Liquid Atomization Research Articles

Deformation and aerobreakup of RP-2 droplets from hypersonic shock waves

The shock-induced atomization and burning of liquid fuel droplets are paramount for hypersonic propulsion and detonation-based combustion systems. The present work experimentally explores the atomization and aerobreakup of liquid RP-2 droplets in a hypersonic shock tube. The shock tube is operated with normal shocks propagating between Mach 5–10 interacting with RP-2 droplets with diameters between 200 and 300 µm. The droplet deformation and breakup dynamics are characterized by ultra-high-speed 5 MHz shadowgraph imaging diagnostics. For all hypersonic shock-droplet interactions, the droplets first undergo structural deformations with subsequent breakup occurring from a shear-stripping mechanism along the periphery of the droplet. The structural changes and droplet deformation rate are found to be self-similar among all cases, and the rate of deformation collapsed to a unified non-dimensional timescale. The complete breakup time of the fuel droplets were analyzed, and theoretical scaling arguments were used to quantify the effects of the Mach number, Weber number, and Ohnesorge number. The experimental data is then used to develop a modified boundary layer stripping model to estimate the breakup time of liquid drops. The model leverages the concept of displacement and momentum thickness to provide a numerical solution to estimate droplet breakup times when exposed to a high-speed gas stream. The model is compared to the experimental RP-2 data and water data available in the literature. The model predicts the breakup time for a range of droplet sizes between 200 and 2000 µm within a reasonable accuracy. The results can be used to optimize liquid fuel injection for hypersonic and detonation-based combustion systems.

Numerical investigation of particle dispersion and collision in a liquid jet flow

A numerical simulation with the Eulerian–Lagrangian point-particle approach is used to study the dispersion of nanoparticles in liquid jet flows. The volume of fluid method is used to simulate the motion of the gas–liquid interface. The particle motion is resolved by the Lagrangian point-particle model, and the collisions among particles are considered. According to the simulation results, the liquid jet atomization process can be divided into four different periods. Moreover, the nanoparticles lead to an increase in the liquid density and viscosity. The influence of the particle motion on the liquid jet breakup process is discussed. The simulation results show that the collisions would restrain particle dispersion. However, the motions and collisions of the particles would help the breakup of the liquid jet.

Oscillating high aspect ratio micro-channels can effectively atomize liquids into uniform aerosol droplets and dial their size on-demand.

Ultrasonic atomization of liquids into micrometer-diameter droplets is crucial across multiple fields, ranging from drug delivery, to spectrometry and printing. Controlling the size and uniformity of the generated droplets on-demand is crucial in all these applications. However, existing systems lack the required precision to tune the droplet properties, and the underlying droplet formation mechanism under high-frequency ultrasonic actuation remains poorly understood due to experimental constraints. Here, we present an atomization platform, which overcomes these current limitations. Our device utilizes oscillating high aspect ratio micro-channels to extract liquids from various inlets (ranging from sessile droplets to large beakers), bound them in a precisely defined narrow region, and, controllably atomize them on-demand. The droplet size can be precisely dialled from 3.6 μm to 6.8 μm by simply tuning the actuation parameters. Since the approach does not need nozzles, meshes or impacting jets, stresses exerted on the liquid samples are reduced, hence it is gentler on delicate samples. The precision offered by the technique allows us for the first time to experimentally visualise the oscillating fluid interface at the onset of atomization at MHz frequencies, and demonstrate its applications for targeted respiratory drug delivery.

Brownian motion in a viscous fluid of particles with constant and time-dependent friction

The Brownian motion (BM) of particles in a fluid under the influence of a moving harmonic potential is described analytically. It is assumed that the bath is viscous and particles constituting it experience Stokes' force with friction coefficients that can depend on time. The generalized Langevin equation (GLE) is derived from the equations of motion for the bath and Brownian particles. It has a familiar form, but its memory kernel generalizes the expressions known from the literature even in the case of constant friction. Analytical solutions of the found GLE are obtained for the mean and mean squared displacements of the Brownian particle, assuming the overdamped character of its motion and both the overdamped and underdamped dynamics of bath particles. In the case of constant friction, the model well describes the BM when the external potential does not move so that the system is in equilibrium. The results determined by the time-dependent friction of the bath particles must be specified for concrete fluids. An example of Lennard–Jones atomic liquid is considered with the recently proposed exponential time dependence of the friction coefficient.

