Asymmetric Microchannel Research Articles

Thermal radiation effect in electroosmosis regulated peristalsis transport of Williamson hybrid nanofluid via an asymmetric tapered channel

AbstractElectroosmosis effects in a peristaltic transport of nanofluids are significant for developing the biomimetic pumping structure at a microscopic extent in physiological medications, for instance, ocular drug delivery systems. The present article addresses the numerical assessment of a peristaltically driven electro‐osmotic flow of a Williamson hybrid nanofluid. The flow is intended to be two‐dimensional, incompressible, unsteady, and subjected to an asymmetric tapered micro‐channel. The characteristics of hybrid nanofluid, which consists of silver (Ag) and copper (Cu) as nanoparticles with base fluid‐blood, are explored in a relative manner with regular nanofluid Ag‐blood. Further, the study includes the impact of linear thermal radiation, energy dissipation through viscosity and resistance phenomena with an externally applied consistent magnetic field. The mathematical model is simplified using dimensionless similarity transformations and numerically solved via MATLAB software. Variations in momentum, thermal energy, and entropy generation against various emerging physical parameters are deliberated through graphical results. Longitudinal velocity towards the center line and heat transfer rate is also analyzed through numerical data illustrated in table form. This study introduces a novel mathematical model for the peristaltically driven electroosmosis flow of Ag‐Cu/blood hybrid nanofluid in a tapered asymmetric microchannel, incorporating external electric and magnetic field effects.

Mass transfer of gas–liquid two‐phase flow in asymmetric parallel microchannels with liquid feed splitting

AbstractDue to size limitations, the gas–liquid absorption capacity of a single microchannel is limited, making it difficult to achieve large‐scale CO2 capture. Therefore, the parallel microchannels combining the advantages of high efficiency and large throughput stand out. However, when the operating condition is high gas–liquid flow rate ratio, the liquid phase between bubbles almost disappears after multiple distributions, which affects the amount of gas–liquid absorption. In this study, the numbering‐up of the asymmetric parallel microchannels in the gas–liquid absorption process was investigated by splitting the liquid feed stream in two. The flow patterns under different operating conditions were obtained. The flow and distribution of gas–liquid two‐phase flow were investigated, and the reason of the distribution deterioration caused by appearance of long slug bubbles was explained by the pressure drop distribution. The total liquid mass transfer coefficient and bubble residence time were derived and obtained, and the mass transfer was further discussed.

Numbering-up and stability strategies of bubbles in yield stress fluids in asymmetric parallelized microchannel

Preparation of foams within microchannels is a clean and capable of precisely controlled synthesis. In this work, high throughput production of bubbles in Carbopol gels (0.05 wt%, 0.1 wt%, 0.2 wt%) in asymmetric parallel channels is investigated. Bubbles in Carbopol gels are strongly unstable, and the asymmetry of the microchannel makes bubble instability more pronounced. A “slug-slug” flow pattern is observed for only 0.05 wt% Carbopol and microchannels with back cavities, and the bubble train is highly unstable. The strategy proposed in this article solves the challenge of numbering-up of bubbles produced in YSFs by strategically reducing the gas pressure, and the stability of bubble train and activation rate of microchannel are improved, which is of great engineering significance for the high-throughput production of high-quality foam materials.

High-Density Microporous Drainage-Integrating Sheath Flow Generator for Streamlining Microfluidic Cell Sorting Systems.

Tremendous efforts have been made to develop practical and efficient microfluidic cell and particle sorting systems; however, there are technological limitations in terms of system complexity and low operability. Here, we propose a sheath flow generator that can dramatically simplify operational procedures and enhance the usability of microfluidic cell sorters. The device utilizes an embedded polydimethylsiloxane (PDMS) sponge with interconnected micropores, which is in direct contact with microchannels and seamlessly integrated into the microfluidic platform. The high-density micropores on the sponge surface facilitated fluid drainage, and the drained fluid was used as the sheath flow for downstream cell sorting processes. To fabricate the integrated device, a new process for sponge-embedded substrates was developed through the accumulation, incorporation, and dissolution of PMMA microparticles as sacrificial porogens. The effects of the microchannel geometry and flow velocity on the sheath flow generation were investigated. Furthermore, an asymmetric lattice-shaped microchannel network for cell/particle sorting was connected to the sheath flow generator in series, and the sorting performances of model particles, blood cells, and spiked tumor cells were investigated. The sheath flow generation technique developed in this study is expected to streamline conventional microfluidic cell-sorting systems as it dramatically improves versatility and operability.

