Types Of Microchannels Research Articles

Mixed‐Ligand Oxidovanadium(IV/V) Complexes Chelated by α‐Hydroxycarboxylate and 2‐(1H‐Imidazol‐2‐yl)pyridine: Localized Structures and Gas Adsorption

AbstractMonomeric oxidovanadium(IV) citrate and malate, [VO(H2cit)(Him‐py)] ⋅ H2O (1) and [VO(R,S‐Hmal)(Him‐py)] (2), and an additive of mixed‐valence oxidovanadium(IV/V) (1H‐imidazol‐2‐yl)pyridine [V2O2(μ2‐O)(glyc)(Him‐py)2(im‐py)] ⋅ [VO2(Him‐py)(im‐py)] ⋅ 9.5H2O (3) [Him‐py=2‐(1H‐imidazol‐2‐yl)pyridine, H4cit=citric acid, R,S‐H3mal=R,S‐malic acid, H2glyc=glycolic acid] have been isolated from the reactions of vanadyl sulfate with α‐hydroxycarboxylate (citrate, malate, and glycolate) and 2‐(1H‐imidazol‐2‐yl)pyridine in acidic solutions, respectively. The citrate or malate chelates to vanadium atom tridentately through α‐hydroxy, α‐carboxy and β‐carboxy groups that different with bidentate glycolate, while the other β‐carboxy acidic group of citrate in 1 remains uncoordinated and participates in strong hydrogen bonds with water molecules. Further substitution of 2‐(1H‐imidazol‐2‐yl)pyridine for citrate in 1 results in the formation of [VO2(Him‐py)(im‐py)]3 ⋅ 4.5H2O (4) in basic solution. With comparable chelation, 1 shares a similar V−Oα‐hydroxy distance [2.214(2) Å] with that observed in FeV‐cofactor [2.156av Å],[1] where a protonated model is suggested for the local chelated environment of FeV‐cofactor in citrate‐substituted V‐nitrogenase variant. Interestingly, 2D porous structure of additive 3 features two types of irregular microchannels with diameters of 16.6 and 6.4 Å, respectively, which can adsorb CO2 and O2 for 9.28 and 29.68 mg/g at 29.89 bar, respectively, while little or no adsorption for H2, N2, and CH4.

Effect of Waveform Channel on the Cooling Performance of Hybrid Microchannel

To improve comprehensive hydrothermal performance of microfluidic cooling, a new type of hybrid microchannel is proposed. In this paper, turbulent flow and heat transfer characteristics of rectangular cross section straight hybrid microchannel, trapezoidal cross section straight hybrid microchannel, and trapezoidal cross section waveform hybrid microchannel (TWHM) are compared numerically by a realizable turbulence model under different pump power and heat flux. The results show that TWHM has a greater pressure drop at the same Reynolds number but has the best heat dissipation performance at the same pump power, in which temperature difference can be reduced up to 55.01%. The effect of arc height and chord length on the cooling performance of TWHM is also studied. As increases or decreases under the same pump power, the friction factor increases, while the total thermal resistance and bottom surface temperature difference decrease gradually. The cooling performance of channels becomes closer as the pump power increases. In addition, with the same cross-sectional area, the cooling performance of the waveform hybrid microchannel can be further improved by optimizing cross-sectional shape . The best cooling performance can be obtained at .

Hydrothermal performance of single and hybrid nanofluids in Left-Right and Up-Down wavy microchannels using two-phase mixture approach

