Effect Of Flow Conditions Research Articles

Influence of Complex Multiphasic Flow on the Thiuram Electrosynthesis in a Microchannel Reactor.

As an important sustainable method for chemical synthesis, organic electrosynthesis experienced a renaissance in recent years for its excellent atom economy. Although microchannel reactors have been proposed to advanced electrosynthesis devices to obtain low energy cost and high reaction performance, the complex multiphasic flow in the electrochemical microchannels are very less reported and the effects of flow condition on the electrosynthesis reaction are less reported. Taking the electrosynthesis of tetraethyl thiuram disulfide (TETD) as a typical case, we developed a visualized electrochemical microchannel reactor equipped with fluorine-doped tin oxide (FTO) loaded glass electrode to investigate the gas-liquid-liquid triple phase flow pattern and the main factors influenced the response current at certain applied cell voltage. The gas-liquid-liquid hybrid flow with low gas hold-up and high liquid flow rate was found crucial for preventing coverage of TETD on the electrode, which provided 23.1 % low current attenuation ratio at 3.0 V cell voltage. The research not only exhibited the complex evolution mechanism of the response current, but also showed the importance of flow condition control for balancing the work efficiency and energy consumption of electrosynthesis process.

The effect of flow conditions on the activity and stability of Pt/LaAlO3 perovskite catalyst during aqueous phase reforming of glycerol

We present a systematic investigation of key reaction parameters (WHSV, hydrogen/gas–liquid ratio, time, pressure) on the activity and stability of Pt/LaAlO3 perovskite catalysts during the aqueous phase reforming of glycerol at 240 °C and 40 bar. Reactor configuration (batch vs continuous) strongly influences product selectivity. While batch conditions promote lactic acid production which contributes to the complete decomposition of LaAlO3 phase and activity loss within 6 h, flow conditions facilitate the hydrogenation of hydroxyacetone and 1,2-propanediol intermediates to improve progression along the desired reforming pathway. After an initial induction period, associated with partial perovskite transformation into LaCO3OH and doubling of Pt nanoparticle size, catalysts remained stable over an extended 30 h experiment. Catalyst activity increased with increasing gas–liquid phase ratio (co-feeding of argon) and particularly after decreasing the reaction pressure into the 2-phase region (20 bar), resulting in 5-fold increase in conversion and complete retention of the LaAlO3 phase.

Effects of flow conditions on the cavitation characteristics of viscous oil around a hydrofoil

Viscous oils, which are media commonly used for fluid power transmission, are characterized by high velocities, temperatures, and pressures when working in fluid components and mechanics. The transient nature of viscous oil makes it susceptible to complex operating conditions, which result in cavitation phenomena and can threaten the normal operation and safety of machinery and components. In this study, a three-dimensional computational fluid dynamics model that accounts for cavitation was developed to study the cavitation characteristics, formation conditions, and development of cavitating flow in viscous oil around a hydrofoil under various flow conditions. Moreover, a visual experimental system in which viscous oil flowed around the hydrofoil was proposed and developed to investigate the cavitation properties with regard to various flow conditions. Both numerical results and experimental data indicated that cavitation occurred on the suction surface of the hydrofoil head, and the cavitation characteristics in viscous oil are significantly influenced by the flow conditions. The maximum vapor volume change rate for the degree of effects on cavitation in viscous oil by flow conditions was calculated to be 1.78 cm3/(m/s), −130.66 cm3/MPa, 0.16 cm3/°C, and 4.52 cm3/°, respectively. Low velocities, high pressures, low temperatures, and small impact angles were proved to be able to suppress cavitation. This study provides a research method, an experimental mean, and data support for cavitation flow of viscous fluids, especially oil. It has significant engineering application significance for the development of fluid machinery.

Computational modeling of blood clot lysis considering the effect of vessel wall and pulsatile blood flow.

