Liquid Length Research Articles

Two-dimensional spreading of frictionless adhesive oil droplets.

When sand flows out of a funnel onto a surface, a three dimensional pile that is stabilized by friction grows taller as it spreads. Here we investigate an idealized two dimensional analogue: spreading of a pile of monodisperse oil droplets at a boundary. In our system the droplets are buoyant, adhesive, and in contrast to sand, friction is negligible. The buoyant droplets are added to the pile one-at-a-time. As the aggregate grows, it reaches a critical height and the 2D pile spreads out across the barrier. We find that, while granularity is important, the growth process is reminiscent of a continuum liquid. A "granular capillary length", analogous to the capillary length in liquids, sets the critical height of the aggregate through a balance of buoyancy and adhesion. At a coarse-grained level, the granular capillary length is capable of describing both steady-state characteristics and dynamic properties of the system, while at a granular level repeated collapsing events play a critical role in the formation of the pile.

Potential of kerosene-diesel blends as alternative fuels for diesel engines: Perspectives from spray combustion characteristics

To explore the application potential of kerosene (RP-3)/diesel blends as alternative fuels for diesel engines, the spray combustion characteristics of neat diesel, neat RP-3 and RP-3/diesel blends (varied from 25 % to 75 % of RP-3) were systematically compared in an optical constant volume combustion chamber under non-evaporating (0 % O2, 293 K), evaporating (0 % O2, 900 K) and combustion (21 % O2, 900 K) conditions. Their spray, evaporation, combustion and soot emission characteristics were visualized using various high-speed imaging techniques. The results show that RP-3/diesel blending ratio has significant effects on the spray and combustion processes. Under non-evaporating condition, higher RP-3 contents slightly decrease the spray penetration but increase the corresponding spray angle and volume. Under evaporating condition, the spray angle and volume follow the similar trend as those under non-evaporating condition except for slight fluctuations, but the liquid length decreases with the increase of blending ratio. Unexpectedly, the vapor penetrations of neat diesel and RP-3 are similar and longer than those of their blends. Under combustion condition, both the ignition delay and flame lift-off length increase with the RP-3 blending ratio. In addition, RP-3 component reduced the peak soot mass by 9.78 %, 14.7 % and 17.56 % for R25, R50 and R75, respectively. In summary, this study suggests that RP-3/diesel blends are suitable alternative fuels for diesel engines, in terms of faster evaporation and lower soot emissions. We recommend a blending ratio of 25 % as the most promising fuel for further investigations in real engines.

Effect of ammonium based ionic liquids on the rheological behavior of the heavy crude oil for high pressure and high temperature conditions

Heavy crude oil (HCO) production, processing, and transportation forms several practical challenges to the oil and gas industry, due to its higher viscosity. Understanding the shear rheology of this HCO is highly important to tackle production and flow assurance. The environmental and economic viability of the conventional methods (thermal or dilution with organic solvents), force the industry to find an alternative. The present study was constructed to investigate the effect of eco-friendly ionic liquids (ILs) on the HCO's rheology, at high temperature and high pressure. Eight different alkyl ammonium ILs were screened for HCO's shear rheology at the temperatures of 25–100 °C and for pressures 0.1–10 MPa. The addition of ILs reduced the HCO's viscosity substantially from 25 to 33% from their original HCO viscosity. Also, it aids to reduce the yield stress to about 15–20% at all the studied experimental conditions. Furthermore, the viscoelastic property of the HCO was studied for both strain-sweep and frequency-sweep and noticed the ILs helps to increase HCO's loss modulus (G″) by reducing storage modulus (G′), it leads to the reduction of the crossover point around 25–32% than the standard HCO. Mean the ILs addition with HCO converts its solid-like nature into liquid-like material. Besides, the effect ILs chain length was also studied and found the ILs which has lengthier chain length shows better efficiency on the flow-ability. Finally, the microscopic investigation of the HCO sample was analyzed with and without ILs and witnessed that these ILs help to fragment the flocculated HCO into smaller fractions. These findings indicate that the ILs could be considered as the better alternative for efficient oil production, processing, and transportation. • Aliphatic ionic liquids reduce the viscosity of heavy oil significantly. • Ionic liquid with [HSO 4 ] - or [H 2 PO 4 ] - anion shows better efficiency. • Ionic liquids addition with heavy oil converts its solid-like nature into liquid-like material. • Ionic liquids helps fragment the flocculated heavy oil into a smaller fraction. • Greater the chain length of ionic liquid, higher is the tendency on improving flow-ability.

