Morphological Study of Cavity and Worthington Jet Formations for Newtonian and Non-Newtonian Liquids

In this article a morphological study of the cavity formation and the liquid column formation of the Worthington jet with lapse of time for the Newtonian liquids of water and glycerine wt 70% solution and for non-Newtonian liquids of acrylic copolymer solution of ACA-wt1%, ACA-wt2%, and ACA-wt3% by a droplet falling to the free surface of the target liquid in the cylindrical container from a height of H = 100, 200, 300, 400, and 500 mm is described. The calculated results by the energy equation for the maximum cavity radius Rmax/d and for the morphological size D · h/d² of the Worthington jet are in agreement with the experimental results. In order to take photographs of the cavity formation and the Worthington jet formation with lapse of time, a CCD camera was used. The falling droplet and the target liquid are the same material. Here d is the mean diameter of the droplet and D and h are the mean diameter and maximum height of the liquid column of the Worthington jet.     

EHD喷印技术相关参数数值分析

目的对基于电-液耦合动力学原理(简称EHD)喷印技术的相关参数,进行锥射流和滴落模式下的数值分析研究。方法在锥射流模式中,对毛细凝结加热液体喷射的物理模型进行调整,以适用于EHD喷印;对滴落模式的液滴沉积过程,引入表面张力概念进行数值分析。运用数值法得到了锥射流的轮廓图,集中讨论了流量和净高度对射流直径的影响;重点研究了液滴直径与电压频率和液体表面张力之间的关系,并将理论结果与实验和经验数据进行了比较分析。结果锥射流模式在一定条件下,射流直径随着流量和净高度的增大而增加;在滴落模式中,得到的液滴直径随电压频率和流体表面张力的增大而减小,且数值分析得到的结果与实验结果相一致。结论对相关参数进行数值分析是对实验研究的补充,为EHD喷印技术研究提供了理论参考。     

Influence of process variables and formulation composition on sphericity and diameter of Ca-alginate-chitosan liquid core capsule prepared by extrusion dripping method

ABSTRACT

The influence of process variables and formulation composition on the sphericity and diameter of the alginate capsules which contained dual cations (Ca-and-chitosan) are characterized in this study. Capsule sphericty was not influenced by needle diameter but instead, capsule diameter increased proportionally with the needle diameter. The combined effects of the liquid core solution and alginate solution on the sphericity of the capsules are tabulated. Spherical capsules can be produced when the following criteria were fulfilled: stirring speed is in the range of 240–300 rpm; calcium chloride concentration is >5 g/L; viscosity of liquid core solution is >203 mPa.s; as well as viscosity of alginate solution is in between 47 and 386 mPa.s. The capsule diameter was predicted using a modified Tate’s law equation and an error analysis was conducted to evaluate the equation. The predicted diameter was well correlated with the experimental data with an average absolute deviation <3.6%.     

Gas jet iimpingement on a liquid surface in the regime of stable oscillations

We consider the impingement of a gas jet on a liquid surface in a stable oscillatory regime, where by the jet-induced cavity shape in various phases of oscillations is periodically reproduced with high precision. This regime is observed during gas jet impingement at an angle of 30°–40° relative to the surface of a liquid with viscosity above 1 Pa s. A mechanism of the impingement of gas jet on liquid in the oscillatory regime is described that accounts for variation of the shape of the cavity on the liquid surface. It is established that oscillations exhibit a relaxation character. It is a specific feature of the oscillatory process that the gas stream flowing out from cavity separates from the surface of liquid. Stable oscillations in the “gas jet–liquid” system can be used for contactless measurement of the physical properties (in particular, viscosity) of liquids.     

Sessile droplet formation in the laser-induced forward transfer of liquids: A time-resolved imaging study

The formation process of sessile droplets in the laser-induced forward transfer of aqueous solutions was analyzed through time-resolved imaging. At the irradiation conditions which lead to the deposition of well-defined droplets, a cavitation bubble is generated in the laser irradiated area. Such bubble evolves into a high-speed liquid jet which propagates towards the receptor solid substrate. Once the jet impinges on the receptor substrate, liquid gently starts accumulating on the impact position, and the growth of a sessile droplet initiates. In a first stage, which only lasts a few microseconds, the forming droplet suffers a fast spreading process. Then, the jet continues feeding the forming droplet for some hundreds of microseconds, but the droplet diameter remains constant, and thus the contact angle increases. Finally, liquid feeding stops due to jet breakup, and the sessile droplet initiates a slow relaxation process in which its contact angle diminishes and its diameter increases. This deposition process results in the deposition of a single sessile droplet up to donor film-receptor substrate distances of the order of the millimeter. At higher separations, satellite droplets appear, and at even higher separations only randomly distributed small droplets are deposited.     

