High Dean Number Research Articles

Experimental investigation on the nearshore transport of buoyant microplastic particles

This paper presents experimental measurements of beaching times for buoyant microplastic particles released, both in the pre-breaking region and within the surf zone. The beaching times are used to quantify cross-shore Lagrangian transport velocities of the microplastics. Prior to breaking the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity, regardless of particle characteristics. In the surf zone the Lagrangian velocities of the microplastics increase and become closer to the wave celerity. Furthermore, it is demonstrated that particles having low Dean numbers (dimensionless fall velocity) are transported at higher mean velocities, as they have a larger tendency to be at the free-surface relative to particles with higher Dean numbers. An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles, valid for both non-breaking and breaking irregular waves. The expression matches the present experiments well, in addition to two prior studies.

Mixing of Viscoelastic Fluid Flows in a Coiled Flow Inverter

Despite having the advantage of a secondary flow pattern in coiled tubes, a very high Dean number is required to induce significant mixing in helical coils, usually implying high shear rates. At ve...

Numerical investigations on the heat transfer characteristics of tube in tube helical coil heat exchanger

Heat transfer characteristics of a tube in tube helical heat exchanger in the laminar flow regime is analysed numerically. Numerical scheme is validated with the experimental results reported in literature. The effect of helix angle on the overall heat transfer coefficient is analysed. The overall heat transfer coefficient increases with Dean number and its rate of increase at higher Dean number is low. The rate of heat transfer is maximum at a helix angle of 27°. Simulation studies show that the secondary flows that originate in a coiled tube due to curvature and torsion produce an additional transport of the fluid over the cross section of the pipe. The overall heat transfer coefficient increases with increase in inner diameter.

Continuous aqueous two-phase extraction of microalgal C-phycocyanin using a coiled flow inverter

In this study, the intensification of C-phycocyanin protein extraction from the green microalgae Spirulina maxima was successfully achieved using aqueous two-phase systems coupled to different continuous-operation extractors. Three systems with different total concentrations of Polyethylene glycol and potassium phosphate salt were tested in three different types of continuous systems: a conventional straight-tube extractor, a helical-coiled extractor, and a coiled flow inverter extractor. Results showed that the coiled flow inverter extractor achieves higher overall performance than the other continuous extractors at the same flow rate and same residence time for all the concentrations tested. Similarly, all the continuous-operation extractors showed higher extraction performance than a batch-operation extractor for similar times tested. It was observed that extraction performance in the coiled flow inverter increases as flow rate increases (coefficient of partition increases 1.74 fold by increasing the flow rate from 10 mL/min to 30 mL/min). The C-phycocyanin extraction in this continuous system was benefited from a decrease in the extraction time with high Dean numbers.

Experimental study of heat transfer enhancement in a helical tube heat exchanger by alumina nanofluid as current flow

In the present study, the heat transfer rate through a shell and helical tube heat exchanger with alumina nanofluid as current flow was investigated and the obtained results were compared to those of the distilled water. Effects of alumina concentration in the nanofluid (0–0.5 vol.%) and the temperature of hot fluid (40–70 °C) were evaluated at different flow rates (2–3.5 L/min). Heat transfer coefficients were determined using Wilson method. The overall heat transfer rate decreased with Dean number at low Dean numbers and increased after passing through a minimum at higher dean numbers due to simultaneous and competitive effects of convective heat transfer coefficient and temperature difference on heat transfer rate. At low Dean numbers, the effect of temperature difference dominated the effect of convective heat transfer coefficient and at high Dean numbers, the convective heat transfer coefficient effect was more determining. Higher temperature of the hot fluid led to higher convective heat transfer coefficient due to increased thermal conductivity of the fluid at higher temperatures. Compared to the distilled water, higher convective heat transfer coefficient was obtained for nanofluid as the current flow at low volume fractions of the nanofluid. The maximum heat transfer rate (9505.6 W) was obtained at a volume fraction of 0.016, flow rate of 3.5 L/min, and temperature of 70 °C.

Multiplicity of forced convective heat transfer of nanofluids in curved ducts

In the present work, a numerical study is made on the fully-developed forced convective heat transfer of nanofluids in a curved square duct using Eulerian-Lagrangian two-phase approach. The curvature ratio of the duct is 0.02 and its hydraulic diameter is 8 mm. The Al2O3-water nanofluids contain spherical nanoparticles with particle diameter of 30 nm and volume fraction of 0.5%. Three different flow structures of nanofluids are obtained through the small perturbations generated by three different computers at the same conditions. The flow has a structural 2-cell, 3-cell or 4-cell at different Dean numbers and on different solutions, which leads to multiple non-uniform nanoparticle concentration distributions and multiple temperature fields. Multiple flow fields are symmetric in a low Dean number region and asymmetric in a high Dean number region, which leads to multiple symmetric (asymmetric) nanoparticle concentration distribution and temperature distribution fields, multiple symmetric (asymmetric) local Nusselt number and local friction factor along the outer wall at low De values (high De values), and finally lead to multiple mean friction factor and multiple mean Nusselt number. A significant enhancement of heat transfer (e.g. 23.79% at De of 335.2) can be achieved at the expense of a slight increase of flow friction (e.g. 6.84% at De of 335.2) in curved square duct through switching the solutions. This study could provide an explanation, from a new respect, for the inconsistent results of convective heat transfer of nanofluid in the literature.

PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics.

Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.

Second law analysis for flow of a nanofluid containing graphene–platinum nanoparticles in a minichannel enhanced with chaotic twisted perturbations

The second law and entropy generation characteristics of a new hybrid nanofluid containing graphene nanoplatelets decorated with platinum nanoparticles are evaluated in a chaotic twisted channel. Although several investigations have been carried out on flows inside chaotic channels in the relevant literature, very few studies have employed nanofluids as working fluids in such configurations. The geometrical perturbations cause formation of counter rotating Dean roll-cells which intensify mixing in the flow and disturb the boundary layer. The intensity of perturbations considerably enhances at higher Dean numbers. The maximum velocity is shifted toward the outer wall due to the centrifugal force, and the maximum frictional entropy generation occurs there. Because the roll-cells lead to more uniform temperature distribution, thermal entropy generation reduces with increase of distance from the inlet of each bend. Moreover, by increasing concentration and Dean number, thermal entropy generation and Bejan number decrease while frictional entropy generation intensifies, however, due to dominance of thermal entropy generation, overall irreversibility of the nanofluid flow reduces. Besides, the temperature gradients become greater at higher wall heat fluxes which lead to the more intense thermal entropy generation. In addition, the difference between the Bejan numbers related to different wall heat fluxes is more noticeable at higher concentrations.

A study on the micromixing performance in microreactors for polymer solutions

Microreactors are widely applied for various polymerization processes to produce polymers with controlled molecular weight and structures. In this work, the mixing of polymer solutions in capillary microreactors was investigated with the aid of the biazo‐coupling reaction system and high‐speed camera. A smaller inner diameter, a higher Dean number and a lower Torsion number could promote the micromixing performance in microreactors. Unlike the mixing of Newtonian fluids in microreactors or micromixers, the mixing of polymer solutions follows different mechanisms and it is more difficult to reach homogeneous condition. However, the good micromixing performance in capillary microreactor systems for polymer solutions still could be obtained with high shear rates and long enough capillary length at relatively high correlated Reynolds numbers (NRe > 29). Furthermore, the micromixing time in the capillary microreactors was evaluated based on a modified stretching efficiency model and its value was in the range of 0.1–8.0 ms. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3479–3490, 2018

나선형 미세채널 내부에 형성되는 딘와류 이용한 미세입자 분리소자

This paper presents a microparticle separator using a spiral microchannel. A particle separator based on the dean vortex was designed, fabricated, and characterized. Two different spiral microchannels were fabricated. Width and initial radius of rotation in the spiral microchannel were fixed to <TEX>$300{\mu}m$</TEX> and 1.75 mm, respectively. Two different depths of the microchannels were designed at <TEX>$50{\mu}m$</TEX> and <TEX>$80{\mu}m$</TEX>. In this experimental study, the equilibrium position of microparticles was monitored by using fluorescent microbeads. In the case of a low dean number (<1.0), lift force and dean drag force were similar, indicating that microbeads were distributed to almost all areas across microchannels. However, in the case of a high dean number (>1.0), dean drag force rather than lift force was dominant, indicating that microbeads moved toward the inner wall of the spiral microchannel.

SPECTRAL NUMERICAL SIMULATION OF MAGNETO-PHYSIOLOGICAL LAMINAR DEAN FLOW

A computational simulation of magnetohydrodynamic laminar blood flow under pressure gradient through a curved bio-vessel, with circular cross-section is presented. Electrical conductivity and other properties of the biofluid (blood) are assumed to be invariant. A Newtonian viscous flow (Navier–Stokes magnetohydrodynamic) model is employed which is appropriate for large diameter blood vessels, as confirmed in a number of experimental studies. Rheological effects are therefore neglected as these are generally only significant in smaller diameter vessels. Employing a toroidal coordinate system, the steady-state, three-dimensional mass and momentum conservation equations are developed. With appropriate transformations, the transport model is non-dimensionalized and further simplified to a pair of axial and secondary flow momenta equations with the aid of a stream function. The resulting non-linear boundary value problem is solved with an efficient, spectral collocation algorithm, subject to physically appropriate boundary conditions. The influence of magnetic body force parameter, Dean number and vessel curvature on the flow characteristics is examined in detail. For high magnetic parameter and Dean number and low curvature, the axial flow is observed to be displaced toward the center of the vessel with corresponding low fluid particle vorticity strengths. Visualization is achieved with the MAPLE software. The simulations are relevant to cardiovascular biomagnetic flow control.

