Search

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A rationale for droplet nucleation during inverse emulsion polymerization (IEP) (reported by previous investigators) is proposed. Based on the idea that smaller monomer droplets are nucleated into polymer particles, while larger droplets serve as reservoirs for monomer (as in a micellar nucleation mechanism) the question of possible monomer‐transport limitation during polymerization is explored. [ABSTRACT FROM AUTHOR]

The simultaneous oblique impact of multiple droplets on a liquid film is an intricate phenomenon prevalent in diverse natural and industrial processes. However, previous studies have primarily focused on single droplet impact, while an in-depth understanding of the more complex multi-droplet scenario remains lacking. The current study aims to numerically investigate the simultaneous oblique impact of two droplets on a water film using a three-dimensional Volume of Fluid (VOF) model. The effects of the Weber number and the impact angle on the crown behavior are carefully analyzed. The results demonstrate that increasing the Weber number enhances the central uprising sheet height but has minor influences on the upstream crown radius and central sheet radius. In contrast, the increase in the impact angle leads to a decreased upstream crown radius and an increased central sheet radius, while the central sheet height remains relatively unaffected. In addition, the splashing threshold for the dual droplet impact cases is significantly lower than that of the single droplet impact cases due to the interactions between the adjacent crowns. The present results provide novel insights into the underlying physics and useful supports in developing predictive models for the intricate multi-droplet impact phenomenon. [ABSTRACT FROM AUTHOR]

Since droplet collision with walls has become a research hotspot, scholars have conducted a large number of studies on the dynamic behavior of electrically neutral droplets colliding with dry walls. However, with the rapid development of electrostatic spray technology, there is an increasingly urgent need to study the dynamic process of collision between charged droplets and walls. In this paper, considering the actual working conditions of electrostatic spray, an electric field model is introduced based on the two-phase flow field. Through the coupling of a multiphase flow field and electric field and a multiphysics field, the dynamic numerical calculation method is used to explore the collision electrodynamic behavior of charged droplets and liquid film. The dynamic evolution process of the formation and development of the liquid crown in the collision zone was clarified, and the critical velocity and critical Weber number of the rebound, spreading, and splashing of charged droplets were tracked. The distribution characteristics of electrostatic field, pressure field, and velocity field under different working conditions are analyzed, and the dynamic mechanism of the charged droplet collision liquid film under multi-physics coupling is revealed based on the electro-viscous effect. It is confirmed that the external electric field can increase the critical velocity of droplet splashing and fragmentation and promote the spreading and fusion behavior of droplets and liquid films. The influence of the impact angle of charged droplets on the collision behavior was further explored. It was found that the charged droplets not only have a smaller critical angle for fragmentation and splashing, but also have a faster settling and fusion speed. [ABSTRACT FROM AUTHOR]

Experimental study on impact phenomena, bouncing time, maximum spreading time, maximum spreading ratio, maximum elongation, and restitution coefficient for a water-based liquid marble impinging on hydrophilic surface. [Display omitted] Liquid marbles are droplets coated by hydrophobic particles. At low Weber numbers (We), when impacting a hydrophilic surface, the marble may bounce on the substrate repeatedly without any rupturing until the quiescence condition is achieved. The marble bouncing has gained far less attention, although its rich underlying physics is due to the interaction between liquid core, hydrophobic grain, and surrounding air. Accordingly, this research experimentally scrutinizes the marble impact and subsequent bouncing on a hydrophilic surface for the first time. Additionally, the conversion of kinetic, gravitational potential, inertial, and surface energies occurring regularly during the impact is exhaustively surveyed. Moreover, the effect of Weber and gravitational Bond numbers (Bo) on the bouncing time, maximum spreading time, maximum spreading ratio, maximum elongation ratio, and maximum restitution are investigated, which characterize the marble impact and bouncing dynamics. This study is one of the limited investigations exploring the effects of the gravitational Bond number on the results. Dimensionless correlations are proposed for the mentioned parameters based on the experimental data. Furthermore, utilizing the simplifying theoretical presumptions, correlations are suggested based on the scale analysis for the spreading time and maximum spreading ratio. The results imply that the mentioned parameters behave differently at low and moderate Weber numbers, though the distinction is more pronounced in the case of the bouncing time, maximum spreading time and maximum spreading ratio. Although increasing with the Weber number when W e < W e c r , the restitution coefficient decreases with the We number for W e > W e c r . In addition, the maximum elongation ratio linearly grows with the Weber number. [ABSTRACT FROM AUTHOR]

[Display omitted] Secondary drops (SDs) generated when falling drops impact a same-liquid bath can potentially generate antibubbles. Different mechanisms of antibubble formation can be identified and their size and formation probability (P Ab) can be predicted. Surfactant solutions were dropped from various heights using a highly stable pulseless microfluidic pump in a same-liquid bath. The impact was recorded using a high-speed camera. The formation of SDs and antibubbles as well as their sizes were evaluated considering the falling-drop height (H FD) and dimensionless parameters. This study reports new mechanisms for antibubble formation from SDs. A decrease in the surface tension yielded a thinner central jet, thereby yielding more SDs. Larger values of the H FD , impact velocity (U), and Weber number (We) increased the SD size and decreased the SD count; the increase in size increased the antibubble size. The number of SDs correlated with the formation of two distinct antibubbles or a single (coalesced) antibubble. The plots for P Ab versus H FD , U, and We exhibited two distinct peaks. A moderate increase in the surfactant concentration enhanced P Ab in the first regime, whereas an excessive concentration limited antibubble formation. Artificial neural modeling can successfully predict antibubble formation. These findings provide valuable insights for the research on controlled antibubble generation. [ABSTRACT FROM AUTHOR]

