Laminar Flow Behavior Research Articles

Fluid Dynamics Effects of a Porous Blockage on Laminar Flow in the Interior Subchannels of a 61-Pin Wire-Wrapped Rod Bundle

Flow blockages in Liquid Metal Fast Reactor (LMFR) fuel assemblies that can cause fuel pin cladding failures require further investigation for the development and optimization of these Generation IV reactor designs. The objective of this study was to experimentally evaluate the effects of a porous blockage accident scenario on laminar flow behavior in the interior subchannels of a prototypical 61-pin wire-wrapped rod bundle. The laminar flow condition is considered because of its importance to natural circulation and loss-of-coolant-accident operating scenarios as well as the limited availability of experimental data. The matched-index-of-refraction method was utilized to obtain two-dimension two-component time-resolved particle image velocimetry (TR-PIV) measurements at three planes centered on blocked and neighboring subchannel regions. Time-averaged first-order and second-order statistics, computed by Reynolds decomposition, were visualized including the mean and fluctuating streamwise and spanwise velocity components. Line profiles described the evolution of flow from upstream regions, to separated flow, and recombination downstream, while a modified Galilean decomposition distinguished differences between flow in the blocked measurement plane and flow in its neighboring counterpart region. Spatial-temporal cross-correlations were performed for the streamwise velocity fluctuations to characterize the convection velocity and decay of traveling vortices in the wake of the porous blockage. The isothermal TR-PIV measurements from this study provide high-fidelity experimental data sets for the validation of computational models and numerical studies to characterize complex fluid phenomena in wire-wrapped rod bundles during the potential accident scenario of a porous, interior flow blockage.

Entropy generation analysis and thermal synergy efficiency in the T-shaped micro-kenics

In this work, three different twist angles of a micro helical insert in a T-shaped are studied numerically in order to evaluate the laminar steady flow behavior of Newtonian fluid in chaotic geometry. In the geometries under consideration, thermal mixing behavior is carried out using fluids having two distinct input temperatures. Under the influence of chaotic advection and low rates of Reynolds number, the second law of thermodynamics is controlled in terms of the entropy generation caused by hydrodynamic and thermal processes. The governing equations are numerically solved using the CFD Fluent code. Thus, the micromixer's configuration demonstrated a very significant improvement in mixing degree while minimizing friction and thermal irreversibilities. The synergy coefficient, which depicts the link between velocity and heat transfer in angle form, is analyzed and the results are provided.

Numerical Investigation of Fin Shape Optimization and Entropy of Magnetohydrodynamics Natural Convection Nanofluid Flow in a Cavity

The purpose of the investigation is to analyze the effect of fin length and position in terms of rotational angle on heat transmission and entropy generation. Different parameters such as Prandtl numbers, Hartmann numbers, Rayleigh numbers, and particle volume fractions are used to analyze nanofluid laminar flow behavior and temperature distribution. The fin has a significant impact on both the isotherm and the streamlines. Findings revealed that increasing the rotational angle of a spinning heat exchanger might result in more consistent temperature distribution along isotherms; larger fins, on the other hand, frequently provide greater heat dissipation due to increased surface area. Furthermore, when Rayleigh numbers increase, so does the temperature distribution between the fins and the surrounding fluid. The presence of a magnetic field affects fluid dynamics and contributes to the generation of entropy. Higher Prandtl numbers can result in the enhancement heat transfer phenomena and the generation of entropy.

Thermo-Hydraulic Phenomena of Water-Al2O3 Nanofluid Flow Over a Rectangular Channel with Trapezoidal Obstacles

