Formation Of Liquid Film Research Articles

Interface heterogeneity of aluminum-steel bimetal parts manufactured via thixotropic-core compound forging

Thixotropic-core compound forging (TCF1) is a promising technology for the precision forming of aluminum-steel bimetal parts. In this paper, the hitherto unexplained mechanisms of the interface heterogeneity in TCFed aluminum-steel bimetal parts were investigated. Moreover, the effects of diffusion heat treatment on the interface heterogeneity and shear strength were studied. A thixotropic 7075 Al core and a 304L steel shell were used in TCF for the forming of a complex bimetal part. Results suggested that the interface heterogeneity in TCFed aluminum-steel bimetal parts is resulted from three aspects: (i) asynchronous material flow and the associated liquid segregation; (ii) tearing and separation of oxide films; and (iii) formation of liquid film at core surface. The local liquid segregation in distal areas of the bimetal part is helpful to improve the interface wettability and the separation of oxide films, thus accelerating the atom diffusion. In this case, reliable metallurgical bonding interface composed of Al-Fe intermetallic compounds (IMCs2) with satisfactory thickness is possible to be obtained. The diffusion heat treatment is helpful to the formation of reliable metallurgical bonding interface by improving the growth of IMCs. The optimal shear strength was tested to be 26.4 MPa after a heat treatment for 475 °C/2 h, indicating the formation of reliable metallurgical bonding. With the further increment in the heat treatment time, the interface heterogeneity will be diminished, whereas the shear strength may be deteriorated due to the overgrowth of IMCs.

In-depth understanding of ionic liquid assisted perovskite film formation mechanism for two-step perovskite photovoltaics

Ionic liquids (ILs) have been widely applied in the one-step fabrication of perovskite with noticeable enhancement in the device performance. However, in-depth mechanism of ionic-liquid-assisted perovskite film formation is not well understood for also important two-step perovskite fabrication method, with better control of crystallization behavior. In this work, we introduced ionic liquid methylammonium formate (MAFa) into organic salt to produce perovskite film via a two-step method. Systematic investigations on the influence of MAFa on the perovskite thin film formation mechanism were performed. Ionic liquid is shown to assist lowering the perovskite formation enthalpy upon the density functional theory (DFT) calculation, leading to an accelerated crystallization process evidenced by in-situ UV-Vis absorption measurement. A gradient up-down distribution of ionic liquid has been confirmed by time-of-flight SIMS. Importantly, besides the surface passivation, we found the HCOO− can diffuse into the perovskite crystals to fill up the halide vacancies, resulting in significant reduction of trap states. Uniform perovskite films with significantly larger grains and less defect density were prepared with the help of MAFa IL, and the corresponding device efficiency over 23% was obtained by two-step process with remarkably improved stability. This research work provides an efficient strategy to tune the morphology and opto-electronic properties of perovskite materials via ionic-liquid-assisted two-step fabrication method, which is beneficial for upscaling and application of perovskite photovoltaics.

Transient CFD Modelling of Air–Water Two-Phase Annular Flow Characteristics in a Small Horizontal Circular Pipe

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable ‘dry-out’ phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance.

Formation of Liquid Film in Heterogeneous Condensation of Water Vapor: Effects of Solid-Fluid Interaction and Sulfuric Acid Component.

Understanding the phenomenon of filmwise condensation on solid surfaces is vital for industrial processes such as air pollutant control and desalination. In this work, we study the formation of condensed liquid films via molecular dynamics simulations, and the effects of solid-fluid interactions and the sulfuric acid component are given major attention. Water is chosen as the fluid, while the solid-fluid interaction is modified to characterize different solid surfaces. The results show that as the solid-fluid interaction decreases, the solid surface transforms from a completely wetting surface to a partially wetting surface, and the film formation process shows significant differences. The condensed liquid on the completely wetting surface forms small liquid films, which merge to form a complete film covering the surface. With the enhancement of solid-fluid interaction, the condensation rate increases first and then remains virtually invariant, resulting in a film formation time that decreases first and then maintains constant. The condensed liquid on the partially wetting surfaces appears as nanodroplets, and the coalescence between nanodroplets leads to the formation of the liquid film. It is found that the stronger the solid-fluid interaction, the more the coalesced droplets tend to be pinned at nucleation sites, the easier it is to form a liquid film, and the shorter the time required for droplet merging. The sulfuric acid component accelerates liquid film formation on both completely wetting and partially wetting surfaces, but the effect of sulfuric acid is more significant on partially wetting surfaces. The 5% molar fraction of sulfuric acid reduces the nucleation time by 72% and increases the condensation rate by 137% under partial wetting, while the same amount of sulfuric acid only increases the nucleation rate by 6% on the completely wetting surface.