Stroke is one of the major causes of global death, which can occur due to blockage in a blood vessel by a clot. The immediate dissolving of the clot is essential to restore the blood flow and prevent tissue necrosis. Clot dissolution can be achieved via thrombolytic therapy using plasminogen activators. In this study, a clot dissolution model is developed for a three-dimensional patient-specific carotid artery that investigates the effect of different vessel wall models on clot dissolution. The lysis pattern of the clot and hemodynamics of blood flow are evaluated using three different models of the vessel wall, namely, rigid, linear elastic, and Mooney-Rivlin hyperelastic. The effect of flow condition is considered by solving the Navier-Stokes equationsfor the free flow domain and the Brinkman equationfor the clot domain with the same pressure and velocity fields. This will result in continuous pressure and velocity over the interfaces of the free flow and clot domains. The blood inflow is assumed to be pulsatile. In addition, the species transport driven by diffusion and convection is considered to be different in the porous medium and plasma. The obtained results show that in all models, the starting time of clot volume decrease is almost the same and the clot starts dissolving from the inner curvature of the artery. However, in the hyperelastic model, dissolving the clot takes longer compared to the other two models. By monitoring the vessel wall deformation, the exact time of vessel recanalization is determined.

Vortex-induced vibration of two circular cylinders in a side-by-side arrangement at moderate Reynolds number: A numerical study

Vortex-induced vibration (VIV) of two transversely vibrating cylinders in a side-by-side (SBS) arrangement is numerically investigated using a combination of direct-forcing immersed boundary and large eddy simulation techniques. The VIV responses of vibrating SBS cylinders at two reduced velocities (UR* = 4.0 and 6.0) are studied for a range of gap ratio 1.0 ≤g*≤ 3.0. Moreover, the influence of mass ratio, damping ratio, and Reynolds number in the amplitude response and efficiency of VIVACE (Vortex-Induced Vibration for Aquatic Clean Energy) from vibrating SBS cylinders are investigated at moderate Reynolds numbers (Re = 1000 and 10 000). The optimal gap ratio for UR* = 4.0 is in the range of 1.0 ≤g*≤ 1.2. Larger than this range, the VIV responses are close to single-cylinder responses. At UR* = 6.0, all gap ratios show lower responses than a single-cylinder case. The vibrating SBS cylinder with a larger damping ratio results in higher maximum VIVACE efficiency with a narrower UR* range for significant efficiency. With almost the same amplitude response, the SBS cylinders with a lower mass ratio result in lower VIVACE efficiency. Using the same mass-damping parameters, it appears that a low mass ratio could be desirable to increase the UR* range of significant VIVACE efficiency and pick the proper damping ratio to reach a high value of maximum VIVACE efficiency. The effect of flow conditions on the amplitude response and VIVACE efficiency of vibrating SBS cylinders with the same VIV parameters is not significant.

Spawning migration behaviour of sea trout (Salmo trutta L.) in a boreal river system: effects of flow conditions and obstacles on migratory activity.

In this study, radio telemetry was used to examine the upstream spawning migration behaviour of anadromous brown trout (sea trout), Salmo trutta L., in a boreal river system, the River Isojoki, western Finland. The aim was to study the movement activity and migration characteristics of trout during the upstream spawning migration, as well as to locate the important spawning habitats and study the spawning characteristics. Furthermore, the authors analysed how flow conditions and a hydropower dam, with adjacent fishways, affected the upstream spawning migration. Tagged trout spawned in both the main stem and four tributaries, with spawning taking place from early October to November. The movement activity of radio-tagged trout was influenced by a hydropower dam (Perus dam), with spring migrators spending prolonged periods at the dam area, postponing the migration upstream. Flow conditions affected the total time spent at the dam area, as well as the movement activity in the free-flowing sections above the dam, with increasing flow stimulating activity. In addition, time of river ascent and location of spawning area had a significant effect on the movement activity of tagged trout. These results are further evidence that synergistic effects of flow and migratory obstacles can negatively influence migrations of anadromous fish, regardless of constructed fishways. The management of flow regimes and the efficiency of fishways are vital, as climate change will likely influence the flow and increase the water temperature of boreal river systems, further aggravating issues caused by obstacles.