According to manufacturing data, a theoretical study of condensation inside a heat exchanger with wires on tubes.examined flow patterns with variable refrigerant mass flow rates. Wire-on-tube condensers are adopted with tubes, which have multiple diameters (3.25, 4.83 and 6.29 mm). In addition to the use of two refrigerants (R-134a, R-600a) working at condensing temperatures of (54.4, 45, and 35 °C). The Equal Equation Solver software (EES) was used to obtain the results for the mass velocity range from 8 to 167 kg s−1m−2. Using the non-dimensionless numbers, the model determines the refrigerant flow pattern. Weber number (We) and Froude number (Fr) were used for mass velocity in a range below 100 kg s−1 m−2, which is recommended flow inside the wire-on-tube condenser. The initial transition of the two-phase flow pattern from stratified to stratified-wavy occurred at beginning of condensation for the quality range (0.78-0.42) was Fr (2.7-2.0) and We (6.1-4.0) for R-134a, while the quality range (0.85-0.39) was Fr (5.0-2.4) and We (7.0-4) for R-600a. Second, as the quality range approached, the stratified-wavy flow was replaced by a plug at quality (0.23-0.06) were Fr (1.5-0.4) and We (3.8-2.1) for R-134a and for R-600a the quality range (0.22-0.05) were Fr (1.7-0.55) and We (3.7-2.2).

The gelation kinetics of agar aqueous solutions were studied by means of the viscosity flow curves using a coaxial Couette cylinder viscometer. The viscosity curves show an unusual sigmoidal trend or an exponential decay to a viscous steady state. An original theory of gelation kinetics was developed considering the coarsening of increasingly larger and more stable clusters due to Ostwald ripening and the breakup of clusters that were too large due to the instability of rotating large particles induced by the shear rate. The developed Bounded Ripening Growth model takes into account the trend of the viscosity curves by means of an autocatalytic process with negative feedback on aggregation according to the logistic kinetic equation, in which the constants  k 1 (γ)  and  k − (ν)  are governed by the surface tension and shear rate, respectively. A dimensionless equation based on the difference between the Weber number and the ratio of the inverse kinetic constant to forward constant, accounts for the behavior of the dispersed phase in equilibrium conditions or far from the hydrostatic equilibrium. [ABSTRACT FROM AUTHOR]

Relevance. An analysis of the current state of the global energy agenda shows that the problem of anthropogenic impact on the planet’s atmosphere by thermal energy facilities is one of the most important for humanity. At the same time, the growth in electricity consumption stimulates the introduction of ever new power generating capacities. For a long time, it was believed that the solution to this problem was the large-scale introduction of non-traditional renewable energy sources (wind generators and solar panels) into the overall balance of electricity generation. However, it is now becoming obvious that renewable energy sources cannot fully cover all electricity needs. The latter creates incentives for the commissioning of new thermal power plants, usually operating on coal fuel. But the main problem of coal energy – its anthropogenic impact – still remains unresolved. This situation creates the prerequisites for the development of new “clean” coal technologies with a full cycle of sequestration of combustion products. One of the most promising technologies for burning coal with low emissions is the combustion of coal in the composition of coal-water fuel. However, coal-water fuel technology has a number of disadvantages. One of the most significant is the high ignition delays of typical (with a characteristic size of 3–5 mm) droplets of coal-water fuel. One of the most promising methods for solving this problem is spraying coal-water fuel in an ultra-fine state (with a characteristic droplet size of 0.1–1 mm). Aim. Experimental study of the conditions and characteristics of crushing droplets of coal-water fuel in a high-speed air flow. Object. Coal-water fuel prepared on the basis of lean coal. Method. Special experimental stand to establish the main characteristics and conditions of dispersion of coal-water fuel droplets. Results. The results of experimental studies show that for stable fragmentation of typical droplets of coal-water fuel, the speed of the latter (during the spraying process) must be at least 40 m/s.

Movement of liquid iron micrometeoroid in the Earth atmosphere is simulated to find the time-dependence of its acceleration, velocity and coordinates as well as the length of luminous trajectory when the micrometeoroid is still melted. In the simulations it is assumed that the maximum size of the stable droplet is determined by aerodynamic fragmentation of the moving droplet occurring when the Weber number exceeds its critical value. Two different initial altitudes h of droplet formation were analysed: 80 km and 50 km, both for a wide range of initial velocities between 6 and 20 km/s. Depending on their initial velocity, exceeding the Earth’s escape velocity equal 11.2 km/s, the maximum radius of solid spherules, emerging from solidified final droplet, is predicted here to lie between (a) 55 and 100 μm for h = 80 km, and (b) 10 and 30 μm for h = 50 km.

