Wavy Channel Research Articles

Effect of Relative Waviness on Low Re Wavy Microchannel Flow

A 3-D, steady, conjugate numerical model is used to study the effect of waviness on laminar fluid flow and heat transfer characteristics associated with microsized wavy channels. The numerical model has been validated against available experimental data. It is observed that transition Re and average Nu are functions of waviness of the channel; however, friction factor remained constant at higher waviness. The augmentation of Nu with waviness is found to be resulting from increased levels of recirculation and secondary flows. Peak vorticity levels showed an increase of six times when relative waviness increased from 0.03 to 0.3 and is about 2.5 times when Re increased from 100 to 200. The effect of chaotic advection is not observed even for higher waviness channels at Re = 100.

A theoretical analysis of Biorheological fluid flowing through a complex wavy convergent channel under porosity and electro-magneto-hydrodynamics Effects

Background and ObjectiveFlow generated via peristaltic waves in naturally occurring physical phenomenon inside human body. Its combination with electric and magnetic forces makes it even more versatile in biomedical engineering applications. The results presented in this article are useful in designing artificial tubes, lab-on-a-chip devices for cell manipulation, drug design, flow amalgamation, micro-scale pumps and micro-bots which can be externally controlled by electric and magnetic sensors. Motivated by the aforesaid facts the current investigation is based on the transportation of a couple stress bio-fluid by peristalsis through a convergent channel under the postulates of creeping phenomena and long wavelength, respectively MethodsA closed form solution is acquired for the axial velocity profile, volumetric flow rate and streamlines, respectively. The physical influence of involved parameters on the rheological characteristics are argued analytically with the help of Mathematica software 12.0.1 in detail. Additionally, the flow system is considered to take place under the both porosity and electro-magneto-hydrodynamics effects, respectively. The amplitude of axial velocity across one wavelength is strongly affected at the larger values of numerous embedded parameters: Darcy number, Hartmann number, Electro-osmotic velocity parameter and non-Newtonian (couple stress) parameter. ResultsWe have observed remarkable effects of embedded parameters on velocity distribution, flow rate and trapping phenomena under porous and electro-osmotic (combination of both magnetic and electric) effects. The circulation of boluses and number of streamlines are reduced/enhanced for larger Hartmann number/Darcy number due strong magnetic/porosity effects. This research study additionally tells us how to control the transportation phenomena of biological fluids by appropriate adjusting the porosity effects (the effects of porous media) and electro-osmotic influences. Moreover, in order to enhance the performance of a peristaltic pump at the micro-scale level, we have used complex peristaltic wave scenario in the boundary walls of the convergent micro-channel.

Numerical study of thermo-hydraulic characteristics for forced convective flow through wavy channel at different Prandtl numbers

The present work numerically investigates the thermo-fluidic and entropy generation characteristics for laminar forced convective flow through wavy channel at different Prandtl number (Pr). Results are presented for the following range of parameters: Reynolds number $$5 \le \text{Re} \le 200$$ , Prandtl number $$0.72 \le \Pr \le 100$$ , dimensionless amplitude $$0.3 \le \alpha \le 0.7$$ and dimensionless wavelength $$0.5 \le \lambda \le 1.5$$ . It is observed that with increase in Pr, the thickness of the thermal boundary layer at trough region decreases slowly for smaller Re, whereas at higher Re, the rate of decrement is higher. The average Nusselt number increases with Pr for all amplitude, wavelength and Reynolds number. The relative heat transfer enhancement compared to equivalent plane channel is presented in terms of enhancement ratio (ER), and it shows a non-monotonic variation of ER with Pr at lower Re and a monotonic one at higher Re. The combined alteration of rate of heat transfer and pressure drop as compared to plane channel is enumerated by performance factor (PF), and the variation of PF with Pr shows non-monotonic behaviour at lower Re and monotonic one at higher Re. The variation of PF shows non-monotonic variation with Re for higher Pr and for smaller wavelength, whereas it monotonically decreases for all Pr at higher wavelength. Thermal entropy generation contribution is higher over the viscous one for all the cases considered. The local thermal entropy generation distribution varies with Re, Pr and geometrical configuration of the channel. For smaller amplitude (α = 0.3), the total entropy generation is minimum in the considered range of Re and Pr.

A shear-rate-dependent flow generated via magnetically controlled metachronal motion of artificial cilia.

