Fluid Surface Research Articles

Physics-Assisted Machine Learning Models for Predicting Pool Boiling Critical Heat Flux for Cryogenic Fluids

Abstract Cryogenic fluid management is highly crucial for NASA?s space missions and one challenge identified by NASA is the tank fill process for pure cryogenic fluids. To date, no predictive tool can accurately estimate the pool boiling curve during this process. We aim to address this gap by first accurately predicting critical heat flux. We use both traditional machine learning and physics-assisted machine learning methods to predict critical heat flux on a large dataset of 1322 datapoints from 53 published studies with a wide range of operational conditions and surface properties. While the traditional machine learning approach used no prior knowledge in modeling, the physics-assisted machine learning approach assumes the correlation form of the Zuber instability model [1,2] and predicts the multiplier for the hydrodynamic instability term to estimate the critical heat flux. Two groups of input features are compared including one with fluid-only properties and another with both fluid and solid surface properties. Various feature selection methods are employed to reduce the redundant features, and multiple machine learning models are used for modeling the dataset. Physics-assisted machine learning methods predict much better than traditional machine learning methods. The inclusion of solid properties further improves the predictions of critical heat flux. The best predictions are obtained using the extreme gradient boosting model based on the physics-assisted machine learning framework resulting in a mean absolute percentage error of 8.88% which is far better than the semi-empirical correlations.

Evolution of vortices at the merging of an ethanol droplet with water in an intrusive mode

The evolution of vortices formed when a freely falling drop of a 95% aqueous solution of ethanol, tinted with brilliant green, merges with water in the intrusive mode has been traced by method of high-speed video recording. The drop smoothly flows into the liquid and forms a subducting lenticular intrusion, in which a weakly expressed ring vortex is formed if the potential surface energy is greater than or of the same order as its kinetic energy. Gradually, the intrusion of lighter liquid begins to float up and contracts around the cavern, which takes on a conical shape. From the center of the pointed bottom of the cavity, which has reached its maximum depth, a compact volume containing a light liquid of droplet is pushed into the thickness of the liquid. After the cavern collapses, the primary intrusion spreads along the free surface of the target fluid. In this case, the submerging volume is transformed into a small spherical vortex, which reaches its maximum depth, and then stops and forms a compact secondary intrusion elongated vertically. Next, the central part of the secondary intrusion begins to flow up and gradually transforms into a new ring vortex. As it approaches the free surface, the diameter of the vortex increases. The slowly rising shell of the intrusion forms the bottle-shaped base of the cylindrical trace of the ring vortex, colored with droplet pigment. Changes in the sizes of the main structural components during the evolution of the flow pattern were traced.

To spill or not: Short-time pouring dynamics of a toppled liquid bottle

A typical culinary setting involves liquid condiments with different constitutive behaviors stored in jars, bottles, pitchers, or spouts. In the dynamic kitchen environment, handling these condiments might require pouring, drizzling, squeezing, or tapping, demonstrating the interplay of the container geometry, the fluid properties, and the culinary expertise. There is, of course, the occasional accidental toppling. We investigate the combined effects of surface properties, fluid properties, and confinement dimensions on the short-time spilling or pouring dynamics of a toppled cuvette. While attesting to the fact that smaller cuvettes (which can be termed as capillaries as well) do not spontaneously spill, larger cuvettes exhibit spilling dynamics that are dependent on the surface property, fluid viscosity, and flow rheology. For Newtonian liquids, it is observed that the spilling dynamics are determined largely by the coupling of viscous and gravity forces with surface properties, inducing non-intuitive behavior at higher conduit dimensions. The inclusion of rheology for non-Newtonian liquids in the soup makes the spilling dynamics not only an interplay surface and fluid properties but also a function of meniscus retraction demarcating a “splatter” of three regimes “not spilling,” “on the verge of spilling,” and “spontaneous spilling.” We not only delineate the interactions leading to meniscus motion but also provide a mapping on whether or not a container would spill if it is momentarily toppled and then immediately returned to upright position. This study aids in understanding the fascinating physics of fluid pouring dynamics and could lead to new kitchen, biomedical, and industrial technologies.

