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In this study, the dynamic process of a droplet moving with a substrate until blocked by air flow is investigated experimentally and theoretically. A sequence of experiments has been conducted to investigate the impacts of wetting properties, droplet volumes, air flow velocities, and droplet velocities. The substrate is driven by a linear motion motor to ensure the droplet moves at a certain velocity alongside the substrate. The air flow that is vertically injected from the nozzles toward the substrate is known as an impinging jet. After the air flow impacts the substrate, it will blow horizontally. When the direction of air flow is opposite to that of the droplet movement, a force will be exerted on the surface of the droplet. This action incurs the deformation of the droplet and the cessation of its movement, eventually resulting in an equilibrium state. The droplet shape and motion processes are recorded by a high-speed camera. A mathematical model considering the effect of droplet contact angle, droplet size, droplet moving velocity, and air flow velocity is established in the state of equilibrium. Correlation factors are used in the model for the drag coefficient and air average velocity acting on the droplet. It is found that the air flow rate required to stop the motion of the droplet increases with the droplet moving velocity and the droplet size but reduces with the increase in the static contact angle. The mathematical model, when equipped with suitable correlation factors, exhibits good agreement with experimental data and could potentially be utilized as a predictor of critical velocity for the cessation of the droplet motion. [ABSTRACT FROM AUTHOR]

3D droplet-based bioprinting technology is an innovative and time-saving additive manufacturing method, which enables spatial patterning of biological materials and biochemical and living cells for multiple clinical and research applications. Understanding the criteria that control droplet spreading behavior during droplet impact is of great importance in controlling printing resolution and optimizing the printing performance. In this experimental work, the spreading of 3D printed cell-laden droplets was studied with side and bottom view images. The droplets contain 1 × 10 7 cells/ml input cell concentration and corresponding Φ = 0.52 % cell volume fraction and impact onto a flat hydrophilic substrate, a pre-printed droplet, and a pre-printed thin liquid film. The cell-laden droplet impact morphology, the maximum spreading factor, and the cell distribution under different printing conditions (89 < W e < 365 , 174 < R e < 414) in a 3D bioprinting process were characterized. It was found that on the hydrophilic flat substrate, the cells homogeneously distributed into a disk structure. The maximum spreading factor, β max , can be well described by the correlation formulas based on the energy balance and volume conservation. A power-law scaling formula was found to describe the maximum spreading in terms of the Weber number for cell-laden droplet impact on both pre-printed droplets and thin liquid films, where β max ∝ W e 0.25 . Input cell concentration, up to 1 × 10 7 cells/ml, was found to have negligible effect on the maximum droplet spreading factor in a 3D bioprinting process. [ABSTRACT FROM AUTHOR]

Couple-stress nanofluids have multiple potential applications in numerous industrial and engineering sectors, such as energy production, medical diagnostics, thermal control systems, and the aerospace industry. Couple-stress nanofluids have the ability to improve the heat exchange properties and elevate the performance of nuclear power plants, solar panels, and other renewable energy sources. Therefore, in the current analysis, a non-homogeneous nanofluid model is considered to examine the non-Newtonian Casson nanofluid flow across a prolonging sheet. The flow has been studied under the significance of generalized Fourier's and Fick's laws, convective boundary conditions, and the heat source/sink. The modeled equations are simplified into a dimensionless lowest-order system of ordinary differential equations by using similarity transformation. The numerical outcomes are achieved by using the "ND-Solve" approach. It has been noticed that the energy field decreases because of the Prandtl number's impacts, whereas it increases with the increase in the heat radiation parameter. The couple-stress nanoliquid's velocity decreases vs increasing values of the magnetic field and mixed convection parameter. The influence of thermal relaxation and couple-stress parameters falls off the energy field. Furthermore, the intensifying effect of Rayleigh number and buoyancy ratio increases the fluid temperature. [ABSTRACT FROM AUTHOR]

