Showing papers on "Volumetric flow rate published in 2003"

Enhancement of microfluidic mixing using time pulsing.

Abstract: Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems is typically difficult. Instead of using complex geometries and/or relatively long channels, we demonstrate the merits of flow rate time dependency through periodic forcing. We illustrate the technique by studying mixing in a simple “T” channel intersection by means of computational fluid dynamics (CFD) as well as physically mixing two aqueous reagents. The “T” geometry selected consists of two inlet channel segments merging at 90 degrees to each other, the outlet segment being an extension of one of the inlet segments. All channel segments are 200 µm wide by 120 µm deep, a practical scale for mass-produced disposable devices. The flow rate and average velocity after the confluence of the two reagents are 48 nl s−1 and 2 mm s−1 respectively, which, for aqueous solutions at room temperature, corresponds to a Reynolds number of 0.3. We use a mass diffusion constant of 10−10 m2 s−1, typical of many BioMEMS applications, and vary the flow rates of the reagents such that the average flow rate remains unchanged but the instantaneous flow rate is sinusoidal (with a DC bias) with respect to time. We analyze the effect of pulsing the flow rate in one inlet only as well as in the two inlets, and demonstrate that the best results occur when both inlets are pulsed out of phase. In this case, the interface is shown to stretch, retain one fold, and sweep through the confluence zone, leading to good mixing within 2 mm downstream of the confluence, i.e. about 1 s of contact. From a practical viewpoint, the case where the inlets are 180 degrees out of phase is of particular interest as the outflow is constant.

Electro-hydrodynamic micro-fluidic mixer

Abstract: Fluid mixing in microchannels is needed for many applications ranging from bio-arrays to micro-reactors, but is typically difficult to achieve. A simple geometry micro-mixer is proposed based on the electro-hydrodynamic (EHD) force present when the fluids to be mixed have different electrical properties and are subjected to an electric field. The electrodes are arranged so that the electric field is perpendicular to the interface between the two fluids, creating a transversal secondary flow. The technique is demonstrated experimentally using the flow of two liquids with identical viscosity and density, but different electrical properties. The volume flow rate and average velocity are 0.26 µl s−1 and 4.2 mm s−1, respectively, corresponding to a Reynolds number Re = 0.0174. The effect of a continuous (DC) electric field and two alternating (AC) – sinusoidal and square – electric fields is explored. At the appropriate parameter values, very good mixing takes place in less than 0.1 s, over a very short distance (within a fraction of the width 250 µm of the electrodes).

Cooling of integrated circuits using droplet-based microfluidics

Abstract: Decreasing feature sizes and increasing package densities are making thermal issues extremely important in IC design. Uneven thermal maps and hot spots in ICs cause physical stress and performance degradation. Many MEMS and microfluidics-based solutions were proposed in the past. We present a cooling method based on high-speed electrowetting manipulation of discrete sub-microliter droplets under voltage control with volume flow rates in excess of 10 mL/min. We also propose a flow-rate feedback control where the hot areas get increased supply of droplets without the need for external sensors and electrothermocapillary control where hot areas attract droplets due to thermocapillarity and are returned to their reservoirs by electrowetting resulting in a self-contained and a self-regulated system.

Electroactive polymer devices for controlling fluid flow

Abstract: The invention describes devices for controlling fluid flow, such as valves. The devices may include one or more electroactive polymer transducers with an electroactive polymer that deflects in response to an application of an electric field. The electroactive polymer may be in contact with a fluid where the deflection of the electroactive polymer may be used to change a characteristic of the fluid. Some of the characteristic of the fluid that may be changed include but are not limited to 1) a flow rate, 2) a flow direction, 3) a flow vorticity, 4) a flow momentum, 5) a flow mixing rate, 6) a flow turbulence rate, 7) a flow energy, 8) a flow thermodynamic property. The electroactive polymer may be a portion of a surface of a structure that is immersed in an external fluid flow, such as the surface of an airplane wing or the electroactive polymer may be a portion of a surface of a structure used in an internal flow, such as a bounding surface of a fluid conduit.