Linear stability analysis in channel with slippery and rough boundaries

This study examines two-dimensional flow stability in a channel with a superhydrophobic wall and small amplitude roughness. We consider two primary cases: (1) the upper surface is smooth and allows slip, while the lower surface is rough and has no slip; and (2) both surfaces exhibit slip behavior. By using the orthogonal modal method for the Orr–Sommerfeld equation, we rigorously assess the flow's linear stability. The results demonstrate that the slip coefficient and rough wave number significantly influence stability characteristics. Variations in the slip coefficient lead to notable changes in stability thresholds, while the rough wave number alters the flow's response to perturbations. These findings enhance our understanding of the interactions between fluid dynamics, surface properties, and stability phenomena in channels, providing valuable insights for optimizing flow control strategies and designing surfaces in various engineering applications.

Experimental and numerical research on jet dynamics of cavitation bubble near dual particles

The current paper delves into the jet dynamics arising from a cavitation bubble in proximity to a dual-particle system, employing both experimental methodology and numerical simulation. The morphological development of a laser-induced bubble as well as the production of jets are captured by utilizing high-speed photography. The principles of bubble morphology evolution and jet formation are revealed by a OpenFOAM solver, which takes into account the effects of two-phase fluid compressibility, phase changes, heat transfer, and surface tension. Fluid temperature variations induced by bubble oscillations are discussed. The results indicate that the jet dynamics can be categorized into three cases, i.e. bubble-splitting double jets, impacting single jet, non-impacting double jets. For bubble-splitting double jets, bubble splitting is induced by an annular pressure gradient towards the bubble axis. This resulted in the production of two unequal-sized sub-bubbles, which subsequently produced double jets in opposite directions. The fluid temperature close to the bubble interface is low, while the bubble center is high. For impacting single jet, it is induced by a conical pressure gradient towards the nearest particle and the jet impacts the particle. The fluid temperature is low near the jet and high near the particle. When the jet penetrates the bubble interface, the temperature inside the bubble reaches its peak. For non-impacting double jets, they are induced by pressure gradients facing each other and they do not impact particles. The temperature inside the bubble increases with the proximity of the two jets.

Optimization Simulation of Mooring System of Floating Offshore Wind Turbine Platform Based on SPH Method

ABSTRACTIn this paper, the Smoothed Particle Hydrodynamics method is used to simulate the dynamic response of the floating offshore wind turbine mooring system in a complex marine environment by using its advantages of dealing with free surface flow and fluid–structure interaction. The single‐cable mooring system and the double‐cable mooring system are introduced into the numerical simulation model of fluid–solid coupling interaction. The first‐order irregular wave and the second‐order regular wave are used to simulate different wave conditions. The operating state of the platform in these two cases is analyzed, and the accurate data such as the velocity change of the geometric center of the platform and the change of six degrees of freedom are obtained. Using visual processing and data analysis, it is found that the optimized double‐cable mooring system structure improves the vibration reduction ability of the platform.

To the Charged Surface Instability Calculation of a Stratified Fluid

The conditions for the development of instability of the charged surface of a stratified fluid in relation to an overload of surface charge are calculated analytically. A rule for selecting the roots of the dispersion equation is formulated to correctly describe the spectrum of wave motions on the free surface.