This study's primary objective is to experimentally investigate the flexural and impact performance of composites composed of hybrid basalt/E-glass fiber-reinforced epoxy infused with multiwalled carbon nano-tubes (MWCNTs) and nano-silica (SiO2) in compliance with ASTM D790 and ASTM D6110 specifications. Recently, manufacturers considered using basalt fiber-based composites for various structural applications due to their excellent mechanical properties, high stiffness, and high strength-to-weight ratio. Each composite laminate was made by hand layup techniques and filled with equal proportions of SiO2 and MWCNT nanoparticles in different weight percentages, such as 0%, 1%, 2%, and 3%. The composites were made by using a symmetric stacking sequence of B/GG/BB/GG/BD/GG/B fibers. MWCNTs and SiO2 were evenly dispersed throughout the epoxy matrix with the assistance of an ultrasonicator and magnetic stirrer. The composite containing 2% fillers has an increased flexural strength by 20% from 307 to 378 MPa and flexural modulus by 30% from 11.181 to 15.901 Gpa, as well as an increased Charpy impact resistance by 45% from 236 to 418 J/m, compared with the composite without fillers. The interfacial interactions between the epoxy matrix, particles, and fibers significantly influenced the composite laminates' flexural and impact characteristics. The accumulation of particles in the epoxy caused by the 3% fillers reduces the flexural strength and flexural modulus and impacts the performance due to the inadequate interfacial contact between the fibers and the epoxy matrix. [ABSTRACT FROM AUTHOR]

In order to have a precise knowledge on how pressure gradients and buoyancy force affect fluid flow and energy distribution in a bending channel, it is important to perform a comprehensive study on flow characteristics and heat transfer mechanisms that trigger out the transition of fluids into a turbulent state, subject to a sustained pressure gradient. The present paper explores a computational modeling on two-dimensional fluid flow and thermal characteristics in a bent square channel of strong curvature. The Newton–Raphson (N-R) iteration method is applied to obtain a bifurcation structure depending on the pressure-driven force, the Dean number (De), covering 0 < De ≤ 5000. As a consequence, four branches of asymmetric steady solutions are identified for each of the cases of the Grashof number, Gn (=1000, 1500, and 2000), where only the first branch is found to exhibit asymmetric two-vortex solutions while the remaining branches encompass twoto four-vortex solutions. The similarity and disparity in the branching structure are also demonstrated. Then, adopting the Adam–Bashforth (A-B) method together with Crank–Nicholson (C-N) formula, the unsteady solutions (US) have been explored, validated by power spectrum density (PSD) and phase space Within the realm of US, two- and three-vortex solutions are found and these solutions exhibit transitions from steady to chaotic behavior profoundly. Effects of the Grashof number with convective heat transfer (CHT) are also compared. By analyzing the Nusselt number (Nu), it is observed that in case of highly chaotic flow, CHT experiences substantial enhancement. This intensified CHT arises from increased turbulence and mixing, facilitating more efficient thermal energy exchange under such chaotic flow conditions. [ABSTRACT FROM AUTHOR]

The present numerical work examines the effect of fractional order parameter on heat transfer and entropy generation for a thermo-magnetic convective flow of nanofluid (Cu-water) in a square porous enclosure that contains semi-circular bottom wall. The Darcy–Brinkmann–Forchheimer model is utilized to evaluate the momentum transfer in porous media, and the Caputo-time fractional derivative term is introduced in momentum as well as in the energy equation. Further, non-dimensional governing equations are simulated through the penalty finite element method, and the Caputo time derivative is approximated by L1-scheme. The study is carried out for various parameters, including Rayleigh number (Ra), Darcy number (Da), radius of the semicircle (r), fractional order (α), and Hartmann number (Ha). The comprehensive results are presented by the contour variation of isotherms, streamlines, and total entropy generation at the selected range of parameters. In addition, thermal transport and irreversibilities due to heat transfer, fluid friction, and magnetic field have been accounted through the numerical variation of mean Nusselt number (N u m) and Bejan number due to heat transfer (B e h t) , fluid friction (B e f f) , and magnetic field (B e m f) , respectively. The key findings of the present study reveal that during the initial evolution period, the Num value increases as α → 1. Additionally, time taken to achieve the steady state condition varies and depends on fractional order α. Furthermore, in the absence of Ha, the heat transfer and entropy generation intensifies with augmentation of Ra and Da for all α, while, the increasing value of Ha shows an adverse impact on the heat transfer rate. [ABSTRACT FROM AUTHOR]

