Liquid Front Research Articles

Wetting of Cu-SiC Composite Material Modified by Nanosecond Laser Radiation and Liquid Spreading over It

In the framework of this work, the surface properties of Cu-SiC composite material were studied when spreading micro- and nanoliter liquids. The Cu-SiC samples with a SiC content of 5 to 20 wt.% were fabricated by spark plasma sintering at temperatures from 700 to 850 °C. The Cu-SiC surfaces were processed by two different methods: using abrasive materials and nanosecond laser radiation. Surface analysis was performed by scanning electron microscopy, profilometry, energy dispersive spectroscopy and Vickers methods. The surface properties (wetting and dynamic characteristics of spreading) were studied using a shadow optical technique when interacting the Cu-SiC surfaces with water (up to 10 μL). It was proved that the recorded deterioration of the wettability properties of Cu-SiC surfaces processed by abrasive materials with an increase in their sintering temperature and the reason for the spontaneous hydrophobization of the Cu-SiC composite materials modified by nanosecond laser radiation, are due to the adsorption of airborne hydrocarbon contaminants, similar to the known wetting inversion of metal surfaces. It was established that the wetting properties of materials prior to modification by laser radiation do not affect the intensity, duration of stages, and steady-state values of contact angles upon wetting inversion of Cu-SiC composite materials. It was also found that the processing of Cu-SiC surfaces by laser radiation makes it possible to change the dynamic characteristics of the liquid spreading (at a flow rate of 5 μL/min, the liquid front speed is more than three times, and the dynamic contact angles are in the range of 30°).

Controlling the advancement of the liquid front of the nitrocellulose membrane assay under the influence of the centrifugal force on the Lab-on-a-Disc platform

Lateral flow immunoassays (LFIs) are ubiquitous point-of-care platforms for chemical and biological tests. They are widely used due to their portability, low cost, fast time of outcome, and absence of the need for presence of highly trained personnel to conduct these tests. One of the ways to enhance the sensitivity of LFIs is by slowing down the flow rate of the analyte through the active sensing area of the test strips (e.g., test line). Some recent developments towards the goal of the improvement of sensitivity of LFIs include placement of the lateral flow assays on the centrifugal microfluidic platforms (so-called Lab-on-discs) where the flow of the analyte through the lateral flow test strip could be sped up or impeded by the centrifugal force applied to the fluid passing through the lateral flow membrane. The finite element analysis (FEA) simulation is performed using ANSYS Fluent software platform and validated by the lateral flow membranes of several pore sizes, from 7 µm to 15 µm, were incorporated onto micromachined discs with integrated microfluidic networks with an accuracy of simulation to be within 15% of experimental values. The present work reports the dependence of the speed of advancement of the liquid meniscus of LFI placed on the Lab-on-a-Disc as a function of the porosity (volumetric fraction of the pores in nitrocellulose or NC membrane), pore sizes, and angular velocity of the spinning disc.

Enhanced in-situ liquid transport investigation setup for pharmaceutical tablet disintegration analysis using terahertz radiation

The disintegration process of pharmaceutical solid dosage forms commences on contact with the dissolution medium and continues with subsequent spontaneous imbibition of the medium in the tablet matrix. Identifying the location of the liquid front in situ during imbibition, therefore, plays a significant role in understanding and modelling the disintegration process. Terahertz pulsed imaging (TPI) technology can be used to investigate this process by its ability to penetrate and identify the liquid front in pharmaceutical tablets. However, previous studies were limited to samples suitable for a flow cell environment, i.e. flat cylindrical disk shapes; thus, most commercial tablets could only be measured with prior destructive sample preparation. This study presents a new experimental setup named open immersion to measure a wide range of pharmaceutical tablets in their intact form. Besides, a series of data processing techniques to extract subtle features of the advancing liquid front are designed and utilised, effectively increasing the maximum thickness of tablets that can be analysed. We used the new method and successfully measured the liquid ingress profiles for a set of oval convex tablets prepared from a complex eroding immediate-release formulation.

Generating signals at converging liquid fronts to create line-format readouts of soluble assay products in three-dimensional paper-based devices.

