Showing papers on "Volumetric flow rate published in 2018"

HCl Flow-Induced Phase Change of α-, β-, and ε-Ga2O3 Films Grown by MOCVD

Abstract: Precise control of the heteroepitaxy on a low-cost foreign substrate is often the key to drive the success of fabricating semiconductor devices in scale when a large low-cost native substrate is not available. Here, we successfully synthesized three different phases of Ga2O3 (α, β, and e) films on c-plane sapphire by only tuning the flow rate of HCl along with other precursors in an MOCVD reactor. A 3-fold increase in the growth rate of pure β-Ga2O3 was achieved by introducing only 5 sccm of HCl flow. With continuously increased HCl flow, a mixture of β- and e-Ga2O3 was observed, until the Ga2O3 film transformed completely to a pure e-Ga2O3 with a smooth surface and the highest growth rate (∼1 μm/h) at a flow rate of 30 sccm. At 60 sccm, we found that the film tended to have a mixture of α- and e-Ga2O3 with a dominant α-Ga2O3, while the growth rate dropped significantly (∼0.4 μm/h). The film became rough as a result of the mixture phases since the growth rate of e-Ga2O3 is much higher than that of α-Ga2O3...

Rapid flow in multilayer microfluidic paper-based analytical devices

Abstract: Microfluidic paper-based analytical devices (μPADs) are a versatile and inexpensive point-of-care (POC) technology, but their widespread adoption has been limited by slow flow rates and the inability to carry out complex in field analytical measurements In the present work, we investigate multilayer μPADs as a means to generate enhanced flow rates within self-pumping paper devices Through optical and electrochemical measurements, the fluid dynamics are investigated and compared to established flow theories within μPADs We demonstrate a ∼145-fold increase in flow rate (velocity = 156 cm s−1, volumetric flow rate = 165 mL min−1, over 55 cm) through precise control of the channel height in a 2 layer paper device, as compared to archetypical 1 layer μPAD designs These design considerations are then applied to a self-pumping sequential injection device format, known as a three-dimensional paper network (3DPN) These 3DPN devices are characterized through flow injection analysis of a ferrocene complex and anodic stripping detection of cadmium, exhibiting a 5× enhancement in signal compared to stationary measurements

Method of plasma-assisted cyclic deposition using ramp-down flow of reactant gas

Abstract: A method is for forming a nitride or oxide film by plasma-assisted cyclic deposition, one cycle of which includes: feeding a first reactant, a second reactant, and a precursor to a reaction space where a substrate is placed, wherein the second reactant flows at a first flow ratio wherein a flow ratio is defined as a ratio of a flow rate of the second reactant to a total flow rate of gases flowing in the reaction space; and stopping feeding the precursor while continuously feeding the first and second reactants at a flow ratio which is gradually reduced from the first flow ratio to a second flow ratio while applying RF power to the reaction space to expose the substrate to a plasma. The second reactant is constituted by a hydrogen-containing compound or oxygen-containing compound.

Thermofluid field of molten pool and its effects during selective laser melting (SLM) of Inconel 718 alloy

Abstract: A physical model coupled with heat transfer and fluid flow was developed to investigate the thermofluid field of molten pool and its effects on SLM process of Inconel 718 alloy, in which a heat source considering the porous properties of powder bed and its reflection to laser beam is used. The simulation results showed that surface tension caused by temperature gradient on the surface of molten pool drives to Marangoni convection, which makes fluid flow state mainly an outward convection during SLM process. Marangoni convection includes convective and conductive heat flux, both of them have effects of on molten pool shape, but the effect of convective heