Variation Of Surface Tension Research Articles

Investigation on the Influence of Microstructure Based on Hydrogen Bonding on Surface Tension by Raman Spectroscopy.

Surface tension and Raman spectra containing hydrogen bonding in acetonitrile aqueous solutions with different mole ratios were obtained. Varied surface tension and hydrogen bonding in the mixed solution were discussed. For this purpose, the OH stretching bands were fitted into three Gaussian components to which different hydrogen-bonded water samples were assigned. Furthermore, the microstructures of binary solution were analyzed. The results indicated that the surface tension decreases dramatically with the enhancement of hydrogen bonds in the mixture. A spectroscopic method for studying the macroscopic properties of aqueous solutions was employed. The direct experiment results provided the relationship between surface tension and microstructure in aqueous solutions.

Impact of surface tension and viscosity on falling film thickness in multi-effect desalination (MED) horizontal tube evaporator

Falling film evaporators are extensively used in many applications because of their higher heat and mass transfer coefficient over low temperature difference. Falling film thickness, which depends on liquid spray density and thermophysical properties, is an important parameter in determining heat and mass transfer performance as it represents thermal resistance. In multi-effect desalination (MED) evaporators, the thermophysical properties such as surface tension and viscosity change due to operating temperature differences, i.e. higher in the first evaporator/effect and lower in the last evaporator/effect. The surface tension variation with temperature is often neglected in most of the film thickness characterization and modeling studies. Therefore, it is needed to analyze surface tension effects distinctly on film thickness. In this study, a 2D CFD model was developed by implementing volume of fluid (VOF) multiphase model to distinguish liquid and gas phases. The effects of viscosity and surface tension were analyzed separately, and it was found that with constant surface tension, viscosity effects account for 66.1% variation in film thickness for operating temperature range of 85 °C–5 °C. However accounting both viscosity and surface tension dependence, the results showed 72% increment in the film thickness. In addition, CFD results exhibited lower conduction thermal resistance of 0.2 m2 K/W at 85 °C against 0.4 m2 K/W at 5 °C, which reflects better evaporator performance at higher temperature. Hence, more focus and detailed analysis are recommended given in increasing the first effect temperature from 65 °C to 85 °C as it would improve thermal performance due to lower thermal resistance rather than decreasing last effect temperature from 40 °C to 5 °C as the thermal resistance would increase.

Experimental investigation of condensate retention on horizontal pin fin tube with varying pin angle

This paper presents the effect of pin fin rotational angle on the condensate retention as function of vapour velocity (0–20 m/s) on four different pin fin tubes, by systematically changing the pin fin angle from 0° – 45° with horizontal axis. While other parameters of pin fin tubes like tooth height, tooth thickness, longitudinal spacing inner and outer diameter remain constant for all 4 tubes tested. Three fluids (2-propanol, distilled water and ethylene glycol) with varying surface tension to density ratio are tested. Experimentation is conducted in a vertical wind tunnel by downward supply of air (to simulate vapour) with velocity from 0 - 20 m/s. By accurate small holes on upper side of the tube a constant flow of condensate was assured on a tube to be tested. At almost all vapour velocities; it is observed that retention angle increases with increase in pin fin angle for all fluids tested. As the vapour velocity increased from 0 to 20 m/s, it is observed that the retention angle for tube A1 increased for all test fluids, whereas with increasing velocity, a decrease in retention angle is observed for tubes A2, A3 and A4 for all fluids tested.

Fluid viscosity but not surface tension, determines the tamponade effect of intravitreal fluids in a novel in vitro eye model of retinal detachment

PurposeTo determine the effect of varying surface tension and viscosity of fluids used as tamponade in an in vitro eye model of retinal detachment. MethodsWe used an in vitro eye model simulating retinal detachment. Fluids with varying surface tension and identical viscosity, and fluids with varying viscosities and identical surface tension were used as tamponade agents to prevent retinal detachment in the model, to determine which of these properties affects each fluid's effectiveness as a retinal tamponade. ResultsThe membrane (simulating retinal detachment) changes over time in a vitro eye model were not affected by varying surface tension given constant fluid viscosity. However, membrane changes were proportional to the viscosity of the fluid, given constant surface tension. ConclusionsThe tamponade effect of an intravitreal fluid against retinal detachment may not be related as previously assumed, solely to surface tension, but rather is proportionally related to its viscosity.

