Showing papers on "Volumetric flow rate published in 2002"

Rapid microfluidic mixing.

Abstract: A preformed T-microchannel imprinted in polycarbonate was postmodified with a pulsed UV excimer laser (KrF, 248 nm) to create a series of slanted wells at the junction. The presence of the wells leads to a high degree of lateral transport within the channel and rapid mixing of two confluent streams undergoing electroosmotic flow. Several mixer designs were fabricated and investigated. All designs were relatively successful at low flow rates (0.06 cm/s, ≥75% mixing), but had varying degrees of success at high flow rates (0.81 cm/s, 45−80% mixing). For example, one design operating at high flow rates was able to split an incoming fluorescent stream into two streams of varying concentrations depending on the number of slanted wells present. The final mixer design was able to overcome stream splitting at high flow rates, and it was shown that the two incoming streams were 80% mixed within 443 μm of the T-junction for a flow rate of 0.81 cm/s. Without the presence of the mixer and at the same high flow rate, a...

Transport of bubbles in square microchannels

Abstract: Liquid/gas flows are experimentally investigated in 200 and 525 μm square microchannels made of glass and silicon. Liquid and gas are mixed in a cross-shaped section in a way to produce steady and homogeneous flows of monodisperse bubbles. Two-phase flow map and transition lines between flow regimes are examined. Bubble velocity and slip ratio between liquid and gas are measured. Flow patterns and their characteristics are discussed. Local and global dry out of the channel walls by moving bubbles in square capillaries are investigated as a function of the flow characteristics for partially wetting channels. Two-phase flow pressure drop is measured and compared to single liquid flow pressure drop. Taking into account the homogeneous liquid fraction along the channel, an expression for the two-phase hydraulic resistance is experimentally developed over the range of liquid and gas flow rates investigated.

The Effects of Compression and Pore Size Variations on the Liquid Flow Characteristics in Metal Foams

Abstract: Open-cell aluminum foams were investigated using water to determine their hydraulic characteristics. Maximum fluid flow velocities achieved were 1.042 m/s. The permeability and form coefficient varied from 2.46×10 -10 m 2 and 8701 m -1 to 3529 × 10 -10 m 2 and 120 m -1 , respectively. It was determined that the flowrate range influenced these calculated parameters, especially in the transitional regime where the permeability based Reynolds number varied between unity and 26.5. Beyond the transition regime where Re K ≥30, the permeability and form coefficient monotonically approached values which were reported as being calculated at the maximum flow velocities attained. The results obtained in this study are relevant to engineering applications employing metal foams ranging from convection heat sinks to filters and flow straightening devices

Investigation of Liquid Flow in Microchannels

Abstract: Liquid flow in microchannels is investigated both experimentally and numerically. The experiments are carried out in microchannels with hydraulic diameters from 244 to 974 µ ma tReynolds numbers ranging from 230 to 6500. The pressure drop in these microchannels is measured in situ and is also determined by correcting global measurements for inlet and exit losses. Onset of turbulence is verified by flow visualization. The experimental measurements of pressure drop are compared to numerical predictions. Results show that conventional theory may be used to predict successfully the flow behavior in microchannels in the range of dimensions considered here. Nomenclature Dh =h ydraulic diameter, µm f = Darcy friction factor H = microchannel height, µm L = microchannel length, mm l = characteristic size of eddies in turbulent flow, m P = pressure, Pa Q =v olume flow rate, m 3 /s Re =R eynolds number U =a verage velocity in microchannel, m/s u = characteristic velocity scale of eddies in turbulent flow, m/s W = microchannel width, µm x + = entrance length, mm α = aspect ratio, H/W � P = pressure difference, Pa δ = uncertainty e = dissipation rate, m 2 /s 3 η =K olmogorov length scale, m µ = fluid viscosity, N · s/m 2 ν = kinematic viscosity, m 2 /s ρ = fluid density, kg/m 3 app = apparent fd = fully developed conditions

A thermal-bubble-actuated micronozzle-diffuser pump

Abstract: A thermal-bubble-actuated micropump by the principles of liquid/vapor phase transition and nozzle-diffuser flow regulation is successfully demonstrated. The micropump consists of a resistive heater, a pair of nozzle-diffuser flow controller and a 1 mm in diameter, 50 /spl mu/m in depth pumping chamber. The actuation mechanism comes from periodically nucleating and collapsing thermal bubbles. A net flow is generated from the nozzle to the diffuser by the nozzle-diffuser flow controller. Two heater designs, single-bubble and dual-bubble actuation mode, have been investigated. In the single-bubble pumping mode, a maximum flow rate of 5 /spl mu/l/min is measured when the driving pulse is 250 Hz at 10% duty cycle under an average power consumption of 1 W. A similar flow rate of 4.5 /spl mu/l/min is achieved in the dual-bubble pumping mode, at the driving pulse of 5% duty cycle at 400 Hz with lower average power consumption, 0.5 W. The static pumping pressure is measured at a maximum value of 377 Pascal when the net volume flow rate is zero. As an application example in a microfluidic device, this valve-less micropump is used in a microfluidic system to enhance the fluid mixing by agitating the flows.