Numerical simulations of water-Al2O3 nanofluid flow in a rectangular channel with two trapezoidal obstacles have been studied, which has rmarkable effect in various engineering applications. The governing equations have been solved using SIMPLEC algorithm and FLUENT software has been used to visualize the simulation results. Motivation of this work is to examine the dynamic behavior of laminar water-Al2O3 nanofluid flow for volume fraction, ψ = 0%, 2%, and 4%. The present study analyzes different hydrothermal flow phenomena with the variation in obstacle height and ψ. Moreover, the simulation results, such as the profiles of velocity, normalized temperature (θ), poiseuille number (CfRe), local Nusselt number (Nu), average Nusselt number (Nuavg) and friction factor (f) have been portrayed with the variations in ψ and Reynolds number (Re). It has been observed that the obstacles increase the convective heat transfer (HT) significantly. At Re = 100, for all the configurations it has been found that the velocity profile become more pronounced for ψ = 4% as compared to ψ = 0%. A linear relationship has been found between the values of f and ψ. It is also found that an increase in Re increases vortex length. It is also shown that variation of volume fraction (ψ) and obstacle height resulted in an indicative change in the normalized temperature and velocity along the center line. In type-1 obstacle configuration, it has been found that Nuavg increases by 6.6% at ψ = 2%, and the same increases by 10.73% at ψ = 4% as compared to that at ψ = 0%. Moreover, it has been found that in type-2 obstacle configuration, value of f increases by approximately 7.9% at ψ = 2% and 13.84% at ψ = 4% as compared to that at ψ = 0%.

Improved mechanical and electrical properties of copper-aluminum joints with highly aligned graphene reinforcement via friction stir spot welding

This study demonstrates the potential of friction stir spot welding (FSSW) for producing highly aligned graphene configurations in copper-aluminum joints, resulting in improved mechanical and electrical properties. Pure copper and AA6061 sheet were welded with 0.5% graphene nanoparticles dispersed in ethanol drop cast at the interface. Under optimized experimental conditions, adding a graphene interlayer results in a 15.6% increase in maximum shear strength, a 46% increase in hardness value, and a 23% reduction in joint electrical resistance. Transmission electron microscopy confirmed that the laminar flow behavior of the material aligns the graphene nanoparticles parallel to the tool surface direction. The mechanical improvements are attributed to the reduction of grain size and the plastic incompatibilities that arise at the metal-graphene interface. The highly aligned graphene configuration provides more conductive paths and acts as a bridge between grains to reduce grain boundary resistance, reducing electrical resistance. These findings pave the way for exploring the possibilities of utilizing the anisotropic properties of graphene in material joining applications.

A Simplified GPU Implementation of the Hybrid Lattice Boltzmann Model for Three-Dimensional High Rayleigh Number Flows

This paper provides an analysis of the numerical performance of a hybrid computational fluid dynamics (CFD) solver for 3D natural convection. We propose to use the lattice Boltzmann equations with the two-relaxation time approximation for the fluid flow, whereas thermodynamics is described by the macroscopic energy equation with the finite difference solution. An in-house parallel graphics processing unit (GPU) code is written in MATLAB. The execution time of every single step of the algorithm is studied. It is found that the explicit finite difference scheme is not as stable as the implicit one for high Rayleigh numbers. The most time-consuming steps are energy and collide, while stream, boundary conditions, and macroscopic parameters recovery are executed in no time, despite the grid size under consideration. GPU code is more than 30 times faster than a typical low-end central processing unit-based code. The proposed hybrid model can be used for real-time simulation of physical systems under laminar flow behavior and on mid-range segment GPUs.

Numerical modeling for thermal behavior of nanomaterial laminar flow and convective heat transfer in appearance of magnetic field

The new computational approach has been incorporated for modeling the nanofluid flow through a cavity involving a wavy inner wall which experiences uniform flux. The fluid was created by loading alumina powders with various shapes within the water. The stream function formulation was applied after employing Darcy law and final equations have been generated. The container is under the impact of Lorentz force in addition to buoyancy forces. With loading additives, Nu enhances about 17.07% and 41.57% depending on the amount of Ha. The greater value of Ha makes the effect of adding nanoparticles become more sensible. With increasing the value of shape factor, Nu increases about 11.76%. As Ha grows, the rate of cooling decreases about 41.31%. With augment of Ra, Nu enhances about 50.41% in absence of Ha.

Effect of inlet gas velocity on laminar flow behavior in shielding device for WAAM process

Effect of inlet gas velocity on laminar flow behavior in shielding device for WAAM process

Hybrid event bed characteristics and its role in high-frequency facies change of the Upper Triassic submarine fan in the West Qinling area of NE Tibetan Plateau