Large Eddy Simulation of Film Cooling: A Review

Film cooling has dramatically contributed to the performance improvement of gas turbines, as it is a very effective cooling technique for gas turbines. Large eddy simulation (LES) began to be used in the study of film cooling 20 years ago, and meaningful results have been found, but it has not yet been intensively reviewed. In this review paper, we analyze and introduce about 70 papers published on LES of film cooling over the past 20 years. Numerical instability must be overcome, and realistic inflow must be generated to perform LES of film cooling. This review summarizes how the groups that performed LES of film cooling solved these problems. In film-cooling research, the main topics are improving the film-cooling performance by preventing the lift-off of the injectant and the effect of flow conditions on film cooling. In addition, LES has also been conducted extensively on the above two topics, and this review focuses on them. Finally, turbulence statistics of film-cooling flow obtained from LES are introduced, and future challenges of film-cooling LES are predicted.

Mechanism and Effects of Cellular Creep in a Microfluidic Filter.

Biomicroparticles such as proteins, bacterium, and cells are known to be viscoelastic, which significantly affects their performance in microfluidic applications. However, the exact effects and the quantitative study of cellular viscoelastic creep within different applications remain unclear. In this study, the cellular-deforming evolution within a filter unit was studied using a multiphysics numerical model. A general cellular creep deformation process of viscoelastic particle trapping in pores was revealed. Two featured variables, namely, the maximum surface displacement and the volumetric strain, were identified and determined to quantitatively describe the evolution. The effects of flow conditions and physical characteristics of the microparticles were studied. Furthermore, a Giardia concentration experiment was conducted using an integrated hydraulic filtration system with a porous membrane. The experimental results agreed well with the numerical analysis, indicating that, compared to pure elastic particles, it is more difficult to release cellular material matters including cells, chemical synthetic particles, and microbes from trapping due to their time-accumulated creep deformation.

Effects of flow condition and chute geometry on the shockwaves formed on chute spillway

Abstract Shock waves have undesirable effects, such as excessive dynamic pressure on spillway walls and the extension of flow beyond spillway conduits. To eliminate these detrimental impacts, designers have attempted to detect the characteristics of these waves. Flow interaction with chute piers generates triple waves in the middle walls and sidewalls of spillway conduits. The present study quantitatively investigated the characteristics of these waves with respect to variations in the bottom inclination angle (θ), wall contraction (φ), and Fr numbers (). The results indicated that with the increment of θ, , (φ, ), and (θ, ), the height () and distance () of the first wave increased, which can be helpful for flow aeration. Furthermore, owing to a boost in θ, , (φ, ), and (θ, ), the height of the second wave was decreased. Therefore, the amount of dynamic pressure on the spillway walls was reduced. Moreover, the distance of decreased with a rise in θ, φ and increased with the increment of and (φ, ). As for , raising φ and (φ, ) elevated the height of this wave and declined its distance. An increase in the height of boosted the flow turbulence and aeration.

Experimental study of two-phase flow structure in churn-turbulent to annular flows

The local phase distribution of adiabatic air-water two-phase flow in churn-turbulent to annular flows was experimentally investigated using the Two-Sensor Droplet-Capable Conductivity Probe (DCCP-2). The experiments were performed in a 2.54 cm inner diameter vertical round pipe at downward flows. Twelve flow conditions in churn-turbulent to annular flows were chosen for the current study. The inlet superficial gas velocity ranged from 5.68 m/s to 17.19 m/s, and the inlet superficial liquid velocity ranged from 1.21 m/s to 2.64 m/s. The DCCP-2 is able to distinguish droplets, liquid ligaments, bubbles, and continuous gas. The radial profiles of volume fraction, frequency, axial interfacial velocity, and chord length of droplets, ligaments and bubbles were measured. The experimental results showed that gas volume fraction had a center-peak distribution, and the maximum gas volume fraction in centerline could exceed 95%. The volume fraction of droplets was very low, only on the order of 0.1%. Droplet concentration also showed a center-peak distribution. Both ligament and bubble volume fraction showed a near-wall peak distribution. The ligament volume fraction in the near wall region could reach 80%, which indicated the existence of a film region near the wall and likely includes surface waves on the film. The volume fraction profile of gas, droplets, ligaments, and bubbles showed the tomography structure in churn-turbulent to annular flows. The effects of flow conditions on phase distribution were also studied. An interesting feature was that both the increase of gas flux and the increase of liquid flux tended to increase the bubble volume fraction. The statistical distribution of droplet size was found to be invariant of radial position. The droplet velocity at centerline was generally larger than the superficial gas velocity, which can be attributed to the gravitational effects at downward flows.

