Laminar Flow Research Articles

Verification of the Inverse Scale Effect Hypothesis on Viscosity and Diffusion by Azo-Amino Acid Schiff Base Copper Complexes

Microdroplets generated in microfluidic devices are attracting attention as a new chemical reaction field and are expected to improve reactivity. One of the effects of microscaling is that the ratio of the force that acts on the diffusion and movement of substances to gravity is different from that of ordinary solvents. Recently, we proposed a hypothesis for determining reaction acceleration through micro-miniaturization: If a reaction is inhibited by setting the volume and viscosity of the solution to conditions that are unfavorable to the reaction on a normal scale, that reaction can be promoted in microfluidics. Therefore, for the purpose of this verification, (1) we used an amino acid Schiff base copper(II) complex with an azobenzene group to demonstrate the polarization-induced orientation in a polymer film (the redirection that is mechanically maintained in a soft matter matrix). Numerical data on optical anisotropy parameters were reported. (2) When the reaction is confirmed to be promoted in laminar flow in a microfluidic device and its azo derivative, a copper(II) complex is used to increase the solvent viscosity or diffusion during synthesis on a normally large scale. We will obtain and discuss data on the investigation of changing the solvent volume as a region. The range of experimental conditions for volume and viscosity did not lead to an improvement in synthetic yield, nor did (3) the comparison of solvents and viscosity for single-crystal growth of amino acid Schiff base copper(II) complexes having azobenzene groups. A solvent whose viscosity was measured was used, but microcrystals were obtained using the diffusion method.

Effect and mechanism of solution flow rate during interfacial polymerization on morphology and performance of hollow fiber membranes

Interfacial polymerization (IP) using m-phenylenediamine and trimesoyl chloride (TMC) is an essential method for producing thin-film composite (TFC) membranes. Nevertheless, IP is highly sensitive to changes in process parameters, especially the TMC solutions flow rate during inside-out TFC hollow fibers (HF) production. Research on the impact of flow conditions (i.e., laminar vs. turbulent flows) of these organic solutions on the final membrane characteristics and corresponding mechanism is still lacking. This research tested different TMC flow rates (0.1–2 mL/min) to produce inside-out TFC HF. With a TMC flow rate increase, (i) the leaf-like structures of the polyamide (PA) layer decreased in size, (ii) the thickness of the PA layer slightly increased, and (iii) the pure water permeability decreased. However, the elemental composition, chemical bonds, and NaCl rejection remained stable. Different fluid regimes are considered to affect the performance of HF membranes by affecting the heat dissipation process during IP reaction. A TMC flow rate in the laminar flow state (i.e., low flow rates) is recommended for synthesizing HFs. The current research provides new insights into the IP reaction mechanism of HF membrane, thus offering valuable guidance to optimize and produce membrane products with better performance.

Experimental study on flow-induced vibration under laminar flow and turbulent flow transition state in helical coiled tube

This study investigates the vibration characteristics induced by single-phase flow at low velocities within helical coiled tube, encompassing laminar and turbulent flow transition regimes. Modal experiments were conducted to ascertain the natural frequencies in the radial and vertical directions within the helical coiled tube. The influence of fluid mass in tube on vibration was considered, revealing the fluid mass has a greater influence on the vibration frequency in the vertical direction. When the coil was filled with water, the radial natural frequency decreased by 0.1 Hz, while the vertical natural frequency decreased by 0.8 Hz.By simplifying the spiral coil into a spring system, the intrinsic causes of the influence of mass on the natural frequency are studied and verified with the experimental data. The results show that the radial natural frequency is only related to the local mass change of the pipe, while the vertical natural frequency is related to the static deformation of the system under the influence of gravity.By conducting single-phase flow induced vibration experiments inside the pipeline, the radial and vertical vibration response characteristics were obtained, and the modal experimental results were analyzed. Findings indicated larger vibration displacements when laminar flow prevailed within the tube, with radial RMS (Root Mean Square) at 10.1 μm and vertical RMS at 14.5 μm. After the transition to turbulent flow, significant reductions in vibration displacements were observed, reducing the radial RMS to 2.3 μm and vertical RMS to 5.5 μm.Based on statistical and frequency-domain analysis methods, the influence mechanism of secondary flow on the vibration of helical coils at low flow rates was revealed, and the importance of friction coupling was clarified. Moreover, this study considered the impact of fluid viscosity on vibration response and experimentally validated the critical role of friction coupling in exciting secondary flows.