Hybrid event beds (HEBs) record disequilibrium in submarine fan evolution attributed to mud-forced dampening turbulence, which could be caused by allogenic and autogenic forcings in either the proximal or distal segment of a lobe-dominated submarine fan on several timescales. Detailed field investigation combined with petrographic and mineralogical analysis of selected outcrop samples indicate that the Upper Triassic submarine fan succession mainly comprises turbidites, HEBs, and debrites in the West Qinling (WQ) area of NE Tibetan Plateau. Five types of HEBs are recognized based on the thickness, sedimentary structure, and texture. Bed-by-bed description and measurement reveal that these HEBs show a distinct distribution pattern throughout the submarine fan succession, including dominance of HEB-1 and HEB-2 beds (∼71.50%) in distributary channel to lobe off-axis (FA1–FA3) and significant portion of HEB-3 to HEB-5 beds (∼54.22%) in lobe fringe to lobe distal fringe environments (FA4–FA5). Textural and petrographic characteristics of mudclasts suggest disaggregation of heterolithic, homogenous and less cohesive mudclasts (MC-1 to MC-4 type) within H1b and H3 interval of HEBs, which could play different roles in the longitudinal mud-driven flow transformation between turbulent and laminar flow behavior patterns. The vertical distributions of the HEB-prone succession are characterized by four types of depositional scenarios, which yields significant allogenic and autogenic signatures combined with the recognition of the dominant HEB types and thickening- or thinning-upward trend of the vertically stacked submarine lobes. This study can enhance our understandings of flow transformation of sediment gravity flows (SGF) along the eastern margin of the Paleo-Tethys Ocean based on the anatomy of several undiscovered deep-water outcrops, which were reflected by the initiation, gradual switching, and avulsion of the high-frequency submarine fan evolution during the Late Triassic.

Microfluidic synthesis as a new route to produce novel functional materials.

By geometrically constraining fluids into the sub-millimeter scale, microfluidics offers a physical environment largely different from the macroscopic world, as a result of the significantly enhanced surface effects. This environment is characterized by laminar flow and inertial particle behavior, short diffusion distance, and largely enhanced heat exchange. The recent two decades have witnessed the rapid advances of microfluidic technologies in various fields such as biotechnology; analytical science; and diagnostics; as well as physical, chemical, and biological research. On the other hand, one additional field is still emerging. With the advances in nanomaterial and soft matter research, there have been some reports of the advantages discovered during attempts to synthesize these materials on microfluidic chips. As the formation of nanomaterials and soft matters is sensitive to the environment where the building blocks are fed, the unique physical environment of microfluidics and the effectiveness in coupling with other force fields open up a lot of possibilities to form new products as compared to conventional bulk synthesis. This Perspective summarizes the recent progress in producing novel functional materials using microfluidics, such as generating particles with narrow and controlled size distribution, structured hybrid materials, and particles with new structures, completing reactions with a quicker rate and new reaction routes and enabling more effective and efficient control on reactions. Finally, the trend of future development in this field is also discussed.

Thermal performance and entropy generation for nanofluid jet injection on a ribbed microchannel with oscillating heat flux: Investigation of the first and second laws of thermodynamics

In current numerical study, forced flow and heat transfer of water/NDG (Nitrogen-doped graphene) nanofluid in nanoparticles mass fractions ( φ ) of 0, 2% and 4% at Reynolds numbers ( Re ) of 10, 50, 100 and 150 are simulated in steady states. Studied geometry is a two-dimensional microchannel under the influence of nanofluid jet injection. Temperature of inlet fluid equals with T c = 293 K and hot source of microchannel is under the influence of oscillating heat flux. Also, in this research, the effect of the variations of attack angle of triangular rib (15°, 30°, 45° and 60°) on laminar nanofluid flow behavior inside the studied rectangular geometry with the ratio of L / H = 28 and nanofluid jet injection is investigated. Obtained results indicate that the increase of Reynolds number, nanoparticles mass fraction and attack angle of rib leads to the increase of pressure drop. By increasing fluid viscosity, momentum depreciation of fluid in collusion with microchannel surfaces enhances. Also, the increase of attack angle of rib at higher Reynolds numbers has a great effect on this coefficient. At low Reynolds numbers, due to slow motion of fluid, variations of attack angle of rib, especially in angles of 30°, 45° and 60° are almost similar. By increasing fluid velocity, the effect of the variations of attack angle on pressure drop becomes significant and pressure drop figures act differently. In general, by using heat transfer enhancement methods in studied geometry, heat transfer increases almost 25 %.