Optimization study of stacked micro-channel heat sinks for micro-electronic cooling

Abstract: With smaller inlet flow velocity, a micro-channel stack requires less pumping power to remove a certain rate of heat than a single-layered micro-channel, because it provides a larger heat transfer area. A simple thermal resistance network model was developed to evaluate the overall thermal performance of a stacked micro-channel heat sink. Based on this simple model, in this study, a single objective minimization of overall thermal resistance is carried out using genetic algorithms. The aspect ratio, fin thickness and the ratio of channel width to fin thickness are the variables to be optimized, subject to constraints of maximum pressure drop (4 bar) and maximum volumetric flow rate (1000 ml/min). During the optimization, the overall dimensions, number of layers and pumping power (product of pressure drop and flow rate) are fixed. The study indicates that reduction in thermal resistance can be achieved by optimizing the channel configuration. The effects of number of layers in the stack, pumping power per unit area, and the channel length are also investigated.

Microfabricated preconcentrator-focuser for a microscale gas chromatograph

Abstract: The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 /spl mu/m (h)/spl times/50 /spl mu/m (w)/spl times/3000 /spl mu/m (l), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, /spl sim/200 /spl mu/m in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly.

Probe for measuring parameters of a flowing fluid and/or multiphase mixture

Abstract: A probe 10,170 is provided that measures the speed of sound and/or vortical disturbances propagating in a single phase fluid flow and/or multiphase mixture to determine parameters, such as mixture quality, particle size, vapor/mass ratio, liquid/vapor ratio, mass flow rate, enthalpy and volumetric flow rate of the flow in a pipe or unconfined space, for example, using acoustic and/or dynamic pressures. The probe includes a spatial array of unsteady pressure sensors 15 - 18 placed at predetermined axial locations x1-xN disposed axially along a tube 14.for measuring at least one parameter of a saturated vapor/liquid mixture 12, such as steam, flowing in the tube 14. The pressure sensors 15-18 provide acoustic pressure signals P1(t)-PN(t) to a signal processing unit 30 which determines the speed of sound amix propagating through of the saturated vapor/liquid mixture 12 in the tube 14 using acoustic spatial array signal processing techniques. Frequency based sound speed is determined utilizing a dispersion model to determine the parameters of interest.

An apparatus having an array of piezoelectric film sensors for measuring parameters of a process flow within a pipe

Abstract: A apparatus (10, 110, 170) is provided that measures the speed of sound and/or vortical disturbances propagating in a single phase fluid flow and/or multiphase mixture to determine parameters, such as mixture quality, particle size, vapor/mass ratio, liquid/vapor ratio, mass flow rate, enthalpy and volumetric flow rate of the flow in a pipe, by measuring acoustic and/or dynamic pressures. The apparatus includes a spatial array of unsteady pressure sensors (15-18) placed at predetermined axial locations x1 - xN disposed axially along the pipe (14). The pressure sensors (15-18) provide acoustic pressure signals P1(t) - PN(t) to a signal processing unit (30) which determines the speed of sound amix propagating through of the process flow (12) flowing in the pipe (14). The pressure sensors are piezoelectric film sensors that are mounted or clamped onto the outer surface of the pipe at the respective axial location.

Apparatus and method for measuring parameters of a mixture having solid particles suspended in a fluid flowing in a pipe

Abstract: An apparatus 10 and method is provided that includes a spatial array of unsteady pressure sensors 15 - 18 placed at predetermined axial locations xl - xN disposed axiallyalong a pipe 14 for measuring at least one parameter of a solid particle/fluid mixture 12 flowing in the pipe 14. The pressure sensors 15 - 18 provide acoustic pressure signals P1(t) - PN(t) to a signal processing unit 30 which determines the speed of sound amix(ω) of the particle/fluid mixture 12 in the pipe 14 using acoustic spatial array signal processing techniques. The primary parameters to be measured include fluid/particle concentration, fluid/particle mixture volumetric flow, and particle size. Frequency based sound speed is determined utilizing a dispersion model to determine the parameters of interest. the calculating the at least one parameter uses an acoustic pressure to calculate

Abatement of perfluorinated compounds using microwave plasmas at atmospheric pressure

