Porous Microchannel Research Articles

Numerical simulation of the ferro-nanofluid flow in a porous ribbed microchannel heat sink: investigation of the first and second laws of thermodynamics with single-phase and two-phase approaches

In this study, the entropy generation of $${\text{Fe}}_{3} {\text{O}}_{4}$$ –water nanofluid flow in the porous ribbed microchannel heat sink with two approaches is investigated. For modeling, the nanofluid flow inside of porous ribbed microchannel heat sink with two models is classified. The range of Reynolds number and porosity of ribbed blocks is $$10 \le \text{Re} \le 80$$ and $$0 \le \varepsilon \le 75$$ %. The effects of Reynolds number, porosity and compression between microchannel without any rib, microchannel with solid rib and microchannel with LTNE porous rib for two models are investigated. The highest value for the coefficient of heat transfer occurs in the maximum value of volume concentration of nanoparticles, Reynolds number and porosity percent. We realized that, in this investigation, the mixture model represents higher value than single-phase model except in the zero percent of volume fraction of nanoparticles. Also, we showed that the entropy generation increases by increasing the porosity value.

Boiling Heat Transfer Performance of Parallel Porous Microchannels

Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.

Influence of Joule heating and wall slip in electroosmotic flow via peristalsis: second law analysis

Electrokinetic peristaltic slip transport in an asymmetric porous microchannel is studied to explore the entropy production in steady magnetohydrodynamic Jeffery fluid under simulation of Debye and long-wavelength approximations. The emerging two-dimensional bounded problem with electrokinetic body forces is solved numerically. Appropriate combination of heat and momentum equations with Jeffery model, after non-dimensionalization, generated controlling parameters in order to determine velocity, pressure gradient, temperature, entropy production and Bejan number. The trapping mechanism is also visualized by drawing streamlines against governing parameters. The zeta potential signifies the flow and heat response of the system. Former parameters like Brinkman number and Joule heating are compatibly liable for the increase in thermal irreversibilities. The outcomes of the present analysis are applicable in designing the thermofluidic micropumps and biomicrofluidic devices for separation processes and diagnosis.

New method of obtaining heat-resistant biomorphic composites with carbide reinforcement

In this work, an original method of obtaining biomorphic composites of the Me – MeCx type, consisting of several stages, has been proposed. One of the steps is the Infiltration through Nonreactive Solvent (INS) method, which consists in converting biomorphic carbon preforms into porous microchannel MeCx ceramics by transferring a carbide-forming element to carbon through a solvent that does not react with carbon. The interaction of biomorphic alder-based carbon templates with melts of Cu – Ti and Sn – Ti systems has been investigated. It has been shown that as a result of the interaction of biocarbon templates with Cu-10Ti and Cu-20Ti alloys, carbon walls turn into TiC grains of micron and nanometer sizes, which partially repeat the template microstructure. The mechanism of formation of such a structure has been proposed. It has been demonstrated that, upon the interaction with Sn – Ti system, TiC and Ti2SnC layers are formed on the surface of the microchannels with good preservation of the initial template structure.

Heat and mass transfer and thermodynamic analysis of power-law fluid flow in a porous microchannel

Transfer of heat and mass and thermodynamic irreversibilities are investigated in a porous, parallel-plate microreactor in which the working fluid is non-Newtonian. The investigated microreactor features thick flat walls with uneven thicknesses, which can be subject to different thermal loads. The dimensionless governing equations of the resultant asymmetric problem are first derived theoretically and then solved numerically by using a finite volume technique. This results in two-dimensional solutions for the velocity, temperature and concentration fields as well as the distributions of Nusselt number and local and total entropy generations. The results clearly demonstrate the significance of the numerical value of the power-law index and departure from Newtonian behavior of the fluid. In particular, it is shown that by increasing the value of power-law index the Nusselt number on the wall decreases. This leads to the intensification of the temperature gradients in the system and therefore magnifies the local and total entropy generations. Also, it is shown that the wall thickness and thermal asymmetry can majorly affect the heat transfer process and thermodynamic irreversibility of the microreactor. It is noted that the current work is the first comprehensive study of heat transfer and entropy generation in porous micro-chemical reactor with non-Newtonian, power-law fluid.