Transport of silica colloids through unsaturated porous media: experimental results and model comparisons.

Abstract: We present results on the migration of silica colloids through laboratory columns packed with partially saturated quartz sand. The transport of the silica colloids responds to changes in the steady-state volumetric moisture content (theta) and for low theta depends on the wetting history of the sand pack prior to colloid injection. A mathematical model that incorporates a first-order rate law to simulate film straining and a second-order rate law to simulate partitioning at air-water interfaces closely describes colloid transport and mass transfer over the range of experimental conditions tested. The mass-transfer parameters of the model are sensitive to changes in both the level of water saturation and the flow rate. A semiempirical expression, based on a modification of film-straining theory, accounts for the observed variation in the first-order rate coefficient with changes in theta and average porewater velocity. Our work indicates that the presence of the air phase substantially influences porewater concentrations of mineral colloids in water-unsaturated media and that the kinetics of particle removal attributed to air-water boundaries reflects the contribution of multiple mass-transfer mechanisms.

Clogging transition of pedestrian flow in T-shaped channel

Abstract: Pedestrian flow is investigated under the open boundaries in a T-shaped channel where the branch flow joins the main flow at the junction. The pedestrian merging flow is simulated by the use of the lattice-gas model of biased random walkers. When the main flow rate increases under the constant value of branch flow rate, the clogging transitions occur at the main flow or branch flow or both flows. It is shown that the dynamical phase transitions depend on both inlet densities. The four distinct phases are found. The phase diagram is presented for the distinct phases. The scaling of saturated flow rate and transition point is shown. The flow rate exhibits the universal scaling form.

System for measuring change in fluid flow rate within a line

Abstract: A method and system for determining change in a fluid's flow rate within a line. The pressure variation in a second fluid, separated from the first by a pumping membrane, is measured in response to energy applied in a time-varying manner to the second fluid. From the response of the second fluid to the applied energy, changes in the flow rate of the first fluid are determined.

Use of Air-Liquid Two-Phase Flow in Hydrophobic Microfluidic Channels for Disposable Flow Cytometers

Abstract: This paper describes a disposable flow cytometer that uses an air-liquid two-phase microfluidic system to produce a focused high-speed liquid sample stream of particles and cells The susceptibility of thin liquid columns to instabilities may suggest that focusing of sample liquids with streams of air would be difficult The design of channel geometry, control of flow rates, and use of appropriate surface chemistries on the channel walls, however, enabled the generation of thin (15–100 μm) and partially bounded sample streams that were stable and suitable for rapid cell analysis Using an inverted epi-fluorescence microscope with a photo-multiplier tube, we demonstrated that the system is capable of counting the number of beads and C2C12 myoblast cells The effects of different flow rates and surface chemistries of the channel walls on the air-liquid two-phase flows were characterized using optical and confocal microscopy Use of air instead of liquids as a sheath fluid eliminates the need for large sheath liquid reservoirs, and reduces the volume and weight requirements The low manufacturing cost and high volumetric efficiency make the air-sheath flow cytometer attractive for use as a stand-alone device or as an integrated component of bio-artificial hybrid microsystems

Distributed sound speed measurements for multiphase flow measurement

Abstract: A multiphase flow meter distributed system is disclosed that is capable of measuring phase flow rates of a multiphase fluid. The distributed system includes at least one flow meter disposed along the pipe, an additional sensor disposed along the pipe spatially removed from the flow meter, and a multiphase flow model that receives flow related parameters from the flow meter and the additional sensor to calculate the phase flow rates. The flow meter provides parameters such as pressure, temperature, fluid sound speed and/or velocity of the fluid, and the additional sensor provides a parameter indicative of pressure and or temperature of the fluid. Depending on production needs and the reservoir dimensions, the distributed system may utilize a plurality of flow meters disposed at several locations along the pipe and may further include a plurality of additional sensors as well. The distributed system preferably uses fiber optic sensors with bragg gratings. This enables the system to have a high tolerance for long term exposure to harsh temperature environments and also provides the advantage of multiplexing the flow meters and/or sensors together.

Mass flow meter systems and methods

Abstract: A flow meter system that calculates mass flow rate based only on a single pressure signal. A flow controller is arranged in parallel with a restriction such that a constant pressure differential is maintained across the restriction. The pressure, and temperature if not controlled, of the fluid flowing through the restriction is measured on either side of the restriction. The pressure is compared to a plot of pressure versus mass flow rate calculated for the specific restriction and fluid being measured. The constant pressure differential maintained across the restriction yields a linear relationship between pressure and flow rate. If temperature is not controlled, the plot of pressure versus mass flow rate will remain linear, but the slope of the curve will be adjusted based on the temperature of the fluid.

