Tension Coefficient Research Articles

Eigenfrequencies of the Oscillating Surface of a Free-Falling Compound Drop of an Ideal Liquid

The surface oscillations of a two-layer drop of an ideal liquid are analyzed. It is shown that two different oscillation frequencies of the taken mode can exist. The effect of the main parameters of the liquids that compose the drop on the mode oscillation eigenfrequencies is analyzed. It is found that a relative decrease in the outer liquid layer thickness leads to a decrease in the eigenfrequencies of both in-phase and out-of-phase oscillations. An increase in the difference between the surface tension coefficients leads to an increase in the eigenfrequencies. Relative increase in the inner liquid density increases the eigenfrequencies of the in-phase mode and affects only slightly the eigenfrequencies of the out-of-phase mode. Simplified expressions for the dependences of the eigenfrequencies of oscillating free surface of a compound drop on parameters are obtained.

Effects of hydrodynamic impact on water from the viewpoint of cluster theory. Surface tension

Variation of surface tension coefficient σ of distilled water under high-energy impact (hydrodynamic cavitation) was studied by the ring separation method. Force impacts on surface tension of water have been studied experimentally. Conditions have been found under which the surface tension coefficient σ decreases to 20%. The paper explains the produced results on the basis of cluster theory of water structure. The experimentally produced relaxation time of the surface tension of cavitation-activated distilled water to initial value has been found to be 3.5 hours.

Optimization of the endodontic retreatment

Aim. Optimization of an endodontic retreatment by performing the following tasks, including the selection of an optimal and safe solvent.Materials and methods. In order to choose the most suitable solvent for the problem, an experiment was conducted with clove, mint, eucalyptus, orange, and grapefruit oils. The surface tension coefficient was measured by the Rebinder apparatus. In order to justify the choice of an effective essential oil, as well as the dissolving ability and the absence of solvent and debris after irrigation with sodium hypochlorite in the root canal, a tube-shaped electron scanning microscopy was performed.Results. Grapefruit oil has the most dissolving activity (p < 0.05). In addition to the solubility of the filler and siller, grapefruit essential oil is able to dissolve the smear layer.Conclusion. Optimization of the endodontic retreatment with root canals previously filled with gutta-percha, is possible using essential oils, however, a grapefruit oil is the most effective.

Numerical investigation on crown behavior and energy evolution of droplet impinging onto thin film

Droplet impact onto thin film is a ubiquitous phenomenon in many industrial applications. In the present study, the VOF method is adopted to simulate the crown evolution during the impact process with different surface tension coefficient, viscosity and gravity. Especially, the crown behavior is investigated in the energy aspect. The kinetic energy, gravitational potential energy, surface energy and viscous dissipation are taken into consideration. The results reveal that higher surface tension coefficient leads to larger crown diameter. The evolution of gravitational potential energy can be divided into three phases: decrease phase, increase phase and collapse phase. Similarly, the evolution of surface energy can be divided into four phases: increase phase, drop phase, flat phase and collapse phase. The drop phase is caused by the film rupture in the center zone. In the case with zero gravity the flat phase is replaced by a second increase phase. In particular, it is found that larger viscosity will postpone the film rupture and the film even doesn't break at high viscosity.

Surface tension and density of Fe – Mn melts

The article presents original experimental data on surface tension of the melts Fe100 – x Mnx (x = 4 ... 13 wt. %). Surface tension and density of the melt was measured by the method of sessile drop at heating from the liquidus temperature up to 1780 °C and subsequent cooling of the sample in the atmosphere of high-purity helium. Temperature and concentration dependences of surface tension and density of Fe – Mn melts was constructed. Manganese is a surface-active substance in iron melt. The value of surface tension coefficient of Fe – Mn melts decreases while Mn content increases. Experimental data on the surface tension of Fe – Mn melts is consistent with the theoretical dependences (Pavlova-Popiel equation and the Shishkovsky equation). During the study of microheterogeneity of Fe – Mn melts, correlation between the values of kinematic viscosity, surface tension and density was determined. Dependence of the fluidity of Fe – Mn melts on their density in the cooling mode has a linear character which indicates the implementation of the Bachinsky law. Discrepancy of values of the ratio of melt viscosity to the surface tension coefficient was obtained from experimental data and was calculated by the empirical formula. According to the experimental data on viscosity and surface tension of Fe – Mn melts, the authors have evaluated the entropy change in volume of the melt and change of surface entropy of the melt, respectively. Surface entropy of the melt and entropy in the melt volume decreases in absolute value with increase of Mn content in it. According to the results of the work, it was concluded that there is no destruction of the microheterogeneous structure of Fe100 – x Mnx melts (x = 4 ... 13 wt. %) when heated up to 1780 °С.

