Three-dimensional Microchannel Research Articles

Design and Fabrication of a Tunable Optofluidic Microlens Driven by an Encircled Thermo-Pneumatic Actuator.

This paper presents the design, simulation, fabrication, assembly, and testing of a miniature thermo-pneumatic optofluidic lens. The device comprises two separate zones for air heating and fluid pressing on a flexible membrane. A buried three-dimensional spiral microchannel connects the two zones without pumps or valves. The three-dimensional microfluidic structure is realized using a high-resolution three-dimensional printing technique. Multi-physics finite element simulations are introduced to assess the optimized air chamber design and the low-temperature gradient of the optical liquid. The tunable lens can be operated using a direct-current power supply. The temperature change with time is measured using an infrared thermal imager. The focal length ranges from 5 to 23 mm under a maximum voltage of 6 V. Because of the small size and robust actuation scheme, the device can potentially be integrated into miniature micro-optics devices for the fine-tuning of focal lengths.

Heat transfer and fluid flow analysis of microchannel heat sinks with periodic vertical porous ribs

In this study, a detailed numerical analysis of the fluid flow and heat transfer of a three-dimensional microchannel is performed to evaluate the effect of using periodic vertical porous and solid ribs with various geometrical shapes, including rectangular, elliptical, isosceles triangular, backward triangular and forward triangular on the walls of this microchannel. Darcy-Brinkman-Forchheimer equations are used to model transport through the porous medium. The results for microchannels with solid ribs and with porous ribs are compared to each other. It is found that at the lowest studied inlet velocity (uin=0.25m/s), for the rib heights of Hr=0.025mm,0.05mmand0.07mm, the average Nusselt number of the porous-rib microchannel is 2.16, 2.1 and 1.3 times greater than the solid case, respectively; and, 2.505, 3.62 and 4.01 times greater than the no-ribs microchannel, respectively. It is found that for the same increase in the Nusselt number, the porous ribs induces much less pressure drop compared to the solid cases. Accounting the thermal and hydraulic performance simultaneously, Figure of Merit (FOM) is calculated. The results show that porous ribs lead in much better FOMs compared to the solid ribs case. Effects of the height, porosity and Darcy number of the ribs are also investigated.

Optimization of porous fin location and investigation of porosity and permeability effects on hydro-thermal behavior of rectangular microchannel heat sink

Rectangular microchannel heat sink incorporated with porous fin is studied to improve the thermal performance of conventional solid fin microchannel. Three-dimensional microchannel with fixed aspect ratio and hydraulic diameter is considered and porous fin with three different thickness have been analyzed by mounting at various locations. Copper is used as porous medium with a porosity of 0.4 to 0.8 and permeability of 10−8 - 10−12 m2 are considered. The working fluid is water and the simulations were carried out for the Re range, 500 ≤ Re ≤ 1000. The performance improvement of the porous fin over solid fin is presented with the help of slip length. Pressure reduction efficiency is observed by comparing pressure drop values with and without slip effect. The parametric optimization of fin location has been done with the help of combined hydro-thermal performance. Further, the effect of porous parameters like porosity, permeability and quadratic drag factor on pressure drop and heat transfer coefficient is studied for various fin thicknesses. It is observed that the porous fin with porosity 0.4 and permeability 10−8 m2 has shown better heat transfer characteristics.

Microfluidic Bioreactor Made of Cyclo-Olefin Polymer for Observing On-Chip Platelet Production.