Heat transfer model analysis of fractional Jeffery-type hybrid nanofluid dripping through a poured microchannel

This study investigates the impact of coupled heat and mass transfer on the peristaltic migration of a magnetohydrodynamic (MHD) stress-strain Jeffery-type hybrid nanofluid flowing through an inclined asymmetric micro-channel with a porous medium. The fundamental two-dimensional momentum and energy transport equations are simplified under the assumptions of long wavelength and low Reynolds number. To solve the momentum and heat transfer problems, two advanced fractional derivative approaches are employed: the fractal integral and the Prabhakar fractional derivative. The pressure difference is determined using numerical integration techniques, such as the Stehfest and Tzou's algorithms. The results are presented through graphs and tables, which illustrate the effects of various parameters on the velocity, heat transfer, and trapping phenomena. As a result, we concluded that, pressure gradients grow with higher Reynolds numbers and channel-inclined angles. The heat transfer rate is observed to decrease as the Darcy number and the orientation of the electromagnetic field increase. When comparing the fractional derivative approaches, the fractal operator exhibits a more significant impact on the momentum profiles compared to the Prabhakar fractional operator. This difference is attributed to the distinct characteristics of the integral kernels associated with each fractional derivative definition. Furthermore, when comparing hybrid nanofluids, water-based (H2O + Ag + TiO2) hybrid fluids have a somewhat more significant effect than (C6H9NaO7 + Ag + TiO2) hybrid nanofluids.

Analysis of activation energy on the Johnson–Segalman nanofluid through an asymmetric microchannel: Numerical study

Activation energy and thermal radiation as a means of heat transfer are significant and fascinating phenomena for scientists and researchers because of their significance in cancer treatment. As a result, heat kills cancer cells and shrinks tumors, making hyperthermia therapy a cutting-edge cancer treatment. This paper examines the peristaltic motion of a Johnson–Segalman nanofluid across an asymmetric pliable microchannel under the impact of activation energy. We obtained the governing equations for the non-Newtonian nanofluid. Partial differential equations (PDEs) are reduced to ordinary differential equations (ODEs) under the assumption of large wavelengths and tiny Reynolds number assumptions. The flow patterns and trapping phenomena were numerically generated using the NDSolve command of the computational mathematical software Mathematica. The influence of important liquid parameters was examined with graphical representations of the results. The current study reveals an enhancement in the heat generation parameter, an enhancement in the temperature and a reduction in the concentration.

Investigation of thermal radiations impacts with double diffusive convection for Prandtl nanofluid with slip in an asymmetric ciliated channel

Thermal radiations are extensively utilized in the medical sciences, and the investigation of thermal radiation combined with double diffusive phenomena is the burning research area because of its enormous applications in treatment of various diseases. Cilia play significant part in many physiological processes of animal and humans. A novel mathematical prodigy for Prandtl nanofluid with thermal radiations and double diffusion convection by implementing slip at boundaries is presented for cilia induce flow in an asymmetric microchannel. Mathematical scheme for the physiological flow is developed and then pertinent equations are designed exploiting low Reynolds number and long wavelength simplifications. Solution for the physiological nanofluid is gathered by emphasizing on the novel BVP4C technique in MATLAB and resulting outcomes are elaborated with aid of graphical illustrations. Pros and cons of various physical flow parameters like thermal slip parameters, Prandtl fluid parameters, Grashof parameter, Prandtl parameter , Brownian motion parameter, thermal radiation parameter, Brinkmann number, Soret parameter are examined on the velocity, magnetic force function, temperature profile, concentration and nanoparticles volume fraction. It is reported that slip parameter really effects the nanofluid transport within the ciliated microchannel, it reduces the fluid flow, diffusion phenomena of the nanoparticles in the ciliated microchannel surges when radiation parameter is strengthened. The reported investigation will be instrumental in heat radiation effect for regulation of blood circulation to cure the cancer tissues in multiple drug delivery systems and will pave the way for the designs of certain diagnostic and pharmacological devices.

