Microchannel Width Research Articles

Experimental investigation and optimization of laser induced plasma micromachining using flowing water

In this study, laser induced plasma micromachining using flowing water (F-LIPMM) was performed to create micro-channels on stainless steel surface. The effects of process parameters (water speed, laser pulse energy, frequency and scanning speed) on the responses of micro-channel width, depth, material removal rate (MRR) and heat affected zone (HAZ) were investigated based on response surface methodology (RSM). The regression models for the machined width, depth, MRR and HAZ were developed, and the adequacies of the developed models were subsequently verified by analysis of variance (ANOVA) method. Finally, grid structures consisting of desired micro-channels were created with the optimum process parameters: water speed of 8 m/s, pulse energy of 10.4 μJ, frequency of 15.8 kHz and scanning speed of 2.7 mm/s. The uniform micro-channels with smooth bottoms, side-walls and small HAZ were obtained, and the results showed that the predicted responses using the developed models were comparable with the experimental results.

Assessment machining of micro-channel textures on PCD by laser-induced plasma and ultra-short pulsed laser ablation

Micro-channels are one of the most common surface textures for applications, however, the machining of micro-channels on polycrystalline diamond (PCD) is still facing challenges due to its intrinsic properties of high brittleness and hardness. In this paper, fabrication of micro-channels by laser induced plasma (LIP) and laser ablation directly (LAD) machining methods on PCD surface is experimentally investigated. For comparing the processing capacity, the influence of different laser process parameters (including overlap, power, frequency, scanning speed and the number of passes) on the geometry and material removal rate of micro-channels is assessed. Results show that the process parameters have a significant influence on the formation of micro-channels, and LIP exhibits higher efficiency compared to LAD in the case of the plasma formation with the high overlap and laser power. The micro-channel depth and width produced by LIP increase with the increasing overlap, laser power and number passes, and that reduce with the increasing frequency and scanning speed; the MRR produced by LIP increases with the increasing overlap, laser power and scanning speed, and that reduces with the increasing frequency and number of passes. Meanwhile, LIP reduces the oxidation reaction inside the micro-channels compared to LAD due to the shielding effect of distilled water.

Effect of Tool Electrode-Workpiece Gap in the Microchannel Formation by Electrochemical Discharge Machining

Microchannels in a glass-based substrate are widely used in biomedical, and microfluidic devices, buried redistribution lines (RDLs), etc. Tool electrode-workpiece gap and tool feed rate are very important process parameters for the fabrication of microchannels using electrochemical discharge machining (ECDM) process. This paper reports the effect of these parameters on the material removal and geometric characteristics of the microchannels formed in soda-lime glass substrates. Microchannels were fabricated with alkaline electrolytes i.e. NaOH and KOH with varying concentrations at different tool electrode-workpiece gaps. Experiments were performed using a DC power supply with high carbon steel needles as tool electrode. Finite element based thermal model showed a similar trend between the predicted microchannel depth and width with the experimental values. Compared to KOH electrolyte, higher channel depth and width were obtained with NaOH electrolyte for a given parametric setting. At higher tool electrode-workpiece gap and tool feed rate, lower channel depths were obtained. Higher microchannel widths were obtained at a gap of 20 μm and 10 μm with NaOH and KOH electrolyte, respectively. Tool wear was found to be decreasing as the tool electrode-workpiece gap and the tool feed rate was increased. KOH electrolyte resulted in lower tool wear compared to NaOH electrolyte.

Numerical analysis on thermal performance of a trapezoidal micro-channel heat sink using an improved version of the augmented ε-constraint method

This work proposes the use of an improved version of the augmented ε-constraint method (AUGMENCON2) for the analysis of the thermal performance of a micro-channel heat sink. In order to highlight the strength and the effectiveness of this new approach, a trapezoidal micro-channel heat sink has been considered. The geometrical configuration namely the micro-channel widths and depth are the main variables considered in this study. Surrogate models based on the response surface methodology have been adopted to approximate the thermal resistance and the pumping power which provide an indication of the thermal performance of the micro-channel heat sink. A two-objective nonlinear problem have been formulated and implemented within the general algebraic modelling system. Global Pareto optimal solutions have been computed using the proposed method. Despite being a relatively straightforward method, the AUGMENCON2 provides a reasonable level of accuracy and shortens the required computational time in comparison to two existing approaches.