We previously proposed a microfluidic bioreactor with glass–Si–glass layers to evaluate the effect of the fluid force on platelet (PLT) production and fabricated a three-dimensional (3D) microchannel by combining grayscale photolithography and deep reactive ion etching. However, a challenge remains in observing the detailed process of PLT production owing to the low visibility of the microfluidic bioreactor. In this paper, we present a transparent microfluidic bioreactor made of cyclo-olefin polymer (COP) with which to observe the process of platelet-like particle (PLP) production under a bright-field, which allows us to obtain image data at a high sampling rate. We succeeded in fabricating the COP microfluidic bioreactor with a 3D microchannel. We investigated the bonding strength of COP-COP layers and confirmed the effectiveness of the microfluidic bioreactor. Results of on-chip PLP production using immortalized megakaryocyte cell lines (imMKCLs) derived from human-induced pluripotent stem cells show that the average total number of produced PLPs per imMKCL was 17.6 PLPs/imMKCL, which is comparable to that of our previous glass–Si–glass microfluidic bioreactor (17.4 PLPs/imMKCL). We succeeded in observing PLP production under a bright-field using the presented microfluidic bioreactor and confirmed that PLP fragmented in a narrow area of proplatelet-like protrusions.

Effect of PCM and porous media/nanofluid on the thermal efficiency of microchannel heat sinks

The present study is a genuine attempt to improve the thermal behavior and hydraulic performance of a conventional microchannel heat sink (MCHS) using porous material, phase change material (PCM) and nanofluid. Three-dimensional microchannels with square, circular and flattened circular geometries are examined numerically by considering the thermal conduction in solid parts. Various factors are examined, including the effect of the number of channels, fluid velocity passing through channels, porous substrate thickness, PCM layer thickness, Darcy number, porosity coefficient, thermal conductivity ratio in the porous material, volume fraction and nanoparticle diameter. According to the findings, for a critical thickness of the porous substrate, the thermal performance is at its minimum. With increasing values of Darcy number, porosity coefficient, nanoparticle diameter and PCM thickness, the thermal performance of MCHS decreases. An MCHS with square geometry displays a better thermal performance compared to the other two geometries. Furthermore, the use of porous material, nanofluid and PCM improves the thermal behavior compared with a conventional microchannel. The thermal performance of MCHS with PCM is approximately 47% and 17% higher than that of a microchannel with the porous substrate and a microchannel incorporating a combination of the porous layer and nanofluid.

Uniform Deposition and Effective Confinement of Lithium in Three-Dimensional Interconnected Microchannels for Stable Lithium Metal Anodes.

Lithium dendrite formation has hindered the practical implementation of lithium metal batteries with higher energy densities compared with those of conventional lithium-ion batteries. Herein, a nanoconfinement strategy to access dendrite-free lithium metal anodes comprising three-dimensional (3D) hollow porous multi-nanochannel carbon fiber embedded with TiO2 nanocrystals (HTCNF) is reported. The transport of the lithium ions is facilitated by the 3D architecture. Functioning as nanoseeds, the TiO2 nanocrystals guide the lithium ions toward forming uniform deposits, which are further confined inside the hollow carbon fibers and the 3D HTCNF layer. Site-selective deposition coupled with the nanoconfinement of lithium metal modifies the Li plating/stripping behavior and effectively suppresses the dendrite growth. The HTCNF-Li cell delivers a stable cycling performance of 1300 h with a voltage hysteresis as low as 6 mV. The assembled HTCNF-Li//LiFePO4 full cell displays a compelling rate performance and enhanced cycling stability with high capacity retention (90% after 400 cycles at 0.5 C). Our results demonstrate a new and potentially scalable route to resolve the lithium dendrite growth issue for enhanced electrochemical performances, which can be further extended to other metal battery systems.

Thermal performance evaluation of a microchannel with different porous media insert configurations