Surface tension and density of Fe – Mn melts

The article presents original experimental data on surface tension of the melts Fe100 – x Mnx (x = 4 ... 13 wt. %). Surface tension and density of the melt was measured by the method of sessile drop at heating from the liquidus temperature up to 1780 °C and subsequent cooling of the sample in the atmosphere of high-purity helium. Temperature and concentration dependences of surface tension and density of Fe – Mn melts was constructed. Manganese is a surface-active substance in iron melt. The value of surface tension coefficient of Fe – Mn melts decreases while Mn content increases. Experimental data on the surface tension of Fe – Mn melts is consistent with the theoretical dependences (Pavlova-Popiel equation and the Shishkovsky equation). During the study of microheterogeneity of Fe – Mn melts, correlation between the values of kinematic viscosity, surface tension and density was determined. Dependence of the fluidity of Fe – Mn melts on their density in the cooling mode has a linear character which indicates the implementation of the Bachinsky law. Discrepancy of values of the ratio of melt viscosity to the surface tension coefficient was obtained from experimental data and was calculated by the empirical formula. According to the experimental data on viscosity and surface tension of Fe – Mn melts, the authors have evaluated the entropy change in volume of the melt and change of surface entropy of the melt, respectively. Surface entropy of the melt and entropy in the melt volume decreases in absolute value with increase of Mn content in it. According to the results of the work, it was concluded that there is no destruction of the microheterogeneous structure of Fe100 – x Mnx melts (x = 4 ... 13 wt. %) when heated up to 1780 °С.

Numerical Analysis of Droplet Motion over a Flat Plate Due to Surface Acoustic Waves

Micro-scale systems have gained considerable attention in recent years and a large amount of researches have been done in this field. In this study, the hydrodynamic interference of a droplet is comprehensively investigated under surface acoustic waves. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the dynamical behavior of droplet. For these purposes, a two-dimensional multiple-relaxation-time color-gradient model lattice Boltzmann method is developed. This model is first validated by dynamical behaviors of a droplet subjected to shear flow. Moreover, displacement of a droplet affected by surface acoustic waves is comprehensively investigated. Our obtained simulations agree well with observations. According to our finding, the increase of frequency leads to the increment of required power to change the modes of the system from streaming to pumping or jetting states. Obtained results clearly show that hydrophobicity, reduction of viscosity, and increase of surface tension coefficient significantly influence on the flow control system and grow its sensitivity. Our results demonstrate that the minimum wave amplitude required to initiate pumping mode changes from 0.8 nm to about 1 nm when the frequency ranges are within 20 MHz to 200 MHz. The variations in jetting mode are also observed. Our findings clearly show that the minimum wave amplitude varies from about 2 nm to 4 nm when the frequency is changed from 20 MHz to 200 MHz. According to numerical analysis using lattice Boltzmann method, this work tried to capture the deformations of the fluid/fluid interface affected by surface acoustic waves and simulated the moving contact line in the high density ratio. These two main phenomena are recognized as significant parameter in our problem.

Microfluidic inertial switch with delay response characteristics

This paper proposes an innovation microfluidic inertial switch structure with precise time delay response characteristic, which can be used in the fuze safety and arming system. The switch works on the principle of fluidic inertial force and capillary valve, which makes it sensitive to the unidirection acceleration load and has the ability to recognize the acceleration amplitude. The microfluidic inertial switch has a structure of a J-shaped reservoir, capillary valves, a serpentine delay microchannel and a U-shaped latching microchannel. The acceleration threshold is analyzed theoretically considering the surface tension coefficient of the gas-liquid interface. The delay response time of the switch is studied by finite element simulation based on the Gambit 2.4 and Fluent 6.3 software. The prototype is fabricated by wet etching technology and magnetron sputtering metal technology. Many tests have been done to verify the functions of the switch. The experimental results are matched well to the results of calculation and simulation. When the capillary valve throat widths are 80μm, 120μm, 160μm, the thresholds of the switch are 75.1g, 46.6g, 36.5g. When the switch is loaded with a 75g acceleration load, the delay response is 146.7ms. Finite element simulation and experimental results show that the switch can effectively identify the acceleration threshold, and can achieve a precise delay response under a certain load.

