Liquid Atomization Research Articles

Investigation on High-Viscosity Chemical Waste Liquid Atomizer Based on VOF-DPM

The viscosity of adiponitrile waste liquid is as high as 1000 cp. It is challenging to spray and atomize the waste liquid normally. Based on the coaxial three-channel pneumatic atomizer, a two-stage supersonic steam atomizer is proposed in this paper, and the atomization process is simulated by Fluent software. Compared with the traditional atomization simulation method, the Volume-of-Fluid to Discrete-Phase-Model (VOF-DPM) bi-directional coupling model and Adaptive Mesh Refinement (AMR) technology can save mesh and improve the computational efficiency. The atomization processes of primary breakup and secondary breakup are entirely captured and analyzed. The results show that the Sauter Mean Diameter (SMD) is about 116–180 μm, the SMD decreases with the increase of steam inlet absolute pressure, and the atomization quality can meet the combustion requirements. This study can be used for the performance optimization of the high-viscosity liquid atomizers in the chemical and aerospace industry and shorten the time engineers spend in the simulation calculation to verify the rationality of the structure.

Enhancing Heat Transfer Behaviour of Ethylene Glycol by the Introduction of Silicon Carbide Nanoparticles: An Experimental and Molecular Dynamics Simulation Study.

As the critical component of automotive engine coolant, ethylene glycol (E.G.) significantly matters in heat dissipation. In this study, the key aim is to investigate the heat transfer behaviour of E.G. as nano-additives base fluid. The heat transfer capability of E.G./SiC nanofluid (N.F.) was experimentally and theoretically evaluated via transient hot wire methods and equilibrium molecular dynamics (EMD) simulation, respectively. M.D. simulation exhibited a great ability to accurately forecast the thermal conductivity of N.F. compared with the experiment results. The results confirmed that the thermal stability of N.F. is relatively greater than that of E.G. base fluids. An improvement mechanism of thermal conductivity and thermal stability under an atomic scale via the analysis of mean square displacement (MSD) and radial distribution function (RDF) calculation was elaborately presented. Ultimately, the results indicated that the diffusion effect and the increasing transition rate of liquid atoms are responsible for thermal conductivity enhancement.

Applying surface tension as pressure boundary condition in free surface flow analysis by moving particle simulation method

A model that introduces surface tension as a pressure boundary condition, named the surface tension as pressure (STP) model, was developed for free surface flow analyses by the moving particle simulation (MPS) method. The STP model assigns to surface particles the liquid pressure of Laplace’s formula. The model is an alternative to previous models that apply surface tension as volume force such as the continuum surface force model. Problems that appeared when using the volume force models, such as the dependencies of calculation results on particle resolution and pressure gradient accuracy, were solved by using the STP model. Calculations predicted the theoretical values of the internal pressure of a 3D spherical droplet and the oscillation period of a 2D elliptic droplet over a wide range of surface tension coefficients and droplet sizes with errors less than 10%. Since the STP model is easy to implement, does not increase computation cost from previous models, and does not require surface reconstruction or additional marker particles, the model is suitable for practical and large-scale free surface flow problems that involve violent deformation of the liquid surface such as liquid atomization.

Improving CO2 photoconversion with ionic liquid and Co single atoms

Photocatalytic CO2 conversion promises an ideal route to store solar energy into chemical bonds. However, sluggish electron kinetics and unfavorable product selectivity remain unresolved challenges. Here, an ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate, and borate-anchored Co single atoms were separately loaded on ultrathin g-C3N4 nanosheets. The optimized nanocomposite photocatalyst produces CO and CH4 from CO2 and water under UV–vis light irradiation, exhibiting a 42-fold photoactivity enhancement compared with g-C3N4 and nearly 100% selectivity towards CO2 reduction. Experimental and theoretical results reveal that the ionic liquid extracts electrons and facilitates CO2 reduction, whereas Co single atoms trap holes and catalyze water oxidation. More importantly, the maximum electron transfer efficiency for CO2 photoreduction, as measured with in-situ μs-transient absorption spectroscopy, is found to be 35.3%, owing to the combined effect of the ionic liquid and Co single atoms. This work offers a feasible strategy for efficiently converting CO2 to valuable chemicals.