PurposeThis paper aims to numerically investigate the thermal performance evaluation of a microchannel with different porous media insert configurations.Design/methodology/approachHeat transfer and pressure drop of fluid flow through a three-dimensional (3D) microchannel with different partially and filled porous media insert configurations are investigated numerically. The number of divisions and positions of porous material inside the microchannel for 12 different arrangements are considered. A control volume method is used for single-phase laminar flow with the Darcy–Forchheimer model used for the porous media. The geometry of the problem consists of a microchannel with a rectangular cross-section of 0.4 mm × 0.2 mm and length 20 mm, with a stainless steel porous material insert with a porosity coefficient of ε = 0.32 and a Darcy number of Da = 2.7 × 10−4.FindingsNumerical results show that when the transverse arrangement is used, as the number of partitions increases, the thermal performance is improved and the heat transfer increases up to 300% compared to that of the plain microchannel. Comparing the obtained results from the microchannels with transverse and longitudinal configurations, at low Reynolds numbers, the transverse arrangement of porous blocks and at high Reynold numbers, the longitudinal arrangement present the best thermal performance which is virtually four times higher compared to the obtained Nu numbers from the plain microchannel. The results show that as the volume of porous material is constant in the cases with various transverse porous blocks, the pressure drop is not changed in these cases. Also, the highest thermal performance ratio is when the porous material is placed along the walls in a longitudinal direction.Originality/valueTo the best knowledge of the authors, in the previous research, the effect of the arrangement and location of the porous medium in the transverse and longitudinal direction in the microchannel and their effect in different states on the behavior of flow and heat transfer has not been numerically investigated. In this study, the porous media configuration and its placement in a 3D microchannel were numerically studied. The effect of porous material layout and configurations in different longitudinal and transverse directions on the pressure drop, heat transfer and thermal performance in the 3D microchannel is investigated numerically.

Effect of transverse and parallel magnetic fields on thermal and thermo-hydraulic performances of ferro-nanofluid flow in trapezoidal microchannel heat sink

Purpose This paper aims to study the thermal and thermo-hydraulic performances of ferro-nanofluid flow in a three-dimensional trapezoidal microchannel heat sink (TMCHS) under uniform heat flux and magnetic fields. Design/methodology/approach To investigate the effect of direction of Lorentz force the magnetic field has been applied: transversely in the x direction (Case I);transversely in the y direction (Case II); and parallel in the z direction (Case III). The three-dimensional governing equations with the associated boundary conditions for ferro-nanofluid flow and heat transfer have been solved by using an element-based finite volume method. The coupled algorithm has been used to solve the velocity and pressure fields. The convergence is reached when the accuracy of solutions attains 10–6 for the continuity and momentum equations and 10–9 for the energy equation. Findings According to thermal indicators the Case III has the best performance, but according to performance evaluation criterion (PEC) the Case II is the best. The simulation results show by increasing the Hartmann number from 0 to 12, there is an increase for PEC between 845.01% and 2997.39%, for thermal resistance between 155.91% and 262.35% and ratio of the maximum electronic chip temperature difference to heat flux between 155.16% and 289.59%. Also, the best thermo-hydraulic performance occurs at Hartmann number of 12, pressure drop of 10 kPa and volume fraction of 2%. Research limitations/implications The embedded electronic chip on the base plate generates heat flux of 60 kW/m2. Simulations have been performed for ferro-nanofluid with volume fractions of 1%, 2% and 3%, pressure drops of 10, 20 and 30 kPa and Hartmann numbers of 0, 3, 6, 9 and 12. Practical implications The authors obtained interesting results, which can be used as a design tool for magnetohydrodynamics micro pumps, microelectronic devices, micro heat exchanger and micro scale cooling systems. Originality/value Review of the literature indicated that there has been no study on the effects of magnetic field on thermal and thermo-hydraulic performances of ferro-nanofluid flow in a TMCHS, so far. In this three dimensional study, flow of ferro-nanofluid through a trapezoidal heat sink with five trapezoidal microchannels has been considered. In all of previous studies, in which the effect of magnetic field has been investigated, the magnetic field has been applied only in one direction. So as another innovation of the present research, the effect of applying magnetic field direction (transverse and parallel) on thermo-hydraulic behavior of TMCHS is investigated.

Nylon Monofilament Mold Three-dimensional Microfluidic Chips for Size-exclusion Microchip Electrophoresis: Application to Specific Online Preconcentration of Proteins.