Effects of contact angle hysteresis on drop manipulation using surface acoustic waves

Surface acoustic waves have gained much attention in flow control given the effects arising from acoustic streaming. In this study, the hydrodynamic interference of a drop under surface acoustic waves is comprehensively investigated and the contact angle hysteresis effects are considered, too. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the dynamical behaviors of drop. For these purposes, a multiple-relaxation-time color-gradient model lattice Boltzmann method is developed. In these case studies, wave frequency and amplitude were in the ranges of 20–60 MHz and 0.5–2 nm, respectively. In addition, the density ratio of 1000, the kinematic viscosity ratio of 15, Reynolds numbers of 4–24, Capillary numbers of 0.0003–0.0008 and Weber numbers of 0–0.4 were considered. Results show that drop would not move, but would incline in the direction of wave propagation equal to radiation angle when the wave amplitude is low. However, the drop will initiate to move as wave amplitude is progressively augmented. Meanwhile, the increase in frequency leads to an increment of required power to change the modes of the system from streaming to pumping or jetting states. The obtained results clearly show that a reduction in viscosity and an increase in surface tension coefficient significantly influence the flow control system and enhance its sensitivity. Also, the contact angle hysteresis modeling can improve the numerical results by up to 20%.

The Surface Tension Effect on Macrovolume Destruction of a Liquid During Its Free Fall

In this paper, we present the methodology and results of an experimental study on the effect of the surface tension coefficient and the initial volume of a water core on the dynamics of its destruction upon free fall in air with a nonzero initial velocity. At a twofold decrease in the liquid surface tension coefficient, the distance at which the complete destruction of the water core with the formation of a cloud of drops occurs is shown to decrease by 30% while the dependence of the distance of complete destruction on the initial core volume has a minimum.

Role of Marangoni Convection in a Repetitive Laser Melting Process

To effectively interpret the fluid flow dynamics in the molten metal pool, a numerical model was established. The moving repetitive Gaussian laser pulse is irradiated in the work piece. The consideration of laser scanning speed makes the transport phenomena complex. The continuity and momentum equations are solved to get the flow velocity of the molten metal in the melt pool. The energy equation is solved to know the temperature field in the work piece. The algebraic equations obtained after discretization of the governing equations by Finite Volume Method (FVM) are then solved by the Tri Diagonal Matrix Method. Enthalpy-porosity technique is used to capture the position of the melt front which determines the shape of the melt pool. Marangoni convection is considered to know its effect on the shape of the melt pool. The surface tension coefficient is taken as both positive and negative value while calculating the Marangoni force. The two possible cases will cause the Marangoni force to distort the flow dynamics in the melt pool . It's dominance over the buoyancy force in controlling the melt pool shape is focused in the present study. Further, the present model will present an insight to the consequences of laser scanning velocity over the melt pool dimensions and shape.

A control volume finite element method for three‐dimensional three‐phase flows

SummaryA novel control volume finite element method with adaptive anisotropic unstructured meshes is presented for three‐dimensional three‐phase flows with interfacial tension. The numerical framework consists of a mixed control volume and finite element formulation with a new P1DG‐P2 elements (linear discontinuous velocity between elements and quadratic continuous pressure between elements). A “volume of fluid” type method is used for the interface capturing, which is based on compressive control volume advection and second‐order finite element methods. A force‐balanced continuum surface force model is employed for the interfacial tension on unstructured meshes. The interfacial tension coefficient decomposition method is also used to deal with interfacial tension pairings between different phases. Numerical examples of benchmark tests and the dynamics of three‐dimensional three‐phase rising bubble, and droplet impact are presented. The results are compared with the analytical solutions and previously published experimental data, demonstrating the capability of the present method.

On the sea spray aerosol originated from bubble bursting jets

Here we provide a theoretical framework revealing that the radius of the top droplet ejected from a bursting bubble of radius and can be expressed as for or as for , with the numerically fitted constants , , the Ohnesorge number, the Bond number, and , and indicating the liquid density, dynamic viscosity and interfacial tension coefficient, respectively. These predictions, which do not only have solid theoretical roots but are also much more accurate than the usual 10 % rule used in the context of marine spray generation via whitecaps for mm, agree very well with both experimental data and numerical simulations for the values of and investigated. Moreover, making use of a criterion which reveals the mechanism that controls the growth rate of capillary instabilities, we also explain here why no droplets are ejected from the tip of the fast Worthington jet for . In addition, our results predict the generation of submicron-sized aerosol particles with diameters below 100 nm and velocities for bubble radii , within the range found in natural conditions and in good agreement with experiments – a fact suggesting that our study could be applied in the modelling of sea spray aerosol production.