Unsteady Laminar Pulsating Flow in a Saturated Porous Microchannel in the Presence of Electrical Double-Layer Effects

Abstract The forced convection of a pulsating flow in a saturated porous parallel-plates microchannel driven by a periodic pressure in the presence of an electrical double layer is investigated. Such configuration is very important but seldom considered in literature. Analytical solutions for electrical, momentum, and temperature fields are obtained by means of a substitution approach. The results show that the flow fields depend highly on the electro-osmotic parameter κ, the angular velocity parameter Ω, as well as the Darcy number Da.

The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel

Microchannels are widely used in electrical and medical industries to improve the heat transfer of the cooling devices. In this paper, the fluid flow and heat transfer of water–Al2O3 nanofluids (NF) were numerically investigated considering the nanoparticle shape and different cross-sections of a porous microchannel. Spherical, cubic, and cylindrical shapes of the nanoparticle as well as circular, square, and triangular cross-sections of the microchannel were considered in the simulation. The finite volume method and the SIMPLE algorithm have been employed to solve the conservation equations numerically, and the k-ε turbulence model has been used to simulate the turbulence fluid flow. The models were simulated at Reynolds number ranging from 3000 to 9000, the nanoparticle volume fraction ranging from 1 to 3, and a porosity coefficient of 0.7. The results indicate that the average Nusselt number (Nuave) increases and the friction coefficient decreases with an increment in the Re for all cases. In addition, the rate of heat transfer in microchannels with triangular and circular cross-sections is reduced with growing Re values and concentration. The spherical nanoparticle leads to maximum heat transfer in the circular and triangular cross-sections. The heat transfer growth for these two cases are about 102.5% and 162.7%, respectively, which were obtained at a Reynolds number and concentration of 9000 and 3%, respectively. However, in the square cross-section, the maximum heat transfer increment was obtained using cylindrical nanoparticles, and it is equal to 80.2%.

Boston Ivy Disk-Inspired Pressure-Mediated Adhesive Film Patches.

Boston ivy (Parthenocissus tricuspidata) climbs brick walls using its tendril disks, which excrete a sticky substance to perform binding and attachment. While the cellular structures and adhesive substances involved have been identified for decades, their practical applicability as an adhesive has not yet been demonstrated. A Boston ivy disk-inspired adhesive film patch system is reported in which structural and compositional features of the Boston ivy disk are mimicked with a form of thin adhesive film patches. In analogy to the sticky disk of a mature ivy in which porous microchannels are occupied by catechol-containing microgranules on the bound site, 3,4-dihydroxylphenylalanine bolaamphiphile nanoparticle (DOPA-C7 NP)-coated alginate microgels are two-dimensionally positioned into the cylindrical holes that are periodically micropatterned on the flexible stencil film. Finally, it is demonstrated that the pressurization of the patch breaks the microgels filled in the holes, releasing the polysaccharides and leading to crosslinking with DOPA-C7 NPs via ligandation with combined Ca2+ and Fe3+ ions, thus enabling development of a pressure-mediated adhesion technology.

Direct Simulation Monte Carlo investigation of fluid characteristics and gas transport in porous microchannels

The impetus of the current research is to use the direct simulation Monte Carlo (DSMC) algorithm to investigate fluid behaviour and gas transport in porous microchannels. Here, we demonstrate DSMC’s capability to simulate porous media up to 40% porosity. In this study, the porous geometry is generated by a random distribution of circular obstacles through the microchannel with no interpenetration between the obstacles. The influence of the morphology along with rarefaction and gas type on the apparent permeability is investigated. Moreover, the effects of porosity, solid particle’s diameter and specific surface area are considered. Our results demonstrate that although decreasing porosity intensifies tortuosity in the flow field, the tortuosity reduces at higher Knudsen numbers due to slip flow at solid boundaries. In addition, our study on two different gas species showed that the gas type affects slippage and apparent gas permeability. Finally, comparing different apparent permeability models showed that Beskok and Karniadakis model is valid only up to the early transition regime and at higher Knudsen numbers, the current data matches those models that take Knudsen diffusion into account as well.