Biological toxicity evaluation of traditional medicine white tea extract liquid

Purpose: The aim of this study was to evaluate the safety and toxicity of intravenous use of White Tea Extract Liquid (WT) in rabbits through routine blood tests and biochemical and histopathological means. Design and methods: This study used the WT product produced by the company and the New Zealand rabbits at 2.0~2.5 kg of weight. Rabbits were divided into two groups: Control and WT groups. In the WT group, the diluted WT injection volume needed to be injected was calculated according to their body weight on days 1, 4, 7 and 11...... for 4 weeks respectively. During the1, 2 and 4 weeks of the experiment, blood routine, blood biochemistry and the histopathological sections of the heart, spleen, lung, trachea, kidney, bladder, uterus, testicle, stomach, liver, small intestine, big intestine were evaluated in the study. Findings: By comparison, the blood routine test did not deviate from the normal ranges provided by the diagnostic laboratory. The blood biochemical indexes of all experimental rabbits are within a reasonable range and did not detect clinically significant abnormalities between treatment and control groups. The WT had no obvious inflammatory change in the whole tissue and no harmful effect on the organs of various systems of the rabbits’ system for 4 weeks. Conclusions: After intravenous injection for 4 weeks in rabbits, white tea herb atomization liquid did not produce obvious toxic effects on the animals.

Effect of the fractal dimension of nanoparticle aggregates on enhanced thermal transport in nanofluids – a molecular dynamics study

ABSTRACT Equilibrium molecular dynamics simulations are employed to explore the underlying relationship between the strength of liquid layering around a nanoparticle and nanoparticle aggregation, and its effect on thermal transport in nanofluids. Results indicate that the contribution of the liquid phase to the thermal conductivity of the nanofluid is higher in the aggregated state than in the well-dispersed state. Rough aggregates with a low fractal dimension, formed in the presence of strong liquid layering, can hold a larger number of liquid atoms in the vicinity of the aggregate for an extended period compared to rounded aggregates. Additional simulations establish that a rough nanoparticle, like the aggregates of low fractal dimension, can hold a larger number of liquid atoms in the layer adjacent to it than a smooth particle of the same volume. The study indicates that the particles or aggregates of low fractal dimensions improve the thermal transport at the particle–liquid interface, leading to increased thermal conductivity.

Mechanism of Surface Wettability of Nanostructure Morphology Enhancing Boiling Heat Transfer: Molecular Dynamics Simulation

In this paper, the interaction mechanism between the solid–liquid–gas interface phenomenon caused by nanostructure and surface wettability and boiling heat transfer is described, and the heat transfer theory of single wettable nanostructure surface and mixed wettable nanostructure surface is proposed. Through molecular dynamics simulation, the thermodynamic model of the wettable surface of nanostructures is established. The nanostructures are set as four rectangular lattice structures with a height of 18 Å. The solid atoms are platinum atoms, and the liquid atoms are argon atoms. The simulation results show that with the increase of surface hydrophilicity of nanostructures, the fluid temperature increases significantly, and the heat transfer at the interface is enhanced. With the increase in surface hydrophobicity of nanostructures, the atoms staying on the surface of nanostructures are affected by the hydrophobicity, showing a phenomenon of exclusion, and the evaporation rate in the evaporation area of nanostructures is significantly increased. In addition, the mixed wettable surface is influenced by the atomic potential energy and kinetic energy of the solid surface, and when compared with the pure wettable surface under the nanostructure, it changes the diffusion behavior of argon atoms on the nanostructure surface, enhances the heat transfer phenomenon compared with the pure hydrophobic surface, and enhances the evaporation phenomenon compared with the pure hydrophilic surface. This study provides insights into the relationship between the vapor film and the heating surface with mixed wettability and nanostructures.

