Thin-layer Flow Research Articles

Finite-difference lattice Boltzmann method with a block-structured adaptive-mesh-refinement technique

An adaptive-mesh-refinement (AMR) algorithm for the finite-difference lattice Boltzmann method (FDLBM) is presented in this study. The idea behind the proposed AMR is to remove the need for a tree-type data structure. Instead, pointer attributes are used to determine the neighbors of a certain block via appropriate adjustment of its children identifications. As a result, the memory and time required for tree traversal are completely eliminated, leaving us with an efficient algorithm that is easier to implement and use on parallel machines. To allow different mesh sizes at separate parts of the computational domain, the Eulerian formulation of the streaming process is invoked. As a result, there is no need for rescaling the distribution functions or using a temporal interpolation at the fine-coarse grid boundaries. The accuracy and efficiency of the proposed FDLBM AMR are extensively assessed by investigating a variety of vorticity-dominated flow fields, including Taylor-Green vortex flow, lid-driven cavity flow, thin shear layer flow, and the flow past a square cylinder.

Extrusion of dough in ring lubricating layer

Abroad there are developments in which the highly viscous mass conveyed in the pipe surround the circular casing of a low viscosity fluid, thereby reducing friction. In this regard, it seems urgent to develop design of macaroni presses, in which the resistance movement test in the press matrices was minimized, which improves the efficiency of their work, as well as performance. The purpose of research is to solve the problem of non-contact forming pasta - based research and development of a fundamentally new method and apparatus according to contemporary pasta production. Basic analytical problems were solved using the theory of hydrodynamic flow in thin layers, namely the theory of gas lubrication. The contactless molding pasta method reduces friction to nearly zero in the matrices of the pasta press. The research results can be applied in the design of pasta presses using matrices with porous inserts.

Математическая модель течений тонкого слоя жидкости с учетом испарения на термокапиллярной границе раздела

Математическая модель течений тонкого слоя жидкости с учетом испарения на термокапиллярной границе раздела

Water budgets of martian recurring slope lineae

Flowing water, possibly brine, has been suggested to cause seasonally reappearing, incrementally growing, dark streaks on steep, warm slopes on Mars. We modeled these Recurring Slope Lineae (RSL) as isothermal water flows in thin surficial layers driven by gravity and capillary suction, with input from sources in the headwall and loss to evaporation. The principal observables are flow duration and length. At 40% porosity, we find that flow thicknesses reaching saturation can be just 50mm or so and freshwater RSL seasonally require 2–10m3 of H2O per m of source headwall. Modeled water budgets are larger for brines because they are active for a longer part of each day, but this could be partly offset by lower evaporation rates. Most of the discharged water is lost to evaporation even while RSL are actively lengthening. The derived water volumes, while small, exceed those that can be supplied by annual melting of near-surface ice (0.2–2m3/m for a 200-mm melt depth over 1–10m height). RSL either tap a liquid reservoir startlingly close to the surface, or the actual water budget is several times smaller. The latter is possible if water never fully saturates RSL along their length. Instead, they would advance like raindrops on a window, as intermittent slugs of water that overrun prior parts of the flow at residual saturation. Annual recharge by vapor cold trapping might then be supplied from the atmosphere or subsurface.

Online Electrochemical Monitoring of Dynamic Change of Hippocampal Ascorbate: Toward a Platform for In Vivo Evaluation of Antioxidant Neuroprotective Efficiency against Cerebral Ischemia Injury

