Channel Flow Rate Research Articles

Hollow-Channel Paper Analytical Devices

We present a microfluidic paper analytical device (μPAD) that relies on flow in hollow channels, rather than through a cellulose network, to transport fluids. The flow rate in hollow channels is 7 times higher than in regular paper channels and can be conveniently controlled from 0 to several mm/s by balancing capillary and pressure forces. More importantly, the pressure of a single drop of liquid (~0.2 mbar) is sufficient to induce fast pressure-driven flow, making hollow channels suitable for point of care diagnostics. We demonstrate their utility for simple colorimetric glucose and BSA assays in which the time for liquid transport is reduced by a factor of 4 compared to normal cellulose channels.

Microfluidic biosensor for the detection of DNA by fluorescence enhancement and the following streptavidin detection by fluorescence quenching

We reported an optical DNA/protein microfluidic sensor which consists of single stranded (ss) DNA-Cy3 probes on gold surface and simple line-shape microfluidic channel. These ssDNA-Cy3 probes with random sequence in bulk solution or on gold surface exhibits fluorescence enhancement after binding with complementary ssDNA (cssDNA) targets. Particularly it did not require complicated design or hairpin-like stem-loop conformation, which made it easier to be made and applied in analytes detection by fluorescence switching techniques. Using ssDNA-cy3 probes attached on gold surface in a microfluidic channel, strong fluorescence enhancement was measured by ssDNA with cssDNA binding or ssDNA with cssDNA–biotin binding. The following introduction of streptavidin resulted in fluorescence quenching (fluorescence decrease) because of the binding of hybridized DNA–biotin with streptavidin. This sensor showed strong affinity and high sensitivity toward the streptavidin, the minimum detectable concentration for streptavidin was 1pM, equating to an absolute detection limit of 60amol in this microfluidic channel. Microfluidic channel height and flow rate is optimized to increase surface reaction efficiency and fluorescence switching efficiency. In contrast to previously reported optical molecular beacon approach, this sensor can be used not only for the detection of cssDNA target, but also for the detection of streptavidin. This microfluidic sensor offers the promise of analyzing kinds of molecular targets or immunoreactions.

Development of empirical regression-based models for predicting mean velocities in asymmetric compound channels

In this paper, the authors present experimental results of overbank flow in asymmetric rectangular compound channels considering both smooth and rough flumes. The mean velocity distributions in the main channel, floodplain, and the whole cross-section were measured for nine different test models constructed with variable main channel width and step height. The mean velocity measurements are then related to a dimensionless parameter called the relative depth defined as the ratio of the depth above the floodplain bed to the depth above the main channel bed. The variations and interactions of the three outlined mean velocities have been investigated with respect to relative depth. A set of single-variable regression models has been developed for estimating the three mean velocity types using relative depth as the only independent variable. Another set of multiple-variable regressions models has been derived using two additional dimensionless parameters which take into account the width dimensions of the constructed asymmetric compound channel. The application of several key statistics and validation procedures has indicated the high significance and reliability of the developed models in predicting the three mean velocity types. The predicted mean velocities can then be used to estimate the corresponding channel flow rate using the continuity equation.

The capillary channel flow experiments on the International Space Station: experiment set-up and first results

This paper describes the experiments on flow rate limitation in open capillary channel flow that were performed on board the International Space Station in 2011. Free surfaces (gas–liquid interfaces) of open capillary channels balance the pressure difference between the flow of the liquid in the channel and the ambient gas by changing their curvature in accordance with the Young-Laplace equation. A critical flow rate of the liquid in the channel is exceeded when the curvature of the free surface is no longer able to balance the pressure difference and, consequently, the free surface collapses and gas is ingested into the liquid. This phenomenon was observed using the set-up described herein and critical flow rates are presented for steady flow over a range of channel lengths in three different cross-sectional geometries (parallel plates, groove, and wedge). All channel shapes displayed decreasing critical flow rates for increasing channel lengths. Bubble ingestion frequencies and bubble volumes are presented for gas ingestion at supercritical flow rates in the groove channel and in the wedge channel. At flow rates above the critical flow rate, bubble ingestion frequency appears to depend on the flow rate in a linear fashion, while bubble volume remains more or less constant. The performed experiments yield vast data sets on flow rate limitation in capillary channel flow in microgravity and can be utilised to validate numerical and analytical methods.