Toward the heat convection enhancement of nanofluids flowing in a 3D microchannel affected by a nonuniform magnetic field

AbstractIn the present investigation, the behavior of laminar convective flow and heat transfer in a three‐dimensional horizontal square duct using different water‐based nanofluids (Fe3O4/water, and carbon nanotubes/water) is numerically investigated. The channel is subjected to a periodic partial or full magnetic field. The outer surface is subjected to a constant heat flux density. The problem is numerically solved via the finite volume method with a second‐order precision. The numerical simulations covered a range of the Reynolds number 50 ≤ Re ≤ 400, Hartmann number 0 ≤ Ha ≤ 50, and concentration of nanoparticles 0 ≤ ϕ ≤ 0.02 for different modes of the magnetic field application and direction. Examination of the hydrodynamic and thermal behavior shows significant heat transfer performances obtained when applying transversal and partial periodic magnetic fields simultaneously. More precisely, it is found that the favorable protocol improved the heat transfer rate by 85% in the duct flowing by the Ferrofluid at Ha = 50. Furthermore, findings illustrate that the overall heat transfer rate presented in terms of the mean Nusselt number and the highest compromise (heat transfer augmentation‐pressure losses diminution) are obtained in the case of Fe3O4 nanoparticles for all taken values of Reynolds and Hartmann numbers, whatever the manner and direction of the applied magnetic field.

The effect of using connecting holes on heat transfer and entropy generation behaviors in a micro channels heat sink cooled with biological silver/water nanofluid

The main objective of the present paper is to investigate the effect of using connecting holes on the hydrothermal performance and irreversibility behavior of laminar forced convection flow of a nanofluid (NF) inside a microchannel heat sink (MCHS). The biologically synthesized silver/water NF is employed as coolant. The influences of the volume concentration of NF (φ), the Reynolds number (Re) and the number of connecting holes on the performance features of MCHS and NF are considered numerically. It was observed that the CPU temperature is reduced and became more uniform due to boosting of Re and φ, and the consequence augmentation of the convective heat transfer. However, the pumping power and frictional irreversibility get raised as Re and φ are increased. The figure of merit is above unity for all Re and φ which indicate that the utilization of connecting holes is a suitable option to improve the MCHS performance from the first-law point of view. The heat transfer irreversibility, however, increased by using the connecting holes. Also, the merit of NF over the pure water is observed for Re of 500 and 2000 and φ of 0.1% and 1%.

Application of Pt-Loaded Honeycomb Catalysts in Air Detritiation

In nuclear fusion reactor facilities, the multi-confinement system and the air detritiation system (ADS) are very important to prevent tritium leaking to the environment. A high-performance tritium oxidation catalyst is strongly required in the ADS. In this study, the air resistance and catalytic performance of honeycomb detritiation catalysts are investigated. Then, the honeycomb catalysts are applied in a glove-box detritiation system as well as in an ADS, and the detritiation performance is tested with tritium. Honeycomb catalysts have a much lower air resistance and an excellent scale-up effect due to the behavior of laminar flow. Thus, the honeycomb catalyst increases the reaction space velocity by nearly 100 times without decreasing the conversion rate of H2. Even at an extremely low tritium concentration, the honeycomb catalyst transforms tritium over 95% into tritiated water. In short, Pt-loaded honeycomb catalysts have a huge advantage in and broad potential for air detritiation.

Underground energy storage utilizing concrete building foundation: Experimental and numerical approach

Space heating and cooling represent 63% of total building energy demand. In the present study, the concept of concrete foundation piles was used as an underground storage medium. This system requires no additional drilling costs or space, unlike conventional boreholes. A laboratory-scaled experiment facility was designed to experimentally investigate the thermal response of a concrete pile during the charging and discharging processes. The amount of energy stored and released during each process was evaluated. A flow rate parametric study was also conducted to explore the effect of the laminar and turbulent flow behavior. In order to complement the experimental study, an extensive CFD model was developed and compared with the experimental data. There was good agreement between the numerical and experimental results for each process at different flow rates. The results revealed that increasing the flow rate increases not only the heat rejection and extraction but also the storage efficiency.