Pore-scale study of droplet settling on a heterogenous surface structure

Equilibrium contact angle of a droplet is influenced by surface characteristics and fluid properties. In addition to increasing the solid–liquid contact line, surface roughness also alters the surface free energy, which has a significant influence on contact angle values. Droplets are more likely to impinge on vertices as surface roughness increases. Anisotropic wetting of chemically heterogeneous surfaces further controls the total surface free energy. The free energy Lattice Boltzmann method is utilized to study the effects of wettability heterogeneity and roughened surfaces. Initial model comparisons with experiments showed excellent agreement. The rough surface is modeled with different pillar shapes on a smooth wall, with surface wettability ranging from hydrophilic to neutral conditions. The length scale of surface patterns matches the droplet size, making the Cassie–Baxter and Wenzel equations inapplicable. Results indicate that droplets pin on the vertices of rectangular pillars, while frustum shapes facilitate movement. Studies cover nearly neutral wet, moderately wet, and strongly wet conditions. The effects of relative surface roughness, roughness distribution, mixed wetting surfaces, and body force on equilibrium contact angle are examined. Additionally, the interaction between fluid flow and surface roughness elements shows that smaller spacing and greater height of roughness elements enhance thermal performance, with Nusselt numbers fluctuating significantly. Findings suggest that the ratio of droplet size to pillar surface area is crucial for minimizing surface free energy. On superhydrophilic surfaces, droplet pinning at pillar edges causes the surface to behave hydrophobically. In mixed-wet rough surfaces, pillar wettability significantly influences the equilibrium contact angle.

Exploring the Bio-Mechanisms of Rod-Shaped Bacteria Moving on Rigid Substrate Coated with Non-Newtonian Williamson Slime

Bacteria are single-celled organisms that come in various shapes and sizes, often classified based on characteristics like shape, DNA, and movement mechanisms. Among them, gliding bacteria have a unique way of moving: they slide along surfaces without external structures like flagella or cilia. Instead, they create wave-like motions along their surface to glide across slimy areas. How fast can bacteria move, and does their speed change on different surfaces? Do they glide faster on smooth surfaces or slow down on rough or sticky ones? And when they move through thicker, more complex fluids, how do they adapt, and does this impact their speed? Researchers have investigated these questions by studying how surface properties and fluid dynamics affect bacterial movement. This study also aims to analyze the locomotion of gliding bacteria over a layer of Williamson fluid with a rigid substrate using the dynamics of an undulating sheet. The methodology involves converting the fundamental partial differential equations into a fourth-order nonlinear ordinary differential equation through the Stokes flow approximation and solving it by the regular perturbation technique. The impacts of different physical parameters on gliding speed, flow rate, energy loss, and slime velocity are visually illustrated and discussed. The results show that the glider's speed decreases with a lower viscosity ratio, while higher Weissenberg numbers and occlusion ratios improve the glider's motility. Additionally, the flow rate of the Williamson fluid decreases as the viscosity increases, and power loss experienced by the glider rises with an increase in viscosity. These findings highlight how fluid properties influence bacterial movement and energy efficiency, providing insights for developing microfluidic devices and studying microbial motility.

Magmatic and rock-leaching contributions to the metal load in hydrothermal fluids at þeistareykir, Iceland

Magmatic-hydrothermal systems are key environments to study the transfer of elements from the deep Earth to the surface and the mobilization and re-distribution of elements within the crust. These systems have been recognized as potential active analogue sites for ore deposition. The source of fluids and their metal load is split between the relative contributions from degassing of underlying magma and interactions between the hydrothermal fluid and the host rock. Here, we combine analyses of noble gases and volatile metals in fluids and rocks from the þeistareykir geothermal field (NE Iceland) to provide constraints on the relative contribution of these two sources. Helium isotope data suggest 80–85% originated from magma degassing. The 3He/4He ratio, corrected for atmospheric contamination (Rc/Ra) correlates with volatile metal abundances in surface fluids and indicates that Bi and Hg are predominantly derived from magma degassing. It is also shown that the deep geothermal reservoir fluid is dominated by magmatic input, except for Mn, Fe, Co, Cu, Ti and V, using the elemental signature of magmatic degassing and water-rock interaction. The spatial variations in Rc/Ra and surface fluid volatile metal contents among the wells suggest an impact of the local and regional structures on the fluid's pathway from depth to surface.