Microfluidic thin-layer flow cell for conducting polymer growth and electroanalysis

The design and fabrication of a low cost and versatile poly(dimethylsiloxane) (PDMS)-glass microchip configured to house an electrochemical thin-layer flow cell is reported. The microchip contains an integrated electrochemical cell comprising a sputtered channel gold working electrode (110μmx5mm) and a reference and auxiliary electrode housed together in the channel outlet. The facile fabrication method allows for the production of fully disposable, gasket-free thin-layer cells for a range of channel depths (35–180μm), that are suitable for low-cost, chip-based electroanalytical applications. The microchip was found to exhibit thin-layer behaviour during a series of voltammetric experiments conducted in ferrocyanide/ferricyanide. The cell was observed to experience a high resistance to current, which was dependent on the distance from the channel working electrode to the auxiliary electrode.Polyaniline (PANI) monoliths were grown electrochemically onto the channel electrode (5mm in length). The thickness of these monoliths was shown to be uniform along the length of the electrode. This demonstrates that the IR drop along the channel was not significant over this electrode length. The growth behaviour of the PANI on-chip was further examined in terms of channel depth and flow rate. It was observed that, under certain flow conditions, PANI monolith thicknesses were limited to approximately half the channel depth being employed. This was attributed to increasing volumetric flow rates during PANI growth. Increasing flow and hence convection rates were due to the displacing of channel volume during voltammetric electropolymerisation of PANI.The microfluidic electrochemical cell incorporating the PANI-modified channel electrode was then used for the amperometric detection of ascorbic acid. When the working channel electrode was placed closest to the channel outlet, the microchip was capable of the detection of ascorbic acid at a sensitivity of 15.7μAmM−1cm−1 which is greater than reported previously under similar conditions.

Microfluidic synthesis of alginate 6-methoxyenthylamino numonafide (MEAN)– eluting microspheres for catheter-directed delivery to liver tumors

Purpose Amonafide has demonstrated potent efficacy to treat a broad range of solid tumors including HCC but clinical application has been limited due to severe toxicities. These toxicities have been mitigated with a new metabolically stable drug, 6-methoxyenthylamino numonafide (MEAN). Local transcatheter delivery to liver tumors using drug-eluting beads could also reduce toxicity of this drug. We aimed to test the hypothesis that microfluidic techniques can be used to synthesize MEAN-eluting alginate microspheres. Materials and Methods Microspheres were produced via custom-made microfluidic set-up, consisting of microfluidic chip, syringe pumps and optical microscope. Continuous synthesis of MEAN loaded magnetic alginate microspheres was performed by controlling the flow rate of oil (Qo) phase (N’-hexadecane and span 80) and aqueous (Qa) phase (alginate, magnetic clusters, and MEAN) constituents. Fluorescence measurements (λex=445 nm and λem=550 nm) were used to quantify MEAN elution rates from these alginate spheres into release media in triplicate tests. Imaging of these magnetic microspheres was performed using a 7T MR scanner (Bruker). Results Microfluidic methods effectively produced hydrophilic, deformable, and non-aggregated biodegradable alginate microspheres with a mono size range of 30~70 um (size dependent upon channel size and flow rates). Encapsulation of MEAN and magnetic clusters in the alginate microspheres was confirmed with fluorescent microscopy. The magnetic clusters embedded into the alginate matrix controlled drug release rates and prevented initial burst drug release. Strong T2-weighted image contrast was achieved due to the magnetic clusters within these microsphere drug carriers. Conclusion Microfluidic methods effectively produced MEAN-eluting magnetic alginate microspheres. These microspheres offer the benefits of controlled drug release and visibility with MR imaging. Future animal studies should verify efficacy of selective transcatheter delivery to liver tumors.

Conductance calculation of slot channels in laminar gas flow regime at small pressure difference

In vacuum systems gas flows not only through slot channels with constant cross section but also through slot channels with variable cross-section. The relationship obtained analytically for the conductance calculation of three types of slot channels in viscous flow regime at small pressure difference at the ends of the channel is presented in this paper. This relationship is recommended for the calculation of flow rates in vacuum systems channels with variable cross-section with a minimal clearance at a certain point along their length. The experimental study of slot channels conductance was carried out.