Embedded large eddy simulation of boundary layer transition behind a micro-ramp

Boundary layer transition induced by surface roughness elements plays an important role in aerodynamic and aero-thermodynamic design of subsonic/supersonic/hypersonic vehicles. However, the effect of three-dimensional isolated roughness element in the process of promoting/suppressing boundary layer transition is far from being fully understood, particularly in the incompressible laminar flow. In the present study, the laminar-to-turbulent transition induced by a three-dimensional isolated micro-ramp element immersed in an incompressible laminar boundary layer is investigated numerically. The embedded large eddy simulation (ELES) combining the intermittency transition model and the wall-modeled large eddy simulation (WMLES) S − Ω model is employed for the first time. Numerical results on the time-averaged/instantaneous flow field and the statistical flow fluctuations are analysed and validated thoroughly by the existing experimental measurements. It is found that the interaction of the secondary and the tertiary streamwise vortices causes a high level of wall shear and an inflectional velocity distribution in the near-wall region. An additional eddy system that develops nonlinearly from the unstable inflectional flow may trigger the boundary layer transition. The present study validates that the ELES combined with the WMLES S − Ω model is an efficient simulation tool for industrial wall-bounded flows allowing effective compromise between flexibility, cost, and accuracy.

Influence of Surface Roughness on Symmetric Airfoil Flow Properties and Reynolds Number

Collaborative Aircraft Design Optimization: Investigating Roughness Management of Wings to Reduce Drag and Improve Performance This study investigates the potential of roughness control of aircraft wings based on joint design optimization. By adding roughness points to specific wings, our goal is to reduce drag and improve the overall performance of the aircraft. A multi-modal design optimization (MDO) framework combining aerodynamics, modelling, and performance analysis was used in this study. We measure the effect of tissue on the boundary layer, the progression of laminar flow, and the potential for weight savings due to reduced friction. This study investigates how roughness control interacts with other design factors such as flow components or blade materials to achieve optimal performance. The ultimate goal is to create a collaborative design that uses tissue management to contribute to next-generation fuel efficiency and high performance. Keywords – CFD, Surface Roughness, Wind Tunnel, Aerodynamic Efficiency.

Eleven Years After Scimitar Syndrome Repair With the Lugones Technique: Usefulness of Four-Dimensional Flow Magnetic Resonance Imaging.

Anatomic and physiologic assessment of surgical repair of scimitar syndrome can be challenging. We evaluated the first patient who underwent the Lugones procedure in 2012 using 4D flow magnetic resonance imaging. With this technology, we demonstrate that the reconstructed right pulmonary venous return drains into the left atrium with laminar flow, just as normal pulmonary veins do.

Characteristics of turbulent core–annular flow with water-lubricated high viscosity oil in a horizontal pipe

Direct numerical simulations are performed to investigate the characteristics of a turbulent core–annular flow with water-lubricated high viscosity oil in a horizontal pipe. Six different superficial velocity ratios ( $\,j_w/j_o = 0.057\unicode{x2013}0.41$ ) are examined by changing the water superficial velocity $j_w$ for a fixed oil superficial velocity $j_o$ . The pressure drops in the pipe and the shapes of the phase interface agree well with those from previous experiments. The oil core flow is almost a plug flow, and the gaps between the phase interface and pipe wall are narrow and wide near the upper and lower surfaces of the pipe, respectively, due to the buoyancy. Within a narrow gap, water is confined mostly in a valley region of the wavy phase interface and hardly goes through its crest. On the other hand, water near the phase interface at a wide gap convects downstream almost at the core speed and the flow near the wall is similar to that of single-phase wall-bounded turbulent flow. The annular flow is characterized by three different regimes depending on the clearance Reynolds number ( $Re_c$ ) based on the core velocity and local gap size: laminar Couette flow driven by the core for $Re_c \le 600$ , transitional flow for $600 < Re_c < 2500$ and turbulent flow for $Re_c \ge 2500$ . The minimum pressure drop occurs at $j_w/j_o = 0.11$ in the early transition regime. For all $j_w/j_o$ considered, the negative lift force acting on the core comes from the pressure force which balances the buoyancy.