Analytical model for the condensation heat and mass transfer characteristics of binary zeotropic mixtures

An analytical model was developed to study the condensation heat and mass transfer characteristics of binary zeotropic mixtures for annular flow inside a horizontal tube. The model was based on non-equilibrium film theory including consideration of the surface tension variation in the liquid phase as the concentration changes. The model was validated by comparing the calculated heat transfer coefficient with experimental data from the literature for methane/ethane mixtures with various compositions and mass fluxes. The model was then used to study the effects of composition, mass flux, inlet pressure and tube diameter on the heat and mass transfer resistances in the vapor phase and the heat transfer coefficient during condensation of methane/ethane mixtures. The results showed that the mass transfer resistance in the vapor phase was important in the high vapor quality region with the heat transfer resistance in the liquid phase being more significant in some cases.

Theoretical analysis of engine coolant cavitation with different additives based on ultrasonic induced bubble dynamics

Cavitation, the process of formation and collapsing of vapor cavities is of great importance to material erosion degradation and enhanced physicochemical process by ultrasound. Commonly the ultrasonic cavitation bench test is utilized to study the cavitation correlate properties of different materials or coolants, which is time consuming and costly compared to numerical tests and lack of micro perspective analysis. Therefore, a mathematical model is needed to study cavitation bubble dynamics under different circumstances beforehand. Different types of ultrasonic waves are used to identify their ability to control bubble evolution and collapse intensity. Rectangular wave is found to be the most efficient to produce large radius and bubble wall speed compared with triangular and harmonic wave. As a potential mechanism to damage rigid wall, shock pressure is evaluated with variations of viscosity and surface tension. It is found that both decreased surface tension and increased viscosity can reduce shock pressure and thereby the cavitation potential, while viscosity shows less effect. Testing is achieved by comparing effects of typical coolants with different percentage of ethylene glycol (EG), propylene glycol (PG) and glycerin. PG is found to be the most efficient to suppress shock pressure followed by EG and glycerin the worst.

An Experimental Investigation of Properties of Nanofluid and Its Performance on Thermosyphon Cooled by Natural Convection

An attempt is made here to characterize thermal conductivity of water-based Al2O3 nanofluid and then use the same in a circular finned thermosyphon (TPCT) to measure its thermal performance. The concentration of Al2O3 nanofluid is varied within 0.05–0.25% by volume. The thermal conductivity of nanofluid is increased with concentration of Al2O3 nanoparticles as well as with temperature. A maximum of 26.7% enhancement of thermal conductivity is observed at 45 °C for 0.25% concentration by volume of nanofluid in comparison to that of de-ionized (DI) water. Variations of surface tension and contact angle of Al2O3 nanofluid are also compared with DI water. One of the smallest TPCT with different heat inputs (4 W, 8 W, and 12 W) and different inclinations (30 deg, 45 deg, 60 deg, and 90 deg) is tested for different concentration of Al2O3 nanofluid, which will find application in smaller electronic units. It is found that use of nanofluid decreases the wall temperature distribution of TPCT. Thermal resistance of TPCT decreases whenever TPCT is filled with nanofluid and a maximum of 36.4% reduction in thermal resistance is noted for 0.25% volume of nanoparticles at 4 W with an inclination of 60 deg. It is also found that performance of TPCT is higher at 60 deg inclination compared to other inclinations, especially for lower heat input.

Large-Scale and Well-Ordered Assembly of Microspheres in a Small Container.

Colloidal self-assembly monolayers (SAMs) formed by the Langmuir?Blodgett (LB) process have been widely applied in modern research. The quality of the closely packed 2D or 3D arrays would determine their performance and applications. Herein, we study the influence of the surface wettability of containers on the self-assembly process of polystyrene microspheres using LB technology. It is found that the variation of surface tension at the gas/liquid/solid phase determines the quality of the PS colloidal SAMs. By carefully controlling the surface wettability of the containers, a square centimeter level of well-ordered polystyrene (PS) microsphere SAMs in a small polyethylene (PE) container can be achieved. This method can be used to fabricate PS SAMs with different sphere sizes. In addition, the PS SAMs can be easily transferred onto silica-coated silicon and silicon wafers for further fabricating triangle antenna arrays at a square centimeter level that allows for the study the IR resonances of antennas with conventional IR instrument. The present study provides a simple approach to the fabrication of large-scale and well-ordered colloidal SAMs for further applications.

