Microbubble generator excited by fluidic oscillator's third harmonic frequency

Efficient generation of sub-millimetre microbubbles was recently made possible by pulsating the flow of gas supplied into a parallel-exits aerator, using a fluidic oscillator for the purpose. Without moving parts, it can generate oscillation at high frequency, an important factor due to bubble natural frequency rapidly increasing with the desirable decrease of their size. This paper discusses development of an unusual oscillator – a part of an integral oscillator/aerator unit – capable of generating a particularly high driving frequency, in the kilohertz range, in a layout that promotes a strong third harmonic frequency of the basic oscillation.     

Spray characteristics of a swirl atomiser in trigger sprayers using water–ethanol mixtures

Pressure swirl atomisers are widely used in both industry and daily life. It is critical to understand the spray transient behaviour for better design of these systems. This paper presents an experimental study of conical liquid sheets breakup from a swirl atomiser nozzle in trigger sprayers. Spray and atomisation characteristics were measured and analysed. Water–ethanol mixtures were used to simulate different fluids on the breakup and atomisation quality of the spray development process with a wide range of surface tension while maintaining relatively small changes in fluid viscosity and density. The spray images were taken by a high speed digital camera and post‐processed to analyse the global spray structure, spray cone angle, and breakup length. The droplet size and its distribution were measured using a laser diffraction technique. It was observed that the surface waves grow rapidly on the cone‐shaped liquid sheets and breakup into liquid ligaments and droplets during the initial stage of fluid dispensing. Then the spray transitions into the developed stage. Near the end of the dispensing process, the liquid cone collapses with poor atomisation (large droplets) due to momentum loss. The comparison between different fluids showed that the spray cone angle and liquid breakup length decreased with the increase of ethanol percentage ratio. The percentiles parameters, Sauter mean diameter (SMD) and particle size distribution were measured and compared for different locations. High surface tension fluids produce larger droplets than lower surface tension fluids, which have the same trend as the percentiles parameters and SMD. Results also show that droplet size and its distribution depend on the location of the measurement. Generally speaking, smaller droplet size is found for a location away from the nozzle axis in the vertical direction. In the horizontal direction, larger droplet sizes are found for a location closer to the nozzle exit. © 2013 Canadian Society for Chemical Engineering     

The initial stage of fuel spray penetration

Effects of droplet evaporation, break-up and air entrainment on diesel fuel spray penetration have been studied theoretically at the initial stage of spray penetration when the influence of air entrainment is small (up to 0.1-0.2 ms after the start of injection). Theoretical plots of spray penetration versus time are compared with experimental results obtained using an optical single cylinder rapid compression test rig based on a Ricardo Proteus engine. Three models of spray penetration have been compared. In the first, neither break-up nor air entrainment are taken into account. The break-up processes (bag and stripping) are taken into account in the second model, while in the third model both bag break-up and air entrainment processes are considered. It has been found that the agreement between the predictions of the third model with experimental measurements is better than that for the first two models.     

Monodisperse Droplet Generators as Potential Atomizers for Spray Drying Technology

Spray drying is a widely used unit operation for manufacturing powders of different characteristics. Many technological improvements have been made in the last few decades, and a great amount of research work is still being conducted. Recently, the hybrid spray-drying technique was reported, which combines the ink-jet technology with spray drying in order to produce particles of uniform characteristics.^[1-4¹, ², ³, ^4] The monodisperse droplet generators (MDGs) have certain features that make them attractive for use as atomizers in spray-drying operations. In this article, a comprehensive introduction to a variety of monodisperse droplet generators is provided. The advantages and limitations of these generators are discussed. The fundamental equations for predictions of the average droplet size are summarized. The discussion given in this study is aimed at the development of a hybrid technology that marries a suitable MDG with the existing spray-dryer technique (yet with some modifications) to manufacture the product with uniform characteristics containing micro- to nanosized particles.     

Monodisperse Droplet Generators as Potential Atomizers for Spray Drying Technology