Effective monitoring of cerebral ascorbate following intravenous antioxidant treatment is of great importance in evaluating the antioxidant efficiency for neuroprotection because ascorbate is closely related to a series of ischemia-induced neuropathological processes. This study demonstrates the validity of an online electrochemical system (OECS) for ascorbate detection as a platform for in vivo evaluation of neuroprotective efficiency of antioxidants by studying the dynamic change of hippocampal ascorbate during the acute period of cerebral ischemia and its responses to intravenous administration of antioxidants including ascorbate and glutathione (GSH). The OECS consists of a selective electrochemical detector made of a thin-layer electrochemical flow cell integrated with in vivo microdialysis. With such a system, the basal level of hippocampal ascorbate is determined to be 5.18 ± 0.60 μM (n = 20). This level is increased by 10 min of two-vessel occlusion (2-VO) ischemia treatment and reaches 11.51 ± 3.43 μM (n = 5) at the time point of 60 min after the ischemia. The 2-VO ischemia-induced hippocampal ascorbate increase is obviously attenuated by immediate intravenous administration of ascorbate (2.94 g/kg) or glutathione (5.12 g/kg) within 10 min after ischemia and the ascorbate level remains to be 3.75 ± 1.66 μM (n = 4) and 5.30 ± 0.79 μM (n = 5), respectively, at the time point of 60 min after ischemia. To confirm if the attenuated hippocampal ascorbate increase is attributed to the antioxidant-induced oxidative stress alleviation, we further study the immunoreactivity of 8-hydroxy-2-deoxyguanosine (8-OHdG) in the ischemic hippocampus and find that the 8-OHdG immunoreactivity is decreased by the administration of ascorbate or GSH as compared to the ischemic brain without antioxidant treatment. These results substantially demonstrate that the OECS for ascorbate detection could be potentially used as a platform for evaluating the efficiency of antioxidant neuroprotection in cerebral ischemia treatment.

A flow electrolysis cell with a thin aqueous phase and a thin organic phase for the absolute determination of trace ionic species

A novel thin-layer electrolysis flow cell based on the ion transfer at the liquid|liquid interface was proposed for the absolute determination of a sub-nanomole ionic species. By using the conducting polymer-coated electrode as an electrode in organic phase, the flow cell was developed as a laminate structure with a thin aqueous layer and a thin organic layer, which were set between an Ag/AgCl electrode and the conducting polymer-coated electrode. Its simple structure made it possible to miniaturize the flow cell, and the required sample volume was reduced to only 1μl. In the present electrolysis cell, both quantitative extraction and quantitative back-extraction of total amount of the ionic species were achieved. This advantage was applied to two methods for absolute determination. One is that by flow injection method, and the other is that by pre-concentration into the thin organic phase followed by back-extraction of the species from the thin Org to the thin aqueous phase (i.e., the stripping technique). In these methods, coulometrical determination of sub-nanomol ionic species was realized without a calibration curve.

Apparent transfer coefficient for ORR at polycrystalline platinum under convection conditions: a potential modulation study

The oxygen reduction reaction has been studied in the thin-layer flow through cell at polycrystalline platinum in 0.5 M H2SO4 at different flow rates. The apparent transfer coefficient (α′) and the corresponding Tafel slope have been calculated using the previously introduced ac voltammetry method [1, 2]. In addition to the correction of the high electrolyte resistance in the thin-layer cell, the contribution from other adsorption processes presented by the adsorption resistance has been also subtracted. The effect of increasing convection on the obtained α′ and Tafel slopes has been examined and it was found that the apparent cathodic transfer coefficient is 0.5 (corresponding to a Tafel slope of −120 mV dec−1) in all cases independent of the flow rate or frequency, suggesting that the first electron transfer to oxygen is the rate-determining step. The difference between Tafel slopes obtained here, i.e., by ac voltammetry method, and that obtained from usual Tafel slopes is due to the potential dependence of oxygen adsorbates, which in the method used here is—at least in part—separated from the potential dependence of the rate constant.

The flow of thin layer of plastic anisotropic material on the surface of elastic half-space

The paper presents the study of problem of a thin layer flow on the surface, limiting the elastic half-space, articulated in the framework of the generalized theory of the flow in a thin layer.

Microfluidic thin-layer flow cell for conducting polymer growth and electroanalysis