Thermal mixing performances of shear-thinning non-Newtonian fluids inside Two-Layer Crossing Channels Micromixer using entropy generation method: Comparative study

In this work, a numerical comparative study is carried out to investigate a laminar steady flow behavior of shear-thinning non-Newtonian fluids in three chaotic geometries: Two-Layer Crossing Channel Micromixer, C-shaped channel and serpentine channel. The process is validated for non-Newtonian flow in a complex geometry which heated by a constant flux. Secondary flow structures are formed in the chosen geometries enhance significantly the fluid dynamic performances. To characterize this performance Poincaré map method is presented for different geometries with various cases of fluid power-law index. Thermal mixing behavior with two different inlet temperatures of shear-thinning fluids in the considered geometries is performed. For various cases of fluid power-law indexes, the TLCCM displayed thermal mixing degree enhancement of 42–84% relative to the thermal mixing degree in both C-shaped and serpentine channels. The second law of thermodynamics is controlled in terms of entropy generation due to the thermal and hydrodynamic process, as a function of low rates of generalized Reynolds number and power-law index, under the effects chaotic advection. Thereby, the TLCCM configuration exhibited very important enhancement of mixing degree than that obtained in other considered geometries, with minimization of friction and thermal irreversibilities.

On the transition behavior of laminar flow through and around a multi-cylinder array

We numerically investigated the transitional behavior of two-dimensional laminar flows through and around a square array of 100 circular cylinders. The solid fraction of the array ϕ ranged from 0.007 85 to 0.661 and the Reynolds number Re (based on the free-stream velocity and the side length of the array) varied from 40 to 200. Globally, the first transition appears at the onset of vortex shedding, where the critical Reynolds number Recr is estimated from the Stuart-Landau equation. The results show that Recr ranges from 40 to ∼45 for the investigated range of ϕ. It is found that Recr increases quadratically with ϕ and the critical Reynolds number for an individual cylinder (Rdcr) increases linearly with ϕ. The subsequent transitions largely depend on ϕ, as revealed from the total drag and lift coefficients, Strouhal number, and the instantaneous vorticity field. For sufficiently small ϕ at high Re, the global vortex shedding is suppressed due to the weakened interaction between cylinders in the array. Several more cases with ϕ of 0.007 85 for Re between 400 and 4000 are also calculated to visualize the suppression behavior. The global transition behaviors are closely related to the secondary frequency (SF) observed from the power spectra of the local velocity. It is highly possible that the SF results from the cylinder interaction in the array. The local instabilities induced by cylinder interactions would promote the onset of global vortex shedding at small Re. Also, the local instabilities still exist even though the global vortex shedding is suppressed at large Re.

Effect of granular properties on hydrodynamics in coarse-grid riser flow simulation of Geldart A and B particles

In this work, a three-dimensional coarse-grid two-fluid model (TFM) simulation by varying granular properties like granular viscosity, frictional viscosity, and solids pressure has been performed. Simulated predictions were subsequently compared with experimental results in the case of Geldart A or B particles. Laminar flow behavior is also studied and coarse-grid simulation predictions were less realistic for laminar flow. This flow regime which although consumes less computational resources falls short for large-scale riser scale up. Flow regime in our simulation was fast fluidization and simulation predicts with minimum error near riser inlet. More specifically, granular viscosity, frictional viscosity and solids pressure for Type A particles predict with minimum error especially near riser inlet at a lower height. For Type B particles, these three solid properties correspond closely with experimental results near inlet at a lower height whereas, at a higher height, turbulence increases and simulation results deviate from experimental studies.

Modeling and Simulation of Newtonian Fluid Flow through Two-Dimensional Backward-Facing Step Channel with Finite Element�s Technique

Objectives: In this study, the behavior of laminar, incompressible and Newtonian fluid flow through the two dimensional backward facing step channels with the expansion ratio 1:2 is studied. Methods: The governing system of non-linear partial differential equations is worked out with the Galerkin least square finite element method. For computation purpose, the finite element based package COMSOL Multi-Physics 5.0 is used. Findings: The streamline pattern of the velocity field and pressure isobars is conferred at different Reynolds numbers. The minimum and maximum velocity magnitudes as well as pressure at the inlet and outlet including their differences are measured. Moreover, the reattachment length of the vortex organized at the corner of downstream of observed geometry is calculated and contrasted with experimental investigation of Armalyetal and CFD investigation of. Applications: Such fluid dynamics has frequently been used in industries including polymers, petro refineries, paints, biological systems etcetera. Keywords: Finite Element’s Technique, Newtonian Fluid Flow, Non-Linear Partial Differential Equations

Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors

The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.