Microchannel Of Length Research Articles

Design, Simulation, and Fabrication of a Copper-Chrome-Based Glass Heater Integrated into a PMMA Microfluidic System.

In this paper, the development of a copper–chrome-based glass microheater and its integration into a Polymethylmethacrylate (PMMA) microfluidic system are presented. The process highlights the importance of an appropriate characterization, taking advantage of computer-simulated physical methods in the heat transfer process. The presented system architecture allows the integration for the development of a thermal flow sensor, in which the fluid flows through a 1 mm width × 1 mm length microchannel across a 5 mm width × 13 mm length heating surface. Using an electrothermal analysis, based on a simulation and design process, the surface heating behavior curve was analyzed to choose a heating reference point, primarily used to control the temperature point within the fluidic microsystem. The heater was characterized using the theory of electrical instrumentation, with a 7.22% error for the heating characterization and a 5.42% error for the power consumption, measured at 0.69 W at a temperature of 70 °C. Further tests, at a temperature of 115 °C, were used to observe the effects of the heat transfer through convection on the fluid and the heater surface for different flow rates, which can be used for the development of thermal flowmeters using the configuration presented in this work.

Computational Microfluidic Channel for Separation of Escherichia coli from Blood-Cells

Microfluidic channels play a vital role in separation of analytes of interest such as bacteria and platelet cells, etc., in various biochemical diagnosis procedures including urinary tract infections (UTI) and bloodstream infections. This paper presents the multi physics computational model specifically designed to study the effects of design parameters of a microfluidics channel for the separation of Escherichia coli (E. coli) from various blood constituents including red blood cells (RBC) and platelets. A standard two inlet and a two outlet microchannel of length 805 m with a channel width of 40 m is simulated. The effect of electrode potentials and the effect of electrode placement along the channel length and also the levitation of electrodes from the channel wall are studied to optimize the selective particle separation throughput. Simulated results show the efficient separation of E-coli with a mean diameter 0.68 m is achieved at low voltages (less than 20 V) when electrodes placed near to the micro channel and also noticed that the applied electric potential is inversely proportional to the number of electrodes placed along the microfluidic channel. The computer aided multi physics simulations with multiple governing parameters could be advantage in design optimization of microfluidics channels and support precise bioparticle separation for better diagnosis.

Scrutinizing premixed syngas combustion and its dynamics in micro-scale

Increasing demands in the next-generation power-generation device such as unmanned aerial vehicles (UAV), microsatellite thrusters, micro-chemical reactors and sensors calls for fuels with high specific energy and low emissions to meet the current demand of green energy. Fuel-lean synthesis gas (syngas) meets both these requirements exhibiting promising route to clean and green environment. Thus, it is of critical importance to characterize syngas combustion and understand its properties in micro-combustion industry. In addition to complicated flame dynamics in microscale systems, varying the syngas-fuel mixture composition as well as the boundary conditions and geometry of a combustor significantly affect the burning process in the system. This work investigates the characteristics of a premixed syngas flame in a horizontal two-dimensional micro-channel of length 20 mm and half-width 1 mm by means of computational simulations using the ANSYS Fluent commercial software. A fixed temperature gradient is employed at the upper wall such that the temperature grows linearly, from 300 K at the inlet to 1500 K at the outlet, to account for the conjugate heat transfer. The chemical kinetics of the combustion process is imitated by the San Diego mechanism with 46 species and 235 reactions, which is implemented using the Chemkin mechanism in ANSYS Fluent. Stoichiometric premixed burning of a syngas fuel comprised of carbon monoxide (CO), methane (CH4) and hydrogen (H2), with various compositions and inlet velocities, is considered. These results are postprocessed to characterize various combustion properties such as ignition, stabilization and extinction properties and FRIE event. It is further shown that how instability can be eliminated by increasing the inlet flow velocity to form a stable, stationary flame. As a result, it is demonstrated how various combustion characteristics depend on the inlet velocity and composition of a syngas mixture.

Augmented electroosmotic flow and simultaneous desalination in microchannels embedded with permselective membranes

Ion-selective nanoporous membranes are widely used in many engineering and technological applications, such as biomolecular separation, desalination, sample preconcentration and fuel cells etc. In this paper, we study steady-state electrokinetic flow of electrolytes in a micro-fluidic channel with permselective membranes embedded at the middle of the walls. Distribution of the ion concentrations and the fluid flows at varied cross-membrane voltages are investigated. It is shown that such systems possess the combined advantages of fast flow generated by electroosmosis of the second kind and desalinating functionalities. It is demonstrated that the membrane-embedded microchannel of length 60 μm and width 10 μm may achieve 89% of salt rejection 15 times of classical electroosmotic flow speed under a cross channel field of 40 V/cm and a cross 400 mV membrane voltage. This kind of microfluidic devices could be used in small- or medium- scale desalination plants and microfluidic pump systems.