The design and fabrication of a low cost and versatile poly(dimethylsiloxane) (PDMS)-glass microchip configured to house an electrochemical thin-layer flow cell is reported. The microchip contains an integrated electrochemical cell comprising a sputtered channel gold working electrode (110μmx5mm) and a reference and auxiliary electrode housed together in the channel outlet. The facile fabrication method allows for the production of fully disposable, gasket-free thin-layer cells for a range of channel depths (35–180μm), that are suitable for low-cost, chip-based electroanalytical applications. The microchip was found to exhibit thin-layer behaviour during a series of voltammetric experiments conducted in ferrocyanide/ferricyanide. The cell was observed to experience a high resistance to current, which was dependent on the distance from the channel working electrode to the auxiliary electrode.Polyaniline (PANI) monoliths were grown electrochemically onto the channel electrode (5mm in length). The thickness of these monoliths was shown to be uniform along the length of the electrode. This demonstrates that the IR drop along the channel was not significant over this electrode length. The growth behaviour of the PANI on-chip was further examined in terms of channel depth and flow rate. It was observed that, under certain flow conditions, PANI monolith thicknesses were limited to approximately half the channel depth being employed. This was attributed to increasing volumetric flow rates during PANI growth. Increasing flow and hence convection rates were due to the displacing of channel volume during voltammetric electropolymerisation of PANI.The microfluidic electrochemical cell incorporating the PANI-modified channel electrode was then used for the amperometric detection of ascorbic acid. When the working channel electrode was placed closest to the channel outlet, the microchip was capable of the detection of ascorbic acid at a sensitivity of 15.7μAmM−1cm−1 which is greater than reported previously under similar conditions.

Indoor allergen assessment quantified by a thin-layer electrochemical cell and magnetic beads

We report the electrochemical determination of mite allergen in real house dust by using a thin layer electrochemical flow cell and magnetic beads. Der p1, which is an allergen from Dermatophagoides pteronyssinus, was immunochemically sandwiched between two dispersed monoclonal antibodies; one was modified on the surface of magnetic beads and the other was modified with alkaline phosphatase. After washing the beads, a small volume of p-aminophenol phosphate (p-APP) was added to produce p-aminophenol (p-AP). And then the p-AP concentration was measured electrochemically with a homemade electrochemical cell. The Der p1 assay was completed within 30min and a low detection limit of 0.3ng/mL was achieved. This is because the diffusion distance of Der p1 and the detection antibody was reduced to 22.3μm by using dispersed magnetic beads. Only 10min was required to complete the entire immunoreaction, and 54% of the Der p1 was confirmed to have immunoreacted in only 1min of mixing. Furthermore, the p-APP volume could be reduced using the thin-layer electrochemical flow cell. This is advantageous in terms of concentrating p-AP, and provides a high signal-to-noise ratio measurement in a short time. We achieved a high correlation (r=0.967, p<0.001) between our assay and a conventional enzyme-linked immunosorbent assay (ELISA) for real house dust measurements.

Development of an acetylcholinesterase immobilized flow through amperometric detector based on thiocholine detection at a silver electrode

This paper describes the use of a commercially available thin-layer flow through a detector with the sensing block customized in an original design for acetylcholinesterase (AChE) immobilization and suitable for inhibition studies by flow injection analysis (FI). AChE was chemically linked onto a gold disk substrate adjacent to a silver disk electrode. The downstream positioned silver electrode, poised at 0.08V vs. Ag/AgCl, KCl 3M, permitted the sensitive amperometric detection of liberated thiocholine (TCh) using acetylthiocholine (ATCh) as enzyme substrate. A typical Michaelis–Menten curve was obtained for ATCh within the concentration range 1×10−5–1×10−2M with a Kmapp of 5.93×10−4M. ATCh quantification was achieved with a limit of detection (LOD) of 5.3×10−6M. The utility of the developed FI setup was demonstrated for AChE inhibition studies using neostigmine as model compound. The IC50 for neostigmine was obtained to be 1.45×10−7M.

Electrooxidation of ethanol on Pt-based and Pd-based catalysts in alkaline electrolyte under fuel cell relevant reaction and transport conditions

Aiming at a detailed kinetic understanding under fuel cell relevant, but nevertheless well-defined reaction and transport conditions, the electrooxidation of ethanol on Pt-based (Pt/C, PtRu black) and Pd-based (Pd/C, Pd/CeO2/C) catalysts in alkaline solution was investigated at temperatures up to 100°C and at controlled electrolyte flow in a high temperature/high pressure thin-layer flow cell. Most important, the data reveal drastic effects of the reaction temperature. The apparent activation energies for ethanol oxidation on the different catalysts were determined and found to vary significantly with potential and the catalyst used. The addition of Ru to Pt and CeO2 to Pd/C improves the tolerance toward catalyst poisoning at low potentials, while for higher potentials and especially at higher temperatures the activity of the monometallic catalysts is higher. For reaction at 0.5V and 80°C, the Pd/C catalyst exhibits the highest activity, both in terms of metal mass specific and active surface area normalized rates; the addition of an oxophilic component is beneficial only for lower potentials. Overall, the results illustrate the need for model studies under close to realistic reaction conditions for the understanding of reactions in fuel cells.