We present a lithography-free procedure for fabricating intrinsically three-dimensional microchannels within PDMS elastomers using nylon monofilament molds. We embedded nylon monofilaments in an uncured PDMS composite to fabricate straight channels of desired length, for use as molds to form the microchannels. Next, we fabricated two layer devices consisting of dialysis membranes, which preconcentrate specific proteins in accordance with molecular weight, in between two layers of PDMS substrates with embedded microchannels. Because of the membrane isolation, analyte exchange between two fluidic layers can be precisely controlled by an applied voltage. More importantly, given that only small molecules pass through the dialysis membrane, the integrated membrane is suitable for molecular sieving or size exclusion for a concentrator prior to microchip electrophoresis. Researchers can use our microchip design for online purification and preconcentration of proteins in the presence of excess reagent immediately after fluorescent labeling. This method's technical advantage is that three-dimensional microstructures, such as microchannels that have a circular cross-section, are readily attainable and can be fabricated in a straightforward manner without using specialized equipment. Our method is a low-cost, environmentally sustainable procedure for fabricating microfluidic devices, and will render microfluidic processes more accessible and easy to implement.

Three-dimensional microchannel reflecting cell size distribution for on-chip production of platelet-like particles

Recently, microfluidic bioreactors that trap injected megakaryocytes (MKs) by application of fluid force to them have been proposed as small test benches to evaluate the in vitro platelet production process. However, making a flow rate constant after trapping MKs remains a challenge and bottleneck because the cross-sectional area of the microchannel decreases due to the trapped MKs. Therefore, we present a microfluidic bioreactor containing a three-dimensional microchannel that has been designed based on the cell size distribution of immortalized megakaryocyte cell lines (imMKCLs). As results, we succeeded in trapping imMKCLs with small variations in the cross-sectional area along the flow path. Through experiments on on-chip production of platelet-like particles (PLPs) for 12 h using imMKCLs derived from human-induced pluripotent stem cells, we found that the average number of the total produced PLPs per imMKCLs was 23, 24, 16, and 14 when the applied pressures was 10, 50, 100 and 200 kPa, respectively. From these results, we confirmed that the proposed microfluidic bioreactor can be applied as a test bench for evaluating of the on-chip PLP production.

Role of solutal free convection on interdiffusion in a horizontal microfluidic channel

We studied the role of solutal free convection on the transport of a buoyant solute at the microfluidic scales, 5--500 \textmu{}m, both for a two-dimensional slit and a three-dimensional microchannel. Our theoretical predictions using both asymptotic analytical solutions and accurate numerical resolutions describe the different solute transport regimes.

Effects of Thermal Annealing on Femtosecond Laser Micromachined Glass Surfaces.

Femtosecond laser micromachining (FLM) of fused silica allows for the realization of three-dimensional embedded optical elements and microchannels with micrometric feature size. The performances of these components are strongly affected by the machined surface quality and residual roughness. The polishing of 3D buried structures in glass was demonstrated using different thermal annealing processes, but precise control of the residual roughness obtained with this technique is still missing. In this work, we investigate how the FLM irradiation parameters affect surface roughness and we characterize the improvement of surface quality after thermal annealing. As a result, we achieved a strong roughness reduction, from an average value of 49 nm down to 19 nm. As a proof of concept, we studied the imaging performances of embedded mirrors before and after thermal polishing, showing the capacity to preserve a minimum feature size of the reflected image lower than m. These results allow for us to push forward the capabilities of this enabling fabrication technology, and they can be used as a starting point to improve the performances of more complex optical elements, such as hollow waveguides or micro-lenses.

Integrating blood cell mechanics, platelet adhesive dynamics and coagulation cascade for modelling thrombus formation in normal and diabetic blood.

Normal haemostasis is an important physiological mechanism that prevents excessive bleeding during trauma, whereas the pathological thrombosis especially in diabetics leads to increased incidence of heart attacks and strokes as well as peripheral vascular events. In this work, we propose a new multiscale framework that integrates seamlessly four key components of blood clotting, namely transport of coagulation factors, coagulation kinetics, blood cell mechanics and platelet adhesive dynamics, to model the development of thrombi under physiological and pathological conditions. We implement this framework to simulate platelet adhesion due to the exposure of tissue factor in a three-dimensional microchannel. Our results show that our model can simulate thrombin-mediated platelet activation in the flowing blood, resulting in platelet adhesion to the injury site of the channel wall. Furthermore, we simulate platelet adhesion in diabetic blood, and our results show that both the pathological alterations in the biomechanics of blood cells and changes in the amount of coagulation factors contribute to the excessive platelet adhesion and aggregation in diabetic blood. Taken together, this new framework can be used to probe synergistic mechanisms of thrombus formation under physiological and pathological conditions, and open new directions in modelling complex biological problems that involve several multiscale processes.