Numerical treatment of entropy generation and Bejan number into an electroosmotically-driven flow of Sutterby nanofluid in an asymmetric microchannel

This article aims to investigate the electrokinetic peristaltic flow of the Sutterby nanofluid through an asymmetric microchannel with a porous medium and the Joule heating parameter. The magnetic field is applied in the transverse direction and the electric field on the flow direction. The flow model consists of the continuity, momentum, heat, and electric potential equations, with appropriate boundary conditions. The Debye-Hückel linearization approximation is considered. Under the long wavelength and small Reynolds number approximation, the lengthy equations were reduced. The resultant coupled equations are numerically solved by the renowned NDSolve coding using Mathematica software. Entropy and Bejan number are also incorporated in this study. The velocity, temperature, and the phenomenon of entrapment are analyzed in depth with the aid of graphical representations. Streamlines of various waveforms are also discussed. The analysis discovered that the velocity of the fluid enhanced for porosity parameter and reverse effects is observed on the quantity of the magnetic parameter.

Anisotropic flow physics in diamond microchannels: Design implications for microfluidic rectifiers handling Newtonian fluids

The study explores anisotropic flow behavior in microchannels, which is crucial for advancing microfluidic rectifiers. Specifically, the investigation focuses on the directional flow behavior of Newtonian fluids within diamond-shaped microchannels, a topology holding significant promise across various disciplines. Unlike non-Newtonian fluids, Newtonian fluids lack inherent directional traits, needing high Reynolds numbers for inertial effects necessary for effective rectification in asymmetric flow structures. High Reynolds numbers in microchannels are challenging, but diamond microchannels uniquely exhibit inertial effects even at low Reynolds numbers, yet their potential for designing rectifiers is largely unexplored. The study presents two unique asymmetric diamond microchannel designs and conducts thorough three-dimensional numerical analyses to assess fluid flow across different design parameters. Rectification is quantified through fluid diodicity, demonstrating that configurations with higher width and aspect ratios and shorter lengths produce significant rectification effects. Examining velocity profiles and flow resistances in both directions illustrates irreversible flow physics. Notably, the observed maximum diodicity for the proposed design reaches 1.61 for Newtonian fluids, surpassing most previous designs by 11%–40%. Quantitative relationships between flow resistances in both directions and design variables through regression analysis allow determining flow resistances within ±8% and fluid diodicity within ±7% and ±10%, respectively, based on constant flow rate and pressure drop. These correlations provide valuable insights for the initial design of microfluidic rectifiers using these configurations. The results offer essential guidance for effectively designing microfluidic rectifiers using diamond microchannels in various scientific applications.

Enhancement of pool boiling performance through an asymmetric dual V-groove microchannel structured surface

In pool boiling, microchannels on the heated surface change the bubble dynamics and consequently improve the heat transfer. In this study, two new microchannel configurations, i.e., asymmetric dual V-groove microchannels (VM) and orthogonally intersecting asymmetric dual V-groove microchannels (OIVM) have been introduced to study enhancement in pool boiling. The heat transfer enhancement due to the modified surfaces was established by comparing the heat transfer rates from the reference flat surface. Experiments have been performed using deionized water under saturation temperature at one atmosphere to evaluate the steady state heat transfer characteristics. The bubble dynamics and interface morphology at various heat flux levels have been captured using high-speed camera. The experimental observations have revealed that both the microchannel configurations exhibit a substantial improvement in heat transfer compared to that of flat surfaces. The OIVM surface demonstrates the highest rates of heat transfer and increase of 5.3 times in the maximum heat transfer coefficient (HTC) and 2.4 times in the critical heat flux (CHF) were observed compared to that of flat surfaces. Similarly, the VM surface demonstrates an improvement of 2.2 fold in HTC and 1.7 fold in CHF compared to the flat surface. Moreover, the OIVM surface demonstrates better heat transfer rates than that of modified surfaces investigated in the past studies. The increased heat transfer rate with the OIVM surface can be ascribed to large area for heat exchange, increased bubble initiation sites, bubble motion promoted macroconvection and efficient rewetting mechanism.