Surface Tensions of Picoliter Droplets with Sub-Millisecond Surface Age.

Aerosols are key components of the atmosphere and play important roles in many industrial processes. Because aerosol particles have high surface-to-volume ratios, their surface properties are especially important. However, direct measurement of the surface properties of aerosol particles is challenging. In this work, we describe an approach to measure the surface tension of picoliter volume droplets with surface age <1 ms by resolving their dynamic oscillations in shape immediately after ejection from a microdroplet dispenser. Droplet shape oscillations are monitored by highly time-resolved (500 ns) stroboscopic imaging, and droplet surface tension is accurately retrieved across a wide range of droplet sizes (10-25 μm radius) and surface ages (down to ∼100 μs). The approach is validated for droplets containing sodium chloride, glutaric acid, and water, which all show no variation in surface tension with surface age. Experimental results from the microdroplet dispenser approach are compared to complementary surface tension measurements of 5-10 μm radius droplets with aged surfaces using a holographic optical tweezers approach and predictions of surface tension using a statistical thermodynamic model. These approaches combined will allow investigation of droplet surface tension across a wide range of droplet sizes, compositions, and surface ages.

Thermal effects on the instability of coaxial liquid jets in the core of a gas stream

The breakup of coaxial liquid jets in a co-flowing gas stream under the radial thermal field is studied by the linear instability theory. A simplified physical model is established, and an analytical dimensionless dispersion relation for temporally axisymmetric perturbations is derived and solved numerically. The outer liquid-gas surface tension coefficient is assumed to be a linear function of temperature. Due to the radial temperature gradients, the time-dependent spatial variation of surface tension gives rise to a shear stress and induces Marangoni force upon the flow. The effects of different process parameters on the characteristics of unstable modes including the para-sinuous mode and the para-varicose mode are explored. It is found that the para-sinuous mode always dominates the jet instability in the parametric regions and the increasing temperature ratio of the surrounding gas stream and the inner liquid jet (T31) can reduce the maximum growth rates of unstable modes and corresponding dominant wavenumbers. The Reynolds number destabilizes the jet instability, and the Weber number suppresses it at relatively long wavelengths for both isothermal and non-isothermal situations. The Marangoni number and the Peclet number have a destabilizing effect for T31 &amp;lt; 1, but it is opposite for T31 &amp;gt; 1. These theoretical predictions would provide insight into underlying physical mechanisms of thermal jet breakup and compound droplet formation.

Filler flocculation in elastomer blends - an approach based on measured surface tensions and monte carlo simulation

ABSTRACTElastomer materials in car and truck tires require the addition of filler particles for reinforcement and durability as well as the enhancement of other properties of the final product. During the post-mixing stages the previously dispersed filler undergoes (re-)agglomeration in a process called flocculation. The resulting filler network morphology strongly influences the mechanical properties of the rubber material. This means that the structure itself, its dependence on the physicochemical properties of the underlying components, and its attendant influence on, for instance, the dynamic rubber moduli are of significant interest. In this work we discuss a modelling approach to these questions applied to binary blends consisting of natural and styrene-butadiene rubber plus filler of variable type. Our Monte Carlo flocculation simulator utilizes a lattice model of the components, whose thermodynamic development is governed by measured interface or surface tensions. The algorithm minimizes the free enthalpy while the number of MC moves provides a rough measure of time due to the local nature of the moves. We investigate two blend ratios (NR/SBR), i.e., 50/50 and 70/30, as well as two filler volume fractions ϕ, i.e., ϕ and ϕ, for variable filler surface tension (both dispersive and polar part, i.e., and ). Our results include the scattering momentum transfer characterizing the aggregate size, the fractional interface lengths between the components, and simulated transmission electron micrographs at selected conditions. We discuss how the combination of these quantities can provide information on both the storage and the loss modulus of the materials.