This article investigates the fluid dynamics and heat transfer properties in a trapezoidal enclosure containing a heated cylindrical object. It involves the interaction of multiple physical processes such as the magnetic field, thermal radiation, porous materials, and aqueous copper oxide nanoparticles. The governing partial differential equations are analyzed numerically through the continuous Galerkin finite element algorithm. The analysis takes into account various physical parameter factors, including the Richardson number (0 – 5) , the Hartmann number (5 − 40) , the Darcy number (0.001 − 0.1) , thermal radiation parameter (0.5 − 2) , and nanoparticle volume concentration (0.01 − 0.1). The physical mechanism of thermal and mass transfer in the enclosure caused by various factors is fully explored. In addition, the multiple expression programming (MEP) technique is implemented to report a comparative analysis of flow profiles and thermal distribution. The findings demonstrated that at low Ri, the primary flow within the cavity is driven by the shear friction generated by the moving walls. The growing importance of radiative heat transfer reduces the effectiveness of convective heat transfer, resulting in a decline in the average Nusselt number with R. The heat transfer rate rises up to 27.7% as ϕ augments; however, its value declines by 9.37% against Ha. The expected results obtained by the MEP approach are very consistent with the numerical ones. There is no doubt that the new MEP concept provides a valuable tool for researchers to predict the heat transfer behavior of any data set in cavities of different shapes. It is expected to provide new idea for the development of efficient cooling systems and the improvement of energy efficiency in various engineering applications. [ABSTRACT FROM AUTHOR]

Thermal analysis is an important method to evaluate the thermal stability of polymer materials; however, efficiently describing the complex pyrolysis process of polymers remains a great challenge. In this paper, a new dual-competitive parallel-reaction kinetics model is proposed for describing the thermogravimetric lines of material pyrolysis processes. In the proposed method, peak analysis, dual-competitive reaction form, and parallel reaction mechanism are combined to build the kinetic model of resin polymer pyrolysis. The model includes peak-determined reaction components, and each reaction component is divided into two competitive reactions. The two competitive reactions are obtained by conducting initial peak analysis and subsequent global parameter optimization. The rebuilt thermogravimetric line via the proposed model agrees well with the experimental data, with few reaction compositions and low computational cost. In addition, the pyrolysis of synthetic polymers and natural biomass are also successfully described by the model with high accuracy. This work provides an updated kinetic model for describing polymer pyrolysis accurately, which may advance the thermal analysis in developing polymers of complex pyrolysis behavior. [ABSTRACT FROM AUTHOR]

Establishing a clean, low-carbon, and efficient energy system is paramount for the sustainable development of industries and human society. Multiphase flows are encountered extensively in various energy applications, including transportation, conversion, and utilization of fossil, renewable, hydrogen, and nuclear energies. These flows encompass a wide range of phenomena, such as fluid flow, heat and mass transfer, combustion, and chemical reactions. However, multiphase flows are highly intricate due to the coexistence of multiple phases, states, and components, as well as the interactions among them that occur across diverse spatiotemporal scales. Consequently, both academia and industry face significant challenges in comprehending and harnessing multiphase flows. Thus, establishing connections between basic research and industrial applications in the field of multiphase flows is fundamental and indispensable for advancements in energy science and technologies. [ABSTRACT FROM AUTHOR]

This paper presents the first numerical evidence of an intermittency route to period-2 thermoacoustic instability in a subcritical single-element liquid rocket engine burning hydrogen peroxide/kerosene as we decrease the equivalence ratio (ϕ) from fuel-rich to fuel-lean. To achieve this, three-dimensional compressible large eddy simulation algorithms combined with the Euler–Lagrangian framework are used. A one-equation eddy sub-grid turbulence model with a partially stirred reactor sub-grid combustion model is employed to simulate the spray turbulent combustion process in a high-pressure liquid-fueled combustor based on open-source platform OpenFOAM. This paper focuses on examining the transition process of the dynamical states in the thermoacoustic system and the synchronization between multiple subsystems. The results indicate that, as the equivalence ratio reduces continuously (1.5 ≤ ϕ ≤ 0.5), the system dynamics shift from period-1 oscillations (ϕ = 1.5) to period-2 oscillations (ϕ = 0.5) via intermittency (1.3 ≤ ϕ ≤ 0.9). Under the equivalence ratio of 0.7 (ϕ = 0.7), a transient mode switching between period-1 and period-2 was also observed. The synchronization processes between the pressure and combustion subsystems in terms of phase-locking and frequency-locking are responsible for the emergence of complex dynamical states. The cycle snapshots analysis also provides more details on the synchronization processes between the pressure and the multiple subsystems, such as vortex dynamics, mixture fraction, and combustion heat release. In summary, this paper sheds light on the complex non-linear thermoacoustic oscillations and the underlying physical mechanisms related to the two-phase flow of spray combustion in liquid rocket engines using three-dimensional large eddy simulations, paving the way for developing passive or active control methods. [ABSTRACT FROM AUTHOR]