Cilia beating is a naturally occurring phenomenon that can be utilized in fluid transport in designing several biomechanical devices. Inspired by the ubiquity of bio-fluids (which are non-Newtonian), we report the characteristics of shear-rate-dependent viscosities on fluid flow generated by the wavy propulsion of magnetic cilia. We assume that the metachronal waves of these cilia form a two-dimensional wavy channel, which is filled with generalized Newtonian Carreau liquid. Galilean transformation is employed to relate fixed and moving frames. The constitutive equations are reduced under the classical lubrication assumption. The resulting fourth-order nonlinear differential equations are solved via a perturbation approach using the stream function. The effects of four dominant fluid parameters (shear thinning/thickening, power-law index, and zero- and infinite-shear-rate viscosity), magnetic parameter (Hartmann number), and metachronal wave parameters on fluid velocity, pressure rise per wavelength, and trapping phenomenon are shown in graphical results and explained thoroughly. This study could play an advisory role in designing a magnetic micro-bot useful in the biomedical industry.

Integral transform analysis of convective heat transfer within wavy walls channels

The generalized integral transform technique (GITT) is employed in the hybrid numerical-analytical solution of the two-dimensional Navier–Stokes and energy equations in wavy walls channels. The flow is considered laminar and incompressible for a Newtonian fluid with temperature-independent physical properties, while the walls temperatures are kept uniform along the channel length. The streamfunction-only formulation is adopted, which eliminates the pressure field and automatically satisfies the continuity equation. A thorough convergence analysis is performed for the streamfunction field, temperature field, friction factor, and local Nusselt number to illustrate the method robustness. The verification of the present GITT results is also performed by comparing the centerline velocity, friction factor, average temperature, and local Nusselt number with equivalent results from the COMSOL Multiphysics simulation platform, with overall very good agreement. The influence of the governing parameters such as Reynolds number and wavy-wall amplitude on the velocity and temperature fields is also analyzed, demonstrating their importance in the convective heat transfer behavior.

Heat Transfer Improvement in a Wavy Vortex Generator Miniature Channel Using Nanofluids

In this article, the thermal and frictional characteristics of interrupted wavy mini-channel are experimentally investigated as the wavy vortex generator miniature channel (WVGMC) using SiO2–H2O and Al2O3–H2O nanofluids. Its performance characteristics are compared to the common configurations of cooling mini-channels, that is, the wavy mini-channel (WMC), straight mini-channel (SMC), and the miniature channel. The effect of the geometric shape of mini-channels, mass flow rate, coolant fluid type, and the concentration of nanoparticles on the thermal and hydraulic performance inside the different geometries are investigated. The range of Reynolds number and weight fraction of nanoparticles are considered to be 500–2000 and 0–0.3 wt%, respectively. The results show that the highest Nusselt number and overall performance are obtained in the WVGMC for all coolant fluids. The Nusselt number is improved about 27.5%, 22%, and 26.5% for the distilled water, SiO2–H2O nanofluid, and Al2O3–H2O nanofluid in the WVGMC compared to WMC, respectively. Also, the friction factor is increased in the WVGMC; for example, this enhancement rate is about 8.2% for the water flow compared to WMC. The SMC show the least Nusselt number for both nanofluids. In all geometries, the thermal performance is increased using the nanofluids than that for the deionized water. Thus, the WVGMC is suggested as an efficient geometry to design the cooling mini-channels.

Computationally efficient optimization of wavy surface roughness in cooling channels using simulated annealing

This article reports a computationally efficient optimization for wavy surface roughness in cooling channels based on simulated annealing. Our approach rapidly calculates the performance metrics of cooling channels using closed-form models and approximates an optimum design via a random optimization technique, simulated annealing. The proposed method optimizes the wall roughness of cooling channels for maximizing the heat transfer rate while satisfying the pressure drop constraint. The channel wall smoothly converges and diverges throughout to locally modulate the heat transfer rate and the pressure drop. For a given pressure constraint and heat load distribution, the optimizer is able to compare more than 10,000 possible channel designs within a minute and generate a distinct channel design that achieves the optimization objective. The channel temperature predicted by the optimizer differs up to 10.9% to the estimations by a finite volume model. Lastly, optimized wavy channel designs are introduced that exhibit up to 2.7 times greater performance factor than a conventional channel geometry. This work demonstrates the potential of algorithm-based optimization techniques for designing efficient thermodynamic systems.