The correct interpretation of the result from a point-of-care device is crucial for an accurate and rapid diagnosis to guide subsequent treatment. Lateral flow tests (LFTs) use a well-established format that was designed to simplify the user experience. However, the LFT device architecture is inherently limited to detecting analytes that can be captured by molecular recognition. Microfluidic paper-based analytical devices (μPADs), like LFTs, have the potential to be used in diagnostic applications at the point of care. However, μPADs have not gained significant traction outside of academic laboratories, in part, because they have often demonstrated a lack of homogeneous shape or color in signal outputs, which consequently can lead to inaccurate interpretation of results by users. Here, we demonstrate a new class of μPADs that form colorimetric signals at the interfaces of converging liquid fronts (i.e., lines) to control where colorimetric signals are formed without relying on capture techniques. We demonstrate our approach by developing assays for three classes of analytes-an ion, an enzyme, and a small molecule-to measure using iron(III), acetylcholinesterase, and lactate, respectively. Additionally, we show these devices have the potential to support multiplexed assays by generating multiple lines in a common readout zone. These results highlight the ability of this new paper-based device architecture to aid the interpretation of assays that create soluble products by using flow to constrain those colorimetric products in a familiar, line-format output.

Effect of casting temperature on halo in the solidification microstructure of direct-chill casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys

The effect of casting temperature on the halo structure of direct-chill (DC) casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys was investigated. The results indicated that the microstructure consists of fine primary Si, α-Al dendrite halo, and fine fibrous coupled eutectic structure, Al2Cu, and Al8FeMg3Si6 phase. The formation of halos was systematically analyzed. The temperature gradient at the solid–liquid interface front played an essential role in the development and growth of the halo. As the casting temperature elevated, the temperature gradient of the solid–liquid interface front increased, the solid–liquid interface became stable, the α-Al dendrite halo was less developed, the number of large-sized Si atomic clusters in the melt decreased and the growth of primary Si was inhibited.

Numerical investigation of thermal failure of a fuel subassembly foot wall during molten material relocation under various flow blockage scenarios in sodium-cooled fast reactor

The innovative Fuel Assembly Inner DUct Structure (FAIDUS) design inherently offers a quick relocation path for the molten core material to descend downwards via the inner duct and arrive at the foot of the Subassembly (SA) following the local core meltdown during Total coolant Flow Blockage (TFB) accident. With its high thermal energy and continual heat generation, the amassed molten mass targets the surrounding foot structure, causing the foot wall to fail. The thermal damage progression and discrete failure of the foot wall govern the later phase of the melt relocation that signals the accident state. To understand the thermal damage progression of SA foot, transient numerical simulations are performed using a commercial computational fluid dynamics solver, ANSYS Fluent. An enthalpy-porosity approach based solidification/melting model is employed to predict the wall failure mechanism and associated event sequences. The computational model is validated against the wall failure test results available in the literature. Subsequently, the foot wall failure analysis is undertaken using a 2-D axisymmetric physical model for various plausible blockage occasions that initiate the TFB accident near the SA foot. The numerical solution endeavors to explicate the transient behavior of molten pool, convection-diffusion controlled phase interface development, thermal transport mechanism, liquid front propagation across the foot cross-section, and associated thermal hydraulics. The present findings indicate that the standard SA foot design perpetuates the accident scenario by releasing the molten mass through the ruptured wall segment after failure. To address this, an improved slotted discriminator-based foot design is proposed in the present study, and the effectiveness of the modified foot design in realizing a positive melt relocation to the core catcher is examined. The simulation results suggest that the modified foot design permits the intended melt release to the core catcher, confirming the Controlled Material Relocation (CMR) strategy and restraining the accident propagation to neighboring SA.

Liquid Column Separation Due to Fluid Hammer Occurrence in Propellant Lines

When a pressurized liquid enters a pipeline with a closed end and under vacuum conditions, the resulting liquid front suddenly is brought to rest at the end of the pipe. This type of flow configuration is found in propulsion systems of satellites during priming operation and induces a fluid hammer followed by a column separation, generating a multiphase gas/vapor bubble. This paper aims at explaining the column separation mechanism by solving the momentum equation for the liquid column moving in the pipeline when column separation occurs and by applying the integral form of the conservation principles to expansion and compression waves within the flow. The resulting model provides the velocity and position of the liquid front during column separation. Thus, the size and duration of the multiphase bubble can be determined, and the variables involved in the process are identified, which helps the analysis of applications where this complex phenomenon is involved. It is shown that the initial velocity of the liquid front during column separation is the main parameter, which itself is a function of the fuel tank pressure and the fluid hammer pressure rise. The comparison of the predictions with experimental data shows an excellent agreement.