Surface adsorption and bulk properties of polyoxyethylene–polyoxypropylene random copolymer-type double-chained surfactants in quaternary-ammonium-salt-type amphiphilic gemini ionic liquids

Recently, a few studies have been reported on the layer structure of ionic liquids using X-ray and neutron scattering. However, the nanostructural features of ionic liquids remain unclear. Herein, the surface adsorption and bulk properties of polyoxyethylene (EO)–polyoxypropylene (PO) decyl tetradecyl ether-type nonionic surfactants (C10-C12POxranEO24PO13−x, where x represents the length of the PO chain linked to alkyl chains; x = 0, 5, 8, and 13) in quaternary-ammonium-salt-type amphiphilic gemini ionic liquids containing oxygen or nitrogen in the spacer (2C12(Spacer) NTf2, where (Spacer) = (2-O-2), (2-O-2-O-2), (2-N-2), (2/2-N-2), and n represents the alkyl chain length; n = 10, 12, and 14 for the 2-O-2 spacer, and n = 12 for all others) are elucidated by surface tension, small- and wide-angle X-ray scattering, and viscosity measurements. The surface tension of the C10-C12POxranEO24PO13−x surfactants in the gemini ionic liquids containing oxygen in the spacer increased as the surfactant concentration increased, and it became comparable to that of C10-C12POxranEO24PO13−x alone, indicating that the gemini ionic liquid adsorbed at the air–liquid interface was replaced with C10-C12POxranEO24PO13−x following its addition. In the bulk, 2Cn(Spacer) NTf2 and C10-C12POxranEO24PO13−x formed a layered structure, and the layer spacing depended on the alkyl chain length and spacer structure of the gemini ionic liquid and the length of the PO chain linked to the alkyl chains of the surfactants.

Modeling Spray C and Spray D with FGM within the framework of RANS and LES

In this study, two different diesel-like igniting sprays are investigated: Engine Combustion Network (ECN) Spray C and D. In particular, this study focuses on the respective performances of the RANS and LES models to predict a turbulent, igniting spray using the OpenFOAM platform. The breakup model, discretization schemes, and case setups, including the combustion model, are kept constant in order to mitigate any potential effect on the simulation apart from intrinsic differences due to turbulence modeling. A classic κ-ε model is applied for the RANS approach, while a dynamic structure model is used to solve the momentum equation in the LES approach. The κ-ε model constants are tuned to obtain a suitable prediction of inert experiments. Both approaches exhibit a reasonable agreement with the inert experiments regarding the global spray characteristics, the liquid length, and the vapor penetration. However, the transient local properties, including the spatial distribution of mixture fraction variance and the species distributions, are not identical. For reacting conditions, the Flamelet Generate Manifold (FGM) model is adopted in both the LES and RANS simulations, using several enthalpy levels as the fourth dimension in the tabulation to account for local heat loss. The results show good agreement between the two turbulence models, in terms of liquid length, vapor penetration, and lift-off length, while a short ignition delay is registered for both sprays and turbulence frameworks. Turbulence–chemistry interaction (TCI) is considered by applying a presumed probability density function (β-PDF) to the mixture fraction, and is found to play a key role in the reproduction of species distribution in the domain.

Evidence for growing structural correlation length in colloidal supercooled liquids.