Extended series solutions and bifurcations of the Dean equations

AbstractSteady, incompressible flow down a slowly curving circular pipe is considered. Both real and complex solutions of the Dean equations are found by analytic continuation of a series expansion in the Dean number, $K$. Higher-order Hermite–Padé approximants are used and the results compared with direct computations using a spectral method. The two techniques agree for large, real $K$, indicating that previously reported asymptotic behaviour of the series solution is incorrect, and thus resolving a long-standing paradox. It is further found that a second solution branch, known to exist at high Dean number, does not appear to merge with the main branch at any finite $K$, but appears rather to bifurcate from infinity. The convergence of the series is limited by a square-root singularity on the imaginary $K$-axis. Four complex solutions merge at this point. One corresponds to an extension of the real solution, while the other three are previously unreported. This bifurcation is found to coincide with the breaking of a symmetry property of the flow. On one of the new branches the velocity is unbounded as $K\rightarrow 0$. It follows that the zero-Dean-number flow is formally non-unique, in that there is a second complex solution as $K\rightarrow 0$ for any non-zero $\vert K\vert $. This behaviour is manifested in other flows at zero Reynolds number. The other two complex solutions bear some resemblance to the two solution branches for large real $K$.

Numerical simulation of Dean number and curvature effects on magneto-biofluid flow through a curved conduit

A numerical study is performed to investigate the magnetohydrodynamic viscous steady biofluid flow through a curved pipe with circular cross section under various conditions. A spectral method is applied as the principal tool for the numerical simulation with Fourier series, Chebyshev polynomials, collocation methods and an iteration method as secondary tools. The combined effects of Dean number, Dn , magnetic parameter, Mg , and tube curvature, δ, are studied. The flow patterns have been shown graphically for large Dean numbers as well as magnetic parameter and a wide range of curvatures, 0.01 ≤δ≤ 0.2. Two-vortex solutions have been found. Axial velocity has been found to increase with an increase of Dean number, whereas it is suppressed with greater curvature and magnetic parameters. For high magnetic parameter and Dean number and low curvature, almost all the fluid vortex strengths are weak. The study is relevant to magnetohydrodynamic blood flow in the cardiovascular system.

Effects of Dean Number and Curvature on Fluid Flow through a Curved Pipe with Magnetic Field

Abstract Numerical study is performed to investigate the Magnetohydrodynamics fluid flow through a curved pipe with circular cross-section under various conditions. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The Magnetohydrodynamics incompressible viscous steady flow through a curved pipe with circular cross-section is investigated numerically to examine the combined effects of high Dean Number D n , magnetic parameter M g and non- dimensional curvature δ . The flow patterns have been shown graphically for large Dean Numbers as well as magnetic parameter and a wide range of curvatures 0.01 ≤ δ ≤ 0.4 .Two vortex solutions have been found. Axial velocity has been found to increase with the increase of Dean Number and decrease with the increase of curvature and magnetic parameter. For high magnetic parameter, Dean Number and low curvature almost all the fluid particles strength are weak.

Experimental study of aerosol distribution and concentration variation through curved ducts

This paper presents an experimental investigation of an aerosol problem by adopting two methods. One approach utilizes scanning electron microscope to study the realistic aerosol deposition status in a typical duct bend. Through scanning electron microscope images and on-site observation, the aerosols tend to deposit and accumulate more on the outer bend wall and bend outlet wall. The other approach is to design systematic experiments to measure aerosol concentration variation and distribution through 90-degree curved ducts. This experimental method is simple for realistic applications. Measured results show that the average particle volume concentration diverges greatly after flowing through the bend. The loading ability decreases significantly for larger particles at bend outlet under higher Dean number.

Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers

Turbulent pulsatile flows through pipe bends are prevalent in internal combustion engine components which consist of bent pipe sections and branching conduits. Nonetheless, most of the studies related to pulsatile flows in pipe bends focus on incompressible, low Womersley and low Dean number flows, primarily because they aim in modeling blood flow, while internal combustion engine related flows have mainly been addressed in terms of integral quantities and consist of single point measurements. The present study aims at bridging the gap between these two fields by means of time-resolved stereoscopic particle image velocimetry measurements in a pipe bend with conditions that are close to those encountered in exhaust manifolds. The time/phase-resolved three-dimensional cross-sectional flow-field 3 pipe diameters downstream the pipe bend is captured and the interplay between different secondary motions throughout a pulse cycle is discussed.