The increasing demand for polymer dielectrics in different scenarios, such as electrical insulation cable, requires elevated electrical and mechanical properties. In order to understand the relationship between mechanical properties and the structure of grafted monomers in a grafted polypropylene (PP) system, a design framework based on the transfer-learning method has been proposed for designing grafted side chain structure in PP system. 22 samples of polypropylene-grafted polymer are synthesized. Through a well-trained multi-layer perceptron model for predicting glass transition temperature (Tg), mechanical properties of the grafted PP have been well predicted by the transfer-learning method. Meanwhile, the grafting group structures are divided into nine substructures. By assembling these substructures, the chemical space is established for prediction. Moreover, candidates with satisfied deep traps and flexible mechanical properties are screened out for reference. This work turns qualitative understanding into a quantitative analysis based on mathematical models and broadens the application of polymer materials design with a small dataset. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the time-averaged aerodynamics of sessile droplets at the verge of shedding on hydrophilic and hydrophobic surfaces. A high-resolution particle image velocimetry system was used to measure/reconstruct the velocity and pressure fields in the droplet symmetry plane and obtain the time-averaged aerodynamic loading. It was found that the stagnation angle (the angle bounded by the substrate and the ray emanating from the droplet center connecting to the stagnation point) decreases with decreasing contact angle due to the shrinking size of the horseshoe vortex. The air pressure reaches the maximum near the stagnation point and its minimum near the droplet apex where flow separation occurs. In the near wake of droplets, a recirculation region, where the velocity reduces to nearly zero and the pressure is low, is generated due to the flow separation. The normalized length of the recirculation region decreases with increasing contact angle since droplets with higher contact angles need flows with lower Reynolds number to reach the point of shedding. In addition, the aerodynamic drag over droplets was evaluated by the wake integral method, analyzing the contribution of momentum deficit, Reynolds stress, and pressure deficit. The drag coefficient of the droplets, at the verge of shedding, was independent of the contact angle. This work shows that the drag coefficient of droplets with different contact angles at the verge of shedding can be similar even though the droplet shape, Reynolds number, and flow structures are different. [ABSTRACT FROM AUTHOR]

We investigate numerically the dynamics of a drop containing a bubble impacting onto a pool of the same liquid. We show that the bubble can be engulfed into the pool after impact only for a limited range of impact velocities and bubble sizes. Below a critical Weber number, the compound drop bounces from the surface. By contrast, above a second threshold in Weber number, the bubble bursts during impact. Depending on the bubble size, we identify two different mechanisms responsible for this higher impact velocity threshold, with central bursting at lower bubble sizes, or dimple bursting at larger bubble sizes. We then characterize and model the dynamics of the cavity, to finally provide an overview of the mechanisms affecting the bubble stability in the liquid. [ABSTRACT FROM AUTHOR]

A surfactant-coated droplet attached to a rough wall subjected to shear flow is investigated using a coupled lattice Boltzmann with the finite difference method, where a contact angle hysteresis model is introduced into the method to characterize the surface roughness. The method is first verified by the equilibrium contact angle of a semi-circular droplet setting on the bottom plane. It is then adopted to explore the surfactant role on the droplet motion and deformation on a rough wall with two representative hysteresis windows. For the hysteresis window of (0°, 180°), i.e., the contact line remains pinned, the addition of surfactants first promotes droplet deformation and then hinders droplet deformation with increasing effective capillary number. However, for the hysteresis window of (70°, 110°), the addition of surfactants always promotes droplet motion and deformation. Finally, the surfactant role on droplet breakup is presented. For the hysteresis window of (0°, 180°), the addition of surfactants hinders droplet breakup. However, for the hysteresis window of (70°, 110°), the addition of surfactants promotes droplet breakup. [ABSTRACT FROM AUTHOR]