Using video microscopy, we measure the long-time diffusion coefficients of colloidal particles at different concentrations. The measured diffusion coefficients start to deviate from theoretical predictions based on random collision models upon entering the supercooled regime. The theoretical diffusion relation is recovered by assigning an effective mass proportional to the size of structurally correlated clusters to the diffusing particles, providing an indirect method to probe the growth of static correlation length scales approaching the glass transition. This method is tested and validated in the crystallization of mono-disperse colloids in quasi-two-dimensional experiments. The correlation length obtained for a binary colloidal liquid increases by a power law toward a critical packing fraction of ∼0.79. The system relaxation time exhibits a power-law dependence on the correlation length in agreement with dynamical facilitation theories.

Characterization of ammonia spray combustion and mixture formation under high-pressure, direct injection conditions

Ammonia has the potential to replace fossil fuels in internal combustion engines (ICEs). However, ammonia is characterized by unfavorable combustion characteristics and a propensity to form pollutants during combustion. The pilot-ignited high pressure, direct-injection of ammonia is promising regarding its prospective performance with ammonia as fuel. In this work, optical investigations (Mie-scattering (MS), shadowgraphy (SG), OH* chemiluminescence (CL)) and heat release rate (HRR) analysis are complemented by 1-D spray modeling to provide fundamental insight into distinctive features of ammonia spray combustion and mixture formation under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). CL measurements reveal that ammonia spray flames do not stabilize after ignition by a diesel pilot injection. Instead, the lift-off length gradually increases until the end of injection and beyond. To aid in the interpretation of the lift-off behavior, a 1-D, mixing-limited spray model is validated by experimental results for ammonia spray penetration and stationary liquid length (LL) under non-reactive conditions. Modeling results reveal that ammonia sprays are marked by low temperatures close to the nozzle exit, followed by a rapid decrease in mean equivalence ratios well below 1. Based on a mechanism that suggests flame stabilization by product re-entrainment and subsequent auto-ignition, the inhibition of flame stabilization in ammonia sprays is explained by high mixing requirements with combustion products to undergo auto-ignition. Implications of the lack of a self-stabilized flame on combustion characteristics are discussed and diesel post-injections, fuel pre-heating and reduction of the natural lift-off length are suggested as measures to avoid extensive pollutant formation in regions upstream of the lift-off length after the end of ammonia injection.

Controlling gas–liquid segment length in microchannels using a high-speed valve

Segmented flow, one of the most important flow patterns in microchannels, has been widely employed in gas–liquid microreactor systems because it enhances mass transfer through the biphasic interface. The segment length is determined by the channel parameters (e.g., size, material type), fluid flow rate, and fluid properties. Thus, it is difficult to manipulate the gas–liquid segment length without affecting the residence time of the fluid. In this work we successfully achieved regularly segment length control by introducing a high-speed valve into a gas–liquid microchannel system while varying the frequency of the valve installed in the gas-phase tube to allow gas and liquid segment lengths to be controlled within a large range. In contrast, the segment lengths were almost constant under the same conditions without the high-speed valve. Furthermore, a gas/liquid flow rate ratio in the range of 0.7–1.2 was deemed necessary for steady segmented flow. Finally, a correlation was proposed to predict the segment length using parameters such as valve frequency and fluid flow rate, and it matched the experimental data well. This segment length control strategy will improve the performance of gas–liquid reactions in microreactors and advance the design of microreactor systems.

Liquid flow and breakage behaviors of two liquid jets impacting on the wire mesh with different impinging angles