Novel microfabricated nozzle array with grooves for microdroplet generation

A novel micronozzle array with grooves was specially designed for high-throughput microdroplet generation and high-efficiency mixing of heterogeneous systems without surfactants. The microgrooves, with a width of 25 μm between micropores, could significantly prevent the dispersed phase from spreading on the membrane surface and reduce the microdroplet size and polydispersity at sufficiently high fluxes of the dispersed phase. Through different oil–water systems, the effects of flow conditions, system physical properties, and flow patterns on droplet size were investigated in the micronozzle array device. Under the jetting flow pattern, the n-hexane, dichloromethane, and ethyl acetate droplets could obtain average diameters of 35 μm, 31 μm, and 24 μm, respectively, and the coefficient of variation was between 20% and 40%. The dripping and jetting flow regions were demarcated to fully understand the transition of the flow pattern. Furthermore, a droplet size prediction model was established based on force equilibrium. The micronozzle array proposed in this work has great potential for future practical applications.

Parametric study of the {beta }-{sigma } two-fluid model for simulating fully suspended slurry flow: effect of flow conditions

As proven in a recently published paper [Messa GV, Matoušek V (2020) Analysis and discussion of two fluid modelling of pipe flow of fully suspended slurry. Powder Technol 30:747-768.], the beta-sigma two-fluid model is capable of accurately reproducing the main features of turbulent, fully-suspended slurry flows in horizontal pipes provided that suitable values of the two parameters beta and sigma are chosen. At present, the case-specific nature of beta and sigma and their lack of a clear physical meaning are the main obstacles that must be overcome to give the beta-sigma two-fluid model value not only as interpretative tool, but also as a predictive one. An important preliminary step to achieve this goal is to disclose the mathematical essence of the beta-sigma two-fluid model, namely, to interpret the fluid-dynamic solution on the grounds of the structure of the differential and discretized equations. Such a methodological approach is applied here to the benchmark case of turbulent slurry flow between two infinite, horizontal, parallel plates, focusing, in particular, on the influence of the bulk-mean velocity of the slurry and the volumetric concentration of the solids in the flow. The study provides not only deeper insight into the beta-sigma model, but also indicates important implications for alternative two-fluid models.

Micro‐computed tomography for the 3D time‐resolved investigation of monodisperse droplet generation in a co‐flow setup

AbstractDroplet generation in microfluidic devices has emerged as a promising approach for the design of highly controllable processes in the chemical and pharmaceutical industry. However, droplet generation is still not fully understood due to the complexity of the underlying physics. In this work, micro‐computed tomography is applied to investigate droplet formation in a circular channel in a co‐flow configuration at different flow conditions (Ca < 0.001). The application of an in‐house developed scanning protocol assisted by comprehensive image processing allows for the time‐resolved investigation of droplet formation. By tracking different droplet parameters (length, radii, volume, surface, Laplace pressure) the effect of flow conditions on droplet progression is determined. As characteristic for the squeezing regime, final droplet size was nearly independent of Ca for higher Ca tested. For lower Ca, the final droplet size increased with decreasing Ca, which points to the leaking regime that was recently introduced in the literature.

Effect of Flow Condition on the H2S Corrosion Inhibition of a Supermartensitic Stainless Steel with a Gemini Surfactant

A nonionic Gemini surfactant obtained from palm oil has been used as corrosion inhibitor of UNS S41425-type supermartensitic stainless steel in an H2S-containing environment under hydrodynamic conditions at 50 °C. Techniques involved potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy measurements. Results have shown that under static conditions, the best inhibitor performance was obtained by applying 25 ppm and it affected both anodic and cathodic electrochemical reactions. Under hydrodynamic conditions, in the absence or presence of inhibitor, the corrosion rate increased with an increase in the rotating speed due to an enhancement in the reactants and inhibitor mass transfer.