Study on kerf width deviation of microchannel with various medium in laser transmission cutting by diode pump fiber laser

Fabrication of kerf width is an important characteristic of micro-channels. This paper presents an experimental study on the differences of kerf width of microchannels at different medium. In this research, laser transmission micromachining operation is conducted on thick polymethyl methacrylate (PMMA) at partially submerged condition in water and in air for a comparative study to achieve desired results. The diode pump fiber laser with wavelength in near infrared region (1064 nm) has been used here to perform the study. The kerf width of the micro-channels in different medium has been taken as machining responses. 64 number of runs based on full factorial design of response surface methodology has been applied here to conduct the experiments. The effect of different medium on kerf width has been studied.

Numerical analysis on thermal performance of a trapezoidal micro-channel heat sink using an improved version of the augmented ε-constraint method

This work proposes the use of an improved version of the augmented e-constraint method (AUGMENCON2) for the analysis of the thermal performance of a micro-channel heat sink. In order to highlight the strength and the effectiveness of this new approach, a trapezoidal micro-channel heat sink has been considered. The geometrical configuration namely the micro-channel widths and depth are the main variables considered in this study. Surrogate models based on the response surface methodology have been adopted to approximate the thermal resistance and the pumping power which provide an indication of the thermal performance of the micro-channel heat sink. A two-objective nonlinear problem have been formulated and implemented within the general algebraic modelling system. Global Pareto optimal solutions have been computed using the proposed method. Despite being a relatively straightforward method, the AUGMENCON2 provides a reasonable level of accuracy and shortens the required computational time in comparison to two existing approaches.

Effects of geometrical parameters and Reynolds number on the heat transfer and flow characteristics of rectangular micro-channel using nano-fluid as working fluid

The combined effects of Reynolds number and geometrical parameters on heat transfer and flow of Al2O3–H2O nanofluid under laminar flow condition in single rectangular microchannel was investigated numerically. In the process of the actual flow and heat transfer of nanofluids, the nanoparticles concentration distribution is nonuniform in the flow field. A proposed simulation method carefully considering the nanofluids thermophysical properties are nonuniform and dynamic in the channels was adopted to improve the simulation accuracy. The results show that the local heat transfer coefficients increase with the aspect ratio and design variable β (the ratio of the microchannel width to the wall thickness) at the fully developed flow region because the nanoparticles enriched near the solid-fluid interface and then heat transfer is enhanced as the aspect ratio and design variable β increase. The effect of aspect ratio on heat transfer coefficient is remarkable. But design variable β has a very mild effect on heat transfer compared with aspect ratio. The difference of heat transfer performance between a conventional channel and a microchannel is decreased with the increase of aspect ratio. The Poiseuille number of the microchannel is related to not only aspect ratio but also the design variable β and Reynolds number, and it is smaller than that of the conventional scale rectangular channels when the Reynolds number is less than about 1000.

Integrated vortex micro T-mixer for rapid mixing of fluids

This article reports a novel design of a micromixer showing efficient mixing by creating vortex flow in a microchannel. The main microchannel splits and recombines into two sub-channels at a tangential position that facilitates the generation of vortex flow. The height and width of the sub-channels are half the height and width of the main microchannel. The fluid flow and the mixing characteristics of the micromixer were demonstrated by performing numerical and experimental studies at different Reynolds numbers (Re = 2.5≈40). The micromixer was fabricated using a standard soft lithography process. The fluid streams from the subchannels create vortex flow in the main microchannel which increases the interface area. The idea of creating multiple vortex flow zones by repeating the design of vortex T-mixer was successfully shown in mixing enhancement. The design of the micromixer is promising for mixing the fluids in a short length of the microchannel (5.5 mm at Re = 10 and 2.6 mm at Re = 40).