Unsteady Flow and Heat Transfer Characteristics of Primary and Secondary Corrugated Channels

Abstract Direct numerical simulations (DNS) have been performed using open source computational fluid dynamics (CFD) package openfoam to investigate the unsteady flow and heat transfer characteristics of primary and secondary corrugated wavy channels for fixed values of wavelength and amplitude by varying Reynolds number (Re). Computations are carried out by considering only one module of the wavy channel and applying periodic boundary conditions to reduce the time for computations. Numerical method has been validated thoroughly against the numerical and experimental results reported in the literature. Steady as well as unsteady flow characteristics in the primary and secondary corrugated channels have been elaborated and explained with the help of streamlines, velocity contours, isosurfaces of velocity, and Q value. Temperature and Nusselt number contours are presented to illustrate the heat transfer characteristics of wavy channels.

Heat transfer enhancement through periodic flow area variations in microchannels

In this study, annular microchannels with a microscale gap of 300 μm were implemented through the concentric superposition of two macro-sized cylinders. Flow area variations along the streamwise direction were created by introducing sinusoidal wave profiles on either the inner or outer wall of the annular gap while keeping the other wall flat. These variations introduced re-entrant effects along the flow direction. Numerical studies using the finite volume method were performed to elucidate the single-phase, steady-state thermal and hydrodynamic performances of the wavy channels, using water as the fluid medium, with an operating Reynolds number range of 800–2200. The predicted results were validated using the available measured data and classical correlations. This study demonstrated the viability of attaining enhanced heat transfer rates of up to 360% of the original straight channel through the inducement of flow area variations with single wavy-walled channels. Despite magnifications of the friction factors, the single wavy-walled channels attained a 120% increment in heat transfer coefficient when evaluated at the same pumping power. Overall, single-walled wavy passages were deemed suitable for heat exchanger designs demanding very high heat removal rates and efficiencies while the conventional serpentine channels were apt for moderately enhancing heat transfer while requiring low pumping power.

EFFECTS OF PULSATING FLOW ON CONVECTION IN WAVY CHANNELS WITH PHASE SHIFT

EFFECTS OF PULSATING FLOW ON CONVECTION IN WAVY CHANNELS WITH PHASE SHIFT

Sharkskin-Inspired Magnetoactive Reconfigurable Acoustic Metamaterials.

Most of the existing acoustic metamaterials rely on architected structures with fixed configurations, and thus, their properties cannot be modulated once the structures are fabricated. Emerging active acoustic metamaterials highlight a promising opportunity to on-demand switch property states; however, they typically require tethered loads, such as mechanical compression or pneumatic actuation. Using untethered physical stimuli to actively switch property states of acoustic metamaterials remains largely unexplored. Here, inspired by the sharkskin denticles, we present a class of active acoustic metamaterials whose configurations can be on-demand switched via untethered magnetic fields, thus enabling active switching of acoustic transmission, wave guiding, logic operation, and reciprocity. The key mechanism relies on magnetically deformable Mie resonator pillar (MRP) arrays that can be tuned between vertical and bent states corresponding to the acoustic forbidding and conducting, respectively. The MRPs are made of a magnetoactive elastomer and feature wavy air channels to enable an artificial Mie resonance within a designed frequency regime. The Mie resonance induces an acoustic bandgap, which is closed when pillars are selectively bent by a sufficiently large magnetic field. These magnetoactive MRPs are further harnessed to design stimuli-controlled reconfigurable acoustic switches, logic gates, and diodes. Capable of creating the first generation of untethered-stimuli-induced active acoustic metadevices, the present paradigm may find broad engineering applications, ranging from noise control and audio modulation to sonic camouflage.

CHEMICAL REACTION AND RADIATION ABSORPTION EFFECTS ON CONVECTIVE FLOWS PAST A POROUS VERTICAL WAVY CHANNEL WITH TRAVELING THERMAL WAVES

CHEMICAL REACTION AND RADIATION ABSORPTION EFFECTS ON CONVECTIVE FLOWS PAST A POROUS VERTICAL WAVY CHANNEL WITH TRAVELING THERMAL WAVES

Dynamically tunable elasto-inertial particle focusing and sorting in microfluidics.