The aim of this study is to explore the hydrothermal attributes of three types of nanofluid containing the silver nanoparticles, aluminum oxide nanoparticles, and hybrid silver–aluminum oxide nanoparticles in two different types of microchannel, namely Left-Right and Up-Down wavy microchannels. The multi-phase mixture model is utilized to numerically simulate the flow at constant pumping powers. The results unmask that the secondary flow formed due to the wavy structure is more severe for the Left-Right wavy microchannel compared to the Up-Down one. Also, a maximum 330% enhancement in the convective heat transfer coefficient was observed for the Up-Down wavy microchannel working with the silver nanofluid, while the same value for the Left-Right one was 200%. Although the impact of using the nanofluids is more dominant for the Up-Down wavy microchannel, the Left-Right one exhibited better cooling performance in terms of the Nusselt number. It was observed that utilizing the nanofluids has minor impact on improving the bottom surface temperature uniformity for the Left-Right wavy microchannel, while for the Up-Down one this effect is more dominant. Lower amounts of thermal resistance were obtained in the case of using the nanofluids for both wavy structures, with more impact on the Up-Down one.

Microchannel structure design for hydrogen supply from methanol steam reforming

A methanol steam reforming-based microreactor is an extraordinary setup for hydrogen supply; nevertheless, the heat transfer capability and flow resistance of the microreactor may be restricted by each other, which calls for further structure design and investigation. To comprehensively improve the performance of a direct microchannel (DM) with the implementation of on-board hydrogen supply, the concepts of sinusoidal- and dimple-structured microchannels are synchronously introduced. Four types of microchannels for methanol steam reforming (MSR) are studied: direct microchannel (DM), direct microchannel with dimples (DMD), sinusoidal microchannel (SM), and sinusoidal microchannel with dimples (SMD). The influence of microchannel structure on the reformer’s flow and heat transfer properties is evaluated by Nusselt number, resistance coefficient, and heat transfer efficiency factor using numerical simulation. Results show that the SMD is the optimal structure. Moreover, the effects of reaction temperatures, methanol feeding fluxes, and steam/CH3OH mole ratios on the MSR performance are experimentally investigated. The effect of microchannel structures on the hydrogen production performance is also explored to validate the numerical simulation results. It is revealed that the integrated structure with both sinusoidal waves and dimples exhibited the best performance, demonstrating enhancements in heat and mass transportation as well as excellent H2 production capacity.

Impact of flow feedback on bubble generation in T-junction microchannels under pressure-driven condition

Under pressure-driven conditions of gas, the bubble size was experimentally studied in different types of T-junction microchannels having widths of 300 μm and heights of 100 μm. The bubble length increases with the flow rate, and we observed that it also increased with the driving pressure. This was proved through the published formulas for the bubble flow pressure difference using the experimental results. Three types of downstream channels—normal, movable, and deformed walls (of different lengths)—were used to study emerging bubbles, and a nonlinear relationship was observed between them. The channel type directly influenced the bubble size by affecting the resistance of the channel with bubbles. Furthermore, the difference between the resistances of a normal channel and a deformed channel with the same typical dimension was determined using a comparator structure between two parallel channels to evaluate the effect of flow resistance on bubble generation. The adjustment of the flow rate at downstream will give feedback to the bubble generation in the double T-junction channel.

Experimental Study and Mechanism Analysis of the Flow Boiling and Heat Transfer Characteristics in Microchannels with Different Surface Wettability.

In this paper experiments have been conducted to investigate the flow boiling and heat transfer characteristics in microchannels with three different surface wettability. Three types of microchannels with a super-hydrophilic surface (θ ≈ 0°), a hydrophilic surface (θ = 43°) and an untreated surface (θ = 70°) were prepared. The results show that the average heat transfer coefficient of a super-hydrophilic surface microchannel is significantly higher than that of an untreated surface microchannel, especially when the mass flux is high. The visualization of the flow patterns states that the number of bubble nucleation generated in the super-hydrophilic microchannel at the beginning of the flow boiling is significantly more than that in the untreated microchannel. Through detailed analysis of the experimental data, flow patterns and microchannel surface SEM images, it can be inferred that the super-hydrophilic surface microchannel has more active nucleation cavities, a high nucleation rate and a large nucleation number, a small bubble departure diameter and a fast departure frequency, thereby promoting the flow and heat transfer in the microchannel. In addition, through the force analysis of the vapor-liquid interface, the mechanism that the super-hydrophilic microchannel without dryout under high heat flux conditions is clarified.

Machine learning assisted fast prediction of inertial lift in microchannels.

Inertial effect has been extensively used in manipulating both engineered particles and biocolloids in microfluidic platforms. The design of inertial microfluidic devices largely relies on precise prediction of particle migration that is determined by the inertial lift acting on the particle. In spite of being the only means to accurately obtain the lift forces, direct numerical simulation (DNS) often consumes high computational cost and even becomes impractical when applied to microchannels with complex geometries. Herein, we proposed a fast numerical algorithm in conjunction with machine learning techniques for the analysis and design of inertial microfluidic devices. A database of inertial lift forces was first generated by conducting DNS over a wide range of operating parameters in straight microchannels with three types of cross-sectional shapes, including rectangular, triangular and semicircular shapes. A machine learning assisted model was then developed to gain the inertial lift distribution, by simply specifying the cross-sectional shape, Reynolds number and particle blockage ratio. The resultant inertial lift was integrated into the Lagrangian tracking method to quickly predict the particle trajectories in two types of microchannels in practical devices and yield good agreement with experimental observations. Our database and the associated codes allow researchers to expedite the development of the inertial microfluidic devices for particle manipulation.

Serpentine square wave microchannel fabrication with WEDM and soft lithography

The use of microfluidic devices or systems is not limited to any particular department or sector. Presently, from the biomedical to cosmetic, environmental protection to engineering, the application of these devices is increasing enormously. The study on fabrication of such devices become one of the most developing fields of investigation in the current time. Microchannel fabrication via conventional so-called traditional fabrication techniques is a challenging task. Various researchers are developing different types of materials and techniques to fabricate microchannel for different kinds. Some of the materials are polymers, ceramics, and metals. In this article, an interesting process for the manufacturing of serpentine square wave microchannel with polydimethylsiloxane (PDMS) has been offered and explored. The complete process of fabrication of the microchannel has been discussed. It includes major two steps: serpentine square wave mold preparation and serpentine square wave microchannel fabrication. Primarily, the mold of the microchannel of serpentine square wave type with proper dimensions has been produced with the support of wire electric discharge machining and then using these molds, serpentine square wave microchannel of PDMS has been prepared by the soft lithography technique. The proposed process is helpful to manufacture microchannel as per the designed dimensions. From this study, researchers will be benefited by obtaining the guideline related to the serpentine square wave type microchannel fabrication with a cost-effective way.

The effect of magnetic field on the twisted porous ribs with various porous layers and pitches: The first and second laws of thermodynamics study with two-phase approach

Heat sinks are always in the center of electronic cooling researchers' attention. Microchannels are utilized in electronic cooling devices owing to their increased surface and better thermal performance than that of normal heat sinks. In this numerical investigation, the first and second laws of thermodynamics impact of twisted porous ribs on the microchannel are studied. The effects of the Reynolds number, the Hartman number, and the volume fraction of nanoparticles are investigated. The range of the dimensionless number for the Hartmann number and the Reynolds number is 0 to 20 and 250 to 1000, respectively. All types of microchannel in this study consist of clear microchannels in two groups; group one (No. 1, 2 and 3) and group two (No. 4, 5, and 6). The obtained results show that at the end of each porous rib, the reported parameters depict a decrease. Twisted porous ribs cause a significant decrease in the expanding thermal boundary layer. Also, the microchannel with triple-layer porous ribs (No. 3) exhibits considerable performance in the entropy generation. Finally, since group one has a double pitch, it has the better thermal performance and increasing the Hartmann number is one of the reasons for the increasing velocity gradient near the microchannel wall and friction factor.

Protein-Stabilized Palm-Oil-in-Water Emulsification Using Microchannel Array Devices under Controlled Temperature.