Simulation of enhancement techniques impact on fluid dynamics and thermal mixing of laminar forced convection flow

Simulation of enhancement techniques impact on fluid dynamics and thermal mixing of laminar forced convection flow

Similar Solutions for Changing Characteristics of Natural Convection Laminar Flow around a Vertical Rectangular Inclined Plane Surface

The study investigates laminar natural convection flow around a vertical rectangular inclined plane surface, specifically focusing on the effects of viscous and pressure stress work. Previous research primarily addressed these effects in two-dimensional natural convection flow scenarios, while this study extends the analysis to encompass three exterior situations, accounting for variations in fluid properties outside compressible boundary layers. Employing numerical methods, the study aims to predict essential flow parameters including Prandtl’s number (Pr), controlling parameter (C), and additional parameters (A, B, D, E, ∅). The investigation yields velocity profiles (F'(0), S'(0)), temperature profiles , skin frictions (F''(0), S''(0)), and heat transfer coefficients θ'(0). Numerical results are presented to illustrate the impact of different parameters on these flow characteristics. Additionally, tabulated data in Tables-2 and Tables-3 offer further insights into the predicted flow parameters and their variations under varying conditions.

The effect of high values of relative surface roughness on heat transfer and pressure drop characteristics in the laminar, transitional, quasi-turbulent and turbulent flow regimes

AbstractThis study investigated the effect of large values of relative surface roughness on the heat transfer and pressure drop characteristics using simultaneously measured heat transfer and pressure drop data. Experiments were conducted using a horizontal circular tube with a base inner diameter of 5 mm and length of 4 m. One smooth and two rough tubes, with relative roughnesses of 0.04 and 0.11, were tested at different constant heat fluxes between Reynolds numbers of 100 and 8 500. Water was used as the test fluid and the Prandtl number varied between 3 and 7. Contrary to the trend in the Moody Chart, a significant increase in laminar friction factors with increasing surface roughness was observed. Both the friction factors and Nusselt numbers as functions of Reynolds number showed a clear upward and leftward shift with increasing surface roughness across the different flow regimes. Furthermore, the boundaries between the flow regimes were the same for the pressure drop and heat transfer results. The width of the transitional flow regime was narrower for rough tubes and had a differing trend. The quasi-turbulent and turbulent flow regimes occurred at lower Reynolds numbers for increasing roughness. When investigating the relationship between heat transfer and pressure drop, it was found that an increase in surface roughness favoured heat transfer in the quasi-turbulent flow regime. This is useful for rough tubes as the quasi-turbulent flow regime onsets early with regards to the Reynolds number in tubes with large roughnesses.

CFD simulation of liquid food flow in a coiled tube UVC reactor

The coiled tube reactor is the most efficient UVC reactor for disinfecting microorganisms in liquid food flow. Thus, it is critical to investigate the effective parameters for designing a coiled tube UVC reactor. In this study, CFD simulation is used to investigate the turbulent and laminar flow of Newtonian and non-Newtonian fluids. In turbulent flow, disinfection in the tube area is nearly uniform, with the exception of regions near internal lamps, where the most disinfection has occurred. The variation of log10 reduction in terms of tube turn number is linear. Increasing the non-Newtonian behavior increases the disinfection of microorganisms in the reactor. Furthermore, the effect of tube diameter on coiled reactor performance is investigated. Reducing the diameter of the reactor's tubes improves its performance. Finally, two correlations are obtained for the influence of the effective parameters on the log10 reduction of this type of reactor.

Pollution by total suspended solids and its relationship with the liquid-solid flow of the lower basin of Usumacinta River in Tabasco, Mexico

Rivers are natural environments that collect water from basins and transport it in laminar flow to the sea. Gradual changes occur due to the erosion of the walls and the bottom of rivers and the deposition of solids that the current carries. In the Usumacinta River basin, there is a sinusoidal correlation between liquid and solid flow. The term solid flow refers to the amount of sediment in motion, gaining its name from the product between liquid flow and the concentration of suspended solids. 21 simple samples of surface water were taken from June to December 2017, in the municipalities of Tenosique, Emiliano Zapata and Jonuta, in the state of Tabasco, Mexico. The concentrations of total suspended solids exceed the maximum permissible limits of the NOM-001-SEMARNAT-1996 (Mexico), for urban public use. Moreover, according to CE-CCA-001/89 (Ecological Water Quality Criteria in Mexico), the surface water of the lower basin of the Usumacinta River is classified as polluted.