In this work, an attempt has been made to explore numerically the thermo-fluidic transport process in a novel M-shaped enclosure filled with permeable material along with Al2O3-Cu hybrid nanoparticles suspended in water under the influence of a horizontal magnetizing field. To exercise the influence of geometric parameters, a classical trapezoidal cavity is modified with an inverted triangle at the top to construct an M-shaped cavity. The cavity is heated isothermally from the bottom and cooled from the top, whereas the inclined sidewalls are insulated. The role of geometric parameters on the thermal performance is scrutinized thoroughly by changing the sidewall inclination, number, and height of the top inverted triangular undulation under similar boundary conditions. The governing equations transformed into dimensionless form are solved by using a computing code written in the finite volume approach. The analysis is conducted by considering a wide range of parametric influences like sidewall angles (γ), number (n), and height (δ) of the top triangular undulations, modified Rayleigh number (Ram), Darcy number (Da), Hartmann number (Ha), and hybrid nanoparticle concentrations (φ). Furthermore, the artificial neural network (ANN) technique is implemented and tested to predict the overall thermal behavior of the novel cavity to predict new cases. The results revealed that the design of sidewall inclination (γ) is an important parameter for modulating the thermo-flow physics. The M-shaped cavity (compared to trapezoidal) reveals either a rise or drop in the fluid circulation strength depending upon the magnitude of δ, but the heat transfer rate always increases due to an increase in the cooling length. The heat transfer increment is ∼61.01% as δ increases. Single undulation with higher depth is the optimum choice for achieving improved heat transfer (which may go up to ∼355.75% for δ = 0.5 and γ = 45°). A decrease in Da or Ha causes a drop in the flow strength, which consequently leads to a drop in the heat transfer rate. Furthermore, the concepts of ANN will help researchers predict the behavior for such complicated cavity shapes with a multiphysics approach. This will save efforts as well as computing time for exploring the thermal behavior of any range of a dataset. [ABSTRACT FROM AUTHOR]

Phase separation can be observed when vinaigrette is poured on a kitchen plate under certain conditions. The phase separation in vinaigrette, which comprises olive oil, vinegar, and mustard for stabilization and taste, is characterized by the outward spreading of olive oil from the main film. This phase separation and the phenomena that trigger it were investigated in this study. Moreover, the spreading dynamics of the vinaigrette were examined by analyzing the spreading factor and its rate. The spreading of different formulations of the vinaigrette was probed in this regard by varying the mass concentration of vinegar from 10% to 40% and the amount of mustard from 0.1 to 0.5 g. The emulsion films were placed on a white tile substrate with similar characteristics to those of a kitchen plate at 21 °C and a relative humidity of 50%. The spreading dynamics followed two distinct regimes; increasing the vinegar concentration of mustard-free formulations led to decreases in the spreading factor of the first regime and the spreading rate. The addition of mustard had a similar effect on the spreading factor of the first regime. The variations in these two parameters were related to changes in the system viscosity. The latter was found to be a function of the mustard and vinegar concentrations. Phase separation occurred at vinegar concentrations below 30% because of a competition between the spreading and the existing instabilities in the vinaigrette. This phenomenon did not affect spreading dynamics. [ABSTRACT FROM AUTHOR]

We propose a data-driven threshold model to redefine the boundary between deposition and splashing for drop impact on dry smooth surfaces. The starting point is the collection and digitization of multiple experimental sources with varying impact conditions. The model is based on the theory of Riboux and Gordillo [Riboux and Gordillo, "Experiments of drops impacting a smooth solid surface: A model of the critical impact speed for drop splashing," Phys. Rev. Lett. 113, 024507 (2014)] and is obtained by an uncertainty quantification analysis coupled with machine learning. The uncertainty quantification analysis elucidates the relevance of the impact condition uncertainties when estimating the splashing parameter. The proposed threshold model is trained using a support vector machine algorithm variant that includes uncertainty as a hyperparameter. This threshold model is generalized by complexity reduction and is eightfold cross-validated on the reference data. The results reveal a dependency of the splashing threshold on the impact velocity, the liquid viscosity, the surface tension, and the gas density. Detailed quantification of the prediction performance and a comparison with state-of-the-art models show that the proposed threshold model is the most accurate model to describe the boundaries between deposition and splashing for a wide range of impact conditions. The simplicity and accuracy of this model make it an alternative to existing approaches. [ABSTRACT FROM AUTHOR]