Heat Transfer Characteristics of a Quiescent Fluid over a Moving Flat Surface

Optimizing thermal control methods and enhancing the efficiency of various engineering processes, such as the cooling of hot moving surfaces, is imperative. Therefore, it is crucial to investigate heat transfer and temperature distributions across moving surfaces in stationary fluids. In this study, the combined effects of viscous dissipation, temperature-dependent viscosity, and a moving surface in a quiescent fluid on the temperature and velocity profiles are investigated. A two-dimensional steady laminar boundary layer flow of an incompressible Newtonian fluid, driven by the movement of the surface where viscosity is an inverse function of temperature, is analyzed. The effects of flow parameters, including Reynolds number, Eckert number, Prandtl number, variable viscosity, and surface velocity on temperature and velocity profiles, are determined. The governing boundary layer partial differential equations are transformed into non-dimensional form and solved using the central finite difference numerical method, implemented in MATLAB software. The numerical results demonstrate that an increase in the Reynolds number and the variable viscosity parameter leads to an increase in the velocity profiles. Additionally, an increase in Reynolds number, Prandtl number, variable viscosity, and surface velocity leads to a decrease in temperature profiles. Finally, an increase in the Eckert number results in higher temperature profiles. Therefore, with suitable flow parameters, the temperature of the fluid can be regulated. These findings are useful in cooling hot sheets or metallic plates drawn over a quiescent fluid to obtain high-quality final products.

Steady and periodical heat-mass transfer behavior of mixed convection nanofluid with reduced gravity, radiation and activation energy effects

Significance of this study is to explore Arrhenius activation energy, microgravity, chemical reaction and porous medium effects on Darcy nanofluid over a stretching sheet with nonlinear thermal radiations. Purpose of this study is to enhance the lubrication efficiency, excessive heat reduction, surface roughness and tool wear in drilling, milling, grinding and cutting tools of machining procedures. Use of Brownian and thermophoretic nanoparticles in base liquid is very effective to reduce friction in tool-chip and tool-work interfaces, tool life ability and cooling ability through nanofluid minimum quantity lubrication in machining operations. A refined mathematical model is solved using dimensionless variables; oscillatory stokes conditions and primitive variables. The implicit form of finite difference method is applied for numerical results using Gaussian elimination approach. The numerical and physical outputs are secured using Gaussian elimination methodology in FORTRAN tool and TecPlot-360. Graphs are displayed by using numerical data in Tecplot-360 program. Impact of activation energy (AE), solar radiation (Rd), microgravity (RG), porosity (Ω), thermophoresis (NT), chemical reaction (Kr), Prandtl (Pr) and Schmidt factor (Sc) on oscillating frequency of heat and mass transport is depicted. Amplitude in fluid velocity, surface temperature and volume of concentration is enhanced as radiation, microgravity and activation energy increases. It is noted that the increasing amplitude in fluid velocity, temperature and fluid concentration is found with activation energy, radiation and buoyancy force effects. Steady behavior of skin friction and mass transport decreases as Darcy porous medium and reaction rate decreases. Frequency of oscillating skin friction and oscillating heat transfer increases as Schmidt and Prandtl coefficient increases. Fluctuations and amplitude in the frequency of heat and mass transport enhances as thermophoretic nanoparticle enhances.

Surfactant monolayers at oil–water interfaces. Behavior upon compression and relation to emulsion stability

AbstractSurfactant monolayers modify the surface tension of fluid surfaces, and they confer to the surfaces a resistance to mechanical perturbances, such as compression or dilatation. The resistance can be characterized by elastic and viscous moduli, that affect the phenomena involving the motion of liquid surfaces such as wetting, two‐phase flow, foaming and emulsification, rheology and stability of foams and emulsions. Some of these phenomena, for instance coalescence of bubbles or drops, are extremely rapid, and although coalescence seems correlated with the elastic compression modulus, no quantitative comparison has been made. Indeed, this modulus is frequency dependent, and cannot be measured by most conventional devices at the short timescales during which coalescence events occur. In this paper, we first review the current understanding on foam and emulsion stability, highlighting the role of surface rheology in the stability of these systems, important for their formulation. We present tension measurements for various surfactant systems, nonionic and cationic, at oil–water interfaces. We show calculations of the high frequency elastic modulus using the Gibbs adsorption equation and compare the results to previous measurements at air–water interfaces. The moduli measured imposing a rapid expansion of the monolayers are consistently smaller, in particular at oil–water interfaces. We discuss the possible origin of the differences between the two types of interfaces.

