Three-dimensional Microchannel Research Articles

Numerical investigation of two-phase laminar pulsating nanofluid flow in helical microchannel filled with a porous medium

Numerical results of the thermal and hydraulic characteristics of pulsating laminar flow in a three-dimensional helical microchannel heat sink (HMCHS) filled with a porous medium using Al2O3–water based nanofluid are presented in this paper. The two-phase mixture model with modified effective thermal conductivity and viscosity equations were used to solve the laminar flow governing equations. The detailed results for thermal and flow fields are reported for the effects of amplitude (1–3) and frequency (5–20rad/s). The presence of porous media led to better thermal enhancement and significant improvement in heat transfer performance was observed for sinusoidal velocity inlet conditions as compared to steady flow conditions. In addition, the proposed model showed better accuracy in predicting nanofluid flow.

Numerical simulation of heat transfer and turbulent flow of water nanofluids copper oxide in rectangular microchannel with semi-attached rib

In this research, the effect of utilizing semi-attached rib on heat transfer and liquid turbulent flow of nanofluid water–copper oxide in three-dimensional rectangular microchannel has been investigated. The results of numerical examination of this study in comparison to those of smooth channel have also been evaluated. The range of Reynolds numbers is between 10,000 and 60,000 and the volume fraction of copper oxide nanoparticle in 0%, 2%, and 4% was examined. In this numerical simulation, the effects of the changes in parameters such as dimensions of semi-attached rib, volume fraction of the nanoparticle, and Reynolds number were considered. The results of this study showed that utilizing semi-attached rib in microchannel with a ratio of 0 < R/W ≤ 0.325 in producing stronger vortices, which causes better mixture in fluid layers, is weaker than that with tooth mode of R/W = 0 ratio. However, the main advantage of using tooth with a ratio of 0 < R/W ≤ 0.325 in comparison to ordinary tooth is the increase in heat transfer and reduction in coefficient friction and pumping power.

Biodegradable scaffold with built-in vasculature for organ-on-a-chip engineering and direct surgical anastomosis.

We report the fabrication of a scaffold (hereafter referred to as AngioChip) that supports the assembly of parenchymal cells on a mechanically tunable matrix surrounding a perfusable, branched, three-dimensional microchannel network coated with endothelial cells. The design of AngioChip decouples the material choices for the engineered vessel network and for cell seeding in the parenchyma, enabling extensive remodelling while maintaining an open-vessel lumen. The incorporation of nanopores and micro-holes in the vessel walls enhances permeability, and permits intercellular crosstalk and extravasation of monocytes and endothelial cells on biomolecular stimulation. We also show that vascularized hepatic tissues and cardiac tissues engineered by using AngioChips process clinically relevant drugs delivered through the vasculature, and that millimeter-thick cardiac tissues can be engineered in a scalable manner. Moreover, we demonstrate that AngioChip cardiac tissues implanted via direct surgical anastomosis to the femoral vessels of rat hindlimbs establish immediate blood perfusion.

Numerical investigation of two-phase laminar pulsating nanofluid flow in a helical microchannel

ABSTRACTNumerical investigations on the thermal and hydraulic characteristics of pulsating laminar flow in a three-dimensional helical microchannel heat sink (HMCHS) model are performed using Al2O3-water-based nanofluid. The simulation is performed in the laminar regime for Reynolds number ranging from 6 to 25. The two-phase mixture model with modified effective thermal conductivity and viscosity equations is employed to solve the problem numerically. The detailed results for thermal and flow fields are reported for the effects of amplitude (1–3), frequency (5–20 rad/s), and nanoparticle concentration (1%–3%). The results indicate that the heat transfer performance improves significantly for sinusoidal velocity inlet conditions compared with steady flow conditions.

Nanoporous AuPt alloy with low Pt content: a remarkable electrocatalyst with enhanced activity towards formic acid electro-oxidation

Highly active nanoporous AuPt (np-AuPt) alloys with Pt/Au molar ratio ranging from 0.5:99.5 to 5:95 were successfully synthesized based on dealloying strategy. The synthesized np-AuPt alloys consisted of three-dimensional bicontinuous ligament-pore structure (∼10nm) and microchannels. The electrochemical activity and stability of the np-AuPt alloys for formic acid electro-oxidation was investigated by tuning the Pt/Au molar ratio. Especially, a mass activity of the np-AuPt alloy that was 113 times higher than that of commercial JM-Pt/C catalyst was achieved at a Pt/Au molar ratio of 0.5:99.5. The low Pt/Au molar ratio made the surface Pt atoms be effectively isolated by the neighboring Au atoms, leading to the sole direct dehydrogenation pathway of the formic acid electro-oxidation on the np-AuPt alloys.