Use of fiber optics in deviated flows

Abstract: A system to determine the mixture of fluids in the deviated section of a wellbore comprising at least one distributed temperature sensor adapted to measure the temperature profile along at least two levels of a vertical axis of the deviated section. Each distributed temperature sensor can be a fiber optic line functionally connected to a light source that may utilize optical time domain reflectometry to measure the temperature profile along the length of the fiber line. The temperature profiles at different positions along the vertical axis of the deviated wellbore enables the determination of the cross-sectional distribution of fluids flowing along the deviated section. Together with the fluid velocity of each of the fluids flowing along the deviated section, the cross-sectional fluid distribution enables the calculation of the flow rates of each of the fluids. The system may also be used in conjunction with a pipeline, such as a subsea pipeline, to determine the flow rates of fluids flowing therethrough.

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 amount 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 investigated.

High resolution flow characterization in Bio-MEMS

Abstract: This paper introduces a micro-sensor compatible with Bio-MEMS applications for wide-range thermal flow rate measurements in liquids. Based on the applied materials and geometry, the sensor allows an outstanding resolution at minimum thermal cross-talk, enabling flow rate measurements down to 100 μg/h in water, i.e. 100 nl/h. Active and passive measuring principles, their respective applications, and the dynamic flow range coverage are presented.

An Evaporation-Based Disposable Micropump Concept for Continuous Monitoring Applications

Abstract: An inexpensive and simple pumping principle is described that is capable of delivering both small and constant flow rates (10–1,000 nl/min) over a longer period of time (days to weeks). The concept is based on controlled evaporation of a liquid through a membrane into a gas space containing a sorption agent. As long as the sorption agent keeps the vapor pressure in the gas phase below saturation, fluid evaporated from the membrane is replaced by capillary forces inducing flow from a reservoir. In a feasibility study, a total volume of 300 μl of Ringer's solution has been continuously pumped over a period of six days, resulting in an constant average flow rate of 35 nl/min (590 pl/s). The maximum liquid volume transported is limited by sorption capacity and amount of the sorption agent. Low fabrication costs, high reliability (no moving parts), the suitability for integration into planar system architectures and the lack of a special external energy source besides an environment of regulated temperature are important features of the concept, in particular with regard to its potential application in continuous patient monitoring. Truly continuous flow can be achieved in contrast to many other pump mechanisms leading to discontinuous, pulse-type flow. A challenge for a broader range of applications is the inherent temperature dependence of the flow rate. In its current version, the pump can only be used in a suction-mode.

Fluid power generator

Abstract: A fluid power generator system includes an operating mode in which a continuously variable output corresponding to a wide range of a flow rate is given by selectively combining generators with optimum rated outputs from said plurality of generators according to natural fluid energy and the number of rotations of a wing axial shaft; and control means for controlling the operation of each of the generators on the basis of a tip speed calculated from the flow rate of the operative fluid and the number of rotations of said wing axial shaft, thereby acquiring a maximum output for specific flow rate of the operative fluid In this configuration, the fluid power generator system using operative fluid energy as a driving source can generate a continuously variable output corresponding to a wide range of the flow rate of the fluid and provides a maximum output for an individual flow rate of the operative fluid, thereby increasing a quantity of generated power (by 40% or more than before)

Electrochemical time of flight flow sensor

Abstract: In this paper we propose a time of flight (TOF) micro flow sensor for aqueous fluids using an in situ electrochemically produced tracer. The sensor consists of two electrochemical cells integrated in the flow channel. The upstream cell functions as an oxygen producer and the downstream cell is an amperometric oxygen sensor. Oxygen is produced at the upstream cell and detected at the downstream cell. Since the geometry set-up of the flow channel is known, the flow rate is derived from the time difference between the signals. The measurement results are stable in virtue of its working mechanism. Unlike TOF flow sensors using thermal tracers, there is no need of delicate microstructures in this sensor since the diffusion of oxygen in the wall of the channel is negligible. Backward implicit finite difference simulation is used to analyze the transportation of the oxygen pulse in the channel. The measurement results in different aqueous fluids are shown.

The Tornado Flow Configuration—An Effective Method for Screening of a Solar Reactor Window

Abstract: The working fluid in solar receivers, utilized for effecting chemical reactions, is usually flown through a sealed enclosure provided with a quartz window. When one of the reactants or products of reaction is a powder, care must be taken to prevent contact of the incandescent powder particles with the window, in order to obviate its destruction by overheating. Attempts made in the past to screen the window against particle deposition by a curtain of an auxiliary gas stream showed that very substantial flow rates of auxiliary gas (30-80% of the main stream flow rate) were necessary for perfect window screening. The heat absorbed by the auxiliary gas stream represented a major loss of energy. In an effort to reduce the auxiliary stream flow rate to a minimum, a certain flow pattern akin to the natural tornado phenomenon has recently been developed in our laboratory. It enabled effective reactor window screening by an auxiliary gas flow rate less than 5% of the main gas flow rate. The tornado effect is discussed and demonstrated by a smoke flow visualization technique.

Compact flow meter

Abstract: Apparatus for measuring the composition and flow rate of a fluid (1) comprising a mixture of e.g. oil and water in a pipe (2), wherein an integrated mechanical structure (3) serves as a microwave resonator sensor for providing permittivity measurements and where the mechanical structure also functions as a differential pressure element for providing flow rate measurements.