Rapid Quantification of Escherichia coli in Potable Water by Fluorescence In Situ Hybridization Performed in Liquid (liq-FISH) and a Microfluidic System

Specific and sensitive detection of fecal microbes in potable water is essential for ensuring the safety of water supplies. To this end, because conventional culture-based methods typically require at least 24 h to detect fecal bacteria, rapid and simple microbiological detection methods are considered necessary. Fluorescence in situ hybridization (FISH) is a useful culture-independent technique for selectively and rapidly detecting target bacteria using fluorescently labeled probes that hybridize with intracellular ribosomal RNA. However, typical FISH assays are relatively complicated to perform, making FISH unsuitable for routine tests. In this study, we developed an “in liquid-fluorescence in situ hybridization” assay (liq-FISH) to enumerate Escherichia coli cells, indicator of fecal contamination, rapidly. The assay performs the entire in situ hybridization procedure in liquid and requires only two simple steps—addition of fixative followed by the addition of fluorescent probe. Important processes in FISH, fixation and hybridization, were optimized, and then specificity of the optimized liq-FISH procedure was confirmed by E. coli and other eight gammaproteobacterial species. The findings showed that only E. coli cells fluoresced under a fluorescence microscope; however, filtration process is required to observe and count hybridized cells by fluorescence microscopy. For simple and semi-automated counting following liq-FISH, our developed microscope-based microfluidic counting system was applied. Hybridized cells were injected into a microfluidic device, which permitted the detection and enumeration of E. coli cells flowing through the microchannel (width: 100 μm, depth: 15 μm). The obtained results were compared with those obtained by conventional fluorescence microscopy, and results showed the similarity (r = 0.908). E. coli cells could be counted within 5 h (filtration for concentration of low numbers of E. coli cells (if necessary): 0.5 h, fixation of cells: 2 h, in situ hybridization: 2 h, counting: 0.5 h), and this method would be useful for rapidly quantifying E. coli cells in potable water.

Numerical simulation of subcooled flow boiling in a manifold microchannel heat sink

Recently, various miniaturized electronic systems and the rapid increase in power density of microelectronic devices have created additional requirements for micro-scale heat dissipation technology. To dissipate heat in a micro-scale region efficiently, several creative cooling methods for high heat flux dissipation have been designed on the order of 1000 W/cm2. Due to its high surface-to-volume ratio, the microchannel heat sink has become the most popular one among emerging technologies and an effective tool for high heat flux thermal management. Nevertheless, in common electronic microchannel cooling systems, the traditional parallel microchannel causes a dramatic pressure loss along channel length. In this regard, the manifold microchannel heat sink cooling technology becomes promising with its high heat dissipation potential and moderate pressure drop penalty. The shortened effective flow length compared with the traditional microchannel provides a smaller pressure drop and delays the onset of the critical-heat-flux point. However, while a number of numerical and experimental studies have been conducted for the single-phase flow in the manifold microchannel, two-phase flow boiling in this kind of channel is not widely employed because of its issues with flow pattern prediction. This work develops a new solver based on open source software OpenFOAM to perform the transient process of subcooled flow boiling in the manifold microchannel heat sink. Additionally, heat transfer in the silicon substrate is considered to improve the accuracy of simulation. Similar to single-phase flow simulation for the manifold microchannel, a unit cell model extracted from the whole cooling plate is employed for the two-phase boiling flow to avoid huge computational costs. Through several reasonable assumptions, the symmetry boundary condition is applied on four lateral surfaces in the unit cell, while uniform heat flux is adopted on the bottom wall. A uniform inlet velocity boundary estimated from the total volume flow rate condition is coupled with a fixed temperature value of 7°C lower than saturation temperature. After the mesh independence test, the self-programming solver and numerical methods are validated by comparing numerical results with experimental data. It is determined that the boiling curve obtained by the empirical rate phase-change model with parameters r l= r v=100 agrees well with experimental results. Furthermore, heat transfer and pressure drop performance differences are caused by microchannel width w c and fin width w f. In comparison to sample A ( w c= w f=15 μm), decreasing w c and w f simultaneously leads to lower average wall temperature of the heated surface; the channel pressure drop between inlet and outlet surfaces rises dramatically when the widths decrease. When the total number of microchannels in the manifold microchannel cooling plate remains unchanged, increasing w c results in a decreased w f. Based on experimental results, heat sink sample C shows that the pressure loss can be considerably reduced under the premise of sacrificing a small degree of heat transfer performance, which can be attributed to the increased microchannel hydraulic diameter. The manifold microchannel heat sink with w c> w f is recommended for practical application due to lower pressure loss and average temperature variation.