Spray impacts can be found in several technical applications and consist of many single droplets, which impact under different trajectories on wetted walls. This study investigates the asymmetric crown morphology resulting from an oblique impact ( α = 60°) of a single droplet on a horizontal and quiescent wall film of the same liquid. A droplet generator with an accelerated needle releases the droplets ( D = 1.5 mm) in a controlled trajectory on a thin film ( h f / D = 0.2). The impact process is recorded from two perspectives with two synchronized high-speed cameras. Varying the Weber number within the splashing regime reveals distinct crown morphologies, which are described in detail. For W e < 500, a single central finger develops at the front of the crown, with subsequent detachments of secondary droplets. At higher W e (>500), a collision of the crown with the wall film shortly after impact introduces disturbances into the rim, leading to two fingers in the middle of the front crown. A further increase in W e (>600) intensifies the crown–film interaction, resulting in an early ejection of tiny droplets and a complete breakup of the front rim. The influence of W e on the crown morphology during an oblique impact is also compared to the normal impact (90°). This study paves the way for a classification of impact regimes and a comprehensive picture of the oblique impact process, which deserve more investigation. [ABSTRACT FROM AUTHOR]

Movement of liquid iron micrometeoroid in the Earth atmosphere is simulated to find the time-dependence of its acceleration, velocity and coordinates as well as the length of luminous trajectory when the micrometeoroid is still melted. In the simulations it is assumed that the maximum size of the stable droplet is determined by aerodynamic fragmentation of the moving droplet occurring when the Weber number exceeds its critical value. Two different initial altitudes h of droplet formation were analysed: 80 km and 50 km, both for a wide range of initial velocities between 6 and 20 km/s. Depending on their initial velocity, exceeding the Earth's escape velocity equal 11.2 km/s, the maximum radius of solid spherules, emerging from solidified final droplet, is predicted here to lie between (a) 55 and 100 µm for h = 80 km, and (b) 10 and 30 µm for h = 50 km. [ABSTRACT FROM AUTHOR]

The liquid lithium as core coolant of lithium cooled fast reactor continues to react with neutron emitted from the core to produce helium, which will not only interfere core cooling, but also reduce the efficiency of thermoelectric converter and electromagnetic pump. Therefore, the helium produced needs to be removed. In order to study the gas-liquid separation technology for the helium removal of the core coolant of the lithium cooled fast reactor, the passive gas separator and accumulator device (GSA) for SP-100 reactor of the USA is used for reference. According to its structure and principle, GSA can realize gas-liquid separation and gas storage mainly by the centrifugal force generated by its front vane and main vane, as well as the surface tension generated by its filter and gas storage screen. While Weber number is the ratio of inertial force and surface tension, which can represent both centrifugal force and surface tension. Therefore, Weber number is introduced here as the criterion number, helium and lithium are replaced by air and water, and then air-water separation experiment scheme for theoretical verification is firstly designed. During the experiment, the gas volume portion at the inlet of the experimental prototype will be kept at a low level (less than 1%), the Weber number of the experimental condition will be equal to the one of the actual condition and the inlet of the experimental prototype will contain bubbles with a diameter greater than 200 μm. Then, according to the experimental requirements the experimental prototype has been developed whose main material adopts transparent plexiglass facilitating the observation of its internal fluid conditions. Several structural parameters of the experimental prototype are consistent with the corresponding structural parameters of the GSA. However, since the remaining structural parameters are not clear, the detailed structural design is carried out in the development of the experimental prototype, such as the front vane, the main vane, the filter, the gas storage screen, etc., then the appropriate structural parameters are selected through CFD. Finally, to demonstrate repeatability, three experiments are carried out on the experimental prototype. Every time the experimental conditions include the air-water flow with a gas volume portion of less than 1%, the water velocity close to 0.88 m/s and the bubble size range of 0-900 μm. The experimental results show that the experimental prototype can effectively gather and store the bubbles with the size greater than 200 μm, and make its degassing efficiency exceed 90%, conform to the working principle of the GSA.

The simultaneous oblique impact of multiple droplets on a liquid film is an intricate phenomenon prevalent in diverse natural and industrial processes. However, previous studies have primarily focused on single droplet impact, while an in-depth understanding of the more complex multi-droplet scenario remains lacking. The current study aims to numerically investigate the simultaneous oblique impact of two droplets on a water film using a three-dimensional Volume of Fluid (VOF) model. The effects of the Weber number and the impact angle on the crown behavior are carefully analyzed. The results demonstrate that increasing the Weber number enhances the central uprising sheet height but has minor influences on the upstream crown radius and central sheet radius. In contrast, the increase in the impact angle leads to a decreased upstream crown radius and an increased central sheet radius, while the central sheet height remains relatively unaffected. In addition, the splashing threshold for the dual droplet impact cases is significantly lower than that of the single droplet impact cases due to the interactions between the adjacent crowns. The present results provide novel insights into the underlying physics and useful supports in developing predictive models for the intricate multi-droplet impact phenomenon.

The dynamic behavior of a droplet impinging on a hot surface was examined experimentally using high-speed cameras. De-ionized water droplets with a diameter of 2.25 mm were generated through a 31G injection needle. A sapphire plate with inclination angles ranging from 0° to 60° was heated to 300 °C on a hotplate. Two high-speed cameras with frame rates of 20,000 frames per second were used to visualize the dynamic behavior of water droplets. The Weber number was varied from 5 to 123 by changing the initial height of the droplet from 40 to 210 mm. This corresponds to a normal Weber number range of 6–34 for an inclination angle of 60°. The dynamic behavior of the droplet after impingement was strongly dependent on the surface temperature, inclination angle and Weber number. At lower inclination angles, micro-explosions were observed when the surface temperature was at the Leidenfrost condition. At higher inclination angles, the impinging droplet tended to recover its original spherical shape due to the vapor cushion at the Leidenfrost condition. With increasing Weber number, both maximum spreading diameter and sliding length were increased. [ABSTRACT FROM AUTHOR]

