rings.

Spreading and splashing during a single drop impact on an inclined wetted surface

Experimental observations concerning spreading and splashing processes during a single liquid drop impact on an inclined wetted surface are performed using a high-speed digital camera at 10,000 frames per second. The range of the impact angles is 28.0 ◦ -74.7 ◦ . A 30 vol.% glycerol/water solution, butanol and heptane are selected as experimental fluids. Experimental observations show that both surface tension and viscosity can largely affect the spreading and splashing behaviors. Thereinto, the initiatory spreading velocity is mainly discussed quantitatively, which increases with the increasing of both the impact velocity and the impact angle. Surface tension is the main resistance for splashing, while low viscosity results in prompt splashing and high viscosity should be responsible for delayed splashing. Finally, the splashing thresholds are studied, and normal critical Weber numbers are suggested to denote splashing occurrence.

Special phenomena from a single liquid drop impact on wetted cylindrical surfaces

Experimental observations concerning various outcomes during a single butanol drop impact on wetted cylindrical surfaces are performed using a high speed digital camera at 10,000 frames per second. It is found that outcomes after impact differ a lot when the cylinder-drop curvature ratio alters from 0.091 to 2.395. For the impact on the wetted cylinder with the curvature ratio smaller than 0.5, rebound, spreading, cymbiform liquid sheet and splashing emerge in succession with impact velocity increase. However, for the wetted cylinder with the curvature ratio much larger than 1, rebound, coalescence, dripping and disintegration are observed. Several three-dimensional simulations are also conducted to investigate the spreading process in the cylinder directrix direction. It is found that the spreading length can be increased by increasing impact velocity. The curvature ratio cannot influence the spreading factor when the curvature ratio is less than 0.5.

A numerical analysis of drop impact on solid surfaces by using smoothed particle hydrodynamics method

In this paper, we present a numerical simulation of a single liquid drop impacting onto solid surface with smoothed particle hydrodynamics (SPH). SPH is a Lagrangian, meshfree particle method, and it is attractive in dealing with free surfaces, moving interfaces and deformable boundaries. The SPH model includes an improved approximation scheme with corrections to kernel gradient and density to improve computational accuracy. Riemann solver is adopted to solve equations of fluid motion. An new inter-particle interaction force is used for modeling the surface tension effects, and the modified SPH method is used to investigate liquid drop impacting onto solid surfaces. It is demonstrated that the inter-particle interaction force can effectively simulate the effect of surface tension. It can well describe the dynamic process of morphology evolution and the pressure field evolution with accurate and stable results. The spread factor increases with the increase of the initial Weber number. The numerical results are in good agreement with the theoretical and experimental results in the literature.

Motion of a Single Newtonian Liquid Drop Through Quiescent Immiscible Visco-Elastic Liquid: Shape and Eccentricity

The shape of a single Newtonian liquid drop moving freely under gravity in quiescent non-Newtonian liquid (visco-inelastic and visco-elastic) has been studied. Strong effect of fluid elasticity on the shape of Newtonian liquid drop has been observed. Based on experimental observations, a shape regime graph has been suitably modified for elastic fluids. Correlations have also been proposed for the prediction of eccentricity of the Newtonian liquid drop moving through a non-Newtonian visco-elastic liquid.

Direct-contact heat transfer of a single volatile liquid drop evaporation in an immiscible liquid

A semi-analytical approach was presented to study the transient heat transfer of a single volatile drop evaporation in an immiscible liquid with bubble nucleation inside the drop. The solution was based on the energy equation included both convection and conduction heat transfer from the continuous liquid to the bubble with the concentric spheres model. The radius of the growing bubble had been found and the effect of Pr number, St number initial radius, initial velocity and ratio of density were examined. The Nu number derived as a function to the drop velocity was derived. The present results compared well with available data.

A Numerical Method for Two-Phase Flow Based on a Phase-Field Model

For interface-tracking simulation of incompressible two-phase fluids with high density ratios, a new numerical method was proposed by combining Navier-Stokes equations with a phase-field model based on a van der Waals-Cahn-Hilliard free-energy theory. The method was applied to several benchmark problems. Major findings are as follows: (1) The volume flux derived from a local chemical potential gradient in the Cahn-Hilliard equation leads to accurate volume conservation, autonomic reconstruction of gas-liquid interface, and reduction of numerical diffusion and oscillation. (2) The proposed method gave good predictions of pressure increase inside a bubble caused by the surface tension force. (3) A single liquid drop falling in stagnant gas and merging into a stagnant liquid film was successfully simulated.

Hot Surface Ignition of Automotive and Aviation Fluids

Although ignition of flammable liquids by hot surfaces is well known in the automotive and aviation industries, little fundamental research has been conducted to understand this ignition mechanism and only limited data is available in the literature. In this paper, we present results from over 2,500 ignition tests using a simple, highly reproducible experimental set-up involving a horizontal flat plate, a single drop of liquid and a quiescent environment. Results from the 14 automotive and aviation fluids tested showed that ignition was probabilistic, that the probabilistic behavior occurs over a relatively broad temperature range and that the data can be treated statistically using logistic regression. This statistical approach offers the advantages of inference and diagnostic techniques which parallel those of linear regression, and provides a well-defined relationship between surface temperature and ignition probability.

A Numerical Method for Two-Phase Flow Based on a Phase-Field Model

For interface-tracking simulation of incompressible two-phase fluids with a high density ratio, a numerical method based on the combination of a phase field model, Navier-Stokes equation, and a van-der-Waals Cahn-Hilliard (C-H) free energy was proposed in this study. The method was applied to several two-phase flow problems, by which it was confirmed that (1) the volume flux caused by a local chemical potential gradient in the C-H equation plays an important role in (a) volume conservation, (b) automatic reconstruction of gas-liquid interface, and (c) reduction of numerical diffusion and oscillation, (2) the proposed method gives good predictions of pressure increase inside a bubble caused by the surface tension force, and (3) a single liquid drop falling through a stagnant gas and merging into a stagnant liquid film was simulated well.