The flow and breakage behaviors of two liquid jets is of great importance for liquid–liquid mixing and reaction applications. However, the flow behaviors and breakage processes of two liquid jets impacting on the stainless steel wire mesh (SSM) is not clear. In this work, the high-speed photograph method was employed to study the behaviors of two liquid jets impacting on SSM. Effects of impinging angle (2θ), liquid initial velocity (u0), mesh number (M), and liquid jet diameter (D0) on liquid flow and breakage behaviors were investigated. Experimental results showed that the jets of water-water impacting on the SSM were broken into liquid jets and further broken into daughter droplets. The cone angle of dispersion increased with the increase of 2θ, u0, M, and D0, and reached the maximum value of 180°. The average diameter of daughter droplets at 2θ = 90° decreased maximally by 32%, compared with the condition of 2θ = 30°. For two liquid jets of water-n-hexane impacting on the SSM, a liquid sheet was formed. Under different operating conditions, the breakage mode of liquid sheet could be divided into marginal breakup and internal breakup. The breakage model at mesoscale is the result of surface tension and inertia force, both of which are relevant to the complex impact and flow behaviors. The liquid sheet length (Ls) decreased with the increase of u0 and M. A correlation to calculate Ls/D0 was proposed and the calculated results lied within ± 15% of the experimental values. This study provided a theoretical basis for the guidance of mass transfer enhancement and the reactor design with liquid–liquid system.

Effects of full transient Injection Rate and Initial Spray Trajectory Angle profiles on the CFD simulation of evaporating diesel sprays- comparison between singlehole and multi hole injectors

This paper investigates experimental and computational diesel sprays of single hole and multi hole injectors under vaporizing conditions. Two single hole and two ten-hole injectors with the same nozzle hole size are tested with the 120 MPa injection pressure. Experiments implement Laser Absorption Scattering technique. This method utilizes two wavelengths (Visible and Ultraviolet) of light and fuel's mixture concentrations are measured by attenuations of these lights. On the other hand, sprays are simulated in the Eulerian Langrangian two-phase fluid framework where KHRT and Multicomponent models are used as droplet breakup and evaporation models respectively. Full transient profiles of Injection Rate and Initial Spray Trajectory Angle are used as input boundary conditions for the spray simulation and effects on the spray characteristics are observed. Injection rates are measured with Bosch Long Tube and Initial Spray Trajectory Angles are extracted from the near nozzle field spray images. Experiments reveal that multi-hole injectors (0.101 mm and 0.133 mm) injectors depict longer liquid and shorter vapor penetrations. However, longer simulation liquid and vapor penetrations are seen for single hole injectors due to increased initial ramp-up phase. Sprays of Multi-hole injectors are diffused radially which promote air entrainment, better mixture formation, improved combustion, and lower exhaust emissions. Overall, simulated sprays using unfiltered injection rate profile as an input parameter showed an excellent agreement with experiments. While sprays using low-pass filtered injection rates showed a clear disagreement. Parameters including Liquid Length, Vapor Penetration and Evaporation ratios were found to be influenced by the IR profile rather than ISTA. Whereas vapor equivalence ratios depend on both input parameters plus breakup model constants.

Numerical and experimental study on temperature measurement performance of SNS fiber optic sensor with liquid-sealed

Single-mode-no-core-single-mode (SNS) optical fiber structures have valuable potential to encapsulate as high-precision temperature sensors, due to their great sensitivity. This paper is to improve the temperature sensitivity of SNS fibers by studying the parameters of fiber length, diameter, and refractive index of the seal liquid. Transmission spectra of the fibers are given in both aspects of experiment and numerical simulation. We find that using a slim no-core fiber section sealed with liquid of high refractive index can effectively improve the sensitivity, while the choice of fiber length mainly affects the width of transmission peak. The results may contribute to the development of high-sensitivity optic temperature sensor.