The investigation of the underlying physical processes involved in the impact of droplets has various practical applications in engineering and science. In this research, the spreading velocities within droplet impingement on a sapphire glass were investigated for a wide range of Weber numbers using particle image velocimetry (PIV), which involves tracking the movement of polymeric fluorescent particles (6 µm) within the droplet. The experiments were carried out at room temperature, and the droplets had impact velocities ranging from 0.41 to 2.37 m/s, which corresponded to Weber numbers of 5–183. The results showed that the radial velocity was generally linear over a wide range of spreading radius but the velocity at the exterior radial positions became nonlinear over time due to the influence of capillary and viscous forces. This nonlinearity was more pronounced for lower Weber numbers because the viscosity effects in the droplet were more significant compared to the inertia forces. As the Weber number decreases, the spreading and receding of the droplets are completed faster, leading to different trends in the radial velocity profiles. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The behaviour of bubbles in aqueous solutions of short-chain alcohols depends significantly on the alcohol concentration. At low concentrations, alcohols act as surfactants and slow the rising velocity of the bubble, whereas at higher concentrations, primarily due to the internal arrangement at the molecular level, the desorption of molecules from the bubble surface is facilitated and the mobility of the bubble surface is increased. These factors significantly affect both bubble velocity and deformation. On the basis of experimental data (aqueous solutions of ethanol and propanol in the entire concentration range), two relations were proposed for the estimation of bubble deformation depending on the dimensionless Weber number. The model was successfully verified on an independent data set of the velocity and deformation of bubbles that rise in a stationary liquid. [Display omitted] • Bubble deformation in water-ethanol and water-propanol mixtures was measured. • Bubble deformation can be estimated using the Weber number. • New models were proposed for two alcohol concentration regions. • Results were validated using the experimental bubble velocity data. [ABSTRACT FROM AUTHOR]

The gelation kinetics of agar aqueous solutions were studied by means of the viscosity flow curves using a coaxial Couette cylinder viscometer. The viscosity curves show an unusual sigmoidal trend or an exponential decay to a viscous steady state. An original theory of gelation kinetics was developed considering the coarsening of increasingly larger and more stable clusters due to Ostwald ripening and the breakup of clusters that were too large due to the instability of rotating large particles induced by the shear rate. The developed Bounded Ripening Growth model takes into account the trend of the viscosity curves by means of an autocatalytic process with negative feedback on aggregation according to the logistic kinetic equation, in which the constants k1(γ) and k−(ν) are governed by the surface tension and shear rate, respectively. A dimensionless equation based on the difference between the Weber number and the ratio of the inverse kinetic constant to forward constant, accounts for the behavior of the dispersed phase in equilibrium conditions or far from the hydrostatic equilibrium.

This paper presents a numerical investigation of the three-dimensional dynamics of droplet impact on a thin liquid substrate using the lattice Boltzmann method (LBM). The LBM solver is employed to simulate the fluid dynamics of the droplet-substrate interaction and the subsequent formation of waves on the substrate surface. The study specifically focuses on the influence of Weber number on the collision dynamics between the droplet and substrate, as well as the resulting wave patterns. The simulation results provide insights into the behaviour of the droplet-substrate interface, including the formation of a ‘neck’ region and the fluid recirculation around it. Moreover, the study examines the impact of Weber’s number on the amplitude and frequency of the resulting waves. This research holds significant implications for applications in microfluidic and microelectromechanical systems (MEMS*), where a thorough understanding of droplet impact dynamics is crucial for the design and optimisation of inkjet print heads and other droplet-based systems. By offering an in-depth understanding of the droplet-substrate interaction, this study contributes to the development of more efficient and precise droplet production systems. [ABSTRACT FROM AUTHOR]

Critical Weber numbers (Wecr) for droplet splashing are investigated by considering the geometrical morphologies of hydrophobic micro/nano-textured surfaces and the viscosity of lubricants. A decreasing trend of Wecr with respect to pillar spacing is evident for all textured and lubricant-infused surfaces (LISs), but it is independent of the pillar diameter effect. Additionally, the overall Wecr of the LIS exceeded that of the micro/nano-textured surfaces. The results show that the early droplet splash on micro/nano-textures may be attributed to the slip condition, decreasing the friction loss of airflow and increasing Uair/U0 and K-H instability. Moreover, the slip velocity on the LISs decreases as the lubricant viscosity increases in the order uslip (101) > uslip(105) > uslip(107). Therefore, an increase in slip velocity facilitates earlier droplet splashing on low-viscosity LIS101 than on high-viscosity LIS105 and LIS107. Furthermore, the droplet retraction behavior beyond the maximum spreading varied significantly based on the surface wetting characteristics. [ABSTRACT FROM AUTHOR]