Fluid topology optimization and additive manufacturing of a liquid atomizer using an extensive number of grid points

Additive manufacturing (AM) can fabricate complicated shapes and is useful when manufacturing topology optimized shapes. Fluid parts often consists of three dimensional curves that are suitable for AM fabrication. However, the application of fluid topology optimization and AM has not been investigated yet. However, modeling and solving an optimization problem have not been investigated for a real industrial fluid topology optimization problem of AM parts with tiny channels, i.e., a liquid atomizer which is equipped with an aero-engine fuel injector. In order to reduce computation time, which is an important issue in real industrial problem, the instantaneous sensitivity approximation method is used as a topology optimization method. The optimized part exhibited a reduction in pressure loss compared to that of a conventional part.

World beyond the nearest neighbors

The structure beyond the nearest neighbor atoms in liquid and glass is characterized by the medium-range order (MRO). In the conventional approach, the MRO is considered to result directly from the short-range order (SRO) in the nearest neighbors. To this bottom–up approach starting with the SRO, we propose to add a top–down approach in which global collective forces drive liquid to form density waves. The two approaches are in conflict with each other, and the compromise produces the structure with the MRO. The driving force to produce density waves provides the stability and stiffness to the MRO, and controls various mechanical properties. This dual framework provides a novel perspective for description of the structure and dynamics of liquid and glass.

Effects of gas viscosity and liquid-to-gas density ratio on liquid jet atomization in crossflow

Atomization of liquid jets in gaseous crossflows has many natural and industrial applications, for example, in fuel atomization in gas turbine engines, rocket engines, film cooling, and, recently, suspension and solution precursor plasma spraying processes for the development of advanced coatings. Viscosity and density of the gaseous medium may significantly vary in applications such as plasma spraying, which can affect the instability waves on the liquid jet column, resulting in a major change in the mechanism of primary and secondary breakups. In this study, a numerical model is used to investigate the impact of gas viscosity on breakup mechanisms for a wide range of density ratios and Weber numbers. Due to many challenges, only a few comprehensive atomization measurements have been performed on this subject. However, novel computational models could provide the atomization process with a thorough picture in the last two decades. The incompressible variable-density Navier–Stokes equations are solved by using finite volume schemes, and a geometric volume-of-fluid technique is used to track the gas–liquid interface. In our parametric study, three sets of density ratios and Weber numbers are chosen. In each set, four cases with different orders of magnitude of gaseous Reynolds number are simulated. Different characteristics of jet atomization are analyzed, such as the jet trajectory, breakup location, and surface instabilities generated along the jet column. Ultimately, the effects of gaseous Reynolds number, density ratio, and Weber number on jet deformation and breakup mechanisms are discussed.

Temperature dependence of adhesion properties at liquid-aluminum/solid interfaces

The adhesion problem of the liquid aluminum (Al) and solid surfaces in the production process has not been completely solved. In this paper, by performing the molecular dynamic simulations, we first establish models composed of liquid-Al/Al and liquid-Al/silicon (Si) systems, in which the region of solid temperature is from 100 K to 800 K. Then, the dependence between the adhesion force and the solid temperature is qualitatively investigated. The adhesion mechanism of liquid atoms is explored in terms of their diffusion behavior. The results show that there is an opposite effect of the temperature on adhesion properties between the liquid-Al/Al interface and the liquid-Al/Si interface. The thermal excitation effect induces enlargement of the probability of atomic collisions, which accounts for the increase of the adhesion force at the liquid-Al/Al interface. Conversely, the thermal excitation effect leads to the detachment of the atoms in contact with each other, which reduces the adhesion force at the liquid-Al/Si interface. Our findings reveal that the solid Al surface is aluminophilic but the solid Si surface is aluminophobic. In addition, the adhesion between liquid-Al and solid surfaces can be explained by the variation of the interfacial potential.