Experimental study on long-distance anti-gravity loop heat pipe with submicron-scale porous structure

• An anti-gravity type loop heat pipe (LHP) which can transport heat for a few meters against gravity was proposed. • To generate a capillary force of several hundred kPa, a submicron-scale porous material made of glass was fabricated as a primary wick. • To reduce the heat leak, hydrophilic polytetrafluoroethylene wick was installed at the rear side of the primary wick. • The LHP with the vapor and liquid heat transport length of 4 m was fabricated, and the LHP operation under 4 m anti-gravity condition was accomplished. Although a loop heat pipe (LHP) is capable of transporting heat over a long distance under anti-gravity conditions in principle, it has not been demonstrated yet. This paper reports an experimental study of an anti-gravity type LHP that can transport heat for a few meters against gravity. For a LHP to generate a capillary force of several hundred kPa, a submicron-scale porous material made of glass was selected as the primary wick. The wick properties such as pore radius, permeability, and wettability with the working fluid were evaluated. A flat evaporator-type LHP with a few meters of vapor and liquid transport lines was designed, fabricated, and tested. Firstly, a preliminary experiment was conducted with water as a working fluid under horizontal conditions. The length of the vapor and liquid lines were both 10 m. It was found that there was a large heat leak from the evaporator to the compensation chamber. In addition, the vapor did not reach the condenser because the vapor was condensed in the vapor line. Secondly, experiments were conducted under the horizontal (0 m), 2 m, and 4 m anti-gravity conditions. In order to reduce the heat leak, a hydrophilic polytetrafluoroethylene wick was installed at the rear side of the primary wick. The vapor and liquid transport length were 6.5 m, and the ethanol was selected as a working fluid. These experimental results demonstrated that the LHP could transport heat under horizontal and 2 m anti-gravity conditions, whereas the LHP cannot transport heat under 4 m anti-gravity conditions. Finally, a LHP with a vapor and liquid transport line length of 4 m was fabricated, which was able to operate under 4 m anti-gravity conditions.

Numerical simulations of the spread of point‐source liquid spills in inclined and rolling rectangular packed beds

AbstractLiquid spreading in thin rectangular vertical/inclined and oscillating porous media was simulated using a two‐fluid dynamic model as a preliminary step in the design of fixed‐bed reactors dedicated to marine applications. The model assessed the influence of capillary pressure and mechanical dispersion forces arising from the spatial inhomogeneity of point‐source liquid injections in packed beds with different particle sizes, liquid and gas flow rates, liquid viscosity, static bed tilts, and rolling amplitudes and periods. In mildly static inclined beds, the lateral gravity force component and the capillary pressure force were the main factors affecting the liquid spreading. However, at considerable bed inclinations, the liquid phase accumulation in the lowermost regions of the packed bed tended to shrink the liquid spreading. Dynamic oscillatory evolutions of the liquid spills in the rolling bed enlarged the liquid spreading length as compared to the static vertical bed due to combined lateral liquid flow and increased liquid residence time.

A comprehensive CFD study of the spray combustion, soot formation and emissions of ternary mixtures of diesel, biodiesel and gasoline under compression ignition engine-relevant conditions

In this research, the spray combustion, soot formation and exhaust emissions of diesel, biodiesel, gasoline fuels and their mixtures are analysed in a constant volume chamber. A multicomponent kinetic mechanism (CDBG) suitable for diesel-biodiesel-gasoline mixtures developed by our research group is utilised, and the associated physicochemical properties are thoroughly calculated. Adaptive mesh refinement scheme with appropriate mesh independency analysis are applied. Liquid penetration length, lift-off length, ignition delay and soot formation have been benchmarked against experimental data in the literature. A hybrid RANS-LES model, known as DES model, is used to simulate the turbulent condition. The effects of different ambient temperature/oxygen levels on the flame structure, soot formation and emissions of different ternary mixtures of D75|BD20|G5, D70|BD20|G10 and D65|BD20|G15 were analysed. D65|BD20|G15 resulted in a lower soot mass yield than that of BD100 (pure biodiesel) and D100 (pure diesel) for about 35% and 27%, respectively, at T = 900 K | O2 = 15%. Greater soot mass reductions for the tested fuels were captured by the decrease in ambient temperature from 900 K to 800 K by a factor of ∼1/3 (same ambient O2 concentration). Lower nitrogen oxides (NOx) emissions were obtained for D100 by factors of ∼1/2 at T = 900 K | O2 = 15% compared to BD100. Gasoline-added mixtures revealed lower NOx compared to BD100 (∼20%) yet still higher than D100. Lower carbon dioxide (CO2) and carbon monoxide (CO) emissions were captured for D65|BD20|G15 compared to BD100 and D100.

