Showing papers on "Volumetric flow rate published in 2013"

Optimization of Aerosol Jet Printing for High-Resolution, High-Aspect Ratio Silver Lines

Abstract: Aerosol jet printing requires control of a number of process parameters, including the flow rate of the carrier gas that transports the aerosol mist to the substrate, the flow rate of the sheath gas that collimates the aerosol into a narrow beam, and the speed of the stage that transports the substrate beneath the beam. In this paper, the influence of process parameters on the geometry of aerosol-jet-printed silver lines is studied with the aim of creating high-resolution conductive lines of high current carrying capacity. A systematic study of process conditions revealed a key parameter: the ratio of the sheath gas flow rate to the carrier gas flow rate, defined here as the focusing ratio. Line width decreases with increasing the focusing ratio and stage speed. Simultaneously, the thickness increases with increasing the focusing ratio but decreases with increasing stage speed. Geometry control also influences the resistance per unit length and single pass printing of low-resistance silver lines is demons...

Capillary Flow in an Interior Corner

Abstract: The design of fluids management processes in the low-gravity environment of space requires an accurate model and description of capillarity-controlled flow in containers of irregular geometry. Here we consider the capillary rise of a fluid along an interior corner of a container following a rapid reduction in gravity. The analytical portion of the work presents an asymptotic formulation in the limit of a slender fluid column, slight surface curvature along the corner, small inertia, and low gravity. New similarity solutions are found and a list of closed form expressions is provided for flow rate and column length. In particular, it is found that the flow is proportional to t(exp 1/2) for a constant height boundary condition, t(exp 2/5) for a spreading drop, and t(exp 3/5) for constant flow. In the experimental portion of the work, measurements from a 2.2s drop tower are reported. An extensive data set, collected over a previously unexplored range of flow parameters, includes estimates of repeatability and accuracy, the role of inertia and column slenderness, and the effects of corner angle, container geometry, and fluid properties. Comprehensive comparisons are made which illustrate the applicability of the analytic results to low-g fluid systems design.

The importance of key operational variables and electrolyte monitoring to the performance of an all vanadium redox flow battery

Abstract: BACKGROUND The all vanadium redox flow battery (VRFB) has become the most common type of rfb, however, it is essential to improve our understanding of the importance of key operational variables, including electrode materials, electrolyte flow rate, current density and temperature, on the cell efficiency together with improved methods for cell monitoring. RESULTS Several carbon felts were characterized for their electrode activity. A commercially supplied electrolyte of unknown composition was analysed and was shown to contain a VO2+: V3+ ratio of 4.8:1 (total vanadium species = 1.5 mol dm−3) in 4 mol dm−3 H2SO4. A battery (100 cm2) was assembled using three-dimensional carbon felts and planar carbon feeders as the electrodes with a Nafion® 115 proton exchange membrane. Performance was examined using electrolytes of varying vanadium ion concentration at volumetric flow rating from 0.5–3 mL min1. A suitable volumetric flow rate of electrolyte through each half-cell was found to be in the range 1.5–2.0 mL min−1, corresponding to a mean linear electrolyte velocity of 1.0–10.1 cm s−1 through the carbon felt electrode. At a constant current charge and discharge current density of 100 mA cm−2 the typical voltage efficiencies were 65%. Charge-discharge curves were then simulated using a detailed physical model, which generated good quantitative agreement with experimental cell performance. CONCLUSIONS This study has quantified the effect of key process variables on cell efficiency. A mathematical model has been used successfully to describe charge-discharge performance and the use of open-circuit cell voltage has been shown to provide a simple and useful means of cell monitoring. Copyright © 2012 Society of Chemical Industry

“Batch” Kinetics in Flow: Online IR Analysis and Continuous Control

Abstract: Currently, kinetic data is either collected under steady-state conditions in flow or by generating time-series data in batch. Batch experiments are generally considered to be more suitable for the generation of kinetic data because of the ability to collect data from many time points in a single experiment. Now, a method that rapidly generates time-series reaction data from flow reactors by continuously manipulating the flow rate and reaction temperature has been developed. This approach makes use of inline IR analysis and an automated microreactor system, which allowed for rapid and tight control of the operating conditions. The conversion/residence time profiles at several temperatures were used to fit parameters to a kinetic model. This method requires significantly less time and a smaller amount of starting material compared to one-at-a-time flow experiments, and thus allows for the rapid generation of kinetic data.