Local analysis of micro mixing for the Villermaux-Dushman protocol by using the imaging UV-Vis spectroscopy

The Villermaux-Dushman protocol with UV-Vis analytics is an established tool to characterize the global micro mixing performance in process equipment. The local mixing process is described by a micro mixing model (incorporation model), originally designed for turbulent flows. The novel imaging UV-Vis spectroscopy used in this work uncovers locally resolved micro mixing phenomena in a laminar split-and-recombine (SAR) mixer unit manufactured from selective laser-induced etching (SLE). The local absorbance is recorded with a high spatial resolution camera through a telecentric lens and post-processed into local concentration fields of components. The method unveils discrepancies of the micro mixing time determined from the conventional incorporation model in laminar flow and the locally recorded mixing process. The micro mixing time rather needs to be seen as a mean micro mixing time instead. Furthermore, the spatial information obtained by the imaging UV-Vis spectroscopy gives insight into local micro mixing and selectivity, yielding new approaches to equipment optimization.

Comparative examine of fluid pressure within microchannel through integrated cantilevers for microfluidic applications

This paper aims to explore the concept of a microfluidic pressure sensing mechanism across a microchannel, integrated with different structures of microcantilevers. Various structures of microcantilevers are integrated into a microchannel where laminar fluid flows and the microcantilever senses the fluid velocity and pressure. The different structures of the microcantilever include rectangular, T-shaped, and Pi-shaped designs, which are placed at the centre of the microchannel. The 2D microchannel has a length of 4000 μm and a height of 840 μm, while the microcantilever is positioned at a distance of 2000 μm from the inlet of the microchannel. The analysis of the fluid sensor is observed by plotting graphs of velocity, pressure, displacement of the microcantilever, Reynolds number, and friction factor with respect to the time domain. An inlet velocity of 8.33 µm/s is applied at the microchannel, and the fluidic sensor shows a significant change in the fluid characteristics, comparing them across all types of microcantilevers. The simulation results show that the T-microcantilever has a maximum displacement of 4.97 µm compared to other microcantilevers, with a maximum pressure of 1.58 Pa for the Pi-cantilever. The integrated device is suitable for healthcare applications, measuring fluid pressure in syringes, where the T-microcantilever proves to be more compatible than the other two microcantilevers (R-cantilever and Pi-cantilever). The design and simulation of the microfluidic pressure sensing process are conducted using the FEM tool COMSOL Multiphysics.

Compressed neural networks for reduced order modeling

Reduced order modeling (ROM) techniques, such as proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), have been widely used to analyze stationary flows. Neural networks such as autoencoders are effective to reduce the dimension of non-stationary flow, but their larger storage requirements compared to POD and DMD compromise the expectations on ROM. The present work aims at compressing the autoencoder model via two distinctively different approaches, i.e., pruning and singular value decomposition (SVD). The developed algorithm is then applied to reconstruct the flow fields of typical stationary (i.e., a laminar cylinder flow and two turbulent channel flows) and non-stationary (i.e., a laminar co-rotating vortex pair) examples. It is shown that pruning and SVD reduce the size of the autoencoder network to 6% and 3% for the two simple laminar cases (or 18% and 13%, 20%, and 10% for the two complex turbulent channel flow cases), respectively, with approximately the same order of accuracy. Therefore, the proposed autoencoders optimized by the network pruning and SVD lead to effective ROM of both stationary and non-stationary flows although they require more iterations to converge than conventional methods.

Investigation of the local apparent viscosity in a stirred tank with a shear-thinning fluid through Particle Image Velocimetry.

The local apparent viscosity in a cylindrical stirred tank was investigated using Particle Image Velocimetry in a shear-thinning fluid. Two impellers were studied, a Rushton turbine for validation and an axial impeller HTPG4, for three Reynolds numbers corresponding to the transition regime between laminar and turbulent flows. Mean and instantaneous velocity contours and profiles are analysed. Then, the different contributions to the mean total kinetic energy are investigated with the HTPG4 impeller. The sensitivity of the mean apparent viscosity to the method of determining the shear rate is discussed. This work shows that the mean apparent viscosity is highly sensitive to the method of determining the shear rate. Future work will focus on improving the measurement of the local shear rate.