Droplet formation of yield stress fluids in asymmetric parallelized microchannels

The microemulsion method is limited due to low productivity. Using Carbopol gel (0.05 %, 0.13 %, 0.2 %) and mineral oil as dispersed phase and continuous phase respectively (3 ≤ Qd ≤ 8, 2 ≤ Qc ≤ 350), the numbering-up of YSFs droplets in asymmetric parallel microchannels are experimentally studied. Ca*(10-3-10) and Cac (10-4-10-2) are introduced to divide the two-dual droplet flow pattern which is conducive to production. It is found that yield stress mainly acts on the necking stage of droplet formation, so the continuous phase flow can be increased to shorten the necking time and improve the size uniformity. The influence of rheology on droplet morphology makes the existing multiphase flow pressure drop model no longer applicable. Therefore, a correction pressure drop model of Carbopol slugs and prediction models of droplet size and generation frequency are proposed. This study provides a reference for the high-throughput production of YSFs droplets in microchannels.

Peristaltic rheology and thermal analysis of SWCNT-MWCNT/H2O hybrid nanofluid in a complex microchannel under electroosmotic effects

The primary goal of this research is to investigate the rheology and heat transport of a hybrid nanofluid in an asymmetric microchannel in the presence of an electric field. The mobility of hybrid fluid is caused by peristaltic waves that contract and relax sinusoidally along the channel length. The rheological equations system is simplified by introducing relevant similarity variables, which are then solved using the integration approach. In this study, convective boundary conditions are applied. The electric potential function, velocity profile, pressure gradient, stream function, and temperature profile are all mathematically expressed. The current study’s findings are based on three physiological estimates: first is known as the creeping phenomenon, second as the greater wavelength condition, and third as the Debye–Hückel linearization (DHL). Using two different nanoparticles (SWCNT-MWCNT), the peristaltic mechanism is used to model water-based nanofluids. The three-dimensional graphs of rheological features are generated using Mathematica Software to elaborate the influences of relevant parameters on the rheological characteristics. By enhancing both the Biot number and the heat source/sink parameter in the hybrid fluid, the magnitudes of the temperature profile and the Nusselt number are higher than in the [Formula: see text] nanofluids. The magnitude of velocity profile is enhanced by increasing the Buoyancy forces and slip velocity. The results of simple fluid are obtained in the absence of concentration parameter. To boost the pumping phenomena, the special nature of peristaltic waves is used. The comparative study of nanofluid and hybrid fluid is also addressed. Three-dimensional graphs are plotted to clearly observe the influence of rheological parameters on flow features.

Contribution of electromagnetism in lowering entropy in microchannel

The study examined how entropy can be reduced in an asymmetric microchannel with sinusoidal walls by analyzing the flow of an incompressible micropolar fluid that is electrokinetically driven. The study takes into account the effects of Ohmic and viscous dissipation of energy in a magnetohydrodynamic environment. To model electroosmotic phenomena, the Poisson equation and Nernst–Planck equation were used, which were simplified using Debye–Huckel linearization and a small ionic Peclet number. The energy, rotational momentum, mass, and momentum equations for the micropolar fluid were constructed and linearized using a lubrication approach before being solved analytically. The resulting expressions for velocity microrotation and temperature were then used to compute the Bejan number and the formation of entropy number The study also examined the effects of various thermophysical parameters and discussed their potential applications in fields such as biomedical engineering, pharmaceuticals, energy conservation, cancer treatment, and manufacturing. The findings suggest that entropy generation can be reduced by increasing the micropolar coupling number and temperature difference parameter This study provides a theoretical guide for the operation and thermal control of flow actuation systems with asymmetric geometry.