The impact dynamics of water nanodroplets on flat solid surfaces was studied by molecular dynamics simulations over a wide range of Weber numbers (We) and surface wettability (θ0), where θ0 is the Young contact angle. A phase diagram in the parameter space of We vs θ0 was established accommodating eight impact outcomes noted in the final stage of impact, with three of them, holes rebound, partial-rebound splash, and rebound splash, for the first time being identified and reported. The eight impact outcomes were classified into three categories, i.e., non-bouncing, bouncing, and splash. The results show that the splash is triggered only when Wecr > 140. The boundaries separating bouncing from non-bouncing were determined based on the phase diagram. When θ0 > 160°, the boundary is described as Wecr = a ≪ 1; when 110° < θ0 < 160°, the boundary depends on both We and θ0, with a larger We required to trigger bouncing on a less hydrophobic surface, expressed as Wecr = b + ccosθ0; when θ0 < 110°, bouncing never takes place, and hence, the boundary is determined only by the critical contact angle, expressed as θ0,cr = 110°. Here, a, b, and c are constants. [ABSTRACT FROM AUTHOR]

In this article, we report the morphing of the evaporation kinetics of paramagnetic saline sessile droplets in the presence of a magnetic field stimulus. We explore the evaporation kinetics both experimentally and theoretically and study the kinetics on hydrophilic and superhydrophobic substrates for various magnetic field strengths. We show that the evaporation rates of the paramagnetic droplets are augmented significantly and are observed to be a direct function of the magnetic field strength. Additionally, we note the modulation of the contact line transients due to the presence of the field. The influential role of solvated ions in modulating the flow behavior, and subsequently the evaporation, of droplets is present in the literature. Taking cue, we show using particle image velocimetry and infrared thermography that the magnetic field augments the thermo-solutal advection within the droplets. A mathematical analysis, based on the different internal advection mechanisms, has been proposed. We reveal that the magneto-thermal and magneto-solutal modes of internal ferrohydrodynamics are the dominant mechanisms behind the augmented evaporation dynamics. The experimentally obtained internal velocities are in excellent compliance with the model predictions. Furthermore, the enhanced evaporation rates are predicted accurately using a proposed model to scale the interfacial shear modified Stefan flow. The inferences drawn from these findings may hold several important implications in magnetic field-modulated microfluidic thermal and species transport systems. [ABSTRACT FROM AUTHOR]

The dielectrowetting technique is an important method for controlling surface wettability. Herein, by combining the dielectrowetting technique with high-speed photography, the impact of a water drop on a surface with adjustable wettability is studied. Four different impact phenomena of the drop are identified, and the corresponding phase diagram is provided. As the surface wettability changes, the drop spreading factor and the dynamic contact angle differ for the same Weber number, exhibiting diverse drop behavior. A bubble entrapped on the surface is the most commonly observed phenomenon, and its maximum spreading factor and spreading time are dominated by the Weber number. However, its oscillation period and damping rate are independent of the Weber number. Moreover, a jet occurs on the surface with high hydrophobicity, and the inverse relationship between the jet velocity and radius is in good agreement with the theoretical model. Our work on drop impact based on the dielectrowetting effect can provide a new direction for the study of drop dynamics. Furthermore, the preparation method of the substrate with adjustable surface wettability could be applied in industrial fields such as inkjet printing and coating preparation. [ABSTRACT FROM AUTHOR]

The present article discusses the physics and mechanics of evaporation of pendant, aqueous ferrofluid droplets, and modulation of the same by an external magnetic field. We show experimentally and by mathematical analysis that the presence of a horizontal magnetic field augments the evaporation rates of pendant ferrofluid droplets. First, we tackle the question of improved evaporation of the colloidal droplets compared to water and propose physical mechanisms to explain the same. Experiments show that the changes in evaporation rates aided by the magnetic field cannot be explained on the basis of changes in surface tension or based on classical diffusion driven evaporation models. Probing via particle image velocimetry shows that the internal advection kinetics of such droplets plays a direct role toward the augmented evaporation rates by modulating the associated Stefan flow. Infrared thermography reveals changes in thermal gradients within the droplet and evaluating the dynamic surface tension reveals the presence of solutal gradients within the droplet, both brought about by the external field. Based on the premise, a scaling analysis of the internal magneto-thermal and magneto-solutal ferroadvection behavior is presented. The model incorporates the role of the governing Hartmann number, the magneto-thermal Prandtl number, and the magneto-solutal Schmidt number. The analysis and stability maps reveal that the magneto-solutal ferroadvection is the more dominant mechanism, and the model is able to predict the internal advection velocities with accuracy. Furthermore, another scaling model to predict the modified Stefan flow is proposed and is found to accurately predict the improved evaporation rates. [ABSTRACT FROM AUTHOR]