Large-scale synthesis of nanocrystals in a multichannel droplet reactor

Abstract: We report a multichannel microfluidic droplet reactor for the large-scale, high temperature synthesis of nanocrystals. The reactor was applied here to the production of CdTe, CdSe and alloyed CdSeTe nanocrystals, and found in all cases to provide high quality quantum dots with spectral properties that did not vary between channels or over time. One hour test runs yielded 3.7, 1.5 and 2.1 g of purified CdTe, CdSe and the alloy, respectively, using 0.4 M cadmium precursor solutions and carrier and reagent phase flow rates of 4 and 2 ml min−1. A further nine hour test-run applied to CdTe, utilizing increased carrier and reagent flow rates of 5 and 3 ml min−1, yielded 54.4 g of dry purified material, corresponding to a production rate of 145 g per day. The reactor architecture is inherently scalable and, with only minimal modifications, should allow for straightforward expansion to the kilogram-per-day production levels sought by industry.

Investigation of the 3D flow field in an IC engine using tomographic PIV

Abstract: In-cylinder measurements of the instantaneous 3D flow field are required for further understanding of turbulent mixing and combustion processes in internal combustion (IC) engines as well provide valuable data for the development of large eddy simulation (LES) models for combustion simulation. Tomographic particle image velocimetry (TPIV) is applied within a motored direct-injection spark-ignition (DISI) optical engine to measure the instantaneous volumetric flow field at selected crank-angle degrees (CAD) during the intake and compression stroke. Measurements were conducted using a double-pulse Nd:YAG laser with an average pulse energy of 375 mJ for illumination and four CCD cameras arranged circularly around the optically accessible cylinder. A volume of 47 × 35 × 4 mm 3 was imaged located centrally between the intake valves. The uncertainty of the 3D velocity data was addressed using the principle of mass conservation for the inlet flow. A precision within 9% was found for the calculation of the velocity gradient tensor and is comparable to experiments in generic configurations, indicating that TPIV measurements within a motored IC engine are feasible. Based on the volumetric velocity data, the average structure of the flow field was analyzed showing a clear orientation of the average velocity, which changes during the different phases of the cycle. The 3D turbulent kinetic energy (TKE) is computed and compared to the 2D-TKE determined from in-plane velocity components and reveals distinct regions of large out-of-plane velocity fluctuations. Results from volumetric velocimetry furthermore provides insight into the occurrence and orientation of vortical structures that here are identified by using the Q-criterion. Differences between flow structures during intake and compression strokes are discussed on basis of ensemble-averaged and individual cycle velocity maps as well as the full vorticity vector.

Darcy's law for yield stress fluid flowing through a porous medium

Abstract: We measured the pressure drop vs flow rate during the flow, in a wide range of velocities, of well controlled yield stress fluids through confined packings of glass beads of different sizes. A detailed analysis of the data makes it possible to extract a general expression for the pressure drop vs flow rate curve through a porous medium as a function of the flow rate and the characteristics of the system. This general law has a form similar to the Herschel–Bulkley model describing the rheological behavior of such fluids in simple shear, i.e. it expresses as the sum of a critical (yielding) pressure drop and a flow rate dependent term. This law involves the rheological parameters of the fluid, one characteristic length of the medium, and two coefficients which only depend on the structure of the porous medium. The first coefficient is related to the path of maximum width throughout the porous medium while the second coefficient reflects the pore size distribution. The values of these coefficients were determined in the case of a granular packing.

Flow rate control using mass flow rate control device

Abstract: A process and device enabling accurate mass flow control is described. A mass flow controller can be re-specified corresponding to multiple types of actual process gases and multiple flow rate ranges, even after the mass flow controller has been shipped. Calibration gas data is derived using actual flow rate versus a flow rate setting signal to generate calibration gas data. Actual gas data is derived by measuring actual flow rate versus a flow rate setting signal for each actual gas and saving. Subsequently, prior to operating the mass flow rate control device, the characteristic data for an actual and the calibration gas characteristic data is recalled. The calibration gas characteristic data is then converted to controlled flow rate correction data based on the actual gas characteristic data that is saved to the control unit and the actual gas flow rate is corrected based on this controlled flow rate correction data.