An Optimization of Grooves Structure for Thermal Performance Enhancement in Microchannel Heat Sink

In the current work, the thermal performance of a grooved microchannel heat sink is evaluated at different offset positions inside the channel. For this purpose, the Eulerian–Eulerian approach-based mathematical model is developed and is numerically solved using the finite volume approach. Water is the base fluid to which alumina nanoparticles were added to enhance heat transfer. The effect of the Reynolds number (100–1,000), particle diameter (10–50 nm), the number of grooves (10–80), offset between the grooves (0–1), and particle volume fraction (0–5%) on the dimensionless pressure drop, Nusselt number, and coefficient of performance are investigated, and their impact on the microchannel’s thermal characteristics is quantified. Most importantly, the microchannels with symmetric (Offset = 0) and asymmetric grooves (Offset ≠ 0) were compared, and it was found that offsetting the grooves has an insignificant effect on the microchannel performance. Furthermore, an empirical correlation is proposed to evaluate the coefficient of performance of both symmetric and asymmetric microchannels as a function of the output variables.

Numerical study of bacteria removal from microalgae solution using an asymmetric contraction-expansion microfluidic device: A parametric analysis approach

Microalgae have been remarkably taken into account due to their wide applications in the biopharmaceutical, nutraceutical and bio-energy fields. However, contamination of microalgae with bacteria still appears to be a concern, adversely impacting products’ quality and process efficiency. Microalgae decontamination with conventional techniques is usually expensive and time-consuming. Moreover, damage to microalgae cells is highly possible. Asymmetric contraction-expansion microchannels (Asym-CEMCs) are promising passive microfluidic devices that can overcome conventional techniques' drawbacks with their standing-out features. However, the flexibility of Asym-CEMCs performance arising from their various tunable geometrical parameters results in the fact that their performance for separating a target particle cannot be predicted without an investigation. In this work, for the first time, Asym-CEMCs were numerically studied for the removal of a very conventional bacteria, B. subtilis (1 μm), from one of the most popular microalgae, C. vulgaris (5.7 μm). The influences of the microchannel aspect ratio, length and width ratios of the expansion-to-contraction zones, and the total flow rate on the separation resolution and focusing width of the particles were investigated by a 3D numerical model. The aspect ratio had the strongest influence on the Asym-CEMC performance, however, the length ratio had no considerable effect on the results. A decrease in the aspect ratio augmented the shear-induced lift force and Dean drag force, leading to a significant separation resolution improvement. Microalgae decontamination was also enhanced by an increase in the total flow rate and expansion-to-contraction width ratio. Finally, a locally optimized Asym-CEMC with an aspect ratio of one and expansion-to-contraction width and length ratios of 4.7 and 2.07, respectively, was proposed, leading to complete microalgae decontamination with a high normalized separation resolution of 0.6. In a word, Asym-CEMCs with tailored dimensions are promising for successfully decontaminating microalgae from bacteria.

Analysis of Bejan number and Entropy generation of Non-Newtonian nanofluid through an asymmetric microchannel

This study examines the electro-kinetic peristaltic movement of a Sutterby nanofluid under the influence of entropy generation and Bejan number. The fluid flow was introduced into the undulating asymmetrical microchannel. The Sutterby nanofluid flow was considered in the static electric field in the horizontal direction and the applied external magnetic field in the transverse direction. The mathematical formulation of the implications of Bejan number and entropy generation are also explored. The governing fluid flow equations, such as the continuity, momentum, and temperature equations, are reduced considering the tiny wave number and the small Reynolds number approximation. The resulting nonlinear equations were resolved numerically with the help of the built-in NDSolve coding through the computational mathematical software MATHEMATICA. Graphical illustrations of the fluid velocity profile, temperature, entropy generation, Bejan number, and trapping phenomenon (streamlines) are presented in detail. The results from the Sutterby nanofluid model might have a broad range of applications, such as cancer tissue destruction, disease diagnosis, etc. It was concluded that there is a decrease in the fluid velocity and an increase in the Hartmann number.