The evaporation of nanoscale sodium liquid film on the non-ideal nanostructure surface: A molecular dynamics study

The nanoscale liquid sodium film inside the microporous wick structure is of great importance to understanding the evaporation mechanism of the sodium heat pipe. The novel optimized wick structure is made of several layers of special screen. The surface of each screen exhibits a nanostructure type. Some non-ideal nanostructures may result from experimental faults or limits. And they will have an effect on the evaporation of film. In the present study, molecular dynamics is adopted to investigate this effect. The simulation system consists of the liquid sodium film and the solid surface. The flat surface is set as the reference. Based on the three non-ideal shapes of deposition, the sinusoidal nanostructures, conical nanostructures, and spherical nanostructures are built. The results indicate that the evaporation is suppressed by the above nanostructure surfaces. The weakening effect is through three forms: the potential gradient of the liquid film is intensified and the evaporation difficulty is increased; the heat transfer in the solid-liquid contact region is impeded; the collision heat transfer inside the liquid film is affected due to the delay of the aggregation variation between liquid atoms.

Microscopic mechanism of effects of nanostructure morphology on bubble nucleation: A molecular dynamics simulation

In this study, the effect of nanostructure morphology on bubble nucleation of liquid argon on a platinum solid surface was explored using molecular dynamics methods. We examined the differences in nucleation behavior on smooth and nanostructured surfaces, including trapezoidal, rectangular, and reentrant cavities. The simulation results demonstrated that nanostructured surfaces outperformed smooth surfaces in terms of bubble nucleation, and the corresponding morphology had a significant effect. The reentrant cavity had the shortest bubble initial nucleation time, followed by the rectangular cavity, and the trapezoidal cavity had the longest bubble initial nucleation time. The mechanism of bubble nucleation on solid surfaces was further investigated from two perspectives: heat transfer through the solid–liquid interface and the potential energy constraint. Compared with other surfaces, surfaces with reentrant cavities exhibited a significantly higher heat transfer efficiency. The liquid atoms on the nanostructured surfaces absorb a large amount of heat within a short time, resulting in rapid accumulation of heat in the cavity. The thermal motions of the liquid atoms are enhanced, and the potential energy constraints from the surrounding atoms are overcome to achieve rapid bubble nucleation. Thus, the nanostructures promote bubble nucleation in the heated liquid. Our results provide novel insights into the design of nanostructures to improve the boiling heat transfer performance.

Piezoelectric atomization of liquids with dynamic viscosities up to 175 cP at room temperature

Piezoelectric atomization has been applied in the field of respiratory medicine delivery and chemistry. However, the wider application of this technique is limited by the viscosity of the liquid. High-viscosity liquid atomization has great potential for applications in aerospace, medicine, solid-state batteries and engines, but the actual development of atomization is behind expectations. In this study, instead of the traditional model of single-dimensional vibration as a power supply, we propose a novel atomization mechanism that uses two coupled vibrations to induce micro-amplitude elliptical motion of the particles on the surface of the liquid carrier, which produces a similar effect as localized traveling waves to push the liquid forward and induce cavitation to achieve atomization. To achieve this, a flow tube internal cavitation atomizer (FTICA) consisting of a vibration source, a connecting block and a liquid carrier is designed. The prototype can atomize liquids with dynamic viscosities up to 175 cP at room temperature with a driving frequency of 507 kHz and a voltage of 85 V. The maximum atomization rate in the experiment is 56.35 mg/min, and the average atomized particle diameter is 10 µm. Vibration models for the three parts of the proposed FTICA are established, and the vibration characteristics and atomization mechanism of the prototype were verified using the vibration displacement measurement experiment and the spectroscopic experiment. This study offers new possibilities for transpulmonary inhalation therapy, engine fuel supply, solid-state battery processing and other areas where high-viscosity microparticle atomization is needed.