Inertial particle separation using passive hydrodynamic forces has attracted great attention in the microfluidics community because of its operation simplicity and high throughput sample processing. Due to the passive nature of inertial microfluidics, each inertial sorting device is typically fixed to a certain cut-off size for particle separation that is mainly dependent on the channel geometry and dimensions, which however lacks tunability in the separation threshold to fulfill the needs of different sorting applications. In this work, we explore the use of non-Newtonian viscoelastic fluids to achieve size-tunable elasto-inertial particle focusing and sorting in a microfluidic device with reverse wavy channel structures. The balance and competition among inertial lift force, Dean drag force and the controllable elastic lift force give rise to interesting size-based particle focusing phenomena with tunability in the equilibrium focusing positions. Seven differently sized fluorescent microspheres (0.3, 2, 3, 5, 7, 10 and 15 μm) are used to investigate the effects of the flow rate, viscoelastic fluid concentration and particle size on the tunable elasto-inertial focusing behavior. With the sorting tunability, we have achieved a highly effective sorting of a particle mixture into three subpopulations based on the particle size, i.e., small, intermediate and large subpopulations. We even demonstrate the controllable tunability among three separation thresholds for elasto-inertial particle sorting without changing the geometry and dimensions of the microfluidic device. The tunability of the developed elasto-inertial particle focusing and sorting can significantly broaden its application in a variety of biomedical research studies.

Effect of rotation on forced convection in wavy wall channels

In this paper, flow field and heat transfer performance in stationary and rotating wavy channels with different shapes were numerically investigated. Three different geometries were generated through three different values of phase-shift angles of ∅= 0, 90 and 180° between the two opposite wavy walls. A cell-centred finite-volume technique was employed to solve the three-dimensional governing equations based on the SIMPLE algorithm technique. Besides, the Menter k−−ω SST turbulence model was used to simulate the turbulent flow in the current study. The wavelength and wave amplitude of the channel examined were Lw=20 mm and a = 2 mm, respectively. Numerical simulations were carried out over a range of design and operating conditions including the phase-shift angle of ∅= 0–180°, Reynolds number of Re=1,000–10,000, and rotating speed of Ω= 0–1000 rpm. The results showed that the surface-averaged Nusselt number increases as Re increases for all shapes of the wavy channel, however, at the expense of the raised pressure losses. Also, the wavy channel with a phase-shift of ∅= 0 deg showed the highest enhancement in the performance of heat transfer followed by that of ∅=90 and 180 deg, respectively. The rotation had a strong impact on the flow field and heat transfer performance. With the increase of rotating speed, lower wall heat transfer coefficient significantly increased, while the upper wall heat transfer coefficient exhibited a slight increase, indicating that those three different geometries of the wavy channels had a good versatility at various values of rotating speeds. The numerical results were compared with those available in the literature, and the results were in a good agreement.

A Numerical Analysis of Convection Heat Transfer and Friction Factor for Oscillating Corrugated Channel Flows

The aim of this article is to understand numerically the flow and heat transfer characteristics under oscillating flow conditions for periodically corrugated wavy channel. For the same channel, under steady-state flow conditions, experimental and numerical studies were done under steady-state flow conditions by our two previous studies. Three turbulence models are used, namely the k–ω, the Shear Stress Transport (SST), and the transition SST. According to the previous study, the best agreement with experiments was obtained using the SST turbulence model. Therefore, the SST turbulence model is applied in this study on the oscillating flow. The finite volume method is used as the numerical method. Investigations are performed for air flowing through corrugated channel which has sharp wavy peaks with an inclination angle of 30° and 5 mm minimum channel height. Reynolds number is varied within the range 6294–7380, while keeping the Prandtl number constant at 0.70. Four different sinusoidal oscillating flow conditions are used. Variations of the Nusselt number, friction factor, and thermo-hydraulic performance factor with the Reynolds number are studied.

Effects of surface roughness in microchannel with passive heat transfer enhancement structures

We present a numerical study of the effects of surface roughness, which is unavoidable due to manufacturing tolerance, on laminar flow and heat transfer in microchannels. Three different channel types namely, square channel, wavy channel and dimpled channel are studied. Surface roughness is modeled as a superposition of waves described by Fourier series and exponential correlation function. Up to 2% relative roughness is introduced to one of the four side walls. We introduce the surface roughness by meshing a smooth channel. The boundary nodes are then displaced to introduce surface roughness. Periodic boundaries are used to study the flow and heat transfer features in the fully developed region. The Reynolds number keeps at 500, and 0.5 W/mm2 heat flux is adopted on the bottom of heat sinks. Results show that roughness could increase the overall flow resistance and Nusselt number. While relative roughness is about 2%, pressure drop increased by 3%, 5.3%, 5.9%, Nusselt number increased by 10%, 6.5%, 19.8% in square channel, wavy channel and dimpled channel respectively. Moreover, local influence of roughness highly depends on the geometric shape of the microchannel. The simulation results are expected to provide guidance to roughness control in microchannel manufacturing.