The physics behind the formation of eddies and their effect on an oil drop about to shed due to water shear flow are investigated. The velocities at the frontal periphery of the drop are measured after visualizing the flow and compared with those obtained numerically. A good comparison is observed. It is found that for oleophilic surfaces, two eddies are formed at the back of the drop, while no eddies are formed at the front side. One eddy at the front and three eddies at the rear are observed for drops shedding from oleophobic surfaces. The observations are the same for both experimental and numerical analyses. Eddies, velocity variation, and peripheral pressure distribution are found to be closely related. The pressure distribution along the periphery is studied. The pressure coefficient and the drag coefficient are observed to be higher for drops shedding from the oleophobic surface than from the oleophilic surface for a given volume. Therefore, less critical velocity is necessary for the drop to shed. The velocity variation along the frontal area is responsible for the drag applied. The drag coefficient is observed to increase with the volume. The formation of various eddies and the distribution of pressure along the drop periphery are responsible for the increase in drag coefficient. The pressure drag is observed to be dominant over the viscous drag for all volumes tested. A novel topology is proposed to explain the observations. [ABSTRACT FROM AUTHOR]

This paper presents a study of the impact of various water in Jatropha biodiesel emulsion drops on a stainless steel surface. The composition of the emulsion is varied by changing the volume percentage of water. The effect of the change in the composition and the Weber number (We) is reported. With the increase in the percentage of water, the domination of the viscous force is observed to increase. The emulsions having lower percentages of water (less than 20%) are found to be inertia dominated, while the others (equal or greater than 20%) are viscous dominated. The maximum spreading diameter normalized by the preimpact diameter, βmax, decreases with an increase in the percentage of water due to the increased viscous losses. Consequently, the minimum splat thickness factor and the equilibrium splat thickness factors increase with the percentage of water. Higher viscous losses affect the shape of the drop during spreading as well. Emulsification delays the splashing due to the higher viscous losses. No splashing is observed for the emulsions containing 20 or higher percentage of water, since viscosity dominantly affects the impact. To confirm the effect of the viscosity, βmax obtained from the experiments are compared with that obtained from various existing models. Another purpose of the comparison is to check the suitability of the models for the emulsion drop impact. Only one model among all studied is found to compare well because the model assumes that the characteristic length for viscous dissipation is of the order of splat thickness. [ABSTRACT FROM AUTHOR]

It is known from recent studies that evaporation induces flow around a droplet at atmospheric conditions. This flow is visible even for slowly evaporating liquids like water. In the present study, we investigate the influence of the ambient gas on the evaporating droplet. We observe from the experiments that the rate of evaporation at atmospheric temperature and pressure decreases in a heavier ambient gas. The evaporation-induced flow in these gases for different liquids is measured using particle image velocimetry and found to be very different from each other. However, the width of the disturbed zone around the droplet is seen to be independent of the evaporating liquid and the size of the needle (for the range of needle diameters studied), and only depends on the ambient gas used. [ABSTRACT FROM AUTHOR]

Studies on the evaporation of suspended microlitre droplets under atmospheric conditions have observed faster evaporation rates than the theoretical diffusion-driven rate, especially for rapidly evaporating droplets such as ethanol. Convective flow inside rapidly evaporating droplets has also been reported in the literature. The surrounding gas around the evaporating droplet has, however, been considered to be quiescent in many studies, the validity of which can be questioned. In the present work, we try to answer this question by direct experimental observation of the flow. The possible causes of such a flow are also explored. [ABSTRACT FROM AUTHOR]

In this study, a smartphone-based contact angle measurement instrument was developed. Compared with the traditional measurement instruments, this instrument has the advantage of simplicity, compact size, and portability. An automatic contact point detection algorithm was developed to allow the instrument to correctly detect the drop contact points. Two different contact angle calculation methods, Young-Laplace and polynomial fitting methods, were implemented in this instrument. The performance of this instrument was tested first with ideal synthetic drop profiles. It was shown that the accuracy of the new system with ideal synthetic drop profiles can reach 0.01% with both Young-Laplace and polynomial fitting methods. Conducting experiments to measure both static and dynamic (advancing and receding) contact angles with the developed instrument, we found that the smartphone-based instrument can provide accurate and practical measurement results as the traditional commercial instruments. The successful demonstration of use of a smartphone (mobile phone) to conduct contact angle measurement is a significant advancement in the field as it breaks the dominate mold of use of a computer and a bench bound setup for such systems since their appearance in 1980s. [ABSTRACT FROM AUTHOR]