Molecular dynamics study of the wettability effect on the evaporation of thin liquid sodium film

The nanoscale liquid sodium film exists in the porous wick of the sodium heat pipe. Understanding its evaporation is essential for further exploring the heat transfer inside the heat pipe. Due to the solid–liquid interaction, surface wettability has significant effects on evaporation. In this work, molecular dynamics is adopted to study these effects. A cuboid evaporation system is constructed. It consists of the bottom solid surface and thin liquid sodium film. By changing the potential well depth between solid and liquid atoms, four surfaces with different wettability are built. The 400 K equilibrium evaporation is achieved. The self-diffusion coefficients of liquid atoms on four surfaces are acquired. The non-equilibrium is introduced by increasing the heat source wall’s temperature to 600 K. The main phase of evaporation is in 0–8 ns. The variation of gas atoms number is observed. The evaporation rate, average heat flux, and heat transfer coefficient are acquired. The results indicate that evaporation could be improved with surface wettability. For the 0°, 58° hydrophilic surface, the heat transfer efficiency could reach 96.9 %, 96.3 % respectively. The surface wettability effects are achieved by two paths: it enhances the heat transfer in the solid–liquid contact region and intensifies the atoms’ collision heat transfer inside the liquid film.

Microscopic dynamics and Bose–Einstein condensation in liquid helium

We review fundamental problems involved in liquid theory including both classical and quantum liquids. Understanding classical liquids involves exploring details of their microscopic dynamics and its consequences. Here, we apply the same general idea to quantum liquids. We discuss momentum condensation in liquid helium which is consistent with microscopic dynamics in liquids and high mobility of liquid atoms. We propose that mobile transit atoms accumulate in the finite-energy state where the transit speed is close to the speed of sound. In this state, the transit energy is close to the oscillatory zero-point energy. In momentum space, the accumulation operates on a sphere with the radius set by interatomic spacing and corresponds to zero net momentum. We show that this picture is supported by experiments, including the measured kinetic energy of helium atoms below the superfluid transition and sharp peaks of scattered intensity at predicted energy. We discuss the implications of this picture including the macroscopic wave function and superfluidity.

Evaluation of Liquid Atomization and Spray Drift Reduction of Hydraulic Nozzles with Four Spray Adjuvant Solutions

The droplet size distribution following pesticide application practices can significantly impact droplet drift and non-target organisms (animals and plants). However, the relationship among liquid sheet breakup, drop formation, and droplet drift is an area that has been studied over the past 65 years but is still not fully understood. The objectives of this study were severalfold: to examine the liquid sheet breakup following the use of different adjuvants (sodium dodecyl sulfate, aerosol OT, and silicone at 1%) and their effects on the drift via three commonly used commercial spray nozzles (XR, AIXR, and TXVK). The spray sheet and initial droplet size spectrum for each spray was detected by a particle image velocimetry (PIV) system, and the drift for each treatment was measured in a wind tunnel. The nozzle type and the spray solution were found to significantly affect the liquid sheet breakup characteristics. AIXR produced large droplets, and TXVK with short liquid sheet length produced more small droplets. All adjuvants used in these experiments increased the formation of large droplets upon atomization while simultaneously reducing driftable fines (e.g., drops %<150 µm). The drift potential can be reduced by up to 66.1% when switching from a fine spray quality (TXVK) to a coarse spray quality (AIXR). The SDS adjuvant provided the most effective drift reduction for XR and TXVK nozzles showing reduced drift potential by 69.2% and 66.3%, respectively, while the silicone adjuvant showed the largest drift reduction for AIXR of 78.3%. The correlation between the liquid sheet length and DV0.5 was positive for XR and TXVK nozzles, and there was a significant positive correlation between %<150 µm and drift potential for all nozzles. This work suggests that the drift can be reduced significantly by changing the nozzle type and adding pesticide adjuvant into spray solution, which provided data support for the drift reduction of plant protection drones.