Formation of viscoelastic droplets in asymmetrical parallel microchannels

The dynamics of viscoelastic droplet formation in T-shaped asymmetric parallel microchannels are investigated using a high-speed camera. The effects of fluid viscoelasticity and flow rates of the two phases on the stability and uniformity of droplets, fluid flow distribution, and droplet formation period are explored. The results reveal that the viscoelasticity advances the transition from the squeezing stage to the rapid pinch-off stage, slows down the necking of rapid pinch-off stage and increases the duration of the stretching stage. It is found that the stability is significantly improved by increasing the continuous phase flow rate, and the droplet uniformity is affected by both the flow rates of the two phases and the fluid elasticity. In addition, prediction models for the fluid flow distribution, droplet size and droplet formation period are established. At last, the breakup mode of different elasticity filament and the satellite droplet size are studied. It is concluded that the increased elasticity contributes to the elimination of satellite droplets, and the satellite droplet size are affected by the fluid elasticity and the continuous phase flow rate.

Study of peristaltic activity in non-linear blood analysis of Williamson fluid in a microchannel

The present investigation is modeled to study the effect of homogeneous and heterogeneous reactions on the peristaltic blood transportation of electrically conducting Williamson fluid in an asymmetric microchannel under velocity slip conditions. The mechanism of heat transfer is also examined in conjunction with viscous dissipation and thermal radiation. Implementation of small Reynolds number and large wavelength concepts leads to a reduction in the complexity of the system. Series solutions for velocity, temperature, stream function, and concentration fields are found using the regular perturbation technique. Using Mathematica software, Simpson’s rule was used to evaluate the pumping features such as pressure rise and frictional force. The effects of embedded parameters are portrayed and discussed by using a graphical approach. The skin friction and Nusselt number at the channel walls are established for a choice of assessments of significant parameters and which are exhibited in a tabular manner. It is observed that an enhancement in the values of Weissenberg number fluid velocity reduces at the lower channel wall whereas it increases at the channel upper wall.

Flow boiling of R1336mzz(Z) in tapered microgaps with asymmetric dual-V microchannels

The development of high heat flux cooling technologies has attracted great interest of investigations during the last decades, which motivated a series of investigations regarding flow boiling in microchannels. In a recent investigation, new heat sinks composed of a bottom surface milled with asymmetric Dual-V microchannels combined with a tapered microgap were presented, and the occurrence of boiling inversion was documented for the first time in flow boiling experiments using water as working fluid. It is noteworthy, however, that despite its great thermal properties the use of water as working fluid may not meet some cooling requirements, and the use of refrigerants is necessary. In addition, with the increasing concerns with environmental impacts, novel refrigerants with low environmental impacts have been presented to the market, but limited results are found in the literature for their flow boiling performances. Hence, the present work is focused on flow boiling experiments with the Hydro-Fluoroolefin R1336mzz(Z) in copper heat sinks combined to a tapered manifold. Tests were conducted using three different surfaces, with and without asymmetric Dual-V microchannels, the selected saturation temperature was 41 °C, and inlet mass fluxes varied from 400 to 1000 kg/m2s. Effects of various parameters were evaluated and put in context to the flow patterns observed with a high-speed camera. The best surface promoted the dissipation of up to 93 W/cm2 without reaching the critical heat flux, with wall temperature lower than 74 °C, pressure drop lower than 10 kPa, and maximum heat transfer coefficient reaching 22 kW/m2K.

Peristaltic transport of non-Newtonian nanofluid through an asymmetric microchannel with electroosmosis and thermal radiation effects

Peristaltic transport of non-Newtonian nanofluid through an asymmetric microchannel with electroosmosis and thermal radiation effects