Rapid three-dimensional microfluidic mixer for high viscosity solutions to unravel earlier folding kinetics of G-quadruplex under molecular crowding conditions

Rapid mixing of highly viscous solutions is a great challenge, which helps to analyze the reaction kinetics in viscous liquid phase, particularly to discover the folding kinetics of macromolecules under molecular crowding conditions mimicking the conditions inside cells. Here, we demonstrated a novel microfluidic mixer based on Dean flows with three-dimensional (3D) microchannel configuration for fast mixing of high-viscosity fluids. The main structure contained three consecutive subunits, each consisting of a “U”-type channel followed by a chamber with different width and height. Thus, the two solutions injected from the two inlets would undergo a mixing in the first “U”-type channel due to the Dean flow effect, and simultaneous vortices expansions in both horizontal and vertical directions in the following chamber. Numerical simulations and experimental characterizations confirmed that the micromixer could achieve a mixing time of 122.4μs for solutions with viscosities about 33.6 times that of pure water. It was the fastest micromixer for high viscosity solutions compared with previous reports. With this highly efficient 3D microfluidic mixer, we further characterized the early folding kinetics of human telomere G-quadruplex under molecular crowding conditions, and unravelled a new folding process within 550μs.

Impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel

This article aims to study the impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel. To this aim, compulsory convection heat transfer of water–aluminum oxide nanofluid in a rib-roughened microchannel has been numerically studied. The results of this simulation for rib-roughened three-dimensional microchannel have been evaluated in contrast to the smooth (unribbed) three-dimensional microchannel with identical geometrical and heat–fluid boundary conditions. Numerical simulation is performed for different nanoparticle volume fractions for Reynolds numbers of 10 and 100. Cold fluid entering the microchannel is heated in order to apply constant flux to external surface of the microchannel walls and then leaves it. Given the results, the fluid has a higher heat transfer with a hot wall in surfaces with ribs rather than in smooth ones. As Reynolds number, number of ribs, and nanoparticle volume fractions increase, more temperature increase happens in fluid in exit intersection of the microchannel. By investigating Nusselt number and friction factor, it is observed that increase in nanoparticle volume fractions causes nanofluid heat transfer properties to have a higher heat transfer and friction factor compared to the base fluid used in cooling due to an increase in viscosity.

Advances in fabricating double-emulsion droplets and their biomedical applications

Double-emulsion droplets have found widespread applications in various engineering and biomedical fields because of their capability in encapsulating different components in each layer. The conventional double-emulsion method is the two-stage stirring emulsification method, which suffers from poor monodispersity and low encapsulation efficiency. With recent advances in microfabrication, some novel methods for fabricating double-emulsion droplets have been developed, including microfluidic emulsification (double-T-junction microchannel, double-cross-shaped microchannel and several three-dimensional microchannels), membrane emulsification and coaxial electrospraying. These methods have shown significantly improved droplet features (e.g., size, size uniformity, thickness of each layer, generation throughput capability). Herein, this paper first reviews the state-of-art approaches for fabricating double-emulsion droplets and discusses their advantages and disadvantages. The applications of double-emulsion droplets in biomedical fields, including cell encapsulation, drug delivery and controlled release, and synthetic biology are also discussed. In conclusion, future perspectives are given.

Liquid on Paper: Rapid Prototyping of Soft Functional Components for Paper Electronics

This paper describes a novel approach to fabricate paper-based electric circuits consisting of a paper matrix embedded with three-dimensional (3D) microchannels and liquid metal. Leveraging the high electric conductivity and good flowability of liquid metal, and metallophobic property of paper, it is possible to keep electric and mechanical functionality of the electric circuit even after a thousand cycles of deformation. Embedding liquid metal into paper matrix is a promising method to rapidly fabricate low-cost, disposable, and soft electric circuits for electronics. As a demonstration, we designed a programmable displacement transducer and applied it as variable resistors and pressure sensors. The unique metallophobic property, combined with softness, low cost and light weight, makes paper an attractive alternative to other materials in which liquid metal are currently embedded.

Two-Phase Analysis of A Helical Microchannel Heat Sink Using Nanofluids

A three-dimensional helical microchannel heat sink (HMCHS) model is developed to investigate the heat transfer characteristics using Al2O3–water-based nanofluid. The two-phase mixture model with modified effective thermal conductivity and viscosity equations is employed for solving the problem numerically. The model developed is validated by comparing the results of Nusselt number with available experimental and numerical data for a wide range of Reynolds number. The detailed results of the thermal field are reported for the effects of helix radius (0.15–0.30 mm), pitch (0.5–2.0 mm), number of turns (7–10), and aspect ratio (1.5–3.0). The analysis presents a unique fundamental insight into the complex secondary flow pattern in the channel due to curvature effects.

Small diameter microchannel of PDMS and complex three-dimensional microchannel network

Abstract Polydimethylsiloxane (PDMS) is an important functional material that has been intensively applied in science research, industry, medical devices, plastic surgery, etc. We presented here a new method of fabricating small diameter microchannels in PDMS without using standard cleanroom techniques such as lithography and etching. The as-fabricated microchannels had a round cross-sectional shape, smooth inner surface, and a diameter from 100 μm down to 9 μm. We demonstrated that these microchannels could be applied to construct complicated, three-dimensional (3D) structures of double helix, knots, as well as interconnection along different directions. Together with the merits of PDMS itself, this flexible and versatile technique showed a promising potential for applications in advanced 3D microfluidic devices, and embedded devices in biosystems.

Comparing the Mixing Performance of Common Types of Chaotic Micromixers: A Numerical Study

High-efficiency micromixers are of critical importance in several industrial applications. Implementing chaotic advection to passively enhance fluid mixing is a well-established technique. The purpose of the present study is to compare different configurations of passive mixers. Six different microchannel designs, commonly used in the majority of mixing applications, were numerically evaluated in the present study. Both two-dimensional and three-dimensional serpentine-type microchannel designs were investigated. For each design, the effect of geometrical parameters was studied using a commercial computational fluid dynamics code. Results are presented in terms of mixing efficiency and pressure drop. It is revealed that increasing the flow path by providing compact fluid passages is not the only way to achieve better mixing; inducing a helical flow along the flow length has an additional benefit in improving the mixing performance. The results of this study can be used as a basis for further improving the design of micromixers, while they can also provide the engineers with guiding principles, not for selecting the optimum set of geometrical parameters for a specific microchannel design but for screening out the least efficient micromixer configurations.

Fabrication of three-dimensional SU-8 microchannels by proton beam writing for microfluidics applications: Fluid flow characterisation

The proton beam writing (PBW) technique was used to fabricate microfluidic structures in SU-8 resist. A network of the buried channels was fabricated as part of a project to develop functional microfluidic device for neuronal studies and self-powered microfluidics. Protons with energies between 2.5MeV and 0.75MeV were used to fabricate the buried channels with a minimum feature size of around 1μm and depths of 40–55μm. Roughness of channels sidewalls was around 2.5nm rms. Exposure regime and examples of functional networks fabricated using PBW are described. COMSOL Multiphysics® software was used to model the flow characteristics of fluid in the SU-8 microchannels structured by PBW. The results obtained using PBW are compared with the structures fabricated by UV-lithography.

Miniaturized spray injection systems

Spray production and its miniaturization are common need and goal in Chemical Engineering and Chemical fields. This work aims the production of miniaturized low cost spray injection systems using planar and three-dimensional microchannels, both 73 cm long and 100 ?m diameter, and acrylic as substrate. Tests and simulation used fluid flow rates up to 10 standard mL/min, for gaseous samples, and up to 1 mL/min to liquid ones; tracers and filming were used to understanding fluid behavior. Simulations and experimental results showed good agreement: planar channels seem to be useful for mixing two liquids whereas three-dimensional channels produce small droplets useful for sample pretreatment in miniaturized impactors.

MHD mixed convection and entropy generation in a 3-D microchannel using Al2O3–water nanofluid

In this paper, mixed convection as well as second law of thermodynamics analysis in a three-dimensional microchannel filled with a nanofluid under a magnetic field are numerically studied. The temperature fields, variation of horizontal velocity, thermal resistance, pressure drop, Hartmann and Reynolds numbers are investigated. Moreover, heat, frictional and magnetic entropy generation are surveyed in different volume fractions. Analyzing the results of numerical simulations indicates that with increasing Hartmann number, maximum horizontal velocity along the centre line and the inlet and outlet thermal resistance decrease in the microchannel. On the other hand, by enhancing the strength of the imposing magnetic field, heat entropy generation mitigates, while frictional and magnetic ones increase. However, the increasing of two last is very small compared to heat entropy generation. The ratio of Nuavg/(pressure drop) is greater than 10. Therefore, the thermal gain of this microchannel fairly dominates the loss of pressure reduction.

THE USE OF MICROCHANNELS FOR SEPARATION AND PRECONCENTRATION: COMPARISON BETWEEN THREE-DIMENSIONAL AND PLANAR CONFIGURATIONS

Simulation and experimental measurements were used aiming at better understanding flow behavior in planar and three-dimensional microchannels used for separation or preconcentration. Two different microchannels configurations were designed, manufactured in acrylic and the surface was modified to adsorb volatile organic compounds (VOCs). Both channels configuration are 73 cm long, 100 µm wide and 40 µm deep. Simulation was carried out in COMSOL (FEMLAB) 3.2® and COSMOS flow 5.0® programs, tracer visualization and quartz crystal microbalance data were evaluated according to chromatographic concepts. Due to the higher axial velocity, planar microchannels are more adequate for preconcentration whereas three-dimensional ones show a good performance in the separation process.