Fluidization using pseudoplastic liquids – Elutriation and ANN modeling

Experimental work on elutriation of irregularly shaped sand particles (0.538–2.03 mm diameter) was carried out in three different Perspex columns (47 mm, 72 mm and 92.3 mm) using different non-Newtonian pseudoplastic liquids (0.4–0.8 kg/m³ SCMC solution). The effects of operating parameters, column diameter, bed weight, particle diameter, particle sphericity, liquid rheological properties on the minimum elutriation velocity were examined. The statistically accepted empirical correlation was developed. ANN model could predict the experimental data of minimum elutriation velocity with a correlation coefficient of 0.9951.     

GAS HOLDUP IN BAFFLED BUBBLE COLUMNS OF DILUTE SLURRIES OF FINE POWDERS AND VISCOUS LIQUIDS

ABSTRACT

Experimental gas phase holdup data reported by the authors as taken on two baffled bubble columns and involving slurries of fine powders (average particle diameter ≤90 μm) and dilute suspensions (mass fraction ≤ 20 percent) in viscous fluids are re-examined after correction for a small calculation error in superficial gas velocity. The two bubble columns are: a Plexiglas bubble column, 0.108 m in diameter and 2.25 m tall, equipped with seven 19 mm tubes arranged in equilateral triangular configuration with a pitch of 36.5 mm and a Pyrex glass column, 0.305 m in diameter and 3.24 m tall, equipped with thirty-seven 19 mm tubes arranged in the same configuration. Air and nitrogen are used as gas phase, water and Therminol as liquid phase, and iron oxide powders, glass beads and sand as solid phase. The small column data are at ambient temperature while those belonging to the large column extend from ambient to 473K. These data are examined to assess the influence of column diameter (scale-up), temperature, slurry concentration and viscosity, and superficial gas velocity on gas holdup for baffled columns.

It is found that in the 0.108 m diameter column the holdup is about the same for axial probes of different diameters, 19 mm, 31.8 mm and 50.8 mm, for two-phase systems involving liquids of small (water) and large (Therminol) viscosities. However, when a seven-tube bundle is installed, the holdup increases. This is consistent with the bubble dynamics and observed bubble sizes. This qualitative trend is also upheld by three-phase systems involving dilute slurries of fine powders. In the larger column when fully packed with a thirty-seven tube bundle, the holdup is found to be the same as for the small column. A loosely packed bundle gives smaller holdup at temperatures greater than the ambient due to the larger size of bubbles. The gas holdup is greater for a less viscous system and this is again due to the larger size of bubbles in a more viscous system. The influence of temperature is pronounced and is very characteristic of the nature of liquid involved. For example for water and Therminol the variations are in opposite directions with change in temperature. Bubble splitting and foaming control the nature of these dependencies. With the addition of solids the holdup is almost insignificantly altered at all temperatures.     

Observation of liquid hydrogen jet on flashing and evaporation characteristics

The evaporation speed of liquid hydrogen jet has been measured using high speed CCD camera. In the evaporation process the diameter of injected liquid hydrogen droplet plays important role. The experimental parameters for injection condition had been selected such as injection temperature and size of injection hole diameter which influences injected diameter of liquid droplet. Liquid hydrogen had been injected into the spray chamber that was filled with gaseous helium at room temperature. The liquid hydrogen jet moves in the horizontal direction and the images of the evaporation processes had been acquired from the observation window using high speed CCD camera. With this method it has been shown that evaporation speed of liquid hydrogen is influenced by injection temperature and size of injection hole diameter.     