Transport properties of coupled Brownian particles confined to a microchannel in an asymmetric periodic potential

On the basis of the transport features and experimental phenomena observed in studies of molecular motors, we investigated an overdamped Brownian motion of two coupled particles with an asymmetric periodic potential in a two-dimensional microchannel theoretically and numerically, to reveal the dynamical mechanism of cooperative transport of particles with two heads, where the interactions between two particles are taken into consideration. Moreover, while moving in a confined structure, Brownian particles also could exhibit peculiar kinetic behavior. The dependence of directed current on various parameters is systematically studied. Our results indicate that the direction of motion can be reversed by modulating the coupling strength, free length, and microchannel width. In addition, we have achieved the conditions of forward motion in this study. That is, when the interparticle average horizontal interval Δx > 0.25L, where L is the spatial period of the external potential, the forward motion of coupled Brownian particles effected by the synchronized noise and confined to a microchannel can be generated in the strong-coupling case.

Microembossed copper microchannel heat sink for high‐density cooling in electronics

A microembossed copper microchannel heat sink was designed and fabricated for high-density cooling in electronics. The microchannel width and aspect ratio were investigated to find out the optimised channel size for microembossing. The fabrication method was based on bulk copper forming including tungsten die inductively coupled plasma etching, hot copper microembossing, inlet/outlet ports punching and sealing. The heat dissipation performances were tested by ceramic heater. The maximum temperature decreased to ∼37°C under different heat fluxes, with the maximum temperature decreased by 69.2% at 50 W/cm2 heat flux. The equivalent heat transfer coefficient reached the value of 6492 W/m2 K. High-power chip was used as heat source too. The maximum heat flux reached 304.8 W/cm2 when the chip can still function properly at 90.5°C. High cooling performance with the micro-heat sink proves that microembossing by tungsten die is an alternative process for microchannel heat sink fabrication with batch production and low cost. Taking advantages of simple fabrication process and reutilisation of tungsten die, the technology shows promising potentials in high-density microcooling systems.

Producing Collagen Micro-stripes with Aligned Fibers for Cell Migration Assays.

The orientation of collagen fibers in native tissues plays an important role in cell signaling and mediates the progression of tumor cells in breast cancer by a contact guidance mechanism. Understanding how migration of epithelial cells is directed by the alignment of collagen fibers requires in vitro assays with standardized orientations of collagen fibers. To address this issue, we produced micro-stripes with aligned collagen fibers using an easy-to-use and versatile approach based on the aspiration of a collagen solution within a microchannel. Glass coverslips were functionalized with a (3-aminopropyl)triethoxysilane/glutaraldehyde linkage to covalently anchor micro-stripes of aligned collagen fibers, whereas microchannels were functionalized with a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO)nonionic triblock polymer to prevent adhesion of the collagen micro-stripes. Using this strategy, microchannels can be peeled off to expose micro-stripes of aligned collagen fibers without affecting their mechanical integrity. We used time-lapse confocal reflection microscopy to characterize the polymerization kinetics of collagen networks for different concentrations and the orientation of collagen fibers as a function of the microchannel width. Our results indicate a non-linear concentration dependence of the area of fluorescence, suggesting that the architecture of collagen networks is sensitive to small changes in concentration. We show the possibility to influence the collagen fibril coverage by adjusting the concentration of the collagen solution. We applied this novel approach to study the migration of epithelial cells, demonstrating that collagen micro-stripes with aligned fibers represent a valuable in-vitro assay for studying cell contact guidance mechanisms.