Prediction of sodium leakage droplet size distribution in sodium-cooled fast reactor loop

Sodium spray fire is a significant containment-related safety concern in sodium-cooled fast reactors (SFRs). The droplet size distribution of sodium spray is an important factor affecting the combustion intensity of sodium spray fire. Due to the unstable chemical properties of sodium, water is usually used to simulate sodium to carry out spray experiments, and the droplet size relationship between them needs to be obtained. Based on the unstable wave theory, the droplet size similarity model characterized by liquid physical property parameters and atomization pressure difference is developed and verified from the two aspects of pressure and physical property parameters, and compared with existing models. Furthermore, an experimental facility of water atomization using a nozzle to simulate a break is built and the droplet size of water atomization under the differential pressure range of 1.0 bar–6.0 bar is obtained. The droplet size similarity model is used to predict the sodium atomization droplet size at 300–600 °C under different pressures based on these experimental data.

Simulation of aqueous solutes using the adaptive solvent-scaling (AdSoS) scheme

The Adaptive Solvent-Scaling (AdSoS) scheme [J. Chem. Phys. 155 (2021) 094107] is an adaptive-resolution approach for performing simulations of a solute embedded in a fine-grained (FG) solvent region surrounded by a coarse-grained (CG) solvent region, with a continuous FG ↔ CG switching of the solvent resolution across a buffer layer. Instead of relying on a distinct CG solvent model, AdSoS is based on CG models defined by a dimensional scaling of the FG solvent by a factor s, accompanied by the s-dependent modulation of its mass and interaction parameters. The latter changes are designed to achieve an isomorphism between the dynamics of the FG and CG models, and to preserve the dispersive and dielectric solvation properties of the solvent with respect to a solute at FG resolution. As a result, the AdSoS scheme minimizes the thermodynamic mismatch between different regions of the adaptive-resolution system. The present article generalizes the scheme initially introduced for a pure atomic liquid in slab geometry to more practically relevant situations involving (i) a molecular dipolar solvent (e.g., water); (ii) a radial geometry (i.e., spherical rather than planar layers); and (iii) the inclusion of a solute (e.g., water molecule, dipeptide, ion, or ion pair).

Multiscale modeling of liquid jet breakup in crossflow using an Eulerian/Lagrangian approach

Liquid atomization is a very complex issue, involving multiple length and time scales over several orders of magnitude. To better understand the atomization characteristics of the main injection in a lean premix prevaporize (LPP) combustor, a volume of fluid (VOF)–particle conversion algorithm Lagrangian particle tracking (LPT) coupled approach was proposed to simultaneously reproduce the primary and secondary breakup processes. A VOF model with an adaptive mesh refinement strategy was used to resolve the liquid disintegration on a large scale. The small liquid structures qualified as droplets were transformed into discrete particles based on particle conversion criteria. Next, these particles were tracked using the LPT method to simulate the secondary breakup process. The proposed coupled method used in the Eulerian/Lagrangian framework was validated against liquid jet in crossflow experimental data. The numerical results achieved good agreement with the experimental data. Finally, the proposed method was used to predict the atomization characteristics of the main injection in an LPP combustor under various aerodynamic conditions. Qualitative and quantitative information about liquid deformation and spray characteristics were obtained, which varied depending on the aerodynamic parameters.

Cavitation in Internal Flows of Liquid Jet Through a Throat

The interaction of a liquid with the surrounding air produces unstable waves that disintegrate the liquid into droplets, which is known as liquid atomization. The common internal flow of a liquid atomization nozzle experiences a single-phase flow but might turn into a multiphase flow with the existence of cavitation. Cavitation in internal flow has gotten a lot of attention because of the positive and negative consequences it can have depending on the application. One such advantageous result is that cavitation has been used to promote the atomization of liquid jets by causing gas bubbles in the atmosphere to collapse. Most of the past research on cavitation has focused on the exit orifice’s constant cross-section area. The current study investigates the effect of throat location and geometry on cavitation characteristics. Filtered water was used as the simulation fluid. The high-speed shadowgraph technique was applied to record the images of the internal flow patterns. The placement of the throat was discovered to have a substantial impact on the status of the cavitation. Cavitation began at the inlet of the throat when the throat was placed at the uppermost part of the exit orifice. However, when the throat is placed in the middle of the exit orifice, the cavitation begins at the end of the throat. Four cavitation regimes were identified, namely developing, mixed, super and sudden expansion cavitation. Furthermore, it was found that the discharge coefficient depends on the cavitation’s state and length, except when the cavitation is in the supercavitation regime.