Pumping Power Performance and Frictional Resistance of Textured Microchannels in Gaseous Slip Flows

The investigation of pressure drop characteristics along the microchannels with surface texturing is crucial to arrive at a desired structural size and performance of a microchannel. This study presents the comparison of flow friction and pumping power for two different Reynolds numbers (Re = 1.01 and 50.31) for rarefied gas flows in textured microchannels. The three-dimensional microchannel is computationally modeled with ratios of the height of texture to the height of the microchannel taken as 20, 40, and 60 and texture shapes as rectangular, circular, and triangular. All simulations are conducted in the slip flow regime for the Knudsen number ranging from 1.10 A� 10-3 to 2.07 A� 10-2 and tangential momentum accommodation coefficient (TMAC) ranging from 0.1 to 0.9. The time- and cost-effective Taguchi statistical analysis of the L18 orthogonal array is carried out to find the efficiency of the textured microchannels in terms of Poiseuille number and pumping power per unit mass flow rate. It is found that the height of texture is the most important control factor for efficiency, while the shape is the least important factor for both Reynolds numbers. The second most significant factor for Re = 50.31 is the Knudsen number and that for Re = 1.01 is the TMAC. The present numerical work can be applied for designing micropiping systems and diffusers with lower pumping power, lower frictional resistance, and higher efficiency. ©

Cooling performance of an impinging synthetic jet in a microchannel with nanofluids: An Eulerian approach

Numerical investigations of heat transfer enhancement in a three-dimensional micro-channel with a single synthetic jet were conducted using Al2O3-water, CuO-water and TiO2-water nanofluids. The effects of different types of nanoparticles at particle volume concentrations of 1%, 2% and 5% on the thermal performance in the micro-channel were examined. The numerical tool was validated against existing experimental data on the heat transfer characteristic of nanofluids in micro-channel. Heat transfer enhancement using nanofluids based on the Eulerian single-phase model was assessed for the cases with and without the operation of the synthetic jet. In general, the overall thermal performance was greatly influenced by the thermal conductivity and dynamic viscosity of the working nanofluids. The former corresponds to thermal enhancement by conduction whilst the latter corresponds to convective enhancement due to the periodic oscillation of the synthetic jet diaphragm. As the particle volume concentration of a nanofluid increased, effectiveness of the synthetic jet to provide convective cooling became poorer on account of higher viscosity. Nevertheless, in some cases, this can be overcome by the enhancement in thermal conductivity, depending on the Peclet number of the working fluid. Synthetic jet microchannel with Al2O3-water nanofluid at φ = 5% showed the best overall cooling performance whereas TiO2-water nanofluid at φ = 5% failed to improve the thermal performance.

Numerical investigation on heat transfer behavior of thermally developing flow inside rectangular microchannels

A numerical investigation is conducted to study the heat transfer characteristics of laminar flow in three-dimensional rectangular microchannels with aspect ratios of 0.1–1 and Reynolds numbers of 5–400. In this paper, the effects of aspect ratio and Reynolds number on the local and mean Nusselt numbers are presented in detail. Good agreement on Nusselt numbers is observed between the present results and the data reported in the literature. The results show that the Reynolds number has a great impact on the local Nusselt number in the thermally developing region, especially at lower Reynolds number, while the Reynolds number is independent of the developed Nusselt number. The local Nusselt number is found to increase with decreasing aspect ratio at the same Reynolds number. Additionally, the effects of these parameters on the dimensionless thermal entrance length are also investigated. The dimensionless thermal entrance length for rectangular microchannels monotonously increases by increasing aspect ratio and decreasing Reynolds number, whereas the effect of Reynolds number on the dimensionless thermal entrance length can be basically ignored when Reynolds number is more than 50. Generalized correlations are developed for the local Nusselt number and the dimensionless thermal entrance length.