The storage of propellants in space as well as the transfer and filling of spacecraft tanks is a prerequisite for future long-term space exploration missions. In this work, the vented filling of a partially filled tank, which is envisioned as a spacecraft tank, was investigated experimentally under compensated gravity in the Bremen Drop Tower. Experiments were performed with a partially filled tank and a test liquid HFE-7500. The drop tower provides 9 s of compensated gravity. The shape of the free liquid surface inside a right circular cylinder changes from the normal gravity configuration to a free fall configuration during the test. The filling was initiated after 3.5 s and continued until the end at 9 s. The interaction of the incoming liquid jet with the liquid interface was studied for different volumetric flow rates. A stable, but not steady liquid interface was characterized by a deformation due to the incoming liquid jet and the formation of a geyser. The growth of the geyser and the following disintegration into liquid droplets indicated an unstable liquid interface. Subcritical, critical and supercritical regimes of the volumetric flow rates were identified to classify stable and unstable liquid interfaces. The critical Weber number was found to be 1.04, which corresponds to a critical volumetric flow rate of 1.30 mL s-1. This critical Weber number was compared with the existing literature. Additionally, the behaviour of the liquid interface during the reorientation of the liquid inside the tank was observed. [ABSTRACT FROM AUTHOR]

Under certain low head hydraulic conditions, weir discharge under gravity flow can produce an oscillating nappe characterized by horizontal waves and audible low-frequency acoustic energy, which in some cases can have a significant impact on the local environment. In an effort to better understand the mechanism behind nappe oscillation, an experimental investigation was conducted using a linear weir (1.83 m wide, 1.10 m in height, and 0.076 m in thickness) with four different crest shapes (rectangular, quarter-round upstream, half-round, and quarter-round downstream) at a wide range of unit discharge ranging from 8×10−3 m2/s to 36×10−3 m2/s. Using Particle Image Velocimetry (PIV) techniques, differential pressure measurements, and water surface profiles, the influence of Weber number, angle at which the nappe hits the downstream pool (angle of impact), and nappe projection angle on the nappe oscillation are reported. No significant relationship was found between the Weber number and nappe instability. The results suggest that the nappe is stable for unit discharge between 20×10−3 and 24×10−3m2/s regardless the shape of the weir crest. Also, the stable projection angle is −17° for rectangular and quarter-round upstream weirs and −35° for half-round and quarter-round downstream weirs for the specific tested weir. HIGHLIGHTS Explain the mechanism behind the nappe oscillation precisely.; Discover different types of nappe oscillation.; Propose some mitigation solutions for nappe oscillation.; Help designers choose the appropriate crest shape for nappe stability.; Provide a solution for the existing dams that suffer from nappe oscillation.;

This paper presents the morphological evolution characteristics of a droplet impacting a V-shaped wall by using the lattice Boltzmann method (LBM). Four parameters are investigated comprehensively. The parameters vary over wide ranges: surface wettability ( 60 ∘ ≤ θ eq ≤ 120 ∘ ), Weber number ( 102.27 ≤ We ≤ 3681.82 ), bending angle of the V-shaped wall (90 ∘ ≤ θ ≤ 180 ∘ ), and eccentricity ratio (0 ≤ b ≤ 0.5). Two types of collision are observed: deposition and breakage. For breakage, the number of satellite droplets increases against the increment of We. The splashing occurs for a high We. And the lamella ejection is observed on the hydrophilic wall and the neutral wall. The lamella ejection will be slight against the increase of θ eq , while it will become obvious against the increment of θ . In addition, the nondimensional spreading length, width, and height are measured and analyzed. Regime maps are established based on We, Re, and θ . [ABSTRACT FROM AUTHOR]

In the present paper, experimental and numerical studies for the interaction studies between different liquid droplets and hot metal surfaces were carried out. The obtained results were interpreted using graphs and figures. Droplet impact, spreading, breakup and Leidenfrost phenomenon were observed with the help of a video camera at 100 fps. The interaction studies were done at different surface temperatures and different droplet‐impinging velocities. Three metals and three liquids were selected for the present study. Copper, aluminium and steel were selected as metals with varying roughness factors maintained at different temperatures. At the same time, in liquid entities, methanol, ethanol and kerosene were selected along with water in some portions. The selections of the metals were based on the thermal diffusivity property as it influences the thermal interaction between the droplet and the hot metal surface. The temperature range of the metal surface was kept from 150°C to 425°C, and the impinging velocity range of droplets was in the field of 2.4–4.9 m/s. For computational studies, the Ansys Fluent R3‐2019 version was used. Numerical analysis for the interaction process was carried out using the volume of fluid (VOF) method, solving Navier–Stokes and energy equations in a 2D‐geometry transient simulation. Parameters like surface temperature, heat flux and spreading ratio w.r.t. change in Weber number were investigated and presented in the present paper. Obtained results are useful for better understanding of droplet physics while interacting with hot surfaces which further helps in development of new methods for effective spray system designs. Results show that for a lower value of Weber number, the droplets spread less as compare to high Weber number. Also, spreading ratio of droplets depends only on the surface roughness. [ABSTRACT FROM AUTHOR]

An experimental study is made here to investigate the discharge coefficient for contracted rectangular Sharp crested weirs. Three Models are used, each with different weir width to flume width ratios (0.333, 0.5, and 0.666). The experimental work is conducted in a standard flume with high-precision head and flow measuring devices. Results are used to find a dimensionless equation for the discharge coefficient variation with geometrical, flow, and fluid properties. These are the ratio of the total head to the weir height, the ratio of the contracted weir width to the flume width, the ratio of the total head to the contracted width, and Reynolds and Weber numbers. Results show that the relationship between the discharge coefficient and these variables is a non-linear power function with a determination coefficient of 0.97. The importance and normalized importance analysis show that 56.3 % of the discharge coefficient variation is explained by the head-to-contracted width of the weir ratio followed by lower effects of the other variables, namely 16.5, 13.7, 12.4, and 1.2 % for contracted width to flume width ratio, Reynolds number, the head to the contracted width ratio, and Weber, respectively. The effect of the Weber number on the discharge coefficient is much lower than that of the Reynolds number.