Effective capillary pressure and permeability of a granular material during imbibition in a closed column

We present a method to determine the effective capillary pressure and permeability of a column packed with a granular material by means of imbibition experiments using a closed column and measuring both the liquid uptake and pressure differential that develops ahead of the liquid front. The method is based on finding an intermediate range of pressure differential values, where a Washburn approximation is no longer valid but a recently obtained effective description accurately reproduces the experimental results. To determine this intermediate range of pressures we calculate the goodness of fit corresponding to both the Washburn pressure-solution, valid at short times, and the implicit pressure-solution, which includes the non-linear dependence of the pressure on the liquid uptake and is compatible with finely divided solids. Using a closed column also allow us to compare the effective capillary pressure with the maximum advancing pressure measured using Bartell’s static method. We perform experiments using liquid polydimethylsiloxane, and glass beads or lactose powder. We show that an effective description of the liquid imbibition is possible and determine the corresponding capillary pressure and permeability that characterize the granular system. We observe that the heterogeneity of the system reduces the characterization range. However, it was possible to characterize lactose powder columns, where the heterogeneity leads to spontaneous bubbling and static measurements are not possible.

Deterministic Assembly of Colloidal Quantum Dots for Multifunctional Integrated Photonics.

Colloidal quantum dots (CQDs) are promising for photonic applications toward lasers, waveguides, and photodetectors. However, integration of high-quality photonic elements into multifunctional devices is still restricted by optical losses stemming from the accumulation of defects and disorder in the solution process. Herein, a platform with a directional Laplace pressure is created for eliminating undesired pinning of liquid fronts in the solution process and boosting ordered assembly of CQDs into designable micro-/nanostructures. The versatility and robustness of this method are demonstrated by deterministic patterning of CQDs with different components and photoluminescence spectra onto various substrates. On the basis of this platform, microring lasers with tunable emission modes, low-loss waveguides, and their coupled structures have been reached for direct on-chip generation and propagation of coherent light. A proof-of-concept demonstration of integrated circuits is also conducted by combining microcavity lasers with waveguides for encoding photonic outputs into information bits.

Pore-Scale Study on Convective Drying of Porous Media.

In this work, a numerical model for isothermal liquid-vapor phase change (evaporation) of the two-component air-water system is proposed based on the pseudopotential lattice Boltzmann method. Through the Chapman-Enskog multiscale analysis, we show that the model can correctly recover the macroscopic governing equations of the multicomponent multiphase system with a built-in binary diffusion mechanism. The model is verified based on the two-component Stefan problem where the measured binary diffusivity is consistent with theoretical analysis. The model is then applied to convective drying of a dual-porosity porous medium at the pore scale. The simulation captures a classical transition in the drying process of porous media, from the constant rate period (CRP, first phase) showing significant capillary pumping from large to small pores, to the falling rate period (FRP, second phase) with the liquid front receding in small pores. It is found that, in the CRP, the evaporation rate increases with the inflow Reynolds number (Re), while in the FRP, the evaporation curves almost collapse at different Res. The underlying mechanism is elucidated by introducing an effective Péclet number (Pe). It is shown that convection is dominant in the CRP and diffusion in the FRP, as evidenced by Pe > 1 and Pe < 1, respectively. We also find a log-law dependence of the average evaporation rate on the inflow Re in the CRP regime. The present work provides new insights into the drying physics of porous media and its direct modeling at the pore scale.

Visualization of liquid interface and reaction front flow in partially soluble solvent

In this study, visualization of the reaction in partially miscible solvents has been conducted using the Schlieren method, an indicator addition method and PIV method. The CH3COOH in C4H10O was set on the NaOH in water against the vertical downward direction of the Hele-Shaw cell. It was found that various convection phenomena could be induced by the generation of H2O and CH3COONa during chemical reaction, which were depended on the ratio of initial concentration, R = CCH3COOH,0/CNaOH,0. For R = 1, the horizontal travelling wave was observed from the left-hand side to the right-hand side in the HS, which could be caused by Marangoni convection due to the locally H2O concentration. After that vertical convections were also observed on the interface of the C4H10O and water and below the interface. They could be caused by Rayleigh Tayler instability and the salt finger, respectively. It was found that the time change of the reaction front from the interface was largely divided by R. For R <1, the change in the reaction front position gradually approaches a constant value in a few seconds. On the other hand, for R≧1, the reaction front increased proportionally t0.5.