Electrothermal Transport in Biological Systems: An Analytical Approach for Electrokinetically Modulated Peristaltic Flow

A mathematical model is presented to study the combined viscous electro-osmotic (EO) flow and heat transfer in a finite length microchannel with peristaltic wavy walls in the presence of Joule heating. The unsteady two-dimensional conservation equations for mass, momentum, and energy conservation with viscous dissipation, heat absorption, and electrokinetic body force, are formulated in a Cartesian co-ordinate system. Both single and train wave propagations are considered. The electrical field terms are rendered into electrical potential terms via the Poisson–Boltzmann equation, Debye length approximation, and ionic Nernst Planck equation. A parametric study is conducted to evaluate the impact of isothermal Joule heating and electro-osmotic velocity on axial velocity, temperature distribution, pressure difference, volumetric flow rate, skin friction, Nusselt number, and streamline distributions.

Electrokinetic power generation of non-Newtonian fluids in a finite length microchannel

In order to examine the effects of the fluid type as the electrolyte solvent on the efficiency of electrokinetic energy conversion, a comparative numerical study among three different fluid types of a transient electrokinetic flow through a single circular finite length microchannel has been conducted. The system was initially at an equilibrium non-flow state, and a step change in flow was applied and the calculation proceeding until steady state was achieved. The analysis was based on non-dimensional transport governing equations that were scaled using Debye length as the characteristic length scale and diffusion time as characteristic time scale. The fluid types considered were shear thinning, Newtonian, and shear thickening, and a power law modeled them with the scaled flow behavior index having values of 0.2, 1.0, and 1.8. In order to isolate the electrokinetic effects of the different relationships between the shear strain rate and shear stress, the flow consistency index was adjusted so that in all the cases the flow rate and total pressure drop matched that of water at 25 °C. All other fluid and interfacial properties were the same for all cases. The key observational difference between the various fluid types was that their different axial velocity profile acted on essential the same free charge density profiles. Consequently, the convection current density (i.e., the radial distribution of charge being advected along the channel) was strongly affected by the fluid type. Integration of this quantity to calculate the convection current showed that for the particular fluid properties chosen the shear thinning fluid was 20 % higher than the Newtonian fluid, while the shear thickening fluid was only 4 % lower than the Newtonian fluid. Combined with the effects, these different currents have on the streaming potential, the shear thinning fluid was 50 % more effective in converting flow work to electrical work than the Newtonian fluid, while the shear thickening fluid was only 16 % lower than the Newtonian fluid.

Investigation on Machining of Holes and Channels on Borosilicate and Sodalime Glass Using μ-ECDM Setup

Electro Chemical Discharge Machining (ECDM) is a non-conventional machining process used to machine various conducting and non-conducting engineering materials. The non-conventional machining processes, uses some form of energy to machine materials. These some form of energies includes mechanical, thermal, chemical etc. Some of the mechanical machining processes are Water Jet Machining (WJM), Abrasive Jet Machining (AJM), Ultra Sound Machining (USM) etc., thermal machining processes are Electro Discharge Machining (EDM), Ion Beam Machining (IBM), Plasma Arc Machining (PAM), Laser Beam Machining (LBM) etc., and chemical machining processes are Electro Chemical Machining (ECM), Electro Chemical Grinding (ECG), etc. EDM and ECM machining processes are well developed and established commercially. Currently the main focus is on hybrid machining processes to utilize the advantages of one and overcome the disadvantages of others. ECDM is one such process which combines the features of EDM and ECM to machine non-conducting materials. ECDM process is mainly used for machining, scribing hard and brittle non-conducting materials like soda lime glass, borosilicate glass, PMMA material, silicon wafers etc. In the present work, experiments are conducted to machine holes and channels with a developed μ-ECDM setup. Design of Experiments (DOE) is used to plan and conduct the experiments. Optimized combinations of process parameters- voltage, duty factor and electrolyte concentration are obtained for responses- maximum Material Removal Rate (MRR), minimum Tool Wear Rate (TWR) and Radial Over Cut (ROC) are obtained using main effect plots. Repeatable holes and channels are machined using the obtained optimized parameter for maximum MRR. The response- diameter of micro holes of 0.92mm, micro channels of length 14mm, 0.34mm and 0.63mm width are obtained on borosilicate and sodalime glass with tool diameter 0.3mm of tungsten carbide and tungsten copper alloy material.