Microchannel (MC) emulsification for the preparation of monodisperse oil-in-water (O/W) and water-in-oil-in-water (W/O/W) emulsions containing palm oil as the oil phase was investigated for application as basic material solid/semi-solid lipid microspheres for delivery carriers of nutrients and drugs. Emulsification was characterized by direct observation of droplet generation under various operation conditions, as such, the effects of type and concentration of emulsifiers, emulsification temperature, MC structure, and flow rate of to-be-dispersed phase on droplet generation via MC were investigated. Sodium caseinate (SC) was confirmed as the most suitable emulsifier among the examined emulsifiers, and monodisperse O/W and W/O/W emulsions stabilized by it were successfully obtained with 20 to 40 µm mean diameter (dm) using different types of MCs.

The Electric Field and Microchannel Type Effects on H2O/Fe3O4 Nanofluid Boiling Process: Molecular Dynamics Study

In this computational research, we study the electric field and microchannel type effects on H2O/Fe3O4 nanofluid dynamical manner. The dynamical characteristics of this atomic structure are calculated using molecular dynamics method and we reported physical parameters such as total temperature, total energy, radial distribution function, velocity, density and temperature profiles of H2O/Fe3O4 nanofluid with 2 spherical nanoparticles. Physically, inserting external electric field causes phase transition (boiling process) in H2O/Fe3O4 nanofluid in shorter simulation time. Further, our results show that magnitude of external electric field is a significant parameter in nanofluid dynamical manner in microchannels. By external electric field magnitude increasing, the highest rate of velocity, temperature and density of nanofluid enhance to 0.0071 A·ps−1, 714 K and 0.038 atom·A−3 rates, numerically. Further, by microchannel atomic type variation from Pt to Au one, the rate of temperature and velocity of nanofluids reach to maximum rate at Au microchannel. So we conclude that phase transition of nanofluid in Au microchannel occurs in shorter MD simulation time.

A generalized moving-boundary algorithm to predict the heat transfer rate of transcritical CO2 gas coolers

Abstract This paper presents the development of a CO2 gas cooler model using the moving-boundary (MB) method. The model aims to separate the gas cooler into two regions, supercritical and supercritical liquid, to predict the steady-state thermal heat transfer rate for air-type CO2 heat exchanger. The model uses the latest correlations for refrigerant and air-side heat transfer coefficients and pressure drops. The experimental results of fin-and-tube type and micro-channel type gas coolers were used for model validation. The mean absolute error (MAE) of the gas cooler heating capacity predictions was approximately 4%, while the predictions of the outlet temperature of the refrigerant side were within ± 3 K. The present MB model also showed an improved computational time of up to 10 times faster compared to a discretized model, which can reduce the overall computational effort in the simulation of detailed transcritical cycle model.

Investigation on thermal performance of water-cooled Li-ion pouch cell and pack at high discharge rate with U-turn type microchannel cold plate

The objective of this study involves investigation and simulation on thermal performance of water-cooled lithium-ion battery cell and pack used in electric vehicles at high discharge rate with a U-turn type microchannel cold plate and recommending an optimal cooling strategy by considering the effects of various parameters including different discharge rates, inlet coolant mass flow rates, inlet coolant temperatures, surface area coverage ratios via changing the number of cooling channels, channel hydraulic diameters via changing maximum width of cooling channels, and flow pattern layouts. Experiments were conducted and the simplified heat generation rate calculation method was proposed to use as input heat source in the numerical study. The cold plate with surface area coverage ratio = 0.750 and channel hydraulic diameter = 1.54 mm was suggested to enhance battery cooling. The suggested flow pattern layout corresponding to cross flow with alternate single inlet and single outlet channel decreases the maximum temperature and temperature difference by 32.2% and 950.1%, respectively, when compared to the original flow pattern layout corresponding to parallel flow with 10 inlet channels at one side. The study demonstrated that optimized cooling parameters could maintain the maximum temperature and temperature non-uniformity of 50 V battery pack below 40 °C and 4 °C, respectively.