Abstract: Microwave plasmas sustained at atmospheric pressure, for instance by electromagnetic surface waves, can be efficiently used to abate greenhouse-effect gases such as perfluorinated compounds. As a working example, we study the destruction and removal efficiency (DRE) of SF6 at concentrations ranging from 0.1% to 2.4% of the total gas flow where N2, utilized as a purge gas, is the carrier gas. O2 is added to the mixture at a fixed ratio of 1.2–1.5 times the concentration of SF6 to ensure full oxidation of the SF6 fragments, providing thereby scrubbable by-products. Fourier-transform infrared spectroscopy has been utilized for identification of the by-products and quantification of the residual concentration of SF6. Optical emission spectroscopy was employed to determine the gas temperature of the nitrogen plasma. In terms of operating parameters, the DRE is found to increase with increasing microwave power and decrease with increasing gas flow rate and discharge tube radius. Increasing the microwave power, in the case of a surface-wave discharge, or decreasing the gas flow rate increases the residence time of the molecules to be processed, hence, the observed DRE increase. In contrast, increasing the tube radius or the gas-flow rate increases the degree of radial contraction of the discharge and, therefore, the plasma-free space close to the tube wall: this comparatively colder region favors the reformation of the fragmented SF6 molecules, and enlarging it lowers the destruction rate. DRE values higher than 95% have been achieved at a microwave power of 6 kW with 2.4% SF6 in N2 flow rates up to 30 standard l/min.

Portable gas powered fluid dispenser

Abstract: A caulking gun has a tubular chamber (9) to surround sleeve-like rigid tubes (10) and compressible sausage type containers containing viscous materials including sealants, adhesives, caulking, mastics and the like When rigid tubes (10) are loaded into the chamber, compressed gas is allowed to surround the sleeve and a plunger (80) loaded within the rigid tube (10) to equalize pressure around the outside of the rigid tube (10) If a sausage type container is loaded into the chamber (9), a removable plunger (80) is also provided to form a tight seal between the perimeter of the plunger and the inner surface of the chamber (9) Compressed gas introduced into the chamber (9) preferentially acts on the plunger (80) and an underlying end wall of the sausage to expel the material, without imparting any significant pressure to other parts of the sausage The caulking gun includes a variable flow rate nozzle (20) which may be removed from the device The nozzle (20) may be replaced with similar or different nozzle pieces of various shapes and sizes, if desired Hand operated controls vary the flow rate through the nozzle and control introduction of compressed gas when in use These features may be incorporated into other portable, hand held dispensing devices powered by other pressurized fluids

Apparatus and method for measuring parameters of a mixture having liquid droplets suspended in a vapor flowing in a pipe

Abstract: An apparatus 10,70 and method is provided that includes a spatial array of unsteady pressure sensors 15 - 18 placed at predetermined axial locations xl -xN disposed axially along a pipe 14for measuring at least one parameter of a saturated vapor/liquid mixture 12, such as steam, flowing in the pipe 14 The pressure sensors 15 - 18 provide acoustic pressure signals P1(t) - PN(t) to a signal processing unit 30 which determines the speed of sound amix propagating through of the saturated vapor/liquid mixture 12 in the pipe 14 using acoustic spatial array signal processing techniques The primary parameters to be measured include vapor/liquid concentration (ie, steam wetness or steam quality), vapor/liquid mixture volumetric flow, mass flow, enthalpy, density and liquid droplet size Frequency based sound speed is determined utilizing a dispersion model to determine the parameters of interest

Liquid Flow on Structured Packing: CFD Simulation and Experimental Study

Abstract: A CFD model of the two-phase countercurrent flow in the geometry of the plate-type structured packing Mellapak 250Y was built, tested and verified The model was applied to determine the effect of liquid and gas flow rates and physicochemical properties of the flowing liquids on the interfacial area formed on structured packing The CFD model allowed us to determine the minimum liquid flow rate at which an unbroken liquid film was observed on the packing surface The simulations confirmed that with an increase of the wetting rate the surface of the packing covered with a liquid film increased until the surface was totally covered up, while further slight changes of an interfacial area were the result of wave formation The effect of gas load (F factor) on the film surface was in the range of a calculation error Results of the CFD simulation allow us to predict the stages of film formation during liquid flow, to follow local velocity oscillations, film thickness and velocity profiles of phases

Fully-Developed Thermal Transport in Combined Pressure and Electro-Osmotically Driven Flow in Microchannels

Abstract: Thermally fully-developed heat transfer has been analyzed for combined electro-osmotic and pressure driven flow in a circular microtube. The two classical thermal boundary conditions of constant wall heat flux and constant wall temperature were considered. Such a flow is established by the combination of an imposed pressure gradient and voltage potential gradient along the length of the tube. The induced flow rate and velocity profile are functions of the imposed potential gradient, electro-osmotic mobility of the fluid, the ratio of the duct radius to the Debye length, the established streamwise pressure gradient, and the fluid viscosity. The imposed voltage gradient neuritis in Joule heating in the fluid, with an associated distributed volumetric source of energy For this scenario, the solution for the fully developed, dimensionless temperature profile and corresponding Nusselt number have been determined