Intelligent quantitative assessment on the spray performance of alternative aviation fuel

Drop-in alternative aviation fuel (AAF), as a blend of petroleum-derived kerosene with sustainable jet fuel, has the advantage in CO2 reduction and could be used without any modifications to the engine and aircraft. Therefore, drop-in AAF blending could not scarify the performance compared to traditional jet fuel. For assessing the spray performance quantitatively, traditional jet fuel (RP-3) with blending alternative compositions including paraffins, cycloparaffins, and aromatics was designed. Carbon number distribution and classification distribution in jet fuel compositions that would influence spray performance are well investigated. The cone angle and liquid length are recognized by a shadow image, while Sauter mean diameter (SMD) and velocity are investigated by phase-Doppler anemometry (PDA). The liquid length and droplet size of bicyclohexane, phenyl-cyclohexane, heptadecane, and octadecane conduct a significant deviation compared with RP-3, which complies with the large deviations of Lb (f)[σ0.25 μf0.25 ρf0.25], which extracted the fuel property item from the liquid length, and Oh(f) [μfσ−0.5ρf−0.5], which extracted the fuel property item from the Ohnesorge number. The blending fuels of those cannot be certified as drop-in fuel due to obvious deviation to RP-3, which also presents differences in carbon number distribution and classification distribution. The spray empirical models were established quantitatively to assess the characteristics of the liquid sheet and droplet for discovering the blend fuel effects. The empirical equations of the liquid length and SMD calibrated by evaporation constants can agree well with the experimental data except for blends of bicyclohexane, phenyl-cyclohexane, C17, and C18. The integrated spray performance assessment models developed could benefit from certifying drop-in fuel at the spray level quantitatively.

The effect of heater dimensions with different liquid penetration lengths to dry spots on critical heat flux

• Depending on heater dimension, CHF increased 106% for water and 46% for Novec TM 7100. • Growth and rewetting time scale of dry spot at the center are compared for the CHF. • Width, the shorter of two side lengths, affect the velocity within macrolayer. • The average velocitiy within macrolayer affect the rewetting velocity and CHF. The Critical Heat Flux (CHF) on different heater dimensions for two different working fluids were experimentally evaluated. For a given boiling surface (SiO 2 ), the CHF differences were 107% for water and 46% for NOVEC TM 7100 under different heater dimensions. These differences were not describable with previous studies correlating the CHF with the characteristic length for a given heater dimensions. To understand the effect of the heater dimensions on the CHF, we compared the dry-spot growth time-scale and rewetting time-scale of the dry spot created at the center of the heating surface. The analysis showed that the average velocity in the macrolayer depends on the liquid penetration length, which is the shortest flow path from the end to the center of the heater. The average velocity in macrolayer affect the rewetting velocity and finally the CHF. Based on the analysis considering the dry-spot rewetting phenomena, the dependence of CHF on heater dimension for two different working fluids was well described in this study.

Experimental investigation on flow-induced vibration of a flexible catenary riser conveying severe slugging with variable gas superficial velocity