Active Heat Transfer Enhancement in Single-Phase Microchannels by Using Synthetic Jets

The present work experimentally investigates the effect of synthetic jets on the heat transfer performance in a microchannel heat sink. The heat sink consists of five parallel rectangular microchannels measuring 500 μm wide, 500 μm deep, and 26 mm long each. An array of synthetic jets with 100 μm diameter orifices is placed right above the microchannel with a total of eight jet orifices per channel. Microjets are synthesized from the fluid flowing through the microchannel. Periodic disturbances are generated when the synthetic jets interact with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and penetrates the thermal boundary layer near heated channel wall. The effects of synthetic jets on microchannels heat transfer performance are studied for several parameters including the channel stream flow rate, the synthetic jets strength and operating frequency. It shows that the synthetic jets have higher heat transfer enhancement for microchannel flow at lower channel flow rates. A maximum of 130% heat transfer enhancement is achieved for some test cases. The pressure dynamics introduced by the synthetic jets are also investigated. The synthetic jets cause a minor increase in the pressure drop.

MHD micropumping of power-law fluids: A numerical solution

The performance of MHD micropumps is studied numerically assuming that the viscosity of the fluid is shear-dependent. Using power-law model to represent the fluid of interest, the effect of power-law exponent, N, is investigated on the volumetric flow rate in a rectangular channel. Assuming that the flow is laminar, incompressible, two-dimensional, but (approximately) unidirectional, finite difference method (FDM) is used to solve the governing equations. It is found that shear-thinning fluids provide a larger flow rate as compared to Newtonian fluids provided that the Hartmann number is above a critical value. There exists also an optimum Hartmann number (which is larger than the critical Hartmann number) at which the flow rate is maximum. The power-law exponent, N, strongly affects the optimum geometry depending on the Hartmann number being smaller or larger than the critical Hartmann number.

Seasonal movements with shifts in lateral and longitudinal habitat use by common bream, Abramis brama, in a heavily modified lowland river

AbstractAcoustic telemetry was used to investigate the longitudinal and lateral movements and distribution of adult common bream, Abramis brama (L.), over 43 months in a heavily modified lowland river in eastern England. A positive relationship between activity and temperature was found, with bream moving greater cumulative distances during the warmer months and distributed over a greater longitudinal proportion of the main channel. The occupancy of tributaries was related to temperature, with bream entering shallow tributaries during rising temperatures in the spring, whilst a deeper, slow‐flowing tributary was used more frequently during the cooler autumn/winter months. During the autumn, occupancy of this deeper tributary was positively related to flow rate in the main channel, suggesting that bream use this tributary for flow refuge. The functions of these behaviours are discussed along with potential management of heavily modified lowland rivers.

Microstructure-induced helical vortices allow single-stream and long-term inertial focusing

Fluid inertia has been used to position microparticles in confined channels because it leads to precise and predictable particle migration across streamlines in a high-throughput manner. To focus particles, typically two inertial effects have been employed: inertial migration of particles in combination with geometry-induced secondary flows. Still, the strong scaling of inertial effects with fluid velocity or channel flow rate have made it challenging to design inertial focusing systems for single-stream focusing using large-scale microchannels. Use of large-scale microchannels (≥100 μm) reduces clogging over long durations and could be suitable for non-single-use flow cells in cytometry systems. Here, we show that microstructure-induced helical vortices yield single-stream focusing of microparticles with continuous and robust operation. Numerical and experimental results demonstrate how structures contribute to improve focusing in these larger channels, through controllable cross-stream particle migration, aided by locally-tuned secondary flows from sequential obstacles that act to bring particles closer to a single focusing equilibrium position. The large-scale inertial focuser developed here can be operated in a high-throughput manner with a maximum throughput of approximately 13,000 particles per s.