Instant inactivation and rapid decomposition of Escherichia coli using a high efficiency TiO2 nanotube array photoelectrode

Highly ordered TiO2 nanotube (TNT) array film fabricated by anodisation was used as a photoelectrode in a thin-layer photoelectrochemical flow reactor, exhibiting excellent capability of instant inactivation and rapid decomposition of Escherichia coli (E. coli). With photoelectrocatalytic (PEC) treatment, 100% inactivation of E. coli (1.0 × 107 CFU mL−1) can be achieved within 97 s using TNT, which was almost 2.2 times faster than using a TiO2 nanoparticle (TNP) photoelectrode with a similar film thickness. The high efficiency TNT photoelectrode combining with the thin-layer photoelectrochemical flow reactor would be promising for scaling up application to effectively remove waterborne pathogens.

Effects of forcing geometry on two-dimensional weak turbulence

Using high-resolution particle tracking velocimetry, we study the effects of the forcing geometry on the statistics of an electromagnetically stirred thin-layer flow. We consider two forcing arrangements: one that produces a lattice of vortices as a base flow, and one that produces an array of shear bands. We find that the vortex flow drives stronger fluctuating kinetic energy while the shear-band flow leads to more intense fluctuating velocity gradients. We explain our results by considering the spectral flow of energy in the system. Our results have implications for the design of two-dimensional flow experiments.

From Sample Processing to Quantification: A Full Electrochemical Approach for Neutral Analyte Derivatization, Capillary Electrophoresis Separation, and Contactless Conductivity Detection

A thin-layer electrochemical flow cell coupled to capillary electrophoresis with contactless conductivity detection (EC-CE-C(4)D) was applied for the first time to the derivatization and quantification of neutral species using aliphatic alcohols as model compounds. The simultaneous electrooxidation of four alcohols (ethanol, 1-propanol, 1-butanol, and 1-pentanol) to the corresponding carboxylates was carried out on a platinum working electrode in acid medium. The derivatization step required 1 min at 1.6 V vs. Ag/AgCl under stopped flow conditions, which was preceded by a 10 s activation at 0 V. The solution close to the electrode surface was then hydrodynamically injected into the capillary, and a 2.5 min electrophoretic separation was carried out. The fully automated flow system operated at a frequency of 12 analyses per hour. Simultaneous determination of the four alcohols presented detection limits of about 5 × 10(-5) mol L(-1). As a practical application with a complex matrix, ethanol concentrations were determined in diluted pale lager beer and in nonalcoholic beer. No statistically significant difference was observed between the EC-CE-C(4)D and gas chromatography with flame ionization detection (GC-FID) results for these samples. The derivatization efficiency remained constant over several hours of continuous operation with lager beer samples (n = 40).

Buckling of a thin-layer Couette flow

AbstractWe analyse the buckling stability of a thin, viscous sheet when subject to simple shear, providing conditions for the onset of the dominant out-of-plane modes using two models: (i) an asymptotic theory for the dynamics of a viscous plate, and (ii) the full Stokes equations. In either case, the plate is stabilized by a combination of viscous resistance, surface tension and buoyancy relative to an underlying denser fluid. In the limit of vanishing thickness, plates buckle at a shear rate $\gamma / (\ensuremath{\mu} d)$ independent of buoyancy, where $2d$ is the plate thickness, $\gamma $ is the average surface tension between the upper and lower surfaces, and $\ensuremath{\mu} $ is the fluid viscosity. For thicker plates stabilized by an equal surface tension at the upper and lower surfaces, at and above onset, the most unstable mode has moderate wavelength, is stationary in the frame of the centreline, spans the width of the plate with crests and troughs aligned at approximately $4{5}^{\ensuremath{\circ} } $ to the walls, and closely resembles elastic shear modes. The thickest plates that can buckle have an aspect ratio (thickness/width) of approximately 0.6 and are stabilized only by internal viscous resistance. We show that the viscous plate model can only accurately describe the onset of buckling for vanishingly thin plates but provides an excellent description of the most unstable mode above onset. Finally, we show that, by modifying the plate model to incorporate advection and make the model material-frame-invariant, it is possible to extend its predictive power to describe relatively short, travelling waves.