Numerical investigation of axisymmetric bubble dynamics from a submerged circumferential slit on the cylinder

The boundary element method is adopted to study the ventilating axisymmetric bubble growth from a circumferential slit in a submerged cylindrical wall under vertical flow conditions in this paper. During the bubble growth, mesh subdivision and smoothing techniques are adopted in order to optimize mesh topology. In this study, the effects of inflow velocity, surface tension coefficient, ventilation rate and slit width on the bubble development process are studied. The results show that the bubble shape is mainly affected by the inflow velocity and the surface tension coefficient, the inflow velocity promotes the downward movement of the lower intersection point of the wall and bubble, meanwhile, the surface tension inhibits it. The effect of slit width is mainly reflected in the initial stage of the bubble development. And the bubble size basically increases as the ventilation rate increases. In addition, the effects of the Froude number, Weber number, and ventilation coefficient on bubble growth are analyzed. The maximum dimensionless length and thickness of the bubble increase with the increase of the Froude number and decrease with the increase of the Weber number. As the ventilation coefficient increases, the length decreases first and then stabilizes, the thickness decreases first and then increases.

Quantitative absorption imaging of red blood cells to determine physical and mechanical properties.

Red blood cells or erythrocytes, constituting 40 to 45 percent of the total volume of human blood are vesicles filled with hemoglobin with a fluid-like lipid bilayer membrane connected to a 2D spectrin network. The shape, volume, hemoglobin mass, and membrane stiffness of RBCs are important characteristics that influence their ability to circulate through the body and transport oxygen to tissues. In this study, we show that a simple two-LED set up in conjunction with standard microscope imaging can accurately determine the physical and mechanical properties of single RBCs. The Beer–Lambert law and undulatory motion dynamics of the membrane have been used to measure the total volume, hemoglobin mass, membrane tension coefficient, and bending modulus of RBCs. We also show that this method is sensitive enough to distinguish between the mechanical properties of RBCs during morphological changes from a typical discocyte to echinocytes and spherocytes. Measured values of the tension coefficient and bending modulus are 1.27 × 10−6 J m−2 and 7.09 × 10−20 J for discocytes, 4.80 × 10−6 J m−2 and 7.70 × 10−20 J for echinocytes, and 9.85 × 10−6 J m−2 and 9.69 × 10−20 J for spherocytes, respectively. This quantitative light absorption imaging reduces the complexity related to the quantitative imaging of the biophysical and mechanical properties of a single RBC that may lead to enhanced yet simplified point of care devices for analyzing blood cells.

Numerical modelling of fluid flow and weld penetration in activated TIG welding

This research work emphasis on understanding the weld pool development while carrying out Activated Tungsten Inert Gas (A-TIG) welding by employing Computational Fluid Dynamics (CFD). The influence of temperature coefficient of surface tension (∂γ/∂T) and the concentration of oxygen, the main surface active component on weld bead geometry is studied. A three-dimensional (3D) numerical model has been developed for A-TIG welding process with varying oxygen levels employing ANSYS Fluent for 316LN stainless steel. The general conservation equations consisting mass, energy and momentum were solved in order to acquire the temperature and velocity fields with oxygen levels varying from 50 to 300 ppm in weld pool. The impact of driving forces particularly buoyancy and Marangoni on the weld pool convection were examined. The simulation confirmed that the weld bead shape was influenced mainly by Marangoni convection consecutively dependent on the oxygen content in the weld metal in the course of A-TIG welding. The addition in oxygen content changes the surface tension temperature coefficient ∂γ/∂T from negative to positive gradient causing inward flow. It was found that minor oxygen content in the molten pool until 150 ppm exhibited outward flow and with higher oxygen content beyond 150 ppm exhibited an inward flow. The oxygen content in the weld bead without flux and with flux was found to be 69 and 336 ppm respectively for the type 316LN stainless steel plates welded by A-TIG welding. The simulated weld bead profile was validated by comparing with the experimentally obtained weld bead profile. There was excellent agreement between the two weld bead profiles.