Preparation and evaluation of microfluidic magnetic alginate microparticles for magnetically templated hydrogels

Our aim is to develop a hydrogel-based scaffold containing porous microchannels that mimic complex tissue microarchitecture and provide physical cues to guide cell growth for scalable, cost-effective tissue repair. These hydrogels are patterned through the novel process of magnetic templating where magnetic alginate microparticles (MAMs) are dispersed in a hydrogel precursor and aligned in a magnetic field before hydrogel crosslinking and subsequent MAM degradation, leaving behind an aligned, porous architecture. Here, a protocol for fabricating uniform MAMs using microfluidics was developed for improved reproducibility and tunability of templated microarchitecture. Through iron quantification, we find that this approach allows control over magnetic iron oxide loading of the MAMs. Using Brownian dynamics simulations and nano-computed tomography of templated hydrogels to examine MAM chain length and alignment, we find agreement between simulated and measured areal densities of MAM chains. Oscillatory rheology and stress relaxation experiments demonstrate that magnetically templated microchannels alter bulk hydrogel mechanical properties. Finally, in vitro studies where rat Schwann cells were cultured on templated hydrogels to model peripheral nerve injury repair demonstrate their propensity for providing cell guidance along the length of the channels. Our results show promise for a micro-structured biomaterial that could aid in tissue repair applications.

Electrochemical impedance of electrodiffusion in charged medium under dc bias.

An immobile charged species provides a charged medium for transport of charge carriers that is exploited in many applications, such as permselective membranes, doped semiconductors, biological ion channels, as well as porous media and microchannels with surface charges. In this paper, we theoretically study the electrochemical impedance of electrodiffusion in a charged medium by employing the Nernst-Planck equation and the electroneutrality condition with a background charge density. The impedance response is obtained under different dc bias conditions extending above the diffusion-limiting bias. We find a transition in the impedance behavior around the diffusion-limiting bias and present an analytical approximation for a weakly charged medium under an overlimiting bias.

Influence of Hall current and Joule heating on entropy generation during electrokinetically induced thermoradiative transport of nanofluids in a porous microchannel

A comprehensive theoretical study of entropy generation during electrokinetically driven transport of a nanofluid is of prime concern in the paper. The flow is considered to take place on a wavy channel under the action of an external transverse magnetic field and an external pressure gradient. Navier slips at the walls of the channel and thermal radiation have been taken into account in the study. The theoretical study has been carried out by developing a mathematical model by taking into account the effects of Joule heating, viscous dissipation, and the transverse magnetic field on heat transfer during the electrokinetic transport of the fluid. The derived analytical expressions have been computed numerically by considering the nanofluid as a mixture of blood and ferromagnetic nanoparticles. Variations in velocity, streaming potential, temperature distribution, Nusselt number, and Bejan number associated with the electrokinetic flow in capillaries have been investigated by the parametric variation method. The results have been presented graphically. The present investigation reveals that streaming potential decreases due to the Hall effect, while for the cooling capacity of the microsystem, we find an opposite behavior due to the Hall effect. The study further reveals that the fluidic temperature is reduced due to increase in the Hall current, and thereby thermal irreversibility of the system is reduced significantly. The results presented here can be considered as the approximate estimates of blood flow dynamics in capillaries during chemotherapy in cancer treatment.

Numerical simulation of forced convection in a bi-disperse porous medium channel by creating new porous micro-channels inside the porous macro-blocks

PurposePorous medium has always been introduced as an environment for increasing heat transfer in cooling systems. However, increase in heat transfer and resolving pressure drop in the fluid flow have been focused on by researchers.The purpose of this paper is to study the effects of creating porous micro-channels inside porous macro-blocks to optimize system performance in channels.Design/methodology/approachTo simulate flow field, a developed numerical code that solves Navier–Stokes equations by finite volume method and semi-implicit method for pressure linked equations (SIMPLE) algorithm will be used together with bi-disperse porous medium (BDPM) method. Working fluid is air with Pr = 0.7 in laminar state. Influence of permeability changes by creation of micro-channels containing porous medium in vertical, horizontal and cross-shape patterns will be investigated.FindingsBy creating porous micro-channels inside macro-blocks, not only does the heat transfer increase significantly but the pressure also drops remarkably. Increase in performance evaluation criteria (PEC) is more evident in lower Reynolds numbers that can increase the PEC to 75 per cent by creating cross-shape micro-channels. By changing the permeability of micro-channels, PEC will increase by reducing the pressure drop but it has minor changes in Nu.Research limitations/implicationsThe current work is applicable to optimizing system performance by decreasing the pressure drop and increasing the heat transfer.Practical implicationsThe developed patterns are useful in increasing the system performance including the increase in heat transfer and decrease in pressure drop in systems such as air coolers required in electrical circuits.Originality/valueDevelopment and optimization of system performance by new patterns using BDPM in comparison to the previous patterns.