An implicit finite difference analysis of magnetic swimmers propelling through non-Newtonian liquid in a complex wavy channel

There are many unicellular tiny organisms which can self-propel collectively through non-Newtonian fluids by means of producing undulating deformation. Example includes nematodes, rod shaped bacteria and spermatozoa. Here we use Taylor’s swimming sheet model, with non-Newtonian fluid bounded with in a complex wavy walls of a two-dimensional channel. Oldroyd-4 constant fluid is approximated as cervical mucus and MHD effects are also considered. After utilizing lubrication and creeping flow assumption the reduced non-linear differential equation is solved (by implicit finite difference technique) so that it will satisfy the dynamic equilibrium condition for steady propulsion. For a special (Newtonian) case the expressions of swimming speed and flow rate are also presented. We also demonstrate that the rheological properties of non-Newtonian fluid can assist or resist the pack of micro-organisms (swimming sheet), while the larger undulation amplitude in swimmer’s body and magnetic field in downward direction can enhance the propulsion speed. The solution obtained via implicit finite difference method is also validated by a built in MATLAB routine bvp-4c. This built in function is based on collocation technique. Moreover an excellent correlation is achieved for both numerical methods.

Performance evaluation of melting/solidification mechanism in a variable wave-length wavy channel double-tube latent heat storage system

Abstract Thermal energy storage and recovery in a double-pipe latent heat storage (LHS) system with variable wave-length wavy channels were examined. The presence of wavy channels with variable wave-length makes it possible for the desired aggregation of the solid waves inside the Phase Change Material (PCM) domain. The PCM and the moving water are placed in the outer and inner sides, respectively, in the vertical double tube heat storage unit. Different configurations of variable sinusoidal wave-length were studied compared with fixed wave-length as well as straight channel unit. The wave-amplitude, temperature and Reynolds number of water were also analysed. The significant effects of channel waviness with variable wave-length are presented results in higher heat transfer inside and to/from the PCM domain. Increasing the water temperature and Reynolds number, as well as wave-amplitude, result in a shorter melting/solidification time. Based on the results of the selected case, the time of melting/solidification reduces by almost 70.8/42.8%, respectively, compared with straight wall case. Furthermore, the heat storage/recovery rate is 8.3/3.0 W for melting/solidification, respectively, for the selected configuration which is equal to 2.4/1.7 W for the straight channel case.

Heat transfer and flow characteristics in a sinusoidally curved converging-diverging channel

The objective of this work is to present the thermal performance characteristics and to examine the hydrodynamic structure of the fluid which improves the rate of heat transfer in parallel with the penalty of pressure drop by means of the time-averaged streamlines topology, <Ψ>, streamwise velocity distribution, <u>, vorticity concentration, <ω> and turbulent Reynolds stress, u'v'‾/U2 for the sinusoidal wavy channel. A wide range of experiments were performed for Reynolds numbers, Re ranging from 4 × 103 to 1 × 104 in order to determine the heat transfer rate and the friction factor, f with varying the channel height expansion/contraction ratio, M = Hmin/Hmax such as 0.5, 0.35 and 0.28. The results revealed that a significant heat transfer enhancement was achieved with a considerable penalty of pressure drop. The highest thermal performance factor, TPF was obtained as 1.46 for M = 0.5. Numerical simulations were conducted to confirm the experimental results for the same parameters. The Shear Stress Transport k-w (SST k-w) turbulence model was used to perform numerical analyses. After ensuring the consistency of experimental thermal performance results with numerical predictions, the Particle image velocimetry (PIV) system was utilized for investigating the flow physics in the sinusoidally curved converging-diverging channel for all M values at Re = 4 × 103 where the TPF is maximum.

On the long-term simulation of stochastic differential equations for predicting effective dispersion coefficients

This article discusses some numerical pitfalls associated with the classical solution of stochastic Langevin equations via the Euler–Langevin algorithm for long-term dispersion features. A simple operator-splitting algorithm is proposed to overcome these short-comings and, starting from it, a simple and computationally consistent algorithm for the simulation of stochastic differential equations is presented. Dispersion properties of tracer particles in cylindrical wavy channels and cellular flows are addressed in detail. Numerical results of the two algorithms proposed are compared with numerical results obtained from Brenner’s macrotransport theory.