The development of a sheathless capillary electrophoresis electrospray ionization–mass spectrometry interface based on thin conducting liquid film

A simple two column sheathless CE/MS interface was constructed using polydimethylsiloxane to fabricate a microdevice allowing facile column alignment and electrical connection. One conducting reservoir, two holes and one 1mm length microchannel between the holes were fabricated on the microdevice. The two holes were used for connecting separation capillary and ESI sprayer. The hole for ESI sprayer was fabricated at the edge of the conducting reservoir. The ESI sprayer was inserted through the reservoir to the hole so allowing it to be aligned with the separation column. Because the size of the hole was fabricated slightly larger than the outer diameter of the ESI sprayer, the electrical conduction was established through the thin conductive liquid film formed in the space between the ESI sprayer and the hole. The interface design presented was both easy to fabricate and operate and demonstrated good performance. The dead volume did not significantly affect operation as indicated by a demonstrated preservation of separation resolution. The intra-day precision and inter-day precision for peak areas and migration times observed using this interface were found to be less than 12% and 5%, respectively.

Gas Flow in Micro Channels-Experimental, Computational and Kinetic-Theoretical Investigations

The investigation of fluid flow in a tube or channel commenced from studying experimentally the liquid flow along a circular tube under the pressure difference imposed at both the ends, the results were verified by the exact solution of the Navier-Stokes Eq. under constant pressure gradient assumption (Poiseuille flow). The experimental work has been playing a pioneering role in the investigation of channel flows. In the case of gas for the tube (or channel) flow, according to the global mass conservation law, the pressure gradient is never a constant. The theoretical studies on rarefied gas Poiseuille flow based on constant pressure gradient assumption still compared well with the early experimental work because when pressure difference between the inlet and the outlet is small in comparison with the average pressure, the pressure distribution is approximately a linear one. Recently non-linear pressure distribution was experimentally found in the integrated micro- channel/pressure sensor systems with gas flow in the transitional regime. The mass flow rate of micro channel was exactly measured, challenging the rarefied gas dynamics community to put forward computation or simulation means for the calculation of micro-channel flow, and the flow characteristics in other micro devices. This paper reviews some of these computational efforts. It also presents a strict kinetic solution of the finite length micro-channel flow problem based on the global mass conservation and the exact kinetic theoretical solution of the Poiseuille flow at each section. Calculations and simulations are compared with reviewed experiments to check the agreement between the computational or theoretical results with experimental data. Keywords: Microchannel flow, Poiseuille flow, finite length channel flow, gas flow in channels, lattice Boltzmann method (LBM), information preservation (IP) method, kinetic theoretical solution of microchannel flow, global mass conservation for channel flow

An experimental investigation of forced convective cooling performance of a microchannel heat sink with Al 2O 3/water nanofluid

Experiments were conducted to investigate forced convective cooling performance of a copper microchannel heat sink with Al 2O 3/water nanofluid as the coolant. The microchannel heat sink fabricated consists of 25 parallel rectangular microchannels of length 50 mm with a cross-sectional area of 283 μm in width by 800 μm in height for each microchannel. Hydraulic and thermal performances of the nanofluid-cooled microchannel heat sink have been assessed from the results obtained for the friction factor, the pumping power, the averaged heat transfer coefficient, the thermal resistance, and the maximum wall temperature, with the Reynolds number ranging from 226 to 1676. Results show that the nanofluid-cooled heat sink outperforms the water-cooled one, having significantly higher average heat transfer coefficient and thereby markedly lower thermal resistance and wall temperature at high pumping power, in particular. Despite the marked increase in dynamic viscosity due to dispersing the alumina nanoparticles in water, the friction factor for the nanofluid-cooled heat sink was found slightly increased only.

Fabrication and evaluation of single- and dual-channel (Π-design) microchip electrophoresis with electrochemical detection

A new dual-channel microchip capillary electrophoresis (MCE) has been developed on glass substrates for the first time with electrochemical detection. Dual-channel (called Π-design) as well as single-channel microchips have been fabricated on soda-lime glass using photolithography, wet etching and thermal bonding. Moreover, a laser writing system has been applied for the fabrication of photomasks with the different microchip designs (single- and dual-channel configurations). The microfabricated channels have been characterized by optical, confocal and scanning electron microscopy. The resulting single- and dual-channel microchips have been evaluated using an end-channel amperometric detector based on one (single-channel) or two (dual-channel) 100-μm gold wires aligned at the outlet of the separation channel. Parameters affecting the separation of several phenolic compounds (dopamine, p-aminophenol and hydroquinone) have been studied in the glass microchips. Thus, the influence of separation voltage, detection potential and background electrolyte has been examined in the single-channel microchip. Different total length microchannel has been compared. Furthermore, the possibility of carrying out two simultaneous measurements has been demonstrated in the new dual-channel microchip electrophoresis. The injection format has been checked and resulted to be critical, in such a way that a special and new form is employed for obtaining simultaneous signals at both channels. Analytical characteristics, such as sensitivity and reproducibility have been evaluated and resulted very adequate.