Highly Sensitive Determination of Cadmium and Lead Using a Low-cost Electrochemical Flow-through Cell Based on a Carbon Paste Electrode

A low-cost thin-layer electrochemical flow-through cell based on a carbon paste electrode (CPE), was constructed for the highly sensitive determination of cadmium(II) (Cd(2+)) and lead(II) (Pb(2+)) ions. The sensitivity of the proposed cell for Cd(2+) and Pb(2+) ion detection was improved by using the smallest channel height without the need for any complicated electrode modification. Under the optimum conditions, the detection limits of Cd(2+) and Pb(2+) ions (0.08 and 0.07 µg dm(-3), respectively) were 13.8- and 11.4-fold lower than that of a commercial flow cell (1.1 and 0.8 µg dm(-3), respectively). Moreover, the percentage recoveries of Cd(2+) and Pb(2+) for the in-house designed thin-layer flow cell were higher than those for the commercially available cell in all tested water samples, and within the acceptable range. The proposed flow cell is promising as an inexpensive and alternative one for the highly sensitive monitoring of heavy metal ions.

Quantitative DEMS study of ethanol oxidation: effect of surface structure and Sn surface modification

Using the dual thin layer flow through cell, a semi-quantitative analysis of the volatile products during the electrooxidation of adsorbed and bulk solution of 0.01 M ethanol at polycrystalline platinum, smooth, roughened and Sn modified Pt(11,1,1), Pt(311) electrodes has been done by on-line differential electrochemical mass spectroscopy (DEMS). In addition to the current efficiency of CO(2), that of acetaldehyde was determined as a function of the flow rate. At polycrystalline platinum, ethanol oxidation produces only acetaldehyde; the amount of acetaldehyde further oxidized to acetic acid is negligible due to convection conditions. For comparison and for calibration purposes, i-propanol oxidation was examined for which acetone is the only oxidation product. At Pt(11,1,1), the main oxidation product is acetaldehyde. At Pt(311), in addition to acetaldehyde, acetic acid was also formed. Surface modification with Sn did not increase the reactivity of Pt(11,1,1) instead it led to inhibition of the ethanol oxidation. In the case of Pt(311), the onset potential of oxidation was shifted negatively by 0.2 V in the presence of Sn. The results of the potentiostatic measurements showed that this shift is not associated with the production of CO(2); rather acetic acid and acetaldehyde are the main oxidation products.

Thin layer flow and film decay modeling for grease lubricated rolling bearings

A model is presented to predict lubricant supply layer changes on tracks in rolling bearings due to centrifugal forces and elastohydrodynamic contact pressure. Experimental validation is shown for centrifugal force driven free surface flow, and layer thickness (film thickness) decay in single elastohydrodynamically lubricated contacts. The model allows prediction of lubricant migratory trends in bearings. The pressure ejection driven layer/film thickness decay can be predicted without the need to solve rolling element-raceway starved elastohydrodynamic contact problems for millions of overrollings. The model provides worst case estimates of a required (local) resupply interval, and contributes to improved lubricant related bearing life predictions.

From HCOOH to CO at Pd Electrodes: A Surface-Enhanced Infrared Spectroscopy Study

The decomposition of HCOOH on Pd surfaces over a potential range of practical relevance to hydrogen production and fuel cell anode operation was probed by combining high-sensitivity in situ surface-enhanced IR spectroscopy with attenuated total reflection and thin-layer flow cell configurations. For the first time, concrete spectral evidence of CO(ad) formation has been obtained, and a new main pathway from HCOOH to CO(ad) involving the reduction of the dehydrogenation product of HCOOH (i.e., CO(2)) is proposed.