User-Friendly Microfabrication Method for Complex Topological Structure and Three-Dimensional Microchannel with the Application Prospect in Polymerase Chain Reaction (PCR).

One of the most important challenges in the field of microfluidics is the rapid fabrication of microchips with complex topologies. Although the processing method of microfluidic chips has made brilliant achievements in the past 20 years, almost all traditional processing methods still face huge obstacles in the production of complex topologies and three-dimensional microchannel. Nowadays, the main methods of manufacturing microfluidic chips such as numerical control microprocessing, laser ablation, inkjet printing, photolithography, dry etching, and lithography, galvanoformung and abformung (LIGA) technology are not only inapplicable to the complex topological structure and the rapid processing of three-dimensional microfluidic chips but also rely on expensive processing equipment, complex manufacturing process, and low yield. To solve the problems of these traditional processing methods, we propose a low-cost methodology to obtain a microfluidic chip by sewing the chip pipe to the substrate with an embroidery machine as low as $6. Compared with the above-mentioned traditional microprocessing technologies, the new chip processing technology proposed by us does not involve professional microprocessing equipment and professional skills. Therefore, this new chip processing technology can significantly improve the efficiency of microprocessing.

Poiseuille number behavior in an adiabatically choked microchannel in the slip regime

The influence of subsonic adiabatic choking on frictional resistance inside three-dimensional (3D) microchannels has not been studied for rarefied gas flows. In the present work, the variation of the Poiseuille number with respect to the Mach number has been documented for a 3D microchannel of aspect ratio (width/height) 0.49. Measurements of mass flow rate, static pressure, and temperature have been conducted with nitrogen in highly compressible and slightly rarefied (slip flow) regime: outlet Mach number (0.43–0.99), outlet Knudsen number (4.04 × 10−3–7.04 × 10−3), and pressure ratio (8.17–8.72). The present 3D measurements are compared with available analytical solutions for isothermal and adiabatic flows. A maximum deviation of only 4.8% from the adiabatic slip flow solution points toward the adiabatic nature of the exit choked state, which is being experimentally demonstrated for the first time in the highly compressible slip flow regime. Furthermore, the influence of losses of microchannel end manifolds on the overall pressure drop is calculated to be negligible. We further propose the ranges of the area ratio, Reynolds number, and Knudsen number for which these losses continue to be unimportant for gaseous slip flow. This study gives insights into the influence of subsonic choking on the frictional resistance at various mass flow rates and is relevant for future space expeditions and in certain biological applications.

Electrochemical deposition of a radionuclide nickel-63 on betavoltaic cells for a nuclear battery based on silicon p-i-n junctions

This paper highlights the manufacturing process of two types of betavoltaic cells with a source coated with 63Ni: the flat one and one with a three-dimensional (3D) microchannel structure, obtained by anodizing silicon (Si). Thin-layer deposition of a nickel-63 radionuclide was carried out from the ammonium-citrate based electrolyte solution, designed for production until exhaustion.

Lattice Boltzmann simulations of magnetic particles in a three-dimensional microchannel

A lattice Boltzmann model for magnetic particles in a fluid is established, in which both hydrodynamic and magnetic interactions are fully coupled. The interpolated bounce back scheme is adopted to describe the fluid-particle interaction. We combine the implicit particle velocity updated scheme and the modified momentum-exchange method to make the algorithm stable and also maintain the Galilean invariance. Moreover, MPI + OpenMP hybrid programming mode is used for parallel computing. The model is validated by numerical simulation of the sedimentation of a particle in a tank. We investigate the motion of magnetic particles in a microchannel with carrier fluid under the uniform magnetic field and hybrid magnetic field, and then the magnetic particles flow through a variable-section microchannel is studied. The results indicate that the structures formed by magnetic particles can be regulated by controlling the external magnetic field and flow field; besides, the more ordered structures have more influence on the fluid flow.