Preliminary geometric parameters optimization of lobster-eye-type wide field of view soft x-ray imager

The lobster-eye optical system is widely used in the wide field of view (FOV) soft x-ray imaging device. The payload soft x-ray imager (SXI) onboard the solar wind magnetosphere ionosphere link explorer satellite will apply this technology to achieve panoramic imaging of the dayside magnetosphere. In order to optimize the imaging performance of SXI, we focus on geometric parameters optimization of a lobster-eye lens. The results show an appropriate microchannel ratio of length to width of lobster-eye optics with radius of curvature of 600 mm could be 30:1 (microchannel width of 40 μm and length of 1.2 mm). For a monochromatic parallel light source with energy of 1 keV, this combination of parameters can theoretically provide relatively large total effective area of about 15.52 cm2 and focusing efficiency of about 0.2887 along with spatial angular resolution of about 6 arc min at the center of FOV. Combined with the actual lobster-eye optics, the aberrations from deformation of the microchannel, the deviation of radius of curvature and planar detector are analyzed. For SXI with planar CCD detector, an optimum focal length could be 304.2 mm to ensure better resolution in full FOV.

Realization of Microfluidic Paper-Based Analytical Devices Using a 3-D Printer: Characterization and Optimization

Microfluidic paper-based analytical devices ( $\mu $ PADs) are a clean-room free, cost-effective, and self-pumping flow-based rapid prototyping technique, which is compatible with a varying range of fluids. Until now, $\mu $ PADs have been primarily fabricated using crayons, and plotting-machine and solid-ink printers. These devices can be easily employed for various detection schemes, such as electrical, electrochemical, and optical. The presence of a capillary effect in the chromatograph paper has made $\mu $ PADs independent of a passive device, such as pumps and valves. In this paper, an alternative and a novel method is proposed to achieve the $\mu $ PADs effortlessly using a 3-D printer (3DP), which has many advantages over the existing methods. For creating hydrophobic barriers for microchannel walls, polycaprolactone (PCL) filament was used with fused-deposition modeling (FDM) 3DP. PCL filaments were deposited on the chromatography paper followed by heating for determining the overall dimension and depth of the microchannel at which PCL melts and penetrates into this paper. The $\mu $ PADs are characterized and optimized for two parameters. First, fabrication parameters, such as heating temperature and time duration, were used for the creation of the hydrophobic barrier using a hot air oven. Second, the microchannel parameters, such as microchannel width, boundary thickness, chromatography paper grade, and microchannel source shape (rectangular, triangular, and circular) were used for the fluid-flow by measuring the time taken by fluid to travel a fixed length of the microchannel. After rigorous analysis, it was found that for the creation of the hydrophobic barrier, $\mu $ PADs heated between temperature 120°C to 150°C require 30 min. Under optimized conditions for the fluid flow, the chromatography paper grade 1441 with a triangular source microchannel was found to be best. This paper provides an alternate, simple, and optimized method toward the development of the application-specific $\mu $ PADs, such as the micro-viscometer, which, in turn, can be widely used to monitor various types of fluids including human bodily fluids.

1[formula omitted]3 optical switch with a V-shaped microchannel

A 1×3 optical switch with a V-shaped microchannel is proposed. It can selectively switch optical signals from one channel to another by controlling liquid and air in the V-shaped microchannel. Moreover, it has a simple structure, small volume, very wide operating waveband (from visible light to near infrared), small crosstalk, large extinction ratio and small polarization dependent loss. This 1×3 optical switch can form 1×N, 2×N and M×N switch arrays. The optical transmission characteristics are discussed. The research results indicate that the microchannel width has great influence on the switch performances and the optimum width is 4μm. After the structure and parameters are optimized, the crosstalks of the optical switch are between -25.1 dB and -48.6 dB for 1550 nm wavelength. Moreover, the insertion loss are respectively 0.44 dB, 0.20 dB and 0.47 dB for 1550 nm wavelength and 0.30 dB, 0.18 dB and 0.31 dB for 1310 nm wavelength at three exit ports. In addition, the switch arrays based on this 1×3 optical switch are also introduced.