Dynamic performance investigations of a full-scale unanchored thin-walled steel fluid storage tank via shake table tests

Theoretical models proposed in the literature and seismic design codes make the basis of analysis and the design procedures of fluid storage tanks. These models are derived based on many simplified and approximate assumptions. Under realistic conditions, however, different factors cause violation of these assumptions, causing the fluid flow and fluid–structure interaction (FSI) to diverge from theories. In this research work, 38 swept-sine tests and 63 seismic ground motions were applied to a full-scale highly flexible unanchored thin-walled stainless steel fluid tank. The experimental natural frequencies of the system for three different aspect ratios of 2.1, 2.8, and 3.5 were calculated and compared with the theoretical ones. Damping ratios for different modes were calculated using the half-power bandwidth analysis. Experimental results revealed discrepancies between the theoretical and experimentally detected natural frequencies, especially for the convective mode. Closer matches were found for the aspect ratios of 2.8 and 3.5, for the impulsive mode. Acceleration amplification factors at different heights of the shell were calculated which showed a nonlinear behaviour with a descending trend from the base to the mid-height and then an ascending one towards the fluid surface. Maximum acceleration amplification factor occurred at the surface of the fluid. The axial strains around the base are maximum and decrease bi-linearly towards the upper heights of the shell. Effects of the input excitation frequency content over the structural responses of the system were examined. Frequency characteristics of the input excitation considerably affected the maximum acceleration amplification factors and axial strains in the shell.

Numerical and experimental study on corrosion mechanism of the water-oil two-phase flow in the atmospheric tower top system

The atmospheric tower is the main component of the crude oil refining units and is a critical area of concern due to the risk of corrosion failure. Research on the corrosion mechanism and risk protection of atmospheric tower top systems plays a vital role in the safe operation of refineries. In this paper, the water-oil two phase process flow of the atmospheric tower top system was simulated by Aspen software. A corresponding flow corrosion simulation experiment was designed according to the main characteristic parameters of the simulated stream. The experimental results under varying temperature and impact angle conditions were analyzed by using microanalysis technology and CFD simulation methods. The process and mechanism of corrosion failure of tower top system under ammonia salt and dew point corrosion environment are revealed in physicochemical aspects. The results show that the corrosion rate was highest at the dew point temperature, but as the temperature decreases, the corrosion products adsorbed and accumulated on the surface are more difficult to remove from the surface, which slows down the corrosion rate. When the impact angle increased from 0° to 60°, the increment of the surface fluid impact force and turbulence intensity makes the corrosion products easier to be stripped off, which enhances the mass transfer efficiency between the corrosive medium and the surface to accelerate the corrosion rate. Different phase states and flow modes affected the morphology of corrosion pits on the surface. The depth and size of the pits in only water phase corrosion were larger than those in the two-phase flow corrosion, Additionally, as the impact angle increased from 0°, the morphology of pits changes from a relatively flat pattern to a more undulating shape. The research results reveal the characteristics of the main corrosion types occurring in the atmospheric tower top system of the oil refining industry, and provide a reference for corrosion risk protection methods.

The initial stage of the coalescence of a compound drop in an impact regime

The evolution of the regular fine structure of the colored matter distribution produced, when a freely falling multifluid drop spreads in deep water, is for the first time traced using the techniques of engineering photo and video recording. The flow pattern is studied in the initial stage of the formation of a cavity and a crown during the coalescence of a compound drop, whose core is a drop of alizarin ink solution coated with an oil shell. The distributions of the colored fluid at the cavity bottom and the crown walls include streaky structures, whose formation can be due to the processes of the available potential surface energy (APSE) conversion occurring when the contact surfaces of the merging fluids are eliminated. In the experiments the height of the falling drop was varied. The core position in the compound drop was not checked but was determined by separation conditions. The ink core disintegration into fibers was observable in all the experiments. The areas of the cavity and crown surfaces covered by the colored fluid reached maximum at the central position of the core.