Plastic microchip flow cytometer based on 2- and 3-dimensional hydrodynamic flow focusing

Abstract: This paper deals with design and fabrication of 2- and 3- dimensional microchip type flow cytometers hydrodynamically driven. Flow rate and pressure distrubution have been calculated from Poiseuille flow theory and results were confirmed by computational fluid dynamics. The flow focusing has been evaluated in 2- and 3-dimensional microchip type flow cytometers fabricated with Polydimetylsiloxane molding process. The shape of focused flow was detected with a laser scanning microscope and favourably compared with calculations based on Poiseuille flow assumptions and CFD (Computational Fluid Dynamics) simulation. Simulation and calculation results showed good correlations to each other, and also to the visualized shape of focused flow in microchip. The 3-dimensional focused flow showed the more stable focusing status in laser induced fluorescence measurements than that in 2-dimensional case.

Predicting Heat Transfer During Flow Boiling in Minichannels and Microchannels

Abstract: Flow boiling in small passages in mini- and microchannels is receiving increased attention due to very high heat transfer rates possible with such geometries in electronics cooling, fuel cell, and other emerging applications. These geometries offer potential for significant enhancements in refrigerating and air-conditioning systems as well. Since the effect of surface tension becomes more important at smaller passage dimensions, the flow boiling correlations developed for conventional tubes, larger than 3 mm inner diameter, need to be carefully reviewed. The low flow rate employed in such geometries, coupled with the small channel hydraulic diameter, often results in a laminar flow with all flow as liquid. In the present work, a flow boiling correlation for large-diameter tubes is modified for flow boiling in minichannels by using the laminar single-phase correlation for the heat transfer coefficient for all liquid flow. The trends in heat transfer coefficient versus quality are also compared in the laminar region. Excellent agreement is obtained between predicted values and experimental data. A need for additional experimental data in the transition region is recognized.

Bubble Velocity and Size Measurement with a Four-Point Optical Fiber Probe

Abstract: The possibility to measure the velocity and size of individual bubbles in a high-void fraction bubbly flow is investigated by using a four-point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air-water high-void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single-fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four-point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser-Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four-point optical fiber probe in high void fraction flows.

Sonar-based volumetric flow meter for pulp and paper applications

Abstract: A sonar-based flow measurement technology well-suited for the pulp and paper industry is described. Developed and field proven in numerous applications within the oil and gas industry over the last four years, the methodology provides robust, high-accuracy, volumetric flow rate measurement for a broad range of single and multiphase flow applications. The methodology can be implemented with pressure transducers ported to process fluid or with non-intrusive sensors clamped-on to existing process piping. Sonar-based flow metering technology utilizes an array of sensors to listen to the unsteady pressure field within standard process flow lines. Flow rate is determined using sonar array processing techniques to track the speed at which coherent structures, inherent within the turbulent pipe flow of the process fluid, convect past the sensor array. This convection speed is directly related to volumetric flow rate through a Reynolds number calibration. Results from a single-phase calibration facility are presented demonstrating 0.5% accuracy for pipes ranging from 3 to 16 inches in diameter.

Prediction of 10-mm Hydrocyclone Separation Efficiency Using Computational Fluid Dynamics

Abstract: It has been estimated that particles within the flow field of a 10-mm or mini-hydrocyclone experience local accelerations as high as 10 000 gravitation units. Although their operation is simple, the turbulent, swirling flow field within these devices offers a unique challenge to computational fluid dynamics (CFD). In addition to the computational challenge, very few experimental measurements have been reported in the literature on the flow field of the mini-hydrocyclone to which the CFD results may be compared. This research addresses the issue of predicting the separation efficiency of a volute entry 10-mm hydrocyclone. The feed flow rate is 4.5 litres/m (l/m) yielding a Reynolds number (based on the hydrocyclone diameter) of 9500 and a swirl number of 8.4. Using previously published flow simulation data, a multiphase system (consisting of a discrete oil phase and a continuous water phase) was analyzed for the purpose of obtaining separation information. These separation data were compared with laboratory separation experiments. Results indicate differences less than 20% for each droplet diameter. This information increased the level of confidence in the simulated flow field since there are no published velocity field data for the 10-mm hydrocyclone.