Numerical simulation study on the effects of liquid water atomization on the flow field and performance of aluminum-based water ramjet engines

Numerical simulation study on the effects of liquid water atomization on the flow field and performance of aluminum-based water ramjet engines

Hydrate Formation from Joule Thomson Expansion Using a Single Pass Flowloop

Hydrate risk management is critically important for an energy industry that continues to see increasing demand. Hydrate formation in production lines is a potential threat under low temperature and high-pressure conditions where water and light gas molecules are present. Here, we introduce a 1-inch OD single-pass flow loop and demonstrate the Joule-Thomson (JT) expansion of a methane-ethane mixture. Initially, dry gas flowed through the apparatus at a variable pressure-differential. Larger pressure differentials resulted in more cooling, as predicted by standard thermodynamic models. A systematic deviation noted at higher pressure differentials was partially rectified through corrections incorporating heat transfer, thermal mass and kinetic energy effects. A wet gas system was then investigated with varying degrees of water injection. At the lowest rate, hydrate plugging occurred close to the expansion point and faster than for higher injection rates. This immediate and severe hydrate plugging has important implications for the design of safety relief systems in particular. Furthermore, this rate of plugging could not be predicted by existing software tools, suggesting that the atomization of liquids over an expansion valve is a critical missing component that must be incorporated for accurate predictions of hydrate plug formation severity.

Coordination of distinctive pesticide adjuvants and atomization nozzles on droplet spectrum evolution for spatial drift reduction

Coordination of distinctive pesticide adjuvants and atomization nozzles on droplet spectrum evolution for spatial drift reduction

Multiscale numerical modeling of a complete spray evolution including breakup of liquid jet injection in gaseous cross flow

A direct coupling of the Volume of Fluid method (VOF) and the Lagrangian Particle Tracking (LPT) technique within a Large Eddy Simulation (LES) framework is revisited and assessed by numerically investigating a liquid jet injection into a cross-flowing air (JICF). To close the subgrid scale (SGS) terms appropriate SGS models are considered. In particular, an interfacial SGS term is included into the VOF scalar transport equation in order to achieve a suitable LES and to describe properly the liquid column and the break-up processes (primary and secondary). The dilute spray region including the droplets resulting from the secondary breakup is solved using the LPT approach. Since the latter allows the cell size to be multiple times larger than the droplet diameter, this reduces the computational expenses significantly making it possible to handle the simulation of the whole spray evolution including the complete liquid atomization without complex tunable atomization models. For this purpose, two operating conditions of a JICF existing in the literature are considered. The achieved results are first presented in terms of mesh sensitivity, required computational costs and impact of the interfacial SGS term. Next, comparisons between pure VOF/LES and VOF/LPT/LES for both qualitative features and quantitative properties are provided and discussed. In overall, a good agreement with experiments for the quantitative properties is reported. It is especially found that both the Rosin–Rammler and Gaussian distributions offer nearly a more accurate fit to the particle size distribution except for the range from 0 to 10 μm. Together with the detailed characteristics of vortices evolving and an extended breakup regime map, the spray characteristics including the spray structure are well captured. Finally, even though the interfacial SGS term has an evident influence on the jet and atomization dynamics, its impact on quantitative properties is not so prominent under these operating conditions.

Molecular dynamics study of bubble nucleation on trigonometric nanostructured surfaces

Nanostructures have a crucial impact on bubble nucleation. In this paper, different nano-grooved surfaces are constructed using complex trigonometric functions, and the nucleation process of liquid argon on the surfaces is investigated using molecular dynamics simulations. The nanostructures affect the bubble nucleation location, and the results show that the bubble nucleation always occurs in the groove region during the boiling process. In contrast, the bubbles on the flat surface appear randomly. In addition, bubble growth is also affected by the nanostructure. Increasing nanostructure size can reduce the bubble nucleation time and enhance the bubble growth rate. The nanostructure increases the solid-liquid interface area, which enhances the heat transfer between solid and liquid. Finally, the reasons for bubble nucleation on different nanostructured surfaces are analyzed. The heat transfer between solid and liquid is the leading factor for bubble nucleation when the difference in liquid atoms’ potential energy is slight. As the nanostructure size increases, the substrate attracts more argon atoms to form a non-evaporating liquid layer, improving heat transfer and promoting bubble nucleation.