Simulation of subcooled flow boiling in manifold microchannel heat sink

The manifold microchannel (MMC) heat sink has become the most popular one among emerging technologies for high heat flux thermal management because of its high surface-to-volume ratio. Even though numerous numerical studies have been performed for the single-phase flow in the MMC heat sink, researches on two-phase flow boiling/condensation in this type of microchannel is seldomly reported because of its issues with flow pattern prediction. In the present work, a numerical approach involving two-phase interface capturing, phase change and solid heat conduction is conducted for the simplified MMC unit cell model. Heat and mass transfers of Lee model and interfacial heat resistance model for phase change are validated by the single bubble growth problem. Besides, both phase-change models are shown to provide good predictions against the experimental temperature database, with all of the data points falling within −5% to +20% and −5% to +10% error bands for Lee model and interfacial resistance model, respectively. Furthermore, a liquid-vapor interface region with thin thickness and accurate interface temperature can be obtained by the interfacial resistance model coupled with a homogeneous nucleation-site model.

Combined effect of inlet restrictor and nanostructure on two-phase flow performance of parallel microchannel heat sinks

In this study, the combined effect of nanostructure and inlet restrictor on reducing the instabilities during flow boiling in parallel microchannel heat sinks is investigated experimentally. Four types of microchannel heat sinks are considered; plain microchannel, microchannel with inlet restrictor, nanostructured microchannel, and nanostructured microchannel with inlet restrictor. Different flow regimes such as bubbly flow, slug flow, annular flow, and partial dry out are observed with the variation in applied heat flux and mass flux. The fluctuations in pressure, temperature, and mass flux are characterised in each regime. It is found that the fluctuations increase with power input, which is primarily due to backflow of vapour in the upstream direction of flow. The microchannel with inlet restrictor is more effective in reducing fluctuations and result in less surface temperature compared to the baseline case of plain microchannel without restrictor at the same mass flux. Moreover, if the nanostructured surface is added to the plain microchannel with inlet restrictor, the effectiveness in reducing fluctuations increases at higher heat flux and also produces less surface temperature compared to other types of microchannels.

An experimental study on microchannel heat sink via different manifold arrangements

The current experimental study performed the overall performance of the microchannel heat sink using the heat transfer coefficient, Nusselt number, and pressure drop for three novel manifold configurations. These selected manifolds have a rectangular (R), rectangle with semicircular (RSC) and divergent–convergent (DC) shapes for inlet and outlet. The heat transfer coefficient for all three types of microchannel was reported for the Reynolds number range of 342–857. The experiments were tested at four different heat inputs ranges between 50–125 W. R-type microchannel heat sink showed the worst performance, while the performance of DC-type microchannel heat sinks was the best. At Re of 342, the lowest Nusselt number was observed to be 2.8 at lower Reynolds number 342 for R-type manifold. RSC manifolds MCHS seems to be a better choice compared to R-type and DC-type MCHS with respect to pressure drop and Nusselt number. Compared to R-type microchannel heat sink, 24–32% and 7–10% augmentation in heat transfer coefficients were reported for DC-type and RSC-type microchannel heat sinks, respectively. Based on the released experimental results, it can be stated that DC-type microchannel heat sink is more beneficial in terms of heat transfer enhancement.

Experimental investigation of the continuous two-phase instable boiling in microchannels with triangular corrugations and prediction for instable boundaries

The microchannels with triangular corrugations usually have high heat transfer ability, but the possible continuous two-phase instable boiling with periodically moving gas-liquid interface may cause the oscillations of pressure drop and temperature of walls, and lead to some control issues and security risks. In this paper, acetone is chosen as the working fluid, and an experimental setup with multi-sensors is built. The straight and triangular corrugated microchannels are applied for comparisons and analysis. Both microchannels have same hydraulic diameters of 104.3 μm. After experiments at the working conditions of G = 250–1100 kg/m2 s and qeff = 208–1050 kW/m2, the similarities and differences about continuous instable boiling between two types of microchannels are found. A prediction model with equations and principles are developed, and the wall temperature at inlet is chosen as the judging criteria. The analysis results show that the wall temperature at inlet dominant the instable boundaries, and which can be affected by the working conditions and structural parameters. The prediction model also indicates that the increasing of flow resistance at inlet, decreasing of inlet temperature and heat transfer coefficient at inlet can reduce the area of instable boiling by about 40%, and decrease the slopes of instable boundaries by 24.2–51.7%.