Methods for Joint Determination of the Surface Tension Coefficient of a Liquid and the Contact Angle of Wetting the Hard Surface

This article is devoted to the development of fundamentally new methods for the experimental determination of the physical properties of substances - methods of their joint determination, when not a single property is measured, but two physical properties connected with each other. For example, this is the coefficient of surface tension σ of the liquid and the contact angle θ of wetting the surface by it, which here act as parameters of capillary forces at the interface. The purpose of such methods is not so much a banal arithmetic increase in the obtained experimental data, as a significant increase in their determination accuracy by reducing the statistical error (variance). In such cases, we have the so-called methods of indirect (indirect) measurement, which in this case are based not on the measurement of σ and θ directly, but on the measurement of the height h and weight ∆W of the meniscus hanging on a vertical surface, and on the subsequent solution of the resulting system of two equations that are analytical expressions for h and ∆W (i.e., a system of two equations with two unknowns: σ and θ). In the case of using a Wilhelmy plate in the experiment, the solution of such a system of equations leads to explicit analytical expressions for both unknowns (σ and θ), and in the case of using a cylindrical filament in the experiment, analytical expressions for the unknowns are obtained in an implicit form: in this case, to determine the value of the boundary of the angle θ, a recursive formula is proposed.

Determination of the minimum drop height of the spherical grains in the solution of the treater

One of the main reserves for increasing grain production is the use for sowing high-quality seeds, purified from impurities and pathogens. One of the main ways to protect the seed from various diseases is dressing. The most effective way to protect seeds from disease is wet dressing with the simultaneous release of grain impurities. To develop a device for cleaning and dressing seeds by density using a wet method, an estimate was made of the minimum height of the fall of the grain needed to overcome the surface tension of the liquid. As objects of research, pea seeds were used, having a shape close to a spherical. Therefore, a spherical grains with a density ρz = (1.15-1.45)·103 kg/m3 and a diameter of 2rz = (3.5-10.9)·10-3 m was taken as a model of pea seed. We study the fall of individual spherical grains with minimal (2rzmin = 3.5·10-3 m) and maximum (2rzmax. = 10.9·10-3 m)) linear dimensions that have a density ρz = 1.15; 1.25; 1.35 and 1.45·103 kg/m3. Drop occurs on the surface of the water (ρzh = 1.0·103 kg/m3) and the aqueous solution of the etchant (ρzh = 1.03; 1.06; 1.09; 1.12 and 1.15·103 kg/m3), with Corresponding coefficients σ of surface tension (0.0727; 0.0755; 0.0771; 0.0786; 0.0801, 0.0816 N/m) and hydrodynamic drag coefficients c = 0.4 (0.5 for ρzh = 1.12·103 and 1.15·103 kg/m3). The process of dressing grain is considered at a temperature of 20 °C. It was established that the minimum drop height h to overcome the surface tension of the dressing solution with all spherical grains should be 15.5·10-3 m.

Development of anti-leukemia measures in livestock farms of Kalmykia on the basis of complex diagnosis of the disease

The efficiency of diagnostic methods to control cattle leukemia during health measures in the farms of the Republic of Kalmykia was studied and a plan of anti-leukemia measures was developed. As a result, at a negative growth rate (-90.2%) the ill-being index defining the breadth of incidence in the territory of the republic was reduced by 10.2 times over 2003-2018. At the same time, while over 9 years from 2003 to 2008 the average ill-being index was within 0.42, from 2009 to 2018 it decreased from 0.33 to 0.03. The average tension coefficient, which takes into account the rate of acquisition of Bovine Leukemia Virus in the territory of the Republic by the end of the period (2018), remains zero.

Equilibrium shapes of two-phase rotating fluid drops with surface tension

While rotating single phase fluid drops have been thoroughly investigated, the determination of the shape of a drop consisting of two immiscible liquid phases has not been previously considered. Recently, experiments using rotating micron-scale droplets of liquid helium have been carried out where the liquid can be in a normal or superfluid state depending on the isotope of helium used. Two phases can be present if the helium is a mixture of He3 and He4. Classical results have been very useful in aiding the analysis of single phase liquid helium drops and are similarly needed for two phase drops. In this contribution, the Navier–Stokes equations with surface tension are solved numerically using the finite-element method with surface tension effects on the inner and outer interfaces. The numerical models are time-dependent but are run to a steady state to determine equilibrium shapes. It is found that with an appropriate scaling of the density and surface tension coefficient, the relationships between the angular velocity and the angular momentum and of the outer surface dimensions with angular momentum become very similar to those of a single phase fluid for a broad range of parameters. However, the shapes of the inner drops vary significantly, particularly when the volume of the inner fluid is significantly less than that of the outer fluid. Increasing the relative magnitude of the interfacial surface tension coefficient or decreasing the relative density of the inner region leads to less deformation of the inner drop relative to the outer one.