Optimization and analysis of inverse design method of maximum thrust scramjet nozzles

With the development of scramjet engines and hypersonic vehicles, the importance of the scramjet nozzle has become increasingly prominent. Many studies have attempted to increase the aerodynamic performance of nozzles. Under this circumstance, an inverse design method on the scramjet nozzle has been proposed on the basis of maximum thrust theory. The effectiveness and flexibility of the proposed method have been verified. As an inverse method, the target (i.e., the flow conditions on the key point) is a primary factor in the design process that significantly affects the performance and geometry of the nozzle. The present study investigates the influence of the key point on the shapes and performance of the nozzles. It aims to obtain a relative universal design principle in the inverse design process. First, the inverse design method is introduced briefly to facilitate understanding of the background. Second, the design of experiment (DOE) technique is presented, which can be used to study the effect of factors on the responses. Third, the effects of flow conditions, including Mach number, flow deflection angle, and ratio of mass flow rate, are investigated. The major factors on the thrust, lift, and nozzle length are distinguished successively. The thrust is mainly affected by the Mach number and flow deflection angle. The lift and nozzle length are dominated by the Mach number and ratio of mass flow rate. The influence of the flow deflection angle on the lift and length is negligible. Finally, the conclusion obtained from the DOE study is utilized to optimize an actual nozzle design process. The aerodynamic performance and geometrical configuration of the nozzles can be adjusted quickly. Combined with the inverse design concept, a fast and comparatively accurate design method on scramjet nozzle is formed.

Numerical study on charging characteristics of heat pipe-assisted cylindrical capsule for enhancing latent thermal energy storage

The charging characteristics of a cylindrical Encapsulated Phase Change Material (EPCM) capsule with embedded heat pipe (HP) is investigated numerically for latent heat storage. For the heat pipe-assisted capsule, called EPCM-HP unit, a 3-D transient thermal storage model is implemented combining Lumped Thermal Resistance Network (LTRN) as the heat pipe model with conventional enthalpy-porosity approach as phase change model. The effects of flow conditions (laminar and turbulent), heat pipe condenser length and types of HTFs (Therminol/VP-1 and air) on thermal characteristics of the EPCM-HP unit are simulated, respectively. Results show that embedding heat pipe can reduce the total charging time by 11.26%. The charging process under turbulent flow is more than 10 times faster than that under laminar flow. Increasing the condenser length of heat pipe cannot effectively reduce the charging time of ECPM-HP unit since the thermal resistance also increases and the starting time of convection is delayed. The results also reveal that Therminol/VP-1 (high Pr HTFs) can charge thermal energy faster than air (low Pr HTFs), while the enhancement effect of heat pipe is more significant when using air (low Pr HTFs).

Effect of flow condition of heat exchange medium on temperature profile of magnetic heat pump

Effect of flow condition of heat exchange medium on temperature profile of magnetic heat pump

Changes in milk fat globules and membrane lipids under the shear fields of microfiltration and centrifugation

This study compared the efficiency of centrifugal and microfiltration separation of milk fat globules (MFG) from bovine cream and the changes that take place in the corresponding lipid membranes (MFGM). Creams were washed with water (1:10) and subjected to either centrifugation or microfiltration to fractionate proteins and other non-fat milk components. Protein analyses of the obtained fractions were carried out by gel electrophoresis. Lipid extraction and thin layer chromatography were also employed to separate lipid types and the amount of polar lipids were determined by gas chromatography. The effect of flow conditions on MFG's colloidal properties and MFGM components was evaluated based on estimates of the average rate of energy dissipation in microfiltration and centrifugation processes. Both were equally effective in removing the protein fraction (93% yield) as well as non-fat dry matter (~100% removal). Microfiltration reduced the mean particle size by 0.3 µm, whereas the opposite was observed for centrifugal separation (average size increase by 0.8 µm). The latter process also induced a more significant reduction in the electrostatic charges (zeta potential) of the colloids in the cream, which relates to the changes in the milk fat globule surface composition and the release of MFGM components. The dissociated polar lipids amounted to 24% and 20% upon centrifugation and microfiltration, respectively. Overall, the results suggest that MFG and MFGM are partially damaged under the shear forces typical of centrifugal and microfiltration separation. A high separation efficiency, with minimal fat globule damage and high MFGM yield is possible by adopting microfiltration under carefully optimized conditions.