Influence of System Variables on the Heating Characteristics of Water during Continuous Flow Microwave Heating

A domestic microwave oven (1000 W) was modified to permit the continuous flow of liquids run through a helical coil centrally located inside the oven cavity. Heating characteristics were evaluated by measuring inlet and outlet temperatures of coil as a function of system variables. The influence of number of turns, coil diameter, tube diameter, pitch and initial temperature were evaluated at different flow rates. The average residence time of water was computed by dividing the coil volume by the volumetric flow rate. The influence of Dean number was evaluated. Results from this study showed that (1) higher number of turns resulted in lower heating rate, lower temperature fluctuations, higher exit temperature and longer time to achieve temperature equilibrium; (2) larger tube or coil diameter gave larger coil volume causing the heating rate to decrease; (3) faster flow rates resulted in lower exit temperatures, lower temperature fluctuation, higher Dean number and slightly higher heating rate; (4) higher initial temperatures resulted in higher exit temperatures; (5) higher Dean number resulted in more uniform heating and slightly higher heating rate. Overall, the coil volume was the more dominant factor affecting heating rate as compared with flow rate and Dean number.

UV-C treatment of juices to inactivate microorganisms using Dean vortex technology

A laboratory-scale UV-C treatment device based on Dean vortex technology was tested for its potential to inactivate spoilage microorganisms in cloudy fruit juices. A log 5 and log 6 reduction could be achieved by inactivating Lactobacillus plantarum BFE 5092 and Escherichia coli DH5α in naturally cloudy apple juice at 1.9 and 7.7 kJ/L, respectively. A treatment with 9.6 kJ/L led to an approximately log 4 inactivation of Saccharomyces cerevisiae DSM 70478 and Alicyclobacillus acidoterrestris DSM 2498. The effects of possible influencing parameters such as optical density, turbidity and viscosity were analyzed with regard to the efficiency of the UV-C treatment. The optical density based on dissolved compounds appeared to be the most important factor which influenced the bacterial inactivation efficiency. Cell counts of L. plantarum BFE 5092 could be reduced in quarter-strength Ringer’s solution adjusted with dye from an initial level of approximately 1 × 10 8–1 × 10 1 cfu/mL at an optical density (254 nm) of 20 at 9.6 kJ/L. Only a log 1.5 reduction, however, could be achieved at an optical density (254 nm) of 140 using the same UV-C treatment. Furthermore, no noticeable effect on inactivation could be determined by varying the turbidity or the viscosity of the juices investigated. An increasing flow rate and the consequently higher Dean number clearly improved the efficacy of the UV-C treatment. Thus, the inactivation of L. plantarum BFE 5092 in blood orange juice could be enhanced by an approximately 2.5-log reduction by increasing the Dean number from 32 to 256 at 7.7 kJ/L. The UV-C treatment using Dean vortex technology was shown in this study to effectively inactivate microorganisms even in cloudy juices. The optical density value seemed to be the exclusive determining factor on the efficiency of the UV-C inactivation of microorganisms based on Dean vortex technology, while the effect of suspended solids was negligible as a result of the efficient mixing by Dean vortices.

Stable solution zone for fluid flow through curved pipe with circular cross-section

Numerical study is performed to examine numerically the stable solution for the incompressible viscous steady flow through a curved pipe with circular cross-section. Also the combined effects of high Dean Number Dn and curvature δ on the flow are investigated. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The flow patterns have been shown graphically for large Dean Numbers and a wide range of curvature, 0.01≤δ≤0.9.Two vortex solutions have been found for secondary flow. Axial velocity has been found to increase with the increase of Dean number and decrease with the increase of curvature. For high Dean number and low curvature almost all the fluid particles leave the inner half of the cross-section. The stable solution zone increases with the increase of curvature up to a certain limit, then decrease.DOI: 10.3329/jname.v7i1.3630

A Numerical Study of Flow and Heat Transfer in Internally Finned Rotating Curved Pipes

In this article, the effects of internal fins on an incompressible viscous flow and heat transfer inside rotating curved pipes are numerically studied under the hydrodynamically and thermally fully developed conditions. The fins are assumed to have negligible thickness with the same conditions as the pipe walls. Two thermal boundaries including constant wall temperature and constant heat flux are considered at the pipe wall. First the accuracy of the numerical code written by a finite-volume method based on the SIMPLE algorithm is verified by the available data for the finless rotating curved pipes. Then, the numerical results for the internally finned rotating pipes are investigated in both positive and negative rotation numbers affecting remarkably on the flow and temperature field patterns. Also, the Dean number (KLC) effects on the friction factor, Nusselt number, and other nondimensional parameters are studied in detail. Analyzing the numerical results by the Colburn factor, two optimum fin heights consisting of the four-fifth of the pipe radius at the lower Dean numbers and one-third of the pipe radius at higher Dean numbers are determined in the curved rotating pipe with six internal fins.