Compressible gas-droplet flow and heat transfer behind a condensation shock in an expanding channel

A two-fluid mathematical model of a supersonic gas-droplet mixture flow with account of droplet growth due to vapor condensation behind a condensation shock in a plane expanding channel is constructed. The flow structure in both the inviscid core and the two-phase boundary layer assumed to be laminar is studied numerically. The range of flow parameters is considered in which the spontaneous condensation zone (“condensation shock”) is fairly narrow, and just behind this shock thermal parameters of the phases almost reach thermodynamic equilibrium. Downstream, the droplet radius continues to grow due to the flow expansion and further vapor condensation. Of primary concern is the flow region where the droplets become sufficiently inertial to travel with a velocity slip, and hence to model adequately the velocity and temperature fields in both phases a two-fluid model is required. In addition to the Stokes drag, the Saffman lifting force exerted on the droplets in the boundary layer is taken into account. The Saffman force results in droplet deposition and the formation of a thin liquid film on the channel walls. A parametric numerical analysis of the two-phase flow structure in the inviscid flow region and in the near-wall boundary layer is performed, and the effects of phase transitions (droplet condensation and evaporation, as well as the film formation) on the reduction of the adiabatic channel wall temperature are analyzed.

Numerical simulation of two-phase flow in a multi-gas channel of a proton exchange membrane fuel cell

Understanding the two-phase distribution characteristics within the multi-gas channel of a fuel cell is important for improving fuel cell performance. In the paper, the volume of fluid model is used to predict the dynamic behaviour of water in the multi-gas channel, analyze the pressure drop, velocity distribution, and flow resistance coefficient between different channels, and investigate the influence of operating conditions, surface wettability and channel structure on the two-phase distribution characteristics in the channel. The results show that water undergoes the processes of growth, separation, single droplet transport, wall impact, droplet collision, liquid film formation, and liquid film transport in the multi-gas channel. Inlet velocity and surface wettability significantly affect the pressure drop, water saturation, and surface water coverage. As the inlet velocity and gas diffusion layer surface wettability increase, the flow resistance coefficient and unevenness of the distribution decrease, indicating that the in-channel flow distribution homogeneity is enhanced. The rectangular channel has better water removal and flow distribution uniformity than the tapered channel, and the unevenness of distribution decreases significantly with decreasing rectangular width, from 0.15715 to 0.00315. The research work is a guide to understanding water transport in multi-gas channels, accelerating water removal, and improving inter-channel flow distribution uniformity.

Influence of thermal treatment on electronic properties of inkjet-printed zinc oxide semiconductor

ABSTRACT Additive manufacturing of electronic devices using inkjet printing provides a potential alternative approach in substitution for conventional electronic fabrication processes. However, the complex nature of inkjet printing involves the liquid deposition and film formation from the vaporization of solvent, which makes it different from film created by conventional deposition methods. Inkjet printing of zinc oxide (ZnO), which is a widely utilized semiconductor, produces polycrystalline film composed of nano-size grains, which could significantly influence the properties of printed film. In this study, low-temperature annealing was employed to treat inkjet-printed ZnO for UV photodetection application, and its influence on electrical properties was studied. Band bending was characterized using the Mott-Schottky plot which examines the charge distribution of the films. It is found that the annealing of inkjet-printed polycrystalline ZnO film has improved its electrical properties, which could be attributed to the reduction of band bending due to the merging of grains. The treatment also helps to reduce impurities of the film, such as zinc hydroxide complexes, which are common for solution-derived films. Hence, the study could pay the way for the improvement of electrical properties of inkjet-printed functional materials.

Fuel spray impingement and liquid film formation in a gasoline direct-injection spark-ignition engine

Fuel spray impingement and liquid film formation in a gasoline direct-injection spark-ignition engine

Liquid-Film Formation in a Hole under the Effect of Gravity

Liquid-Film Formation in a Hole under the Effect of Gravity

Y2O3 nanoparticles decorated IN738LC superalloy manufactured by laser powder bed fusion: Cracking inhibition, microstructures and mechanical properties