Characteristic IR-acoustical analysis and surface tension variations in organic liquid mixtures at different temperatures

Abstract Binary liquid mixture containing aniline and O-xylene is used to calculate adiabatic compressibility (β), free length (Lf) and acoustical impedance (Z) from the experimentally measured values of ultrasonic velocities and densities over the entire mole fraction range of aniline at temperatures T = (303.15, 308.15, 313.15 and 318.15) K. Molecular interactions between the components of liquid mixture have been explained on the basis of these thermo acoustical parameters and also by the C H, N H, C N bond stretching. The molecular interaction and presence of functional groups are confirmed from the recorded FTIR spectra and by the computed values of surface tension.

Acoustical effective Debye temperature studies in heterocyclic aromatic functional materials of organic liquid mixtures at four different temperatures T = (303.15, 308.15, 313.15 and 318.15) K

Abstract Debye temperature and Surface tension are theoretically estimated for binary liquid mixtures of heterocyclic aromatic compound Quinoline and m-Xylene using ultrasonic velocity & density measurements over entire mole fraction of Quinoline at different temperatures. An analogy of Debye temperature along with the Viscosity and Surface Tension variations are scrutinized to bring out the molecular contribution to thermal energy changes of binary liquid mixtures. The observed and obtained results are used to explain the molecular association and thermal behaviour between the component molecules of liquid mixtures.

Thermal and transport properties of liquid mixtures – An analogy of molecular interactions

Abstract Molecular contribution for specific heat of liquid mixtures is employed for the analysis of transport properties. Debye temperature and Surface tension are theoretically estimated for binary liquid mixtures of Aniline + Toluene, Aniline + o-Xylene & Aniline + Mesitylene using ultrasonic velocity & density measurements over entire mole fraction of Aniline at different temperatures. An analogy of Debye temperature along with the Viscosity and Surface Tension variations are scrutinized to bring out the molecular contribution to thermal energy changes of binary liquid mixtures. The results are used to explain the thermal behaviour of molecular association among the liquid mixture interface.

Numerical investigation of bubble dynamics and heat transfer in subcooling pool boiling under low gravity

Abstract The numerical simulation of a single vapor bubble growth in subcooling liquid under different gravity conditions has been carried out. In the numerical model, a thin superheated layer and the thermocapillary convection caused by the surface tension variation along the surface are considered. The continuity equation and energy equation are modified to allow for the phase change. In addition, the thermocapillary convection effect has been included in the momentum equation. The vapor-liquid interface is captured by the phase field method. The results show that the bubble behavior in the numerical model agrees well with previous experiments conducted in high subcooling liquid under microgravity. The effects of gravity level, contact angle and wall superheat on the bubble growth, critical subcooling (the liquid subcooling under the condition that the evaporation rate of a bubble is equal to its condensation rate), together with heat transfer have been investigated. The growth period and departure radius both reduce with the increase in gravity level, while the critical subcooling increases slightly. Large contact angle at the three-phase contact line augments the departure radius. However, the critical subcooling decreases as contact angle increases. With the wall superheat increasing, the growth period reduces rapidly, while the departure radius and the critical subcooling increase. What’s more, the non-departing bubble adhering to the surface would prevent heat transfer with a dry spot, which may damage the heating element in application.

Unsteady motion of a long bubble or droplet in a self-rewetting system

Motivated by the potential use of self-rewetting fluids (i.e. fluids that exhibit a non-monotonic variation of surface tension with temperature) in various heat transfer applications, in the present work we formulate and analyse a theoretical model for the unsteady motion of a long bubble or droplet in a self-rewetting system in a non-uniformly heated tube due to a combination of Marangoni effects due to the variation of surface tension with temperature, gravitational effects due to the density difference between the two fluids, and an imposed background flow along the tube. We find that the evolution of the shape (but not of the position) of the bubble or droplet is driven entirely by Marangoni effects, and depends on the initial value of its radius in relation to a critical value. In the case in which Marangoni effects are absent the bubble or droplet always moves with constant velocity without changing shape. In the case in which only Marangoni effects are present the bubble or droplet either always moves away from or always moves towards the position of minimum surface tension; in the latter case it ultimately fills the entire cross-section of the tube at a final stationary position which is closer to the position of minimum surface tension than its original position. In the cases in which either only Marangoni effects and gravitational effects or only Marangoni effects and background-flow effects are present the competition between the two effects can lead to a non-monotonic evolution of the position of the centre of mass of the bubble or droplet. The behaviour of a self-rewetting system described in the present work is qualitatively different from that for ordinary fluids, in which case the bubble or droplet always moves with constant velocity without changing shape.