Spray impacts can be found in several technical applications and consist of many single droplets, which impact under different trajectories on wetted walls. This study investigates the asymmetric crown morphology resulting from an oblique impact (α= 60°) of a single droplet on a horizontal and quiescent wall film of the same liquid. A droplet generator with an accelerated needle releases the droplets (D= 1.5 mm) in a controlled trajectory on a thin film (hf/D= 0.2). The impact process is recorded from two perspectives with two synchronized high-speed cameras. Varying the Weber number within the splashing regime reveals distinct crown morphologies, which are described in detail. For We< 500, a single central finger develops at the front of the crown, with subsequent detachments of secondary droplets. At higher We (>500), a collision of the crown with the wall film shortly after impact introduces disturbances into the rim, leading to two fingers in the middle of the front crown. A further increase in We (>600) intensifies the crown–film interaction, resulting in an early ejection of tiny droplets and a complete breakup of the front rim. The influence of We on the crown morphology during an oblique impact is also compared to the normal impact (90°). This study paves the way for a classification of impact regimes and a comprehensive picture of the oblique impact process, which deserve more investigation.

Today, the discussion of droplet-fluid interaction is one of the most challenging topics in multiphase (liquid-liquid) flows. In the present study, the behavior of two edible oils (olive oil and canola oil) droplets during the rising in the static fluid of water and passing through the water-oil interface was experimentally investigated. Droplet diameters were controlled in the range of 3.8 to 5.6 mm. First of all, the range of dimensionless numbers was compared to experimental data from other researchers and validated. The results revealed that the droplet shape is elliptical, and that the Weber number decreases in the range of 1 to 2, as the aspect ratio increases. Furthermore, the droplet residence time at the two-phase interface was measured, and the parameters that affected it were examined. Although the results showed that the residence time did not follow a consistent pattern, the conclusion was not far off. Weber dimensionless number was used to introduce hydrodynamic forces and internal surface tension of the droplets. It was shown that none of the theoretical relationships can accurately or even roughly predict the residence time of the oil droplets. Finally, the Weber number has been proven to be dependent on the droplet terminal velocity. Terminal velocity increases with the Weber number and the equivalent diameter.

The phenomenon that the drops impact the solid wall widely exists in industrial production. In this paper, the dynamic evolution of a single drop impacting a horizontal hydrophilic wire is explored through experiments and numerical simulation methods. Combined with the phenomena of spreading, retracting and breaking, the movement behavior law of the drop impacting the curved surface is analyzed. Furthermore, the effects of eccentricity, Weber number and wall wettability on drop impact spreading dynamics are studied. The results show that, with the increase of impact eccentricity, the drop impacting the wire appears symmetrical wrapping mode, asymmetrical wrapping mode, unilateral infiltration mode and partial wetting mode in turn. With the increase of the Weber number, the drop morphology appears in turn as spread-retracting, spread-splitting, spread-wrapping and spread-breaking modes when the axis of the drop impacts the wire. In addition, both eccentricity and Weber number have influence on the maximum spreading coefficient and the maximum spreading time. The wettability of wire has a significant effect on the spread-retracting behavior of drops. With the increase of hydrophilicity of wire, the peak dimensionless spreading area and spread-retracting stage of drops increase, and the retracting time is delayed.

The study was focused on investigating the spray and droplet characteristics of spiral and flat-fan nozzles computationally. The Spiral nozzle and the flat-fan nozzle are generally used in fire suppression application. The computational analysis had been carried out in ANSYS. The nozzle parameters like spray pattern, spray flow rate, impact, weber number were examined at different pressures say 1 bar to 3 bar. During this study the volume fraction of air and water were maintained equally. The spray pattern of spiral nozzle is not uniform and the droplets produced from the spray are coarse. The flat-fan nozzle produces a solid-cone pattern spray with oval impact area with a width of approximately ½ of its length. The flat-fan nozzle has higher spray flow rates and higher sprays impact than the spiral nozzles. The spiral nozzle acquires the maximum spray angle and the minimum droplet size and hence it is considered as highly efficient spray nozzle. [ABSTRACT FROM AUTHOR]

In this study, the behaviors of water droplets on superhydrophobic polyester (PET) films as well as on woven and knitted fabrics with different surface microstructures were analyzed. The water droplet volume, height of release (h), and surface inclination were modified to study the dynamic behavior of water droplets using a pressure balance and the Weber number (We). The droplet volume did not affect the static contact angle. However, the shedding and sliding angles decreased with an increase in droplet volume. The water droplets rebounded on the surface of the superhydrophobic PET films with nano-roughness regardless of the surface inclination angle or h. However, the water droplets with h = 10 cm were pinned on the horizontal surfaces of the woven and knitted fabrics with micro-sized pores, where the dynamic pressure (Pd) exceeded the capillary pressure. On an inclined surface, the water droplets rebounded on the surface of the woven fabric, owing to a decrease in Pd and an increase in the surface inclination angle. However, on the surface of the knitted fabric, pinning was observed even when the surface was tilted, regardless of the inclination angle. The sliding velocity of the droplets after rebound decreased in the following order: film, knitted fabric, woven fabric. With an increase in the inclination angle of the surface and the droplet volume, the sliding velocity increased, which was accompanied by a decrease in vertical impact velocity (V) and an increase in the gravitational force. In terms of We, the droplets with a low We rebounded on all superhydrophobic surfaces, whereas the droplets with a high We were pinned on the surface of the woven and knitted fabrics. [ABSTRACT FROM AUTHOR]