Observation of Brownian elastohydrodynamic forces acting on confined soft colloids

Confined motions in complex environments are ubiquitous in microbiology. These situations invariably involve the intricate coupling between fluid flow, soft boundaries, surface forces, and fluctuations. In the present study, such a coupling is investigated using a method combining holographic microscopy and advanced statistical inference. Specifically, the Brownian motion of soft micrometric oil droplets near rigid walls is quantitatively analyzed. All the key statistical observables are reconstructed with high precision, allowing for nanoscale resolution of local mobilities and femtonewton inference of conservative or nonconservative forces. Strikingly, the analysis reveals the existence of a novel, transient, but large, soft Brownian force. The latter might be of crucial importance for microbiological and nanophysical transport, target finding, or chemical reactions in crowded environments, and hence the whole life machinery.

Shape of the Surface of a Magnetic Fluid near Magnetic Bodies in a Constant and Alternating Magnetic Field

Shape of the Surface of a Magnetic Fluid near Magnetic Bodies in a Constant and Alternating Magnetic Field

Revealing the dynamics of stagnant rings of third-grade fluid film with heat transfer in the presence of surface tension

In many engineering applications, including coating and lubrication operations, analyzing the temperature behavior of thin film flows on a vertically upward-moving tube is crucial to improving predictive models. This paper examines a steady third-grade fluid film flow with a surface tension gradient on a vertical tube. The mechanisms responsible for the fluid motion are upward tube motion, gravity, and surface tension gradient. This analysis focuses on heat transfer and stagnant ring dynamics. The formulated highly nonlinear ordinary differential equations are solved using the Adomian decomposition method. The conditions for stagnant rings and uniform film thickness are attained and discussed. The inverse capillary number C, Stokes number St, Deborah number De, and Brinkman number Br emerged as flow control parameters. The temperature of the fluid film rises with an increase in the C, St, De, and Br, whereas it decreases with an increase in thermal diffusion rate. The radius of stagnant rings tends to shrink by the increase in C, St, and De. When the value of De is high, third-grade fluid behaves like solids; only free drainage happens with smaller radius stagnant rings and high temperatures. A comparison between Newtonian and third-grade fluids regarding surface tension, velocity, temperature, stationary rings, and fluid film thickness is also provided.

Lung antimicrobial proteins and peptides: from host defense to therapeutic strategies.

Representing severe morbidity and mortality globally, respiratory infections associated with chronic respiratory diseases, including complicated pneumonia, asthma, interstitial lung disease, and chronic obstructive pulmonary disease, are a major public health concern. Lung health and the prevention of pulmonary disease rely on the mechanisms of airway surface fluid secretion, mucociliary clearance, and adequate immune response to eradicate inhaled pathogens and particulate matter from the environment. The antimicrobial proteins and peptides contribute to maintaining an antimicrobial milieu in human lungs to eliminate pathogens and prevent them from causing pulmonary diseases. The predominant antimicrobial molecules of the lung environment include human α- and β-defensins and cathelicidins, among numerous other host defense molecules with antimicrobial and antibiofilm activity such as PLUNC (palate, lung, and nasal epithelium clone) family proteins, elafin, collectins, lactoferrin, lysozymes, mucins, secretory leukocyte proteinase inhibitor, surfactant proteins SP-A and SP-D, and RNases. It has been demonstrated that changes in antimicrobial molecule expression levels are associated with regulating inflammation, potentiating exacerbations, pathological changes, and modifications in chronic lung disease severity. Antimicrobial molecules also display roles in both anticancer and tumorigenic effects. Lung antimicrobial proteins and peptides are promising alternative therapeutics for treating and preventing multidrug-resistant bacterial infections and anticancer therapies.