The minimum or natural rate of flow and droplet size ejected by Taylor cone?jets: physical symmetries and scaling laws

Abstract: We aim to establish the scaling laws for both the minimum rate of flow attainable in the steady cone-jet mode of electrospray, and the size of the resulting droplets in that limit. Use is made of a small body of literature on Taylor cone-jets reporting precise measurements of the transported electric current and droplet size as a function of the liquid properties and flow rate. The projection of the data onto an appropriate non-dimensional parameter space maps a region bounded by the minimum rate of flow attainable in the steady state. To explain these experimental results, we propose a theoretical model based on the generalized concept of physical symmetry, stemming from the system time invariance (steadiness). A group of symmetries rising at the cone- to-jet geometrical transition determines the scaling for the minimum flow rate and related variables. If the flow rate is decreased below that minimum value, those symmetries break down, which leads to dripping. We find that the system exhibits two instability mechanisms depending on the nature of the forces arising against the flow: one dominated by viscosity and the other by the liquid polarity. In the former case, full charge relaxation is guaranteed down to the minimum flow rate, while in the latter the instability condition becomes equivalent to

Gas–Liquid Flow and Mass Transfer in an Advanced-Flow Reactor

Abstract: Hydrodynamics and mass transfer of gas–liquid flow are explored under ambient conditions in an Advanced-Flow Reactor (AFR), an emerging commercial system designed for continuous manufacture. Carbon dioxide/water is the model system used in this study for a range of flow rates for gas and liquid of 5.6–103 mL/min and 10–80 mL/min, respectively. Bubble size distribution, gas holdup, specific interfacial area, pressure drop, and mass transfer coefficients are determined from flow visualization experiments and compared with conventional gas–liquid contactors. These variables are mainly influenced by the inlet flow rates and inlet composition. Average bubble sizes (dB) of 0.9–3.8 mm, gas holdup (eG) of 0.04–0.68, specific interfacial areas (a) of 160–1300 m2/m3, and overall mass transfer coefficients (kLa) of 0.2–3 s–1 were obtained for the vertical orientation of the AFR. Although effect of gravity is present for this system, no significant effect on the hydrodynamic properties was observed. The measured pre...

A light sheet based high throughput 3D-imaging flow cytometer for phytoplankton analysis

Abstract: This paper reports a light sheet fluorescence imaging flow cytometer for 3D sectioning of phytoplankton. The instrument developed has the inherent advantages of high cell counting throughput and high spatial resolution information derived from flow cytometry and light sheet microscopy. The throughput of the instrument is quantified by the sample volume flow rate of 0.5 μl/min with a spatial resolution as achieved by light sheet microscopy. Preliminary results from 3D morphology of the internal chlorophyll-a structure of two dinoflagellates species show promising application potentials of the method for phytoplankton taxonomy of selected species and species groups.

Microfluidic device for efficient airborne bacteria capture and enrichment.

Abstract: Highly efficient capture and enrichment is always the key for rapid analysis of airborne pathogens. Herein we report a simple microfluidic device which is capable of fast and efficient airborne bacteria capture and enrichment. The device was validated with Escherichia coli (E. coli) and Mycobacterium smegmatis. The results showed that the efficiency can reach close to 100% in 9 min. Compared with the traditional sediment method, there is also great improvement with capture limit. In addition, various flow rate and channel lengths have been investigated to obtain the optimized condition. The high capture and enrichment might be due to the chaotic vortex flow created in the microfluidic channel by the staggered herringbone mixer (SHM) structure, which is also confirmed with flow dynamic mimicking. The device is fabricated from polydimethylsiloxane (PDMS), simple, cheap, and disposable, perfect for field application, especially in developing countries with very limited modern instruments.

Bending of elastic fibres in viscous flows: the influence of confinement ‡

Abstract: We present a mathematical model and corresponding series of microfluidic experiments examining the flow of a viscous fluid past an elastic fibre in a three-dimensional channel. The fibre’s axis lies perpendicular to the direction of flow and its base is clamped to one wall of the channel; the sidewalls of the channel are close to the fibre, confining the flow. Experiments show that there is a linear relationship between deflection and flow rate for highly confined fibres at low flow rates, which inspires an asymptotic treatment of the problem in this regime. The three-dimensional problem is reduced to a two-dimensional model, consisting of Hele-Shaw flow past a barrier, with boundary conditions at the barrier that allow for the effects of flexibility and three-dimensional leakage. The analysis yields insight into the competing effects of flexion and leakage, and an analytical solution is derived for the leading-order pressure field corresponding to a slit that partially blocks a two-dimensional channel. The predictions of our model show favourable agreement with experimental results, allowing measurement of the fibre’s elasticity and the flow rate in the channel.