Pro-atherosclerotic disturbed flow disrupts caveolin-1 expression, localization, and function via glycocalyx degradation

BackgroundEndothelial-dependent atherosclerosis develops in a non-random pattern in regions of vessel bending and bifurcations, where blood flow exhibits disturbed flow (DF) patterns. In contrast, uniform flow (UF), normal endothelium, and healthy vessel walls co-exist within straight vessels. In clarifying how flow protectively or atherogenically regulates endothelial cell behavior, involvement of the endothelial surface glycocalyx has been suggested due to reduced expression in regions of atherosclerosis development. Here, we hypothesized that pro-atherosclerotic endothelial dysfunction occurs as a result of DF-induced reduction in glycocalyx expression and subsequently impairs endothelial sensitivity to flow. Specifically, we propose that glycocalyx degradation can induce pro-atherosclerotic endothelial dysfunction through decreased caveolin-1 and endothelial nitric oxide synthase expression and localization.MethodsWe studied endothelial cells in atherosclerotic-prone DF and atherosclerotic-resistant UF conditions in parallel plate flow culture and in C57Bl/6 mice. The effects of flow conditioning on endothelial cell behavior were quantified using immunocytochemistry. The glycocalyx was fluorescently labeled for wheat germ agglutinin, which serves as a general glycocalyx label, and heparan sulfate, a major glycocalyx component. Additionally, mechanosensitivity was assessed by immunocytochemical fluorescence expression and function of caveolin-1, the protein that forms the mechanosignaling caveolar invaginations on the endothelial surface, total endothelial-type nitric oxide synthase (eNOS), which synthesizes nitric oxide, and serine 1177 phosphorylated eNOS (eNOS-pS1177), which is the active form of eNOS. Caveolin function and eNOS expression and activation were correlated to glycocalyx expression. Heparinase III enzyme was used to degrade a major glycocalyx component, HS, to identify the role of the glycocalyx in caveoin-1 and eNOS-pS1177 regulation.ResultsResults confirmed that DF reduces caveolin-1 expression and abolishes most of its subcellular localization preferences, when compared to the effect of UF. DF down-regulates caveolin-1 mechanosignaling, as indicated by its reduced colocalization with serine 1177 phosphorylated endothelial-type nitric oxide synthase (eNOS-pS1177), a vasoregulatory signaling molecule whose activity is regulated by its residence in caveolae. As expected, DF inhibited glycocalyx expression compared to UF. In the absence of heparan sulfate, a major glycocalyx component, UF-conditioned endothelial cells exhibited near DF-like caveolin-1 expression, localization, and colocalization with eNOS-pS1177.ConclusionsThis is the first demonstration of a flow-defined role of the glycocalyx in caveolae expression and function related to vasculoprotective endothelial mechanosensitivity that defends against atherosclerosis. The results suggest that a glycocalyx-based therapeutic targeted to areas of atherosclerosis development could prevent disease initiation and progression.

Removal of organic matter in stormwater ponds: a plug-flow model generalisation from waste stabilisation ponds to shallow rivers

ABSTRACTThis study investigates the effect of flow conditions on the organic matter concentration, removal efficiency, and reaction kinetics in a stormwater pond in Fortaleza, Brazil. As a result of unauthorized sewage discharges, BOD and COD concentrations were similar to those of combined sewer systems. The concentrations remained roughly the same during the rainy season, which was attributed to sewage network overflow. Removal efficiencies ranged from 70–90%, similar to primary facultative ponds. Fitting different hydraulic models to the field data, it was possible to obtain BOD and COD removal rates that could be described as functions of the Reynolds number. The best fit was achieved considering the plug-flow assumption, and a general BOD model including data reported in the literature for waste stabilisation ponds, stormwater ponds and shallow rivers was derived. Lastly, simulations with this general model were performed to assess the impact of remediation measures on the studied pond.