Secondary Atomization of Fuel Oil and Fuel Oil/Water Emulsion through Droplet-Droplet Collisions and Impingement on a Solid Wall

This paper presents findings from an experimental study investigating the secondary atomization of liquid fuel droplets widely used in the heat and power industry exemplified by fuel oil and environmentally promising fuel oil/water emulsion. The scientific novelty comes from the comparative analysis of the critical conditions and integral characteristics of the secondary atomization of the liquid and composite fuels with the greatest potential for power plants. Here, we used two fuel atomization schemes: droplet–droplet collisions in a gas and droplets impinging on a heated solid wall. The temperature of the liquids under study was 80 °C. The velocities before collision ranged from 0.1 m/s to 7 m/s, while the initial droplet sizes varied from 0.3 mm to 2.7 mm. A copper substrate served as a solid wall; its temperature was varied from 20 °C to 300 °C. The main characteristics of droplet interaction were recorded by a high-speed camera. Regime maps were constructed using the experimental findings. It was established that the critical Weber number was several times lower when water and fuel oil droplets collided than during the collision of fuel oil droplets with 10 vol% of water. The secondary atomization of fuel oil/water emulsion droplets by their impingement on a heated solid wall was found to reduce the typical sizes of liquid fragments by a factor of 40–50. As shown in the paper, even highly viscous fuels can be effectively sprayed using primary and secondary droplet atomization schemes. It was established that the optimal temperature of the fuel oil to be supplied to the droplet collision zone is 80 °C, while the optimal substrate temperature for the atomization of fuel oil/water emulsion droplets approximates 300 °C.

Detailed numerical simulation of multi-scale interface-vortex interactions of liquid jet atomization in crossflow

In this paper, a detailed numerical simulation of liquid jet atomization in crossflow is performed based on the volume of fluid method coupled with the adaptive mesh refinement technique. The multi-scale phase interface evolution and the interface-vortex interaction are reported. It is found that the momentum flux ratio, Weber number, density ratio and viscosity ratio are key variables for the empirical correlation to accurately predict the atomization characteristics. Three breakup regimes, i.e., column bag breakup, surface breakup and ligament breakup, occur due to the great mass and momentum exchanges at the interface. Specially, the Kelvin-Helmholtz instability induces axial surface waves that eventually develop into column bag breakup while the Rayleigh-Taylor instability and surface thinning can induce surface breakup. Relatively, the column bag breakup generates larger liquid structures, presenting a bimodal feature. The produced ligaments either shrink to droplets or further breakup into droplets depending on their size and shape, leading to a log-normal distribution of droplet size. The interface-vortex interaction is distinctive compared to single-phase flows. A vortex core is observed to simultaneously form, grow and dissipate within each bag during the life circle of the bag, and three types of counter-rotating vortex pair exist around the column root, bag membrane and liquid droplets. Vortical structures tend to concentrate near the interface with large deformations, possessing a strong perpendicularity between the phase interface and the vortex. This work offers fundamental basis for better understanding and organization of atomization.

Secondary ultrasonic atomisation mechanisms

Liquid atomisation is the basis for various practical applications such as pharmaceuticals, cosmetics, food industry, etc. In this case, the main challenge is the development of high-performance, highly dispersed atomisation systems. Generally, high-throughput atomisation systems form aerosol with large droplet sizes, and high-disperse atomisation systems have low performance. Secondary ultrasonic atomisation can solve this problem by allowing non-contact crushing of already formed aerosol droplets with large droplet sizes by means of a high-intensity ultrasonic field. For this purpose, a pre-generated stream of liquid droplets is directed into a cylindrical region formed by an emitter in which a high-intensity ultrasonic field is generated. Ultrasonic radiator, is a tube of stepped-variable cross-section, providing the formation of bending-diametral or diametral oscillations at a frequency above 20 kHz. At sufficiently high ultrasound intensity, conditions for further crushing of liquid droplets are realised, which leads to the formation of a highly dispersed aerosol. This paper describes the proposed mathematical model of the atomisation process and finds the regularities of the process depending on the determining parameters of the ultrasonic field and physical and chemical properties of the liquid. Two mechanisms of jet destruction are revealed: direct destruction of droplets when they hit the ultrasonic wave front and cavitation mechanism of droplet and jet destruction. The dominant crushing mechanism depends on the problem parameters and, in turn, determines the minimum size of the resulting droplets. The results of this work will help to optimise the secondary ultrasonic atomisation process and improve liquid atomisation technologies in various applications.