Hydrodynamic Microparticle Separation Mechanism Using Three-Dimensional Flow Profiles in Dual-Depth and Asymmetric Lattice-Shaped Microchannel Networks.

We herein propose a new hydrodynamic mechanism of particle separation using dual-depth, lattice-patterned asymmetric microchannel networks. This mechanism utilizes three-dimensional (3D) laminar flow profiles formed at intersections of lattice channels. Large particles, primarily flowing near the bottom surface, frequently enter the shallower channels (separation channels), whereas smaller particles flowing near the microchannel ceiling primarily flow along the deeper channels (main channels). Consequently, size-based continuous particle separation was achieved in the lateral direction in the lattice area. We confirmed that the depth of the main channel was a critical factor dominating the particle separation efficiencies, and the combination of 15-μm-deep separation channels and 40-μm-deep main channels demonstrated the good separation ability for 3–10-μm particles. We prepared several types of microchannels and successfully tuned the particle separation size. Furthermore, the input position of the particle suspension was controlled by adjusting the input flow rates and/or using a Y-shaped inlet connector that resulted in a significant improvement in the separation precision. The presented concept is a good example of a new type of microfluidic particle separation mechanism using 3D flows and may potentially be applicable to the sorting of various types of micrometer-sized objects, including living cells and synthetic microparticles.

Quantitative visualization of fluid mixing in slug flow for arbitrary wall-shaped microchannel using Shannon entropy

Micro-reactors based on slug flow are among the most promising developments for improving the efficiencies of chemical reactions and unit operations in chemical engineering. Quantitative understanding of the local and global fluid dynamics and their effects on fluid mixing is required for designing effective slug flow micro-reactors. This paper proposes a new method for quantitative two-dimensional assessment of fluid mixing in slug flow. Pixel-wise calculation of local entropy inside a slug is discussed. The proposed method is based on two-phase simulation using the volume of fraction (VOF) algorithm and is thus applicable to the flow pattern in arbitrary wall-shaped micro-reactors. The method consists of three steps. (1) Flow analysis using two-phase VOF algorithm: A series of two-dimensional velocity fields inside the slug along time is obtained for a certain duration. (2) Backward particle tracking from the target image to the initial image: The slug in the initial image is divided into small regions, and each region is assigned a different label. Accumulation of backward particle tracking results reveals a two-dimensional distribution of labels in the target image. (3) Pixel-wise calculation of entropy on the obtained distribution of labels: The resulting image is a quantitative two-dimensional mixing pattern inside the slug. The proposed method was applied to three types of microchannels with different bumps on the walls. The results could quantitatively distinguish the differences in fluid mixing capability among the systems.

Optofluidic control using light illuminated plasmonic nanostructure as microvalve

Optofluidic control is emerging as a promising tool in wide applications like pharmaceutics, chemistry, energy, and biology, due to the development of micro-fluidic chip. They usually require complex optical set-ups or special materials for working fluid or micro-channel. In the present work, a simple optofluidic control method using light illuminated gold nanobrick array in a distributary micro-channel was proposed. The plasmonic nanostructure acts like a microvalve which can be tuned continuously by manipulating the illumination light polarization state or intensity. Two different types of micro-channels were studied to examine the performance of the proposed method. It is found that for h-shaped micro-channel, the mass flow rate can be controlled by simply adjusting the intensity of the incident monochromatic light. As for the Y-shaped micro-channel, the manipulation of mass flow rate is achieved by changing the polarization state of the incident light. On this basis, the detailed influence factor of the light controlled microvalve is investigated to optimize its performance.