Improving the Machining Quality of Micro Structures by Using Electrophoresis-Assisted Ultrasonic Micromilling Machining

Traditional micromilling leaves burrs and has a high surface roughness in the workpiece, which compromises the microstructural machining quality. Electrophoresis-assisted ultrasonic micromilling machining (EUMM) is proposed to solve this problem. An electrophoresis assisted electric field is applied to attract abrasive particles into the machining gap. Combined with the ultrasonic vibrations of the workpiece, the impact and grinding effect of these abrasive particles in the machining gap removes burrs that are generated during machining and reduces the surface roughness of the microstructure. Micro channels were generated for this study to verify the proposed method. The experimental results show that the EUMM significantly reduces burr formation during microchannel milling. The EUMM also decreases the surface roughness (Ra); the bottom roughness using the EUMM (0.33 µm) is lower than that with either the ultrasonic micromilling (UMM) or traditional micromilling. The EUMM also improves the sidewall roughness since the grinding and particle impacts significantly smooth the sidewalls. The particles during EUMM ensure a low surface roughness of 0.34 µm for the vertical sidewalls. Furthermore, the EUMM has a lesser effect on the width of the micro channels; as the spindle speed increases, the microchannel width only increases from 486 to 498 µm.

2 × 2 optofluidic switch chip with an air shutter.

A 2×2 optofluidic switch chip with an air shutter is proposed. It has a simple structure, small volume, small crosstalk, large extinction ratio, small polarization-dependent loss, and broad operation waveband (400-1700nm). This 2×2 switch chip has good scalability and can form a number of optical switches by using different microfluidic driving technologies. The research results show that the microchannel width has great influence on the switch performances in "on" state, where the comprehensive performances of the optical switch are the best at 4.0μm width. By replacing the original symmetrical structure with an optimized semi-tapered structure, the switch performances are further improved. After the structure and parameters are optimized, for 1310nm wavelength, the insertion losses of the proposed switch are 0.41dB in "on" state and 0.15dB in "off" state, the extinction ratios are 52.5dB in "on" state and 28.3dB in "off" state, and the crosstalks are -28.8 dB in "on" state and -52.6 dB in "off" state.

Optimal design and fabrication of surface microchannels on copper foam catalyst support in a methanol steam reforming microreactor

Methanol steam reforming microreactor has been considered as one of the effective way to provide the online hydrogen source for proton exchange membrane fuel cell. In order to further improve the reaction performance of microreactor, the surface microchannels with different sizes and qualities are proposed to optimize the geometrical structure of copper foam as catalyst support. Later, the methanol concentration distribution in copper foams was investigated by numerical analysis using finite element method. Based on the simulation results, different surface microchannels on copper foams are designed and fabricated by laser processing method. The configuration of surface microchannel (quantities, widths and distributions) on copper foams was investigated under different gas hourly space velocities and reaction temperatures and the optimal one was obtained. Our results show that copper foams with surface microchannels can provide a larger diffusion space and enhance the uniform distribution of methanol, leading to improvement in reaction performance. Moreover, it is found that the uniformity of methanol concentration distribution in copper foam can be further improved when reactants pass through microchannel from inlet with larger width to outlet with smaller width. The best reaction performance of microreactor for hydrogen production is obtained for the copper foam with gradient width microchannels because of its larger specific surface area and better loading performance of catalysts.

Analysis of microchannel resistance factor based on automated simulation framework and BP neural network

In this paper, self-design automated simulation and artificial neural network (ANN) model were developed to analyze and estimate the resistance factor in rectangle cross-section microchannels. The main purpose is to obtain a universal solution method through numerical simulation which can solve the resistance factor problem for invariant cross-section microchannels. Through Python language, the automatic coalescent of preprocessing Gambit, computing software CFD and post-processing Tecplot make the simulation framework realize the automatic acquisition of microchannel resistance factor samples. Then, 100 simulation samples with different aspect ratios for Reynolds numbers ranging from 50 to 500 were obtained. After validation, the width and height of microchannels were applied as input data set of the ANN model, and the resistance factor was determined as the target data. In order to improve BP algorithm for training ANN, a new swarm evolution algorithm was realized by combining the strong point of gradient descent method, genetic algorithm and particle swarm optimization, which is called particle swarm evolution algorithm. Finally, the result of resistance factor model was established and verified by several existing measurement value of pressure drop from remarkable experimental.