Correlation and Prediction of Dense Fluid Transport Coefficients. IX. Ionic Liquids

The aim of this paper is to examine the application of a hard-sphere scheme to the correlation and prediction of the viscosity and thermal conductivity of ionic liquids. Ionic liquids present an excellent case, because of their high viscosity. It was found that, regardless of the fact that the scheme had to be extended by orders of magnitude, it was still an excellent scheme for the correlation and prediction of the properties of these liquids; this fact is attributed to its theoretical basis. A database of 461 viscosity and 170 thermal-conductivity measurements for 19 ionic liquids was considered. The average absolute deviation was 2.31 % for the viscosity and 3.15 % for the thermal conductivity, while the expanded uncertainty at the 95 % confidence level was 4.6 % and 6.3 %, respectively. Moreover, if the thermal-conductivity roughness factor is allowed to be temperature dependent, then the average absolute deviation was reduced to 0.91 % for the thermal conductivity, and the expanded uncertainty at the 95 % confidence level to 1.82 %. As the scheme requires knowledge of the density, 1070 measurements of density were employed to derive a Tait-type equation for every ionic liquid considered.     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.     

Fully Stratified Particle-Laden Flow in Horizontal Circular Pipe

This article describes the results of an experimental measurement and visualization of coarse-grained fully stratified particle-water mixtures. This article focuses on the study of the carrier liquid velocity field and behavior and local velocities of conveyed particles. Glass balls and graded pebble gravel of 6 mm mean diameter were conveyed by water in a horizontal smooth pipe loop with a transparent pipe viewing section of inner diameter 40 mm. The measurements were performed in the smooth pipe and the pipe with rough stationary bed created by two layers of spherical particles of the same mean diameter as the conveyed particles. Particle movement along the pipe bottom was studied and the effect of the stationary bed on local velocity values of the carrier liquid and conveyed particles were evaluated. It was concluded that in the flow with stationary bed the maximum liquid velocity is markedly shifted from the pipe center to its top. The coarse-grained particles moved principally in a layer close to the pipe invert, for higher flow velocities particle saltation becomes the dominant mode of transport.     

Surface tension and density data for Fe–Cr–Mo,Fe–Cr–Ni,and Fe–Cr–Mn–Ni steels

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (?_Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.     

Influence of the liquid layer thickness on the growth of droplets controlled by the thermal action of laser radiation

We have studied the growth of droplets in a thin layer of aqueous ethanol solution under conditions of the solutocapillary convective flow controlled by a laser beam. It is established that, with increasing layer thickness, the time necessary for the formation of a droplet separated from the layer increases, while the time required for the droplet to reach its maximum possible diameter (determined by the criteria of stability) decreases. In the initial stage of droplet formation, the diameter exhibits some decrease related to a short-term increase in the solvent evaporation rate.     

Facilitate Gas Transport through Metal‐Organic Polyhedra Constructed Porous Liquid Membrane

Type II porous liquids are demonstrated to be promise porous materials. However, the category of porous hosts is very limited. Here, a porous host metal–organic polyhedra (MOP‐18) is reported to construct type II porous liquids. MOP‐18 is dissolved into 15‐crown‐5 as an individual cage (5 nm). Both the molecular dynamics simulations and experimental gravimetric CO₂ solubility test indicate that the inner cavity of MOP‐18 in porous liquids is unoccupied by 15‐crown‐5 and is accessible to CO₂. Thus, the prepared porous liquids show enhanced gas solubility. Furthermore, the prepared porous liquid is encapsulated into graphene oxide (GO) nanoslits to form a GO‐supported porous liquid membrane (GO‐SPLM). Owing to the empty cavity of MOP‐18 unit cages in porous liquids that reduces the gas diffusion barrier, GO‐SPLM significantly enhances the permeability of gas.     

Expansion behaviour of a binary solid-liquid fluidised bed with different solid mass ratio