Melt Pool Analysis and Mesoscale Simulation of Laser Powder Bed Fusion Process (L-PBF) with Ti-6Al-4V Powder Particles

The laser powder bed fusion (L-PBF) process is accompanied by rapid melting and solidification that results in intense thermocapillary convection within the melt pool. Open-source particle simulation software was utilized to generate a single layer of spherical powder particles of variable diameter. Considering the importance of particle size and the particle size distribution (PSD) in the L-PBF process, three distinct categories of PSD were generated with identical settings. A three-dimensional (3D) thermofluid model was developed in this study, incorporating the generated layer of powder particles of nonuniform size over a thick substrate. A moving volumetric heat source was applied to melt a single track in the powder layer using a user-defined function in FLUENT software. Temperature-dependent material properties including variable surface tension were considered in the computation. The numerical model was used to simulate Ti-6Al-4V powder particles to observe the melt pool flow dynamics. Presence of particles of smaller diameter in the powder mix supported consistent and continuous melt pool flow, while any kind of void enhanced fluid convection in the downward direction, causing a temporal increase in melt pool depth.

Effect of the misorientation angle and anisotropy strength on the initial planar instability dynamics during solidification in a molten pool

The initial planar instability will appear with the solute accumulation ahead of the solid/liquid (S/L) interface during solidification in a molten pool. The instability process is dominated by the misorientation angle and the surface tension anisotropy strength, where the misorientation angle is the angle between the preferred crystalline orientation of base metal and the thermal gradient direction in front of the S/L interface. In this study, their effects on the initial planar instability during gas tungsten arc welding of an Al-alloy are investigated using a modified analytic model and a quantitative phase-field model, respectively. Specifically, we apply the uniform fluctuation spectrum assumption, Aω(0) = kBTM/{γ0[1 − 15γ4cos(4θ0)]ω2}, to represent the influence of thermal noise on S/L interface evolution. The incubation time, average wavelength and detailed interface morphology of the initial planar instability are investigated with varying surface tension anisotropies (determined by anisotropy strength γ4 and misorientation angle θ0). The results indicate that -γ4cos(4θ0) is a reasonable indicator for the effect of surface tension anisotropy on the initial planar instability. Moreover, rather than influencing solute diffusion, the surface tension anisotropy just affects the planar interface stability during the solidification. Finally, the experimental observations with the same welding parameters was carried out, which are in general agreement with the simulated results.

Motion of an air bubble under the action of thermocapillary and buoyancy forces

A novel way to handle surface tension gradient driven flows is developed in the volume-of-fluid (VoF) framework. Using an open source Navier–Stokes solver, Basilisk, and the present formulation, we investigate thermocapillary migration of drops/bubbles in a surrounding medium. Several validation exercises have been performed, which demonstrate that the present solver is a robust one to investigate interfacial flows with variable surface tension. It is well known that it is a challenging task to numerically model the tangential and normal surface forces arising due to interfacial tension. We have shown that the present method does not require the artificial smearing of surface tension about the interface, and thus predicts the theoretical value of the terminal velocity of bubble/drop migrating due to an imposed temperature gradient very well. It is also demonstrated that the present solver provides accurate results for problems exhibiting the gravity and thermocapillary forces simultaneously, and useful for systems with high viscosity and density ratios.

Formation of Liquid–Liquid Micropatterns through Guided Liquid Displacement on Liquid‐Infused Surfaces

AbstractHere a method is demonstrated to pattern liquids of varying surface tension and composition into droplets by utilizing slippery liquid‐infused surfaces prepared on chemically‐patterned substrates. The capability of different liquids to displace the lubricant from higher surface energy regions is studied and it is shown that both high and low surface tension liquids can imbibe the polymer, thereby forming droplets sharply following underlying surface energy patterns. For all liquids tested, droplet arrays of arbitrary shapes of each liquid are formed with precision down to 50 µm. By changing the chemical patterning from fluorinated to aliphatic groups, patterns of mineral and silicone oils are created. Finally, formation of 2D micropatterns of three‐phase liquid systems—fluorinated, organic, and aqueous phases—is demonstrated.