Spray drying is a widely used unit operation for manufacturing powders of different characteristics. Many technological improvements have been made in the last few decades, and a great amount of research work is still being conducted. Recently, the hybrid spray-drying technique was reported, which combines the ink-jet technology with spray drying in order to produce particles of uniform characteristics.^[ 1-4 Patel , K.C. ; Chen , X.D. ; Lin , S.X.Q. Development of a laboratory ink-jet spray dryer . Chemeca 2006 , Auckland , New Zealand , September 17–20, 2006 (CD-Rom) . Patel , K.C. ; Chen , X.D. Drying of aqueous lactose solutions in a single stream dryer (S²D) . Transactions of the IChemE: Food and Bioproduct Processing 2007 , accepted . Patel , K.C. ; Chen , X.D. Production of spherical and uniform-sized particles using a laboratory ink-jet spray dryer . Asia-Pacific Journal of Chemical Engineering 2007 , 2 ( 5 ), 415 – 430 . Patel , K.C. ; Wu , W.D. ; Chen , X.D. Review on generation of monodisperse sprays for manufacturing micro-size uniform particles using a spray drying technology . In Proceedings of Asia-Pacific Drying Conference , Hong Kong , China , August 13–15, 2007 .  ^] The monodisperse droplet generators (MDGs) have certain features that make them attractive for use as atomizers in spray-drying operations. In this article, a comprehensive introduction to a variety of monodisperse droplet generators is provided. The advantages and limitations of these generators are discussed. The fundamental equations for predictions of the average droplet size are summarized. The discussion given in this study is aimed at the development of a hybrid technology that marries a suitable MDG with the existing spray-dryer technique (yet with some modifications) to manufacture the product with uniform characteristics containing micro- to nanosized particles.     

Experimental Splash Studies of Monodisperse Sprays Impacting Variously Shaped Surfaces

Despite numerous studies of the drop impact phenomena, studies of the fundamental mechanisms of how the splash corona and subsequent necking yield splashed droplets, not to mention characteristics of these splashed droplets, remain a subject of great interest. Here, we consider a simple question: After impact, what are the characteristics of splashed droplets? Spatial variations in the fraction of splashed liquid, Sauter mean diameter, and drop-size distribution for water and diesel impacting onto variously shaped rods are reported. Liquid drops of nearly uniform size are continuously injected onto a 2-mm-diameter aluminum cylindrical rod at velocities of up to 17 m/s. The impact face of the rod is flat with angles from θ = 0 to 60° or it has a concave, convex, or conical shape. The experimental results indicate that diesel breaks up more easily than water due to its low surface tension. However, due to increased energy loss through viscous dissipation during drop collapse and spreading, dispersion of diesel drops upon and after impact is less energetic than that of water since diesel droplets do not travel as fast or as far as water droplets. During corona formation, stretching and necking of diesel drops before their snap-off are particularly evident due to diesel's high viscosity. Size distribution of splashed diesel droplets is more uniform than that of water near the impact region and water is more uniform further away.     

A model for fuel spray penetration

A new model for fuel spray penetration (location of spray tip) is suggested and validated against available experimental data. Simple analytical expressions for fuel spray penetration are derived in two limiting cases: the initial stage and the two-phase flow regime. At the initial stage, the effects of droplet drag and entrainment of air are accounted for. In the case of the two-phase flow, it is assumed that the spray droplets have the same velocities as the entrained air. The characteristic time of droplet break-up in the spray is estimated for both bag and stripping break-up mechanisms. For realistic diesel spray parameters, the droplet break-up takes place almost immediately after the droplets leave the nozzle. This leads to a considerable shortening of the initial stage and a rapid conversion of the flow to the two-phase stage. This allows the analysis to be restricted to the two-phase flow approximation for this type of spray. The expressions for spray penetration derived in this paper give more accurate predictions compared with those suggested earlier.     

喷涂聚脲技术领域的新进展——聚天门冬氨酸酯聚脲

介绍了聚天门冬氨酸酯聚脲的主要构成,对比讨论了其特性、反应活性和材料性质,提供了施工应用参考配方。     

Single-droplet drying processes at varying environmental conditions

Abstract

Modeling and numerical simulations of the single-droplet drying process are commonly executed based on the assumption of constant boundary conditions. In this study, the validity of this assumption and its influence on the model prediction of the final particle morphology is investigated. Accordingly, numerical simulations of the single-droplet drying process were conducted at different drying conditions. Five boundary conditions were examined: (a) constant inlet drying air condition based on the most commonly used assumption, (b) varying drying conditions, (c) constant average drying conditions, (d) partially varying drying conditions whereby all drying conditions were changed apart from the droplet’s relative velocity, and (e) velocity varying condition whereby all the drying conditions were averaged apart from the relative velocity of the droplet. The boundary conditions for the last four cases were calculated using three-dimensional simulations of the spray drying process of the particles that possessed pure solvent properties. The final product morphologies have been examined, i.e., the morphologies of hollow or full porous particles as predicted by the simulations of the single-droplet drying process. It has been found that the variation of the drying boundary conditions had considerable influence on the droplet’s shrinking rate as well as on the efficiency of the process, while the dried particle morphology depended on its shell strength. The influence was more pronounced when the initial droplet diameter and its shell strength increased.     