Transient Electrokinetic Transport in a Finite Length Microchannel: Currents, Capacitance, and an Electrical Analogy

Numerical simulations with the fluid mechanics based on the unsteady Navier-Stokes equations and the Poisson-Nernst-Planck formulation of electrostatics and ion transport were used to explore the transient transport of charge through a finite length cylindrical microchannel that is driven by a pressure difference. The evolution of the transcapillary potential from a no-flow equilibrium to the steady-state-steady-flow streaming potential was analyzed by following the convection, migration, and net currents. Observations of the unsteady characteristics of the streaming current, electrical resistance, and capacitance led to an electrical analogy. This electrical analogy was made from a current source (to represent convection current), which was placed in parallel with a capacitor (to allow the accumulation of charge) and a resistor (to permit a migration current). A parametric study involving a range of geometries, fluid mechanics, electrostatics, and mass transfer states allowed predictive submodels for the current source, capacitor, and resistor to be developed based on a dimensional analysis.

Kinetic modeling of temperature driven flows in short microchannels

The temperature driven gas flows in both a two-dimensional finite length microchannel and a cylindrical tube have been studied numerically, with a goal of investigating performance optimization for a nanomembrane-based Knudsen Compressor. The numerical solutions were obtained using the direct simulation Monte Carlo (DSMC) method and a discrete ordinate method for the ellipsoidal statistical and Bhatnagar–Gross–Krook models. The Knudsen number was 0.2 and the length-to-height ratio 5. Three different wall temperature distributions were considered: linear, step-wise, and a non-monotonic profile typical for a radiantly heated Knudsen Compressor's membrane. The short channel end effects are characterized, and the sensitivity of the mass flow to a non-monotonic temperature distribution is shown.

Transient streaming potential in a finite length microchannel

Pressure-driven flow of an electrolyte solution in a microchannel with charged solid surfaces induces a streaming potential across the microchannel. Such a flow also causes rejection of ions by the microchannel, leading to different concentrations in the feed and permeate reservoirs connecting the capillary, which forms the basis of membrane based separation of electrolytes. Modeling approaches traditionally employed to assess the streaming potential development and ion rejection by capillaries often present a confusing picture of the governing electrochemical transport processes. In this paper, a transient numerical simulation of electrochemical transport process leading to the development of a streaming potential across a finite length circular cylindrical microchannel connecting two infinite reservoirs is presented. The solution based on finite element analysis shows the transient development of ionic concentrations, electric fields, and the streaming potential over the length of the microchannel. The transient analysis presented here resolves several contradictions between the two types of modeling approaches employed in assessing streaming potential development and ion rejection. The simulation results show that the streaming potential across the channel is predominantly set up at the timescale of the developing convective transport, while the equilibrium ion concentrations are developed over a considerably longer duration.

Electrokinetically Synchronized Polymerase Chain Reaction Microchip Fabricated in Polycarbonate

This paper presents a novel method for DNA thermal amplification using the polymerase chain reaction (PCR) in an electrokinetically driven synchronized continuous flow PCR (EDS-CF-PCR) configuration carried out in a microfabricated polycarbonate (PC) chip. The synchronized format allowed patterning a shorter length microchannel for the PCR compared to nonsynchronized continuous flow formats, permitting the use of smaller applied voltages when the flow is driven electrically and also allowed flexibility in selecting the cycle number without having to change the microchip architecture. A home-built temperature control system was developed to precisely configure three isothermal zones on the chip for denaturing (95 degrees C), annealing (55 degrees C), and extension (72 degrees C) within a single-loop channel. DNA templates were introduced into the PCR reactor, which was filled with the PCR cocktail, by electrokinetic injection. The PCR cocktail consisted of low salt concentrations (KCl) to reduce the current in the EDS-CF-PCR device during cycling. To control the EOF in the PC microchannel to minimize dilution effects as the DNA "plug" was shuttled through the temperature zones, Polybrene was used as a dynamic coating, which resulted in reversal of the EOF. The products generated from 15, 27, 35, and 40 EDS-CF-PCR amplification cycles were collected and analyzed using microchip electrophoresis with LIF detection for fragment sizing. The results showed that the EDS-CF-PCR format produced results similar to that of a conventional block thermal cycler with leveling effects observed for amplicon generation after approximately 25 cycles. To the best of our knowledge, this is the first report of electrokinetically driven synchronized PCR performed on chip.