Study of the interfacial reactions controlling the spreading of Al on Ni

Despite the importance in high-temperature processing, wettability studies focusing on liquid aluminum (Al) on solid nickel (Ni) at high temperatures are scarce due to the difficulty of performing experiments and the complexity of interfacial physical and chemical activities. The effects of interrelated multi-factors, including intermetallic compounds (IMCs) formation and diffusion on wetting dynamics is still debatable. Therefore, in this study, we investigated the reactive spreading of liquid Al on solid Ni by using the combined pendant/sessile drop method between 750 and 950 °C. The effects of Ni dissolution into Al on the spreading dynamics were limited due to the low Ni solubility below 950 °C. Two continuous Al-rich IMC layers, Al3Ni and Al3Ni2 layers formed at the Al/Ni interface during the isothermal holding stage and affect the final wetting behavior. Additional capillary quenching experiments confirmed that the Al3Ni phase was the first formed phase. At equilibrium, the Al3Ni layer was pinned at the triple-phase line at 750 °C while it can spread ahead of the liquid front at higher temperatures. This process may be the main reason why at higher temperatures a better spreading is observed as the Al3Ni layer has a larger affinity to Al than the pure Ni substrate.

Investigating liquid fronts during spontaneous imbibition of liquids in industrial wicks. Part I: Experimental studies

AbstractA large set of industrial wicks made from sintered polymer beads and fibrous materials were studied. Three types of liquid fronts were observed: sharp, semi‐sharp, and diffuse. The bead‐like microstructure with lower porosity is found to support sharp fronts, while the aligned‐fiber microstructure with higher porosities leads to a smudging/diffusing of the fronts. The previously developed sharp‐front model is found to predict the front height as a function of time quite well in the sintered‐bead wicks and the two “semi‐sharp” fibrous wicks. The liquid‐front height calculated from the liquid mass‐gain data was validated through visual observations for all but the two fibrous wicks generating the diffuse fronts. These latter cases, observed to start off as a sharp fronts, faded with time.

Antimicrobial activity in cultures of endophytic fungi isolated from Talinum triangulare

. Endophytic fungi colonize the interior of plants without causing damage and act in symbiosis with their host. They are also potential sources of compounds with potential applications in industry, agriculture, and medicine, Thus, this study aimed to isolate and identify the endophytic fungi medicinal plant Talinum triangulare and evaluate its potential for the production of antimicrobial substances using the disk diffusion technique and testing in liquid medium front of Staphylococcus aureus ATCC SA 6538, Pseudomonas aeruginosa ATCC PA 0030, and Corynebacterium diphtheria ATCC 27012. Corynebacterium diphtheria was isolated from 3 fungi of the genus Trichoderma and Penicillium, with only the genus Trichoderma fungi showing antimicrobial activity.

The Fluidity of Aluminium Ductile Irons

The fluidity and the effective surface tension of Al-Ductile iron (Fe-3.2C-8.5Al-0.05Mg) were studied at different pouring temperatures. A fluidity test comprising strips 1, 2, 4-and 8-mm-thickness were molded in sodium silicate-bonded silica sand. Our results quantify the increase of melt fluidity with increasing casting modulus and pouring temperature and show that the effective surface tension of the alloy is about 1.8 N/m. Comparing this value with the surface tension of Si-ductile irons and Al-ductile irons of lower Al contents, we conclude that the high level of Al used in this study results in the formation of an alumina film on the advancing liquid front, which raises the effective surface tension, reduces fluidity by 100 mm and reduces the ability of the metal to enter narrow sections from 0.4 to 1.0 mm thickness.

Confluence and cold shut computation based on time field in casting simulation

Numerical simulation technology has been widely used in the foundry industry to analyze and improve casting processes. During the casting filling process, many filling-related defects form easily at the confluences of liquid metal streams. The main filling-related defects are cold shut defects. To calculate the positions of casting defects, the characteristics of liquid metal confluences were analyzed. The flow front of liquid metal was captured by the volume-of-fluid algorithm to obtain a time field, which was used to calculate the time derivatives of the liquid front position and the confluences of liquid metal streams. To distinguish small confluences from the main confluences, the concept of confluent scale was developed, which was used to filter the small confluences based on a threshold. The calculation process was demonstrated through the post-processing of numerical simulation. A “W” shaped casting and a steering wheel casting were calculated to validate the accuracy of the method developed in this study. The positions of cold shut defects were predicted by calculating the confluences of liquid metal streams. The method was proved to be practical by comparing the calculation results with the positions of cold shut defects in an end cover casting. The computation of confluences and cold shut defects can improve the analysis efficiency and provide assurance for the optimization of a casting process plan.

Video-based fractional order identification of diffusion dynamics for the analysis of migration rates of polar and nonpolar liquids: Water and oil studies.

Diffusion dynamics of water and oil are observed in real-time using video images. Savitzky-Golay derivative filtering ensures accurate localization of the liquid front. System identification demonstrates that a fractional-order model with only two parameters may be used to describe the dynamics of the diffusion process. The method paves the way for video-based cellulose filter paper microfluidics and lateral flow assays, which are low cost and have broad diagnostic applications.

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures.

Wicking within woven screens has attracted considerable attention due to its important role in applications concerning phase-change heat transfer and phase separation. In the present study, horizontal spreading experiments are conducted to investigate the wicking performance of woven screens by measuring the volumetric liquid intake into the screens and the liquid propagation fronts through two perpendicular high-speed cameras. Woven screens with micro (single- and multilayer)- and nano (plain, etched, and fluoridated)-porous structures are manipulated through diffusion bonding and chemical processes. The macroscopic observation indicates the substantial enhancement of the wicking capability in multilayer structures, where the interlayer microchannels could compensate for the essential deficiency of single-layer screens by providing low-resistance flow passages. Wicking capability of water is enhanced by the hydrophilic nanograsses along the wires. Furthermore, flow mechanisms within the screens are analyzed by comparisons between apparent and saturated wicking distances. In multilayer structures, the liquid spreads along the entire cross-sectional area in etched screens, while it spreads primarily along the interlayer microchannels in plain and fluoridated screens. The influence of various fluids on the wicking behavior within the woven screens is found to be fully represented by a unique parameter that captures the effects of surface tension and dynamic viscosity in the radial flow model. This work deepens the understanding of the capillary-driven flow within the woven screens with hybrid micro-/nanoporous structures and provides guidance for the design and manufacture of highly efficient wicking structures.

Physicochemical method of fixing mobile sands with local materials

Impregnating composition with water-soluble binders has been elaborated, with the help of which the source of deflation of mobile sands is blocked, and the protective crust obtained on the sandy surface is characterized by resistance to the effects of wind-sand flow, assessed by plastic strength and thickness. The free-flow movement of a binder in a porous body of sand depends mainly on the equivalent diameter of the particles obtained by the joint solution of the internal and external problems of hydrodynamics and the shape factor of the particles. To interpret the experimental results empirically, an indicator of the saturation of the protective crust sand characterizing the impregnation as an unstable process proceeding under the predominant influence of the gravity field with an uneven movement of the liquid front was revealed. The prevalence of the elastic-plastic properties of the protective crust is evidenced by a slight and smooth change in physical and mechanical indicators over time by the third year of operation.

Precursor Film Spreading during Liquid Imbibition in Nanoporous Photonic Crystals

When a macroscopic droplet spreads, a thin precursor film of liquid moves ahead of the advancing liquid-solid-vapor contact line. Whereas this phenomenon has been explored extensively for planar solid substrates, its presence in nanostructured geometries has barely been studied so far, despite its importance for many natural and technological fluid transport processes. Here we use porous photonic crystals in silicon to resolve by light interferometry capillarity-driven spreading of liquid fronts in pores of few nanometers in radius. Upon spatiotemporal rescaling the fluid profiles collapse on master curves indicating that all imbibition fronts follow a square-root-of-time broadening dynamics. For the simple liquid (glycerol) a sharp front with a widening typical of Lucas-Washburn capillary-rise dynamics in a medium with pore-size distribution occurs. By contrast, for a polymer (PDMS) a precursor film moving ahead of the main menisci entirely alters the nature of the nanoscale transport, in agreement with predictions of computer simulations.