In-situ Y 2 O 3 nanoparticles decorated Inconel 738 LC composite by powder mixture is fabricated using laser powder bed fusion with different scan speeds and laser powers. The process window is significantly enlarged with the addition of 0.05 wt% Y 2 O 3 by removing the cracks in the as-printed parts. Well-dispersed Y 4 Al 2 O 9 particles are formed during the reaction between the mixed powders and the laser beam. Obvious enrichment of Zr in the Y 4 Al 2 O 9 particles by substitution for the yttrium is observed, which effectively eliminates the segregation of Zr along the grain boundaries. In this case, the cracks are mitigated since the formation of liquid film is correspondingly hindered at the last stage of solidification. In addition, the gains are coarsened to nearly double the size with the incorporation of Y 2 O 3 nanoparticles before and after heat treatment. As a result, the Y 2 O 3 -inoculated Inconel 738 LC exhibits an improved strength at 850 °C. • The crack is mitigated in IN738LC by the addition of Y 2 O 3 during LPBF. • The added Y 2 O 3 reacts with Al to form well-dispersed Y 4 Al 2 O 9 particles. • Y 4 Al 2 O 9 particles absorb Zr and hinder its segregation along grain boundaries. • Y 2 O 3 addition induces coarser grains due to the low cooling rate caused by Y 4 Al 2 O 9.

Welding solidification cracking susceptibility and behavior of nickel based ERNiMo-2 wire

The welding solidification cracking susceptibility of ERNiMo-2 wire was studied by trans-varestraint test. Results show that the threshold strain and saturated strain are 4% and 8% respectively. In this range, the maximum crack length increases continuously with strain. Solidification cracks occur in interdendrites and extend along solidification grain boundaries. The strain and eutectic M6C which reducing the binding force of grain boundaries, are the main factors affecting the solidification cracking. The segregation of Si and P at the grain boundary is also beneficial to the formation of liquid film, which enlarges the solidification temperature range and further increases the welding solidification cracking susceptibility of weld metal.

Droplet Impingement into a Liquid Film; Numerical Study of Surface Tension Effect on the Crown Formation

An axisymmetric numerical model is conducted to study the droplet impingement into a liquid film and crown formation. Through numerical modeling and experimental validation, the effect of different parameters such as surface tension, Weber number, and film thickness on crown evolution is investigated. Surfactant is added to water, aiming reduction of the surface tension in the surfactant-water mix. It was shown that the crown rim diameter increases with Weber in both water and surfactant-water mixture cases. Likewise, crown rim diameter increases with the film thickness in both different cases of fluids. Additionally, results revealed that surface tension does not affect the crown rim diameter. Nevertheless, crown height increases as surface tension decreases. At low values of surface tension, secondary droplets and the de-wetting region appear. These outcomes can be attributed to the domination of kinetic energy of crown rims in cases with low surface tensions.

Effect of Mixer Structure on Liquid Film Formation and Nox Conversion Efficiency in Selective Catalytic Reduction System

Effect of Mixer Structure on Liquid Film Formation and Nox Conversion Efficiency in Selective Catalytic Reduction System

Elimination of hot cracking in the laser surface re-melting of the IC10 superalloy by controlling the heat input

Hot cracking is a severe defect that occurs during the repair or manufacturing of directionally solidified superalloy by laser metal deposition. In this study, the hot cracking sensitivity of a directionally solidified superalloy, IC10 alloy, in the laser surface re-melting was evaluated and the effects of heat input on the hot cracking was investigated. It is found that the crack number density and the crack length density first increase and then decrease with the increase of heat input under studied conditions, and the crack-free re-melted sample can be achieved under the heat input of 50 J/mm. Meanwhile, the cracks display a typical characteristic of liquation cracks. The formation of liquid film can be ascribed to the liquation of γ-γ' eutectic phases, γ' phases and carbides. The liquation height and the maximum width of liquid channel increase with the increase of heat input, and they are used to describe the capability of liquid feeding. Furthermore, the driving force for crack initiation and propagation induced by thermomechanical conditions are also discussed. These findings provide technical support for achieving successful repair or manufacturing methods of the non-weldable directionally solidified superalloys.

Single droplet impingement of urea water solution on heated porous surfaces

The droplet/wall interaction of urea water solution on surfaces with varying properties is one decisive element for the detailed understanding of liquid film formation in the exhaust gas system of diesel-powered engines. An experimental study was conducted on the single droplet impingement of urea water solution on porous steel surfaces. The outcome of droplet impact was investigated under variation of droplet momentum, wall temperature and surface properties such as pore diameter and surface roughness. Droplet impact is recorded by high-speed shadowgraphy. The results allow the development of regime maps describing the hydrodynamic and thermal phenomena deposition, splash, boiling induced breakup, total rebound and rebound with breakup as a function of dimensionless parameters. Based on systematic investigations the influence of surface properties on the transition boundaries can be shown. The porosity of the sample leads to a significant shift of the wetting boundary to higher temperatures, as the evolving vapour between droplet and surface can escape through the pores. The regimes partial rebound with breakup and partial rebound are introduced to describe the single droplet impingement on porous surfaces. The experimental results serve as database for modelling the droplet/wall interaction in the selective catalytic reduction system.