A flexible catenary riser conveying gas–liquid mixture may experience the severe slugging induced vibration (SSIV) within a specific gas and liquid superficial velocity range. In this work, the SSIV of a flexible catenary riser with aspect ratio of 200 and a horizontal upstream pipeline was experimentally investigated to shed some light on the nonlinear multiphase flow-induced vibration and the correlation with the dynamic behaviour and the flow evolution. The non-intrusive optical measurement with high-speed cameras was employed to capture the vibration displacements of evenly distributed markers along the riser as well as the flow characteristics of gas–liquidmixture in the riser. The first and second types of severe slugging (SSI and SSII) were observed in the standard case (vsg = 0.177 m/s and vsl = 0.094 m/s) with an occurrence frequency ratio of 1:3. Large amplitudes are excited in the slug formation and gas blowout stages, and the latter presents more violent vibration with a faster travelling waves’ propagation speed. When the gas superficial velocity increases while maintaining the liquid superficial velocity, the transition stage is significantly elongated, characterized by the alternate appearance of partially filled gas–liquid mixture and short liquid slugs. Nevertheless, each liquid slug, no matter it is long or short, makes its contribution to the vibration response, presenting the coincidence of the recurrence frequency and the vibration frequency. The response amplitude is associated with the liquid slug length as well as the location of liquid inventory. The contributions of the three regimes (SSII, short liquid slugs and partially filled mixtures) are mainly associated with their occupied time. The severe slugging is the predominant contributor at vsg≤ 0.708 m/s, while its contribution is negligible at higher gas superficial velocities.

Application Of The Phase Doppler Measurement Technique For The Characterization Of Supersonic Gas Atomization

A dual-mode phase Doppler measurement system has been set up for the characterization of the complex spray produced through supersonic gas atomization. The atomizer design has been based on a generic close-coupled configuration operated with water and air, which leads to high local Mach numbers and complex patterns of compression and expansion waves within the gas flow field. As a result, the dense spray is characterized by high particle velocities and a wide range of particle sizes, which proves challenging for experimental investigations. Measurements of local particle size and velocity distributions have been performed in various radial positions within the spray downstream of the atomizer, where the spray is fully developed. The set point of operation, which is defined by the gas stagnation pressure and the liquid mass flow rate, has been varied systematically, covering a wide range. By decoupling both operational parameters, their influence on the atomization result has been investigated independently. Furthermore, the atomizer geometry has been varied in terms of liquid nozzle diameter and liquid nozzle protrusion length. In accordance with data from the literature, the gas stagnation pressure has been observed to lead to decreasing median particle size and dispersion of the particle size, when increased. However, as a novel finding, the atomization result has been shown to be more sensitive to changes in the liquid mass flow rate. Thus, increasing the liquid mass flow rate results in an increase in both the median particle size and the dispersion of the particle size. The relationship between the atomization result and the gas-to-liquid ratio has been clearly shown to be ambiguous, that is, a function of the gas stagnation pressure and the liquid mass flow rate. Neither the liquid nozzle diameter nor the liquid nozzle protrusion length have been found to have an influence on the median particle size. However, the latter clearly influences the dispersion of the particle size in a complicated way, while the effect of the liquid nozzle diameter is more subtle. It has been concluded that the complex coupling between operational parameters and the specific atomizer design evident in supersonic gas atomization requires a deeper understanding of the local gas flow field and its interaction with the liquid flow.

Effect of electrostatic forcing on coaxial two-fluid atomization

Multiphysics control of atomization is an emerging area of research that could lead to the development of more robust and versatile atomizers. We explore primary atomization in a coaxial two-fluid atomizer subject to electrostatic forcing. Our results reveal that electrostatic stresses can improve the momentum transfer between the fluids, enhance the growth rate of interfacial instabilities, and reduce the liquid core length over a wide range of gas-to-liquid momentum ratios. Moreover, these effects were observed to depend strongly on the electric field geometry.

Maximizing friction by liquid flow clogging in confinement

In the nanoscale regime, flow behaviors for liquids show qualitative deviations from bulk expectations. In this work, we reveal by molecular dynamics simulations that plug flow down to nanoscale induces molecular friction that leads to a new flow structure due to the molecular clogging of the encaged liquid. This plug-like nanoscale liquid flow shows several features differ from the macroscopic plug flow and Poiseuille flow: It leads to enhanced liquid/solid friction, producing a friction of several order of magnitude larger than that of Couette flow; the friction enhancement is sensitively dependent of the liquid column length and the wettability of the solid substrates; it leads to the local compaction of liquid molecules that may induce solidification phenomenon for a long liquid column.Graphical abstract