Effect of high-frequency jet velocity perturbations on impinging jets atomization characteristics

The atomization characteristics of impinging jets with high-frequency jet velocity perturbations is studied numerically based on the volume of fluid method. Three typical perturbation modes are considered to mimic the velocity discrepancies of jet flow in real engine conditions. Both the perturbation amplitude and frequency are investigated independently. Results show that the liquid sheet structure and atomization characteristics are significantly changed under the intrinsic perturbation frequency. The spectrum analysis is performed to reveal the specific phenomenon and explore the mechanism of different velocity perturbation modes. The analyses show that the atomization process is sensitive to perturbation frequency but its effectiveness diminishes significantly at excessively high frequencies. Additionally, when the frequency of velocity perturbation approaches the natural intrinsic frequency of sheet waves, resonance occurs within the liquid sheet for certain perturbation mode, leading to dramatic varies in breakup length and spray angle because the velocity superposition of the intrinsic and perturbed flow and its dynamics.

A computational study of a two-fluid atomizing coaxial jet: Validation against experimental back-lit imaging and radiography and the influence of gas velocity and contact line model

Numerical simulations of liquid atomization in a two-fluid coaxial geometry have been performed using a geometric Volume-of-Fluid method. Experimental measurements have been obtained using visible light back-lit imaging and X-ray radiography. Simulations are validated against experiments, using the same geometry and fluid injection rates of air and water, by showing excellent agreement in quantities such as liquid mass distribution in the spray formation region and the liquid jet length statistics and temporal dynamics. At the nozzle exit, the coflowing liquid and gas streams are separated by a cylindrical splitter plate. The liquid is laminar and modeled using a Poiseuille flow while the gas inflow model and the contact line model are varied. For the gas velocity models, the vorticity thickness is shown to have a strong influence on the downstream liquid distribution; the difficulty of its modeling and routes to overcome them are discussed. For the contact line model, pinning the interface to the inner wall of the splitter plate leads to an initial increase in the diameter of the liquid jet just downstream of the nozzle exit. In contrast, pinning to the outer wall of the splitter plate or allowing for a free moving contact line results in a monotonic decrease in the diameter of the liquid jet as the downstream distance is increased, in agreement with the experimental observations and measurements. A sub-grid scale contact line model based on a static contact angle is introduced. The static contact angle is varied in the model, showing that the liquid remains intact longer as the static contact angle is increased.

Reply to "Comment on 'Brownian motion with time-dependent friction and single-particle dynamics in liquids' ".

In this reply, we respond to the comments by Lisý and Tóthová (LT) on our recent work [Phys. Rev. E 105, 064107 (2022)10.1103/PhysRevE.105.064107], where we have extended the microscopic theory of molecular motion in atomic liquids that was originally proposed by Glass and Rice [Phys. Rev. 176, 239 (1968)10.1103/PhysRev.176.239]. Contrary to our conclusion of nonavailability of a physically tractable analytical solution of the equation of motion involving dynamic friction, LT have attempted to obtain an analytical solution giving the velocity autocorrelation function in liquids. We show that the analytical solution of the equation of motion derived by LT is incomplete and not an appropriate solution for the description of atomic dynamics in liquids. It is demonstrated that the generalized statements made by LT regarding the equation of motion giving incorrect results are unjustified in the absence of substantial proofs. Also, until and unless proven otherwise, we do not find any reason for the reconsideration of the theory as suggested by LT.

Shock-induced atomisation of a liquid metal droplet

The present study uses Galinstan as a test fluid to investigate the shock-induced atomisation of a liquid metal droplet in a high-Weber-number regime $(We \sim 400\unicode{x2013}8000)$ . Atomisation dynamics is examined for three test environments: oxidizing (Galinstan–air), inert (Galinstan–nitrogen) and conventional fluids (deionised water–air). Due to the readily oxidizing nature of liquid metals, their atomisation in an industrial scale system is generally carried out in inert atmosphere conditions. However, no previous study has considered gas-induced secondary atomisation of liquid metals in inert conditions. Due to experimental challenges associated with molten metals, laboratory scale models are generally tested for conventional fluids like deionised water, liquid fuels, etc. The translation of results obtained from conventional fluid to liquid metal atomisation is rarely explored. Here a direct multiscale spatial and temporal comparison is provided between the atomisation dynamics of conventional fluid and liquid metals under oxidizing and inert conditions. The liquid metal droplet undergoes breakup through the shear-induced entrainment mode for the studied range of Weber number values. The prevailing mechanism is explained based on the relative dominance of droplet deformation and Kelvin–Helmholtz wave formation. The study provides quantitative and qualitative similarities for the three test cases and explains the differences in morphology of fragmenting secondary droplets in the oxidizing test case (Galinstan–air) due to rapid oxidation of the fragmenting ligaments. A phenomenological framework is postulated for predicting the morphology of secondary droplets. The formation of flake-like secondary droplets in the Galinstan air test case is based on the oxidation rate of liquid metals and the properties of the oxide layer formed on the atomizing ligament surface.