Modelling of a single drop impact onto liquid film using particle method

AbstractThe process of single liquid drop impact on thin liquid surface is numerically simulated with moving particle semi‐implicit method. The mathematical model involves gravity, viscosity and surface tension. The model is validated by the simulation of the experimental cases. It is found that the dynamic processes after impact are sensitive to the liquid pool depth and the initial drop velocity. In the cases that the initial drop velocity is low, the drop will be merged with the liquid pool and no big splash is seen. If the initial drop velocity is high enough, the dynamic process depends on the liquid depth. If the liquid film is very thin, a bowl‐shaped thin crown is formed immediately after the impact. The total crown subsequently expands outward and breaks into many tiny droplets. When the thickness of the liquid film increases, the direction of the liquid crown becomes normal to the surface and the crown propagates outward. It is also found that the radius of the crown is described by a square function of time: rC = [c(t − t0)]0.5. When the liquid film is thick enough, a crown and a deep cavity inside it are formed shortly after the impact. The bottom of the cavity is initially oblate and then the base grows downward to form a sharp corner and subsequently the corner moves downward. Copyright © 2004 John Wiley & Sons, Ltd.

Enhancement Of Single Liquid Drop MassTransfer Coefficients In A Perforated PlateColumn

Mass transfer coefficients (MTCs) have been measured for single solvent drops rising through non flowing and flowing water in a short section of perforated plate extraction colunin and have been compared with the coefficients measured for free rise conditions in an elnpty column for different systems. Single drop mass tra~isfer coefficients were determined as a function of drop size, mass transfer direction, distance between plates and down flow of the continuous phase. The degree of enha~icement of the dispersed phase film coefficie~it due to the presence of plates has been ascertained. From the data obtained, it is co~icluded that only a moderate enhancement due to the presence of down flow is achieved for single liquid drop with a slightly increase in the drop size with increasing downflow and the coefficients for mass transfer directioii from the dispersed phase into the continuous phase (d + c) are slightly higher than that for the opposite direction. (c+ d).

Reviews Of Acoustical Patents

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet at http://www.uspto.gov.

Single liquid drop breakage probabilities and characteristic velocities in Kühni columns

AbstractStudies have been made on the extent and mechanism of breakage of single liquid drops of organic liquids immiscible in water rising through short sections of Kühni liquid‐liquid extraction columns. Information on drop breakage probabilities is required for calculation of drop size distributions developed under counter‐current column operating conditions. The breakage probability data from two small diameter Kühni columns containing one, three or five stages have been correlated as a function of a modified Weber number based on the shearing forces on drops. The critical condition for breakage, giving a maximum stable drop size, is based on an impeller Weber number. Characteristic velocities of drops were measured relative to terminal velocity and the ratio was tentatively correlated with a function of an impeller Reynolds number together with the fractional free area of the perforated plates used to separate compartments. The drops were found to break predominantly at the holes in the plates, not at the turbine, in the region of transitional Reynolds number used in this work. The results apply only to non‐turbulent conditions so further work on larger diameter equipment is called for.

Single liquid drop velocities and breakage mechanism in sections of structured packings

AbstractSingle liquid drop velocities in structured packings have been measured to aid calculation of throughput of liquid extraction columns using characteristic (single drop) velocities. Solvent drops were passed through two types of glass and two types of steel structured packing and further work was done using sloping glass tubes. Existing wall‐effect equations for drop velocity reduction in vertical tubes were considered and that given by Clift et al. [1] was used as a basis for correlation of structured packing data. Drop breakage was studied in order to improve understanding of drop size distribution development in packed columns. Drops broke only rarely within the structured packing; most of the breakage occurred as a drop hit the exposed edges on entry to a piece of packing. An energy balance equation was used to correlate critical conditions for breakage of drops hitting glass blades at various angles. Under the conditions used all those drops moving at terminal velocity had enough energy to break but a condition exists when drops may be small enough to have insufficient energy to break.

Shattering of a liquid drop due to impact

Based on energy and entropy principles, a statistical model describing the shattered state of a single spherical liquid drop after being subjected to a relatively sudden but uniform (over the whole surface area of the drop) impact is developed. The problem is addressed from a fundamental standpoint, with the intention of providing a predictive framework for the various modes of breakup and the size and number of droplets produced. Upon neglecting viscous effects, several results in terms of the energy of impact, non-dimensionalized with respect to the surface energy of the drop before impact, are derived. The model is quite simple and straightforward, yet it appears to predict in a fairly consistent manner certain experimental observations that have been made repeatedly in relation to drop breakup in stirred dispersions, by collision, and exposure to shocks.

Enhancement of evaporation of droplet using EHD effect.

Enhancement of evaporative heat transfer utilizing an electrostatic field is investigated. Since boiling or evaporation of liquid is useful to remove heat from a high-temperature heat source, finding an effective means of enhancement will bring about a most remarkable improvement of heat exchange technology. In order to understand the fundamental characteristics of the EHD (electro-hydrodynamic) effect on evaporation, an experiment has been carried out by placing a single droplet on a high-temperature surface. The electric field is applied between the surface and the thin wire which holds droplets. The time needed for a single liquid drop (of water, KCI solution, ethanol, or cyclohexane) to evaporate is measured at different surface temperatures. The results show that the electric field is very effective in enhancing evaporation of the drop. The mechanism of enhancement is discussed by observing the process with a high-speed video recorder.