Flow dynamics and heat transfer in partially porous microchannel heat sinks

In this study, the flow dynamics and heat transfer in partially filled pin-based microchannel heat sinks (MCHS) are examined. The lattice Boltzmann method is used to analyse the physics of these systems and examine the effects of the flow, pin configuration, size and porous medium height. The results of the study reveal that, unlike the fully filled pin-based MCHS, there is no unique behaviour for the pin configuration effects and the performance of partially filled pin-based MCHS depends on the porous medium size and structure as well as the inertial forces in the flow. In particular, it is found that there are hydrodynamic and thermal-based critical porous medium heights at which the best performance in terms of heat removal switches from the inline to the staggered configuration. The dependence of these critical heights on the Reynolds number and the porous medium properties are analysed and the effects of the flow dynamics are further unravelled through a particle tracing technique. Furthermore, a simple flow model is developed, and is shown to capture well the main trends obtained from the simulations and to bring to light more of the system physics that help explain the interplay between the different parameters.

Heat transfer and entropy generation analysis of non-Newtonian flu flow through vertical microchannel with convective boundary condition

The entropy generation and heat transfer characteristics of magnetohydro-dynamic (MHD) third-grade fluid flow through a vertical porous microchannel with a convective boundary condition are analyzed. Entropy generation due to flow of MHD non-Newtonian third-grade fluid within a microchannel and temperature-dependent viscosity is studied using the entropy generation rate and Vogel's model. The equations describing flow and heat transport along with boundary conditions are first made dimensionless using proper non-dimensional transformations and then solved numerically via the finite element method (FEM). An appropriate comparison is made with the previously published results in the literature as a limiting case of the considered problem. The comparison confirms excellent agreement. The effects of the Grashof number, the Hartmann number, the Biot number, the exponential space- and thermal-dependent heat source (ESHS/THS) parameters, and the viscous dissipation parameter on the temperature and velocity are studied and presented graphically. The entropy generation and the Bejan number are also calculated. From the comprehensive parametric study, it is recognized that the production of entropy can be improved with convective heating and viscous dissipation aspects. It is also found that the ESHS aspect dominates the THS aspect.

Heat transfer performance of a porous copper micro-channel heat sink

A novel porous copper micro-channel heat sink based on the high thermal conductivity and structural stability of porous copper micro-channel material is proposed in this study. A circular cross-sectional and a multi-layer staggered arrangement are the main characteristics of the micro-channel heat sink. Additionally, a heat dissipation model is produced for porous copper micro-channel heat sink by analyzing the heat transfer process. Further, the theoretical heat transfer coefficient is calculated using MATLAB, and the experimental heat transfer coefficient is determined based on an experimental platform. The heat dissipation model is verified by comparing the theoretical and experimental heat transfer coefficients. The relation between the porous copper micro-channel heat sink parameters and the heat transfer coefficient that is obtained based on the heat dissipation model of the porous copper micro-channel heat sink is analyzed. The results exhibit that variations in pore diameter, porosity, porous copper length, porous copper width, porous copper height, and volume flow significantly affect the heat transfer performance.

Scalable Fabrication of Porous Microchannel Nerve Guidance Scaffolds with Complex Geometries.