In situ synthesis of vertical 3-D copper-core/carbon-sheath nanowalls in microfluidic devices

Microfluidic devices with integrated in-channel 3-D nanostructures have been attracting extensive attention because of the potentially superior properties resulting from the synergetic effect of nanomaterials and microfluidics. In this study a novel and facile in situ electrodeposition method was developed to grow nanostructures within a microfluidic channel which was created using PDMS and a 3-electrode system on a silicon substrate. Specifically, novel vertical 3-D copper-core/carbon-sheath nanowalls were obtained using optimized conditions in terms of the concentrations of copper precursor and structure-directing agent, the applied potential and time for electrodeposition, and the flow rate in the microfluidic channel. The mechanism of forming copper-core/carbon-sheath nanowalls is also discussed in conjunction with COMSOL numerical simulation. As the growth of the nanostructures occurs only on the in-channel electrode, the precise growth of nanostructures in a controllable area within the microfluidic device is exhibited and the device is immediately ready for use without further processing. Considering the fact that various metals, metal oxides and polymers can be electrodeposited the developed method opens a new avenue for in situ integration of novel functional nanostructures within microfluidic channels for the development of lab-on-a-chip systems.

Effect of Channel Length and Flow Rate of Supplied Lake Water on Yield of Water Spinach and Nitrogen Removal in Vegetable Production System using Eutrophic Lake Water

Effect of Channel Length and Flow Rate of Supplied Lake Water on Yield of Water Spinach and Nitrogen Removal in Vegetable Production System using Eutrophic Lake Water

Numerical investigation of solid-liquid two phase flow in a non-clogging centrifugal pump at off-design conditions

The solid-liquid two-phase flow fields in the non-clogging centrifugal pump with a double-channel impeller have been investigated numerically for the design condition and also off-design conditions, in order to study the solid-liquid two-phase flow pattern and non-clogging mechanism in non-clogging centrifugal pumps. The main conclusions include: The sand volume fraction distribution is extremely inhomogeneous in the whole flow channel of the pump at off-design conditions. In the impeller, particles mainly flow along the pressure surface and hub; In the volute, particles mainly accumulate in the region near to the exit of volute, the largest sand volume fraction is observed at the tongue, and a large number of particles collide with volute wall and exit the volute after circling around the volute for several times. When the particle diameter increases, particles tend to accumulate on the pressure side of the impeller, and more particles crash with the pressure side of the blade. And larger sand volume fraction gratitude is also observed in the whole flow channel of the pump. With the decrease of the inlet sand volume fraction, particles tend to accumulate on the suction side of the blade. Compared with the particle diameter, the inlet sand volume fraction has less influence on the sand volume fraction gratitude in the whole channel of the pump. At the large flow rate, the minimum and maximum sand volume fraction in the whole flow channel of the model pump tends to be smaller than that at the small flow rate. Thus, it is concluded that the water transportation capacity increases with the flow rate. This research will strengthen people's understanding of the multiphase flow pattern in non-clogging centrifugal pumps, thus provides a theoretical basis for the optimal design of non-clogging centrifugal pumps.

Brink as a device for measurement discharge for partially filled circular channel

Many devices are fabricated to measure discharge in circular open channel. The flow over a free overall (brink phenomenon) can be used as a device to measure discharge in open channels with known the end depth. This paper presents mathematical and experimental studies to evaluate efficiency of the brink as device of measuring low flow rate in horizontal, mild and adverse circular open channels. The general mathematical model is derived using momentum, discharge and Froude number equations for horizontal, mild and adverse slopes for circular open channels. A proposed mathematical model is calibrated by previous and present experimental data. Equation gives accurate discharge from known end water depth is presented. The results of the laboratory experiments showed that the circular flumes can be successfully used to measure the low flow rate in open channels. A relationship of discharge to the end depth for horizontal smooth circular open channels is proposed.

Optimal design of parallel channel patterns in a micro methanol steam reformer

Abstract This study describes the performance of micro methanol steam reformers with channel widths optimized using the simplified conjugate gradient method (SCGM), which uses a minimum objective function of the H 2 mass fraction standard deviation in channels. A three-dimensional numerical model and optimal simplified conjugate gradient algorithm were built to predict and search for the effects of channel widths and flow rate on the performance of chemical reactions. Furthermore, this simulation model was compared to; and corresponded well with existing experimental data. Distributions of velocity, temperature, and gas concentrations (CH 3 OH, CO, H 2 , and CO 2 ) were predicted, and the methanol conversion ratio was also evaluated. The mole fraction of CO contained in the reformed gas, which is essential to preventing poisoning of the catalyst layers of fuel cells, is also investigated. In the optimization search process, the governing equations use the continuity, momentum, heat transfer, and species equations to evaluate the performance of the steam reformer. The results show that channel width optimization can not only increase the methanol conversion ratio and hydrogen production rate but also decrease the concentration of carbon monoxide. The velocity and mixture gas density distributions in channels are discussed and plotted at various locations for an inlet liquid flow rate of 0.3 cc min −1 . Full development is not obtained in the downstream channel flow, the velocity in channel is increased from 1.28 m s −1 to 2.36 m s −1 at location Y = 1 mm–32 mm, respectively. This can be attributed to a continuous increase in the lightweight H 2 species as a result of chemical reactions in the channels.