Studies on droplets impacting surfaces with different wettabilities are of great significance for understanding interface phenomena and controlling droplet behaviors. In this work, the droplet impact processes on five surfaces from superhydrophilic to superhydrophobic at various Weber numbers are investigated through experimental and theoretical methods. The spreading and height factors and the oscillating cycle time and amplitude are analyzed. The results show that as the Weber number increases and the contact angle decreases, the impact droplet generally spreads faster and thus yields a larger maximum spreading factor. The maximum spreading time shortens with the increasing Weber number and contact angle. The height factors on different wettable surfaces show a similar decreasing trend in the early spreading stage. The larger the contact angle, the smaller the minimum height factor. As the Weber number increases, both the height factor and minimum height factor decrease. During the oscillating stage, the oscillation cycle time increases at a larger contact angle while it first increases and then decreases as the Weber number increases. Besides, the modified empirical formulas for predicting the maximum spreading factor and time are proposed to consider the effect of the surface contact angle following the principle of energy conservation. These findings can provide guidance for various practical applications of different wettable surfaces. [Display omitted] • Five surfaces from superhydrophilic to superhydrophobic are fabricated. • The influences of Weber number and surface wettability are investigated. • The spreading and height factors and the oscillation features are analyzed. • Modified formulas for the maximum spreading factor and time are proposed. [ABSTRACT FROM AUTHOR]

This paper concerns the two-dimensional free surface cavity flow past an inclined plate in a finite depth. To close the cavity, a Riabouchinsky model is considered. The fluid is assumed to be inviscid and incompressible and the flow to be steady and irrotational. When the gravity and surface tension are negligible, an exact free streamline solution is derived. We solve the cavity flow problem by using two numerical methods. These methods allow us to compute solutions including the effects of gravity and surface tension. The first method is the series truncation and the second is the boundary integral equations, based on Cauchy integral formula. Numerical solutions are found for different values of the angle of inclination \gamma and for various values of the Weber number, the Froude number. Good agreement between the two numerical schemes and the exact solution provides a check on the numerical methods. [ABSTRACT FROM AUTHOR]

Two-phase flow is commonly encountered in various engineering systems. Momentum fluctuation in two-phase flow can create undesirable and destructive vibrations. These vibrations are known as flow-induced vibrations, which are a fundamental phenomenon in fluid–structure interactions, and have been the center of this type of research in the past few decades. Flow-induced vibrations due to the multiphase flow are a complex phenomenon and its understanding is still immature. Various accidents related to flow-induced vibrations have been reported in heat exchangers and piping systems and it is very important to develop a deeper understanding of flow-induced vibrations in multiphase flow. The present review article aims to discuss the literature related to flow-induced vibrations, with special focus on factors affecting flow-induced vibrations in internal two-phase flow. Various factors affecting the magnitude and dominant frequency of forces are narrated and the correlations previously developed to estimate these quantities are discussed. Dimensionless forces are extracted from the literature and plotted against Weber number, to provide a database for comparison and to serve as a validation tool for any studies conducted using computational fluid dynamics. Furthermore, some important literature on flow-induced vibrations under different conditions is presented in tabular form to better understand these findings. Finally, some concluding remarks and comments on future research prospects and challenges are outlined. [ABSTRACT FROM AUTHOR]

Water-repellent superhydrophobic surfaces are ubiquitous in nature. The fundamental understanding of bio/bio-inspired structures facilitates practical applications surmounting metastable superhydrophobicity. Typically, the hierarchical structure and/or reentrant morphology have been employed hitherto to suppress the Cassie-Baxter to Wenzel transition (CWT). Herein, a new design concept is reported, an effect of concave structure, which is vital for the stable superhydrophobic surface. The thermodynamic and kinetic stabilities of the concave pillars are evaluated by continuous exposure to various hydrostatic pressures and sudden impacts of water droplets with various Weber numbers (We), comparing them to the standard superhydrophobic normal pillars. Specifically, the concave pillar exhibits reinforced impact resistance preventing CWT below a critical We of ≈27.6, which is ≈1.6 times higher than that of the normal pillar (≈17.0). Subsequently, the stability of underwater air film (plastron) is investigated at various hydrostatic pressures. The results show that convex air caps formed at the concave cavities generate downward Laplace pressure opposing the exerted hydrostatic pressure between the pillars, thus impeding the hydrostatic pressure-dependent underwater air diffusion. Hence, the effects of trapped air caps contributing to the stable Cassie-Baxter state can offer a pioneering strategy for the exploration and utilization of superhydrophobic surfaces., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