Microchannel scaffolds accelerate nerve repair by guiding growing neuronal processes across injury sites. Although geometry, materials chemistry, stiffness, and porosity have been shown to influence nerve growth within nerve guidance scaffolds, independent tuning of these properties in a high-throughput manner remains a challenge. Here, fiber drawing is combined with salt leaching to produce microchannels with tunable cross sections and porosity. This technique is applicable to an array of biochemically inert polymers, and it delivers hundreds of meters of porous microchannel fibers. Employing these fibers as filaments during 3D printing enables the production of microchannel scaffolds with geometries matching those of biological nerves, including branched topographies. Applied to sensory neurons, fiber-based porous microchannels enhance growth as compared to non-porous channels with matching materials and geometries. The combinatorial scaffold fabrication approach may advance the studies of neural regeneration and accelerate the development of nerve repair devices.

Study of MHD Second Grade Flow through a Porous Microchannel under the Dual-Phase-Lag Heat and Mass Transfer Model

A semi-analytical investigation has been carried out to analyze unsteady MHD second-grade flow under the Dual-Phase-Lag (DPL) heat and mass transfer model in a vertical microchannel filled with porous material. Diffusion thermo (Dufour) effects and homogenous chemical reaction are considered as well. The governing partial differential equations are solved by using the Laplace transform method while its inversion is done numerically using INVLAP subroutine of MATLAB. The numerical values of fluid velocity, fluid temperature and species concentration are demonstrated through graphs while the numerical values of skin friction, heat transfer rate and mass transfer rate presented in tabular form for different values of parameters that govern the flow. For the first time, a comparison of heat transfer utilizing the classical Fourier’s heat conduction model, hyperbolic heat conduction Cattaneo-Vernotte (CV) model, and the DPL model is carried out for the flow of a second grade fluid. It is found that the differences between them vanish at dimensionless time t=0.4 (for temperature) and at t=0.5 (for velocity), i.e. at a time where the system reaches steady state. The influence of phase lag parameters in both thermal and solutal transport on the fluid flow characteristics have been deciphered and analyzed. The results conveyed through this article would help researchers to understand non-Fourier heat and mass transfer in the flow of second-grade fluids which may play a vital role in the design of systems in polymer industries.

Heat Transfer in Porous Microchannels with Second-Order Slipping Boundary Conditions

The paper presents results of a study of forced convection in a vertical flat and circular microchannels incorporating porous medium under slip boundary conditions of the first and second orders. The problem was solved analytically and compared with numerical simulations based on the lattice Boltzmann method. Effects of porosity and slip velocity on velocity and temperature profiles were investigated. Behavior of the normalized Nusselt number as a function of the Knudsen and Prandtl numbers, as well as the parameter M characterizing porosity of the medium in the microchannel, was also elucidated. Computations indicated that a decrease in porosity (an increase in the parameter M) causes a decrease in the velocity and temperature jumps on the wall, which contributes to the increase in the Nusselt number. Considering the effect of the second-order slip boundary conditions leads to the decrease in the velocity jump on the wall, when the coefficient A2 (this coefficient considers the second-order slip boundary conditions) changes from negative to positive values. The heat transfer rate at high Prandtl numbers increases with the increasing Knudsen number, because of the improved thermal interaction of the flow with the channel wall. Given the second-order boundary conditions, the effect of parameter A2 was not observed at small Prandtl numbers (Pr ≤ 1). For A2 0 the normalized Nusselt number decreases in comparison with the case of A2 = 0 (the first-order boundary conditions). The results by the analytical solution and the lattice Boltzmann method are in a good agreement with each other for A2 ≥ 0, with the differences ≤ 1%. For A2 < 0, the differences between two models are more noticeable. For A2 ≥ 0, predictions by the analytical model lie higher than the numerical results, whereas for A2 < 0, numerical simulations exceed the analytical solution.

Entropy generation and heat transport analysis of Casson fluid flow with viscous and Joule heating in an inclined porous microchannel

The combined effects of the magnetic field, suction/injection, and convective boundary condition on heat transfer and entropy generation in an electrically conducting Casson fluid flow through an inclined porous microchannel are scrutinized. The temperature-dependent heat source is also accounted. Numerical simulation for the modelled problem is presented via Runge–Kutta–Felhberg-based shooting technique. Special attention is given to analyze the impact of involved parameters on the profiles of velocity [Formula: see text], temperature [Formula: see text], entropy generation [Formula: see text], and Bejan number [Formula: see text]. It is established that entropy generation rate decreases at the walls with an increase in Hartmann number [Formula: see text], while it increases at the center region of the microchannel.