Polarization-independent etching of fused silica based on electrons dynamics control by shaped femtosecond pulse trains for microchannel fabrication.

We propose an approach to realize polarization-independent etching of fused silica by using temporally shaped femtosecond pulse trains to control the localized transient electrons dynamics. Instead of nanograting formation using traditional unshaped pulses, for the pulse delay of pulse trains larger than 1 ps, coherent field-vector-related coupling is not possible and field orientation is lost. The exponential growth of the periodic structures is interrupted. In this case, disordered and interconnected nanostructures are formed, which is probably the main reason of etching independence on the laser polarization. As an application example, square-wave-shaped and arc-shaped microchannels are fabricated by using pulse trains to demonstrate the advantage of the proposed method in fabricating high-aspect-ratio and three-dimensional microchannels.

Maximum thermal conductance for a micro-channel, utilising Newtonian and non-Newtonian fluid

This paper investigates the thermal behaviour of two micro-channel elements cooled by Newtonian and non-Newtonian fluids, with the objective to maximise thermal conductance subject to constraints. This is done firstly for a two-dimensional duct micro-channel and secondly for a three-dimensional complex micro-channel. A numerical model is used to solve the governing equations relating to flow and temperature fields for both cases. The geometric configuration of each cooling channel is optimised for Newtonian and non-Newtonian fluid at a fixed inlet velocity and heat flux. In addition, the effect of porosity on thermal conductance is investigated. It was found, in both cases, that the non-Newtonian fluid characteristics result in a significant variation in thermal conductance as inlet velocity is increased. The characteristics of a dilatant fluid greatly reduce thermal conductance on account of shear thickening on the boundary surface. In contrast, a pseudoplastic fluid shows increased thermal conductance. A comparison of the complex micro-channel and the duct micro-channel shows the improved thermal conductance resulting from greater flow access to the conductive area, achieved by the complex micro-channel.

Temperature Dependent Viscosity and Thermal Conductivity Effects on the Laminar Forced Convection in Straight Microchannels

A parametric investigation is carried out on the effects of temperature dependent viscosity and thermal conductivity and of viscous dissipation in simultaneously developing laminar flows of liquids in straight microchannels of constant cross sections. Uniform heat flux boundary conditions are specified at the heated walls. A superposition method is proved to be applicable in order to predict the value of the Nusselt number by considering separately the effects of temperature dependent viscosity and those of temperature dependent thermal conductivity. In addition, it is found that the influence of the temperature dependence of thermal conductivity on the value of the Nusselt number is independent of the value of the Brinkman number, i.e., it is the same no matter whether viscous dissipation is negligible or not. Finally, it is demonstrated that, in liquid flows, the main effects on pressure drop of temperature dependent fluid properties can be retained even if only viscosity is allowed to vary with temperature, the other properties being assumed constant. Viscosity is assumed to vary with temperature according to an exponential relation, while a linear dependence of thermal conductivity on temperature is assumed. The other fluid properties are held constant. Two different cross-sectional geometries are considered, corresponding to both axisymmetric (circular) and three-dimensional (square) microchannel geometries. A finite element procedure is employed for the solution of the parabolized momentum and energy equations. Computed axial distributions of the local Nusselt number and of the apparent Fanning friction factor are presented for different values of the viscosity and thermal conductivity Pearson numbers and of the Brinkman number.

Constructal Optimization of Microchannel Heat Sinks With Noncircular Cross Sections

This article reports the numerical geometric optimization of three-dimensional microchannel heat sinks with rectangular, elliptic, and isosceles triangular cross sections. The cross-sectional areas of the mentioned microchannels can change according to the degrees of freedom, that is, the aspect ratio and the solid volume fraction. Actually, the purpose of geometric optimization is to determine the optimal values of these parameters in such a way that the peak temperature of the wall is minimized. The effects of solid volume fraction and pressure drop upon the aspect ratio, hydraulic diameter, and peak temperature of the microchannels are investigated. Moreover, these microchannel heat sinks are compared with each other at their optimal conditions. Considering the constraints and geometric parameters for the optimization of the present study, it is revealed that microchannel heat sinks with rectangular and elliptic cross sections have similar performances, while microchannels with isosceles triangular cross sections show weaker performances. The optimal shapes of all three kinds of channels are achieved numerically and compared with the approximate results obtained from scale analysis, for which good agreements are observed.