Analysis of the shear-driven flow in a scale model of a phase separator: Validation of a coupled CFD approach using experimental data from a physical model

The effects of shear stress at the interface between a flowing gaseous phase and a liquid-filled cavity, a scenario commonly found in flue gas/slag phase separators are investigated in this study. This effect is frequently disregarded in computational fluid dynamics (CFD) simulations within metallurgy, primarily due to its limited influence on the motion of liquids (e.g., slag, liquid metal) when compared to other factors such as stirring by natural convection or bubbling. This study was undertaken to investigate shear-driven flow in a 1:4 scale model of a phase separator in which a flue gas stream coming from a furnace is mobilizing the flow of a slag melt. To cover a wide range of operating conditions, silicone oil with varying viscosities (20, 50, and 70 cSt) was considered for mimicking viscous slag. Additionally, different volumetric airflow rates (18, 27, and 36 m3/h) were considered to simulate the flue gas flow. Particle image velocimetry (PIV) measurements were conducted on the model. The experimental results were utilized to validate computationally efficient, coupled steady-state simulations of the system. Notably, the steady-state simulations, requiring approximately one hour of CPU time, demonstrated a computation time decrease of two magnitudes compared to conventional Volume of Fluid (VOF) modeling. A stable, laminar flow pattern of the liquid phase with surface velocities of up to approximately 30 mm/s was observed for the case with the lowest oil viscosity and the highest airflow rate, while a steady, turbulent flow was observed in the gas phase. Conversely, the lowest surface velocities, measuring around 5 mm/s, were recorded and calculated for the scenario with the highest oil viscosity and the lowest airflow rate. It was noted that velocities increased proportionally with the airflow rate but exhibited a disproportionate relationship with oil viscosity. The prediction of velocity magnitudes by the steady-state CFD model was highly accurate, with only minor discrepancies observed between the measured and calculated flow patterns. In summary, valuable insights into the often-overlooked shear stress effects at the phase boundary in gaseous-liquid flow over a cavity are provided by our study.

Influence of porosity properties on natural convection heat transfer in porous square cavity

A numerical investigation was conducted to examine free convection heat transfer within a square cavity containing a fluid-saturated porous layer at the bottom under laminar flow conditions. The enclosure's left and right walls experienced heating and cooling, while the top and bottom walls remained adiabatic. The study explored the influence of the Darcy number, porosity number, and dimensionless thickness of the porous layer on heat transmission. This investigation utilized a FORTRAN computation program alongside the finite volume method, effectively solving the equations governing flow and heat exchange within porous materials through natural convection. The flow pattern is determined by the Navier–Stokes equations in the fluid region and the Darcy–Brinkman–Forchheimer formula in the porous region. The energy equation was employed to compute the thermal field. The increase in the Darcy number results in both an increase in heat transfer rate due to enhanced fluid flow through pores and an intensification of fluid flow patterns. Higher porosity leads to higher heat transfer rates due to greater fluid penetration and an increased surface area for heat exchange. The thicker porous layer reduces heat transfer rate due to increased resistance to fluid flow and decreased contact area.

A Simplified Approach for Calculating Heat Transfer Coefficients for Fluid Guiding Elements with Alternating Redirections of Flow

AbstractFluid guiding elements (FGEs), additive manufactured inserts that enhance heat transfer, have shown the potential to reduce the size of pipe‐in‐pipe heat exchangers up to a factor of 20. Due to their unique design, the calculation of the geometrical parameters for a specific application remains challenging and was initially solved by computationally expensive computational fluid dynamics simulations. This work presents a simplified approach, which treats the fluid and the FGE as pseudo‐homogeneous to enable the fast calculation of effective heat transfer coefficients. The approach is developed based on water in laminar flow state and subsequently tested with different fluids.

Effect of cross-flow on heat and mass transfer rates at the outer surface of a spiral tube placed in a cylindrical container and possible application in heat exchanger/reactor design

This research investigates the effect of cross-flow on heat and mass transfer rates at the outer surface of a spiral tube placed in a cylindrical container and its potential application in heat exchanger/reactor design. The study evaluates various parameters such as solution velocity, spiral tube diameter, and pitch through electrochemical methods under laminar flow conditions. Results indicate that the mass transfer coefficient increases with rising solution velocity but decreases with larger spiral tube diameters and pitches. A dimensionless equation is proposed to correlate the mass transfer data for a single spiral tube, which proves valuable for designing and scaling up heat exchanger/reactor systems. The research also highlights the dual functionality of the spiral tube, with the outer surface serving as a catalyst support for an exothermic, diffusion-controlled liquid-solid reaction, while the inner surface acts as a cooler, efficiently absorbing heat generated on the outer surface. The study explores the application of this novel reactor design for heat-sensitive materials and processes requiring swift cooling, such as immobilized cell or enzyme biochemical reactions. The findings contribute to enhancing reactor productivity and achieving high selectivity and yield in electro-organic synthesis.