Substantiation of the design and technological parameters of a multi-fan sprayer module

Currently, precision gardening necessitates the use of robotic universal platforms featuring modular multi-fan sprayers, typically equipped with 4-6 fans. As new technologies emerge, the demands placed on spraying ventilation systems are also evolving. (Research purpose) The objective of this research is to establish the design and technological specifications of the multi-fan sprayer module. (Materials and methods) The research is grounded on fundamental equations of energy and mass conservation in the field of applied gas dynamics, specifically the Bernoulli equation and the flow continuity equation. To analyze the pressure distribution within the fan duct and calculate the gas jet, a specific methodology was employed in this research. Additionally, the research utilizes analytical expressions and industry standards to determine universal parameters and dimensions of fans and liquid atomizers. (Results and discussion) Theoretical calculations were performed to determine the main parameters. The results are as follows: the air consumption required to cover a given crown volume is 11.28 cubic meters per second; the air consumption by one fan is 1.88 cubic meters per second; the air flow rate at the fan outlet reaches 17.9 meters per second; pressure generated by the fan is 192.25 pascals; power required to drive one fan is 0.170 kilowatts; the installed power of the fan motor is 0.204 kilowatts; the jet initial section length is 1.53 meters; the axial jet velocity is 13.6 meters per second; the air consumption is 12.84 cubic meters per second; the round jet diameter is 1.58 meters. (Conclusions) The technological scheme of a multi-fan sprayer has been developed and justified. Calculation equations have been proposed to determine the distribution of static, dynamic, and total pressure in different sections of the sprayer fan. An algorithm for calculating the parameters of the sprayer module has been presented. The numerical values of the parameters for the multi-fan sprayer module have been determined for specific operating conditions.

Effect of atomizer and cross-flows on liquid and gelled Jet A-1 fuel injection

The current study aims to experimentally investigate the effect of atomizer and cross-flow velocities on liquid and gelled Jet A-1 fuels. For gelled Jet A-1, Jet A-1 liquid, Thixatrol® ST and rectified xylene are the base fuel, gellant and solvent, respectively. Gelled Jet A-1 is prepared by adding 85% by weight of base fuel along with 7.5% by weight of gellant and solvent, each at optimum processing conditions. Atomization using a simple-plain-orifice atomizer is investigated to understand its effect on Jet A-1 gel fuel break-up without air cross-flow. Based on the investigation from qualitative flow visualization and quantitative analysis of Jet A-1 gel fuel break-up, a modified simple-plain-orifice atomizer called an internally impinging air-blast atomizer is made. Primary atomization using this new atomizer is studied to understand the break-up of liquid and gelled Jet A-1 gel fuels without any air cross-flow. Secondary atomization of liquid and gel fuel is investigated by transversely injecting fuel into different low-speed subsonic air cross-flow environments. Laser sheet Imaging (LSI) technique is used to capture spray images of both fuels. Break-up mechanisms of both liquid and gel fuels were observed, and the results were compared. Information on the cross-flow air mass flow rate effect on the liquid and gel spray is extracted by developing an algorithm in MATLAB using an image processing tool. Relative droplet size distribution of liquid and gel spray revealed their dependence on cross-flow air mass flow rate. Total droplet count of both liquid and gel fuel decreases significantly as the cross-flow Reynolds’ number increases. At higher cross-flow Reynolds’ number, gel droplets in the flow are observed to be more as compared to liquid fuel.

Nanoscale phenomena during wetting of copper on nickel-based superalloy: A molecular dynamics study

Joining of dissimilar metallic materials such as Inconel alloys and steel by vacuum brazing with copper (Cu) filler metal is highly desirable in a wide range of applications, for example, in construction of rotors for high-speed electrical motors. However, experiments have shown poor wettability of Cu on IN718 during vacuum brazing. In this work, molecular dynamics (MD) simulations are performed to study nanoscale interfacial phenomena that occur during brazing of IN600 and IN718 with steel using Cu. Hybrid potentials data is verified using density function theory (DFT) based energy calculation and melting point test models. The results show that IN600 coheres well with liquid Cu, whereas Niobium containing IN718 exhibits inhibited diffusion of atoms from the Inconel alloy into the liquid Cu. Additionally, the simulations show that liquid Cu atoms diffuse well into the precipitate (γ′′ phase) in IN718 but barely diffuse into the parent γ phase.