Effect of nanostructured surface configuration on the interface properties and heat transfer of condensation process of argon inside nanochannels using molecular dynamics simulation

Present work studies the impact of surface structure on the heat transfer and liquid–vapor interface properties of condensation flow formed inside rough nanochannels compared to the smooth ones, using molecular dynamics simulation. Considering rectangular roughness configuration on the walls of nanochannel, simulations are performed under various saturated temperature conditions to obtain density, velocity, and temperature profiles. Furthermore, the effect of rough elements on the mechanism of liquid film formation and condensation rate as well as the thermal properties of two-phase flow has been investigated. It is observed that the amount of the oscillations in the vicinity of the walls at the end of the simulation time in rough nanochannels, is less than in smooth nanochannels. Results show that the effect of rough structures on the distribution of particles as well as velocity profile is greater at a lower temperature. Also, rough surfaces increase heat transfers at the beginning of the condensation process that leads to higher values of thermal conductivity in the rough nanochannel compared to the smooth nanochannel. Moreover, it is demonstrated that the thermal conductivity of argon condensation in rough nanochannel is approximately equivalent to the value of thermal conductivity in smooth nanochannel by adding one copper nanoparticle to the base fluid of argon.

Inside Front Cover

By fusion of superhydrophobic surface with transistor‐inspired architecture for high‐frequency water kinetic energy harvesting, we report the design of a superhydrophobic surface‐based droplet electricity generator, which allows for timely water droplet shedding at high impact frequency without the formation of unwanted liquid film and is capable of efficient electrical energy harvesting without compromising output performance. This work represents Harvesting energy from high‐frequency impinging water droplets by a droplet‐based electricity generator. image

Experimental Investigation of AdBlue Film Formation in a Generic SCR Test Bench and Numerical Analysis Using LES

In this work, an experimental investigation of AdBlue film formation in a generic selective catalytic reduction (SCR) exhaust gas test bench is presented. AdBlue is injected into a generic SCR test bench resulting in liquid film formation on the lower wall of the channel. The thickness of this liquid film is measured using a film thickness sensor based on absorption spectroscopy. Simultaneously, the wall temperature at the measurement point is monitored, which allows for examining correlations between the evolution of the film thickness and the temperature of the wetted wall. The velocity of the airflow in the channel and the initial wall temperature are varied in the experiments. Correspondingly, the measurements are performed during different thermodynamic regimes, including liquid film deposition and boiling. Repeated measurements have also shown that the film thicknesses are reproducible with a standard deviation of 3.4 %. LES-based numerical simulations are compared to the experimental results of the film thickness during the early injection stage. Finally, a numerical analysis is performed to analyze the AdBlue droplet impingement and subsequent film-formation dynamics.

Numerical Study of Liquid Film Formation around Tubes of Horizontal Falling Film Evaporator

Falling film evaporative heat exchangers are extensively used in processing industries; broad areas of application being refrigeration, desalination and food processing industries. The fundamental aspect of this type of heat transfer process is to extract the process heat in the form of latent heat by liquid which is sprayed over the surface of the process tubes. Formation of liquid film over a fully wetted horizontal round tube of falling film evaporator has been numerically simulated here. Two numerical approaches, Volume of Fluid (VOF) technique and the Eulerian multiphase model are applied to compare their results. The effect of varying flow and geometrical parameters on the film thickness is investigated. Two horizontal tubes of diameter 19.05mm and 25.04mm with three different uniform spacing have been selected for simulation. Film Reynolds numbers 650, 950 and 1250 are considered for the above set of parameters. Ii is observed that the geometrical and flow parameters considerably influence the film thickness. Transient analysis of the film formation has been carried out and parameters like pathline of liquid film and the velocity profile have been obtained for understanding the flow behavior in a better manner. All the simulated results agree well with the published data.

Liquid Film Translocation Significantly Enhances Nasal Spray Delivery to Olfactory Region: A Numerical Simulation Study

Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation and translocation after nasal spray applications were simulated for both a standard and a newly proposed delivery system. Results show that the initial droplet deposition in the olfactory region is highly sensitive to the spray plume angle. For the given nasal cavity with a vertex-to-floor head position, a plume angle of 10° with a device orientation of 45° to the nostril delivered the optimal dose to the olfactory region. Liquid wall film translocation enhanced the olfactory dosage by ninefold, compared to the initial olfactory dose, for both the baseline and optimized delivery systems. The optimized delivery system delivered 6.2% of applied sprays to the olfactory region and significantly reduced drug losses in the vestibule. Rheological properties of spray formulations can be explored to harness further the benefits of liquid film translocation in targeted intranasal deliveries.