In this research, two intensification approaches for CO2 capture via a rotating packed bed (RPB) and nanofluids were examined simultaneously to maximize the experimental mass transfer coefficient. The two intensification approaches were done by using water as a green, environmentally friendly absorption solvent and as the base fluid for preparing nanofluids and also by using centrifugal acceleration in an RPB. Physicosorption of CO2 in an RPB was carried out by applying Al2O3, TiO2, and SiO2 nanofluids to intensify the mass transfer in water, and the operation parameters such as the angular speed of the rotor, concentration and type of nanoparticles, gas and liquid flow rates, and CO2 concentration in mass transfer intensification were evaluated and several nanofluids were selected to survey investigate how they affect the mass transfer at low pressure. The results show that the Al2O3 nanofluid was more effective than other nanofluids and that the 40 nm nanofluid of this type was more efficient than the 20 nm size. Therefore, a correlation is proposed in this paper for liquid volumetric mass transfer coefficient prediction that includes the microconvection of nanoparticles and surface tension. [ABSTRACT FROM AUTHOR]

We simulate the propagation of capillary waves at the interface between two liquid layers of equal density, viscosity and thickness, which flow in stratified conditions inside a turbulent Poiseuille channel. This setup gives us the possibility to single out the effect of inertia and surface tension – in isolation from gravity – on the propagation of interfacial capillary waves. Numerical simulations, which are based on a combined pseudo spectral/phase field method, are run keeping the shear Reynolds number constant, R e τ = 300 , and considering four different values of the Weber number: We = 0. 5 , We = 1. 0 , We = 1. 5 and We = 2. 0. In the present case, waves are naturally forced by turbulence over a broad range of scales, from the larger ones, whose size is of order of the channel height h , down to the smaller dissipative scales. We show that, by increasing the Weber number, the interface is deformed more vigorously, and is prone to sustain the propagation of waves over a broader range of scales. Upon computation of the power spectra of wave elevation, we show that the behavior of waves agrees with the theoretical predictions given by the weak wave turbulence theory, which predicts a decay S η (k) ∼ k − 4 in the inertial regime, followed by a steeper decay at large k , in the surface-tension-dominated regime. We clearly show that the transition between the inertial and the surface-tension-dominated regime is pushed towards larger k by increasing the Weber number. In addition, we show that the two-dimensional frequency–wavenumber spectra of the wave elevation – the dispersion relation – is in good agreement with well established theoretical prediction, ω (k) ∼ k 3 / 2 , and that the range of validity of such prediction broadens for increasing Weber number. [Display omitted] • We study the propagation of capillary waves at a liquid-liquid interface. • Waves are forced by turbulence over a broad range of scales. • Spectra of wave elevation and dispersion relation agree with theoretical predictions. • The Kolmogorov–Hinze scale (KH) depends on the value of Weber number (We). • Transition from inertial to surface-tension-dominated regime occurs at KH scale. [ABSTRACT FROM AUTHOR]

• A numerical work of head-on coalescence of binary drops onto a cylindrical target. • Temporal deformation factor is predicted during the entire droplet collision cycle. • Maximum deformation factor is estimated just after the collision of drops. • Ring drop is observed to be pinched off from the parent merged drop. • A correlation for maximum deformation factor is developed using computational data. In this paper, a numerical exercise in understanding the binary head-on collision of equal-sized vertically aligned drops on the cylindrical substrate is reported. Subsequently, radial spreading of the liquid bridge, impact, and detachment of merged drop from the solid target. Different dimensionless relevant factors, namely Weber number (W e) , contact angle θ , Ohnesorge number (O h) , Bond number (B o) , and diameter ratio D c / D o are used to characterize the coalescence, and subsequent impingement onto the cylindrical substrate. Temporal deformation factor β f is predicted throughout the entire droplet cycle, and the maximum deformation factor β f , m a x is obtained just after the collision of drops because of the significant radial expansion of merged drop. A larger value of β f , m a x is achieved at a higher We for a constant θ , D c / D o , and Oh. Interestingly, the ring drop is pinched off from the parent merged drop when the value of D c / D o is lower at a higher value of We. Again, the possibility of the appearance of the ring is significantly higher when the target surface becomes non-wetting. A correlation for the maximum deformation factor is developed using computational data points, which fits well with the simulated data within ± 6 %. Lastly, a theoretical framework is also predicted to determine the maximum deformation factor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxidised molten droplet-solid surface interaction outcomes studied for We < 150. • A critical Weber number (We ∼ 79) noted for rebound to disintegration transition. • A power law correlation obtained to quantify droplet spreading time with We. • A kinetic model derived to determine the transient droplet spreading rate. • Maximum droplet spread increased with We resulting in decreased solidification time. Molten metal droplet impingement and subsequent solidification phenomena in both inert and non-inert gas environment exist widely in various industrial applications. Exposing a molten droplet to air allows to form an oxide layer on the droplet surface which greatly influences the thermophysical properties of the droplet. While previous studies demonstrated the influence of oxide layer on the spreading dynamics, understanding of the impact dynamics is still missing when solidification is involved. To address this issue, in the present study, high-speed imaging was used to determine the interaction dynamics and solidification behaviour of a molten droplet of three different compositions onto a solid surface over a range of Weber numbers (We < 150) in an open atmosphere. Two distinct outcomes were noted – (1) rebound and (2) disintegration demarcated by a critical Weber number. Upon impingement, each droplet exhibited periodic spreading and recoiling behaviour which was subsequently dampened by the simultaneous solidification process. The maximum droplet spread area and droplet spreading time were shown to increase and decrease with Weber number, respectively following a power law form. It was shown that in all cases, oscillation and solidification time decreased with Weber number. Finally, a recovery type exponential profile was utilised to describe the droplet spreading kinetics. [ABSTRACT FROM AUTHOR]