CFD Model of Particle Agglomeration in Spray Drying

A 3D CFD model of the agglomeration of droplets and particles in a counter-current spray-drying process was developed and verified. An original discrete phase model was elaborated, with an agglomeration module taking into account hydrodynamic segregation of particles, droplet coalescence, and droplet shrinkage for accurate calculations of mass balance of the discrete phase. The characteristic drying curves were applied to the model of particle moisture evaporation, which included the coupling of particle agglomeration with heat, mass, and momentum transfer between the discrete and continuous phases. Two agglomeration zones were observed in the tower: wet particle agglomeration in the atomization zone, and “dry agglomeration” above the air inlets, due to the intensive mixing of particle streams. A comparison of the calculated particle size distributions and experimental data obtained from particle dynamics analysis (PDA) measurements proves the accuracy of the developed methodology. The elaborated model allows the final PSD of the powder in the spray towers to be predicted.     

旋流压力式喷嘴低压喷淋液滴粒径的实验研究

以自来水为喷淋介质,对旋流压力式喷嘴低压喷淋液滴粒径进行了测试,分析了压力、喷孔直径和喷嘴流量对液滴索特平均直径(d_(SMD))的影响规律,研究了旋流压力式喷嘴液滴尺寸的分布规律。采用跨径(K)和均匀度指数(N)来揭示喷嘴低压喷淋质量。实验结果表明,d_(SMD)较大,超过250μm；d_(SMD)随喷孔直径增大而增大,随压力和喷嘴流量增大而减小；喷淋液滴尺寸分布均匀性较好,K小于0．65,N大于4。实验结果可以为旋流压力式喷嘴设计和改进提供重要的实验依据。     

Relationship between deposition properties and operating parameters for droplet onto surface in the atomization impinging spray

Spray coating is one of the most important applications in the industry. The deposition properties of droplet onto surface can be determined by Weber number and K number. While the relationship between the Weber number, the K number and the operating conditions is not understood. In this paper, a comprehensive numerical model based on the Navier-Stokes equation and the particle tracking method was used to simulate numerically the effervescent atomization spray with an impinging surface, and an analytical model was used to predict the droplet velocity. After performing extensive computations at different operating conditions, the formulae of droplet diameter and droplet velocity were obtained with curve fitting technique. The results calculated from the formulae agree with the experimental data. Finally the new formulae relating the Weber number and the K number to the operating parameters were deduced out. The new formulae can be conveniently used to judge the deposition property of droplet onto surface.     

Droplet size distribution and evaporation characteristics of fuel spray by a swirl type atomizer

Spray atomization and evaporation play extremely important roles in mixture formation and combustion processes of direct injection (DI) gasoline engines. In this study, the fundamental characteristics of a swirl spray injected into a constant volume vessel are investigated by means of several laser diagnostic techniques including the laser diffraction-based method for droplet size distribution, the laser induced fluorescence-particle image velocimetry for velocity distributions of droplets and spray-induced ambient air flow, and the two-wavelength laser absorption-scattering technique for concentration distributions of liquid and vapor phases in the spray. The results show that the droplets at outer zone of the spray exhibit larger diameter than those at inner zone under both ambient pressures 0.1 and 0.4 MPa. While this can be partially attributed to the effect of spray-induced ambient air flow, the strength of ambient air flow become small when increasing the ambient pressure from 0.1 to 0.4 MPa, indicating the strong influence of spray dynamics on the droplet size distribution. In the evaporating spray, there are higher vapor concentrations near the spray axis than at peripheral zones. At 4.0 ms after start of injection, spray droplets almost completely evaporate under ambient temperature 500 K and pressure 1.0 MPa, but there are significantly amount of fuels with equivalence ratio below 0.5 in the spray. Reduction in ambient pressure promotes the air entrainment and droplet evaporation, but lowered ambient pressure results in more fuel vapor of equivalence ratio above 1.3 along the spray axis.     

The atmospheric corrosion of zinc: The effects of salt concentration, droplet size and droplet shape

The influence of droplet characteristics on the atmospheric corrosion of zinc was investigated using a multi-microelectrode approach. Arrays of close-packed zinc wires, 500 μm in diameter, were coupled such that the net anodic and cathodic current flowing through each electrode interface was measured as a function of time. Droplets in the range of 1–10 μL placed onto the array showed that electrochemical fields are immediately established and can remain unaltered for significant periods of time. The total charge passed was found to be almost identical for 0.6 M NaCl droplets of varying size when compensating for the electrolyte–zinc contact area, however significant differences in current exchange were observed when varying electrolyte concentration.In contrast to studies on other metals, the highest rates of zinc corrosion, as measured by the microelectrode array, did not occur during drying cycles. It was observed that the initial wetting and subsequent holding at high relative humidity led to the highest measured currents. Corrosion damage during drying cycles, however, appears to be enhanced for large droplets with high contact angle and increased electrolyte concentration. The importance of these observations to the modeling of atmospheric corrosion has been discussed and future developments of the technique are outlined.     