This study reports the effect of particle mass compositions on the bed expansion behaviour of a binary solid liquid fluidised bed (SLFB) system. Experiments were performed comprising equal density (2230 kg m^?3) spherical glass beads particles of diameter 3, 5 and 8 mm and water as fluidising medium with different particle mass ratios varying from 0.17 to 6.0. In the expanded bed, both segregated and intermixed zones were observed depending on the different particle diameter combinations. In a completely segregated SLFB, the bottom monosized layer exhibited a negative deviation ～23% whereas a positive deviation ～25% was found in the top monosized layer when compared with the corresponding pure monosized system. A small mixing zone spanning approximately two particle diameters thick was observed to exist even in a completely segregated SLFB for higher diameter ratio cases. A slight decrease in the mixing zone height was noted with increasing liquid superficial velocity. For lower diameter ratio cases, a relatively lager mixing zone height was observed which increased with increasing liquid superficial velocity. The bed expansion ratio was noted to decrease with increasing solid mass ratio however it increased with increase in the fluidising velocity ratio following a reasonable power law trend. The expanded bed height of the binary mixture was not entirely additive of its corresponding mono-component bed heights and both positive and negative deviations were observed. Finally, a two-dimensional (2D) Eulerian-Eulerian (E-E) model incorporating the kinetic theory of granular flow (KTGF) was used to quantify the binary system hydrodynamics. The model predicted expanded bed height agreed with experimental measurements within ±6% deviation. Presence of a mixing zone was also confirmed by the CFD model and simulated particle phase volume fraction distribution qualitatively agreed with the experimental visualisations.     

Gas-cushioned droplet impacts with a thin layer of porous media

The pre-impact gas cushioning behaviour of a droplet approaching touchdown onto a thin layer of porous substrate is investigated. Although the model is applicable to droplet impacts with any porous substrate of limited height, a thin layer of porous medium is used as an idealized approximation of a regular array of pillars, which are frequently used to produced superhydrophobic- and superhydrophilic-textured surfaces. Bubble entrainment is predicted across a range of permeabilities and substrate heights, as a result of a gas pressure build-up in the viscous-gas squeeze film decelerating the droplet free-surface immediately below the centre of the droplet. For a droplet of water of radius 1 mm and impact approach speed 0.5 m s\(^{-1}\), the change from a flat rigid impermeable plate to a porous substrate of height \(5~\upmu \)m and permeability \(2.5~\upmu \)m\(^2\) reduces the initial horizontal extent of the trapped air pocket by \(48~\%\), as the porous substrate provides additional pathways through which the gas can escape. Further increases in either the substrate permeability or substrate height can entirely eliminate the formation of a trapped gas pocket in the initial touchdown phase, with the droplet then initially hitting the top surface of the porous media at a single point. Droplet impacts with a porous substrate are qualitatively compared to droplet impacts with a rough impermeable surface, which provides a second approximation for a textured surface. This indicates that only small pillars can be successfully modelled by the porous media approximation. The effect of surface tension on gas-cushioned droplet impacts with porous substrates is also investigated. In contrast to the numerical predictions of a droplet free-surface above flat plate, when a porous substrate is included, the droplet free-surface touches down in finite time. Mathematically, this is due to the regularization of the parabolic degeneracy associated with the small gas-film-height limit the gas squeeze film equation, by non-zero substrate permeability and height, and physically suggests that the level of surface roughness is a critical parameter in determining the initial touchdown characteristics.     

Coupled heat and mass transfer during nonisothermal absorption by falling droplet with internal circulation

We considered mass and heat transfer during nonisothermal absorption of a gas by a falling droplet with internal circulation. Gas phase is assumed to be free of inert admixtures and mass transfer is liquid phase controlled. Mass flux is directed from a gaseous phase to a droplet, and the interfacial shear stress causes a fluid flow inside the droplet. Droplet deformation under the influence of interface shear stress is neglected. Absorbate accumulation and temperature increase in the bulk of liquid phase are taken into account. The problem is solved in the approximations of a thin concentration and temperature boundary layers in the liquid phase. The thermodynamic parameters of the system are assumed constant. The system of transient partial parabolic differential equations of convective diffusion and energy balance with time-dependent boundary conditions is solved by combining the similarity transformation method with Duhamel's theorem, and the solution is obtained in a form of Volterra integral equation of the second kind which is solved numerically. Theoretical results are compared with available experimental data for water vapor absorption by falling droplets of aqueous solution of LiBr.     

截顶辅助药型罩对椭球罩射流成型影响研究

为了研究截顶辅助药型罩的结构参数对椭球罩射流成型及侵彻性能的影响,运用仿真软件Autodyn-2D的Euler算法对其有限元模型进行数值模拟计算.结果表明:当辅助药型罩高度为2.5mm,直径为15mm时,截顶椭球罩形成的杆式射流具有最优的形态及侵彻性能,使用优化后的辅助药型罩结构侵彻混凝土靶板时,头部速度提升23.9％...