Hydrodynamic Boundary Condition at Open-Porous Interface: A Pore-Level Lattice Boltzmann Study

In this paper, we follow the pore-level simulation approach to investigate fluid flow over an open-porous interface using the lattice Boltzmann method. As this approach does not require any specific treatment for the interface, the predicted pore-level velocity field is averaged and used to evaluate the available macroscopic boundary conditions for the interface. Two most common interface boundary conditions are evaluated, and the unknown fitting parameters in them are calculated as a function of porosity of the porous region. Analytical solutions of the velocity profile in the close vicinity of the interface are used to validate the numerical methodology. It is shown that the predicted numerical results for penetration depth in the porous region, flow rate in open channel, and velocity profile in the open and porous regions are in excellent agreement with the predictions of the two available models, if the proposed values of their fitting parameters are used.

Spatially selective reagent delivery into cancer cells using a two-layer microfluidic culture system

In this work, we demonstrate a two-layer microfluidic system capable of spatially selective delivery of drugs and other reagents under low shear stress. Loading occurs by hydrodynamically focusing a reagent stream over a particular region of the cell culture. The system consisted of a cell culture chamber and fluid flow channel, which were located in different layers to reduce shear stress on cells. Cells in the center of the culture chamber were exposed to parallel streams of laminar flow, which allowed fast changes to be made to the cellular environment. The shear force was reduced to 2.7dyncm−2 in the two-layer device (vs. 6.0dyncm−2 in a one-layer device). Cells in the side of the culture chamber were exposed to the side streams of buffer; the shear force was further reduced to a greater extent since the sides of the culture chamber were separated from the main fluid path. The channel shape and flow rate of the multiple streams were optimized for spatially controlled reagent delivery. The boundaries between streams were well controlled at a flow rate of 0.1mLh−1, which was optimized for all streams. We demonstrated multi-reagent delivery to different regions of the same culture well, as well as selective treatment of cancer cells with a built in control group in the same well. In the case of apoptosis induction using staurosporine, 10% of cells remained viable after 24h of exposure. Cells in the same chamber, but not exposed to staurosporine, had a viability of 90%. This chip allows dynamic observation of cellular behavior immediately after drug delivery, as well as long-term drug treatment with the benefit of large cell numbers, device simplicity, and low shear stress.

A PLIF and PIV study of liquid mixing enhanced by a lateral synthetic jet pair

In this paper, enhancement of mixing between two water streams of the same flow rate in a planar channel by means of a lateral synthetic jet pair is studied at a net flow Reynolds number of 83 using PLIF and PIV. The synthetic jet pair is operated 180° out-of-phase at a range of actuation frequencies and displacements, with the latter being characterized by the dimensionless stroke length. The extent of mixing is evaluated using PLIF data at a location further downstream in the mixing channel. It is found that at a fixed actuation frequency a higher dimensionless stroke length produces a better mixing, and as the actuation frequency increases a lower dimensionless stroke length is required to achieve a given mixing degree. At a sufficiently high frequency or dimensionless stroke length, a nearly homogenous mixing with a mixing degree greater than 0.9 can be obtained. A functional relationship between actuation frequency and dimensionless stroke length is also obtained by best fitting the experimental data, which can be used for selecting the synthetic jet operating conditions to ensure a good mixing. Furthermore, both PLIF and PIV results show that each synthetic jet actuation cycle produce two opposing vortex pairs, which play an important role in prompting mixing between the two fluid streams. The excellent mixing obtained at a high frequency or a high dimensionless stroke length is found to be largely caused by a strong interaction between these opposing vortex pairs.

High Throughput Single-cell and Multiple-cell Micro-encapsulation

High Throughput Single-cell and Multiple-cell Micro-encapsulation