Modeling Emulsification in Static Mixers: Equilibrium Correlations versus Population Balance Equations

Two different modeling approaches are adopted to model turbulent breakage during continuous emulsification in static mixers. First, a correlation is developed to predict the droplet mean diameter. Second, a population balance equation (PBE) is applied to track the droplet size distribution (DSD) using two different breakage kernels. The performances of the two approaches are assessed against a large number of experimental data. The correlation is fast to develop and is found to be capable of predicting the mean diameter with an acceptable accuracy while the PBE‐based model gives an excellent prediction of the entire DSD.     

Confined crystallization phenomena in immiscible polymer blends with dispersed micro - and nanometer sized PA6 droplets, part 1: uncompatibilized PS/PA6, (PPE/PS)/PA6 and PPE/PA6 blends

In this paper the crystallization behavior of PA6, dispersed as droplets in various immiscible amorphous polymer matrices, is reported. PA6 was melt-mixed at various compositions with PS, (PPE/PS 50/50 wt/wt) and PPE using twin-screw extrusion. The phase morphologies of the obtained blends were analysed using SEM, etching experiments and image analysis. The crystallization behavior of PA6 was investigated by dynamic and isothermal DSC experiments. In case PA6 is dispersed as droplets, fractionated crystallization behavior occurs, characterized by several crystallization events at different, lowered crystallization temperatures. It is found to depend on the blend morphology (size of the droplets) and the thermal history of the samples (heterogeneous nucleation density). The PA6 droplet size distribution is shown to strongly influence the crystallization behavior of the droplets. Vitrification of the matrix appears to cause nucleation in the droplets at the interface. Decreasing the PA6 droplet size results in slower overall crystallization rates.     

生发新理念

有效的防脱发、生发产品将是化妆品行业的重要卖点,并可带来长远丰厚的经济效益。针对脱（秃）发的8大原因,采用中草药提取液,研究出防脱固发生发中药原液ZD-HHG,该产品在防脱固发生发方面具有全面的作用机理和强大的优越性。根据大量实验研究数据探讨了有关产品的原料选择及配方组成。     

筛板上泡沫向喷射工况转变点的新法测定及转变机理

在Φ３００ｍｍ冷模筛板塔上，进行了空气／水物系的泡沫－喷射工况转变实验，提出了一种新的测定工况转变点的方法。对转变点及此时板上的液层高度进行了实验关联，提出预测转变点对角线图。对筛孔上发生的工况转变过程作了新的探讨，得到筛板上工况转变的一般型关联式     

柏纷的新概念--深圳柏纷化妆品营销案例

介绍了柏纷公司产品的开发，生产以及市场推广策略，柏纷公司从化妆品市场的不断变化来决定其每个时期的不同市场特点及营销结构。介绍了柏纷公司开发功效性强，卖点突出及要领新颖的产吕的研发主导思想，以及其产吕能成功立足于化妆品市场的成功经验。     

Confined crystallization phenomena in immiscible polymer blends with dispersed micro- and nanometer sized PA6 droplets, part 2: reactively compatibilized PS/PA6 and (PPE/PS)/PA6 blends

In this paper the relation between the blend phase morphology and the fractionated crystallization behavior of PA6 in reactively compatibilized immiscible PS/PA6 and (PPE/PS)/PA6 immiscible blends is studied. Reactive compatibilization is used as an effective tool for controlling the blend phase morphology, and to reduce the PA6 dispersed droplet size. As reactive compatibilizers, SMA2 and SMA17 are used, which differ in their level of miscibility with the amorphous PS and (PPE/PS) components. With SMA2 a strong shift of PA6 crystallization to much higher supercoolings than before is found after compatibilization resulting in crystallization at temperatures as low as 85 °C. This is ascribed to the strong decrease of the droplet sizes down to 100-150 nm. Nucleation experiments show that heterogeneous bulk nucleation can be reintroduced in the submicron-sized PA6 droplets by adding enough nucleating agents of sufficient small size. The degree of fractionated crystallization is found to depend on the interface between PA6 droplets and surrounding medium, as it is influenced by vitrification of the matrix polymer and by the location of the compatibilizers SMA2 and SMA17. The method used for mixing the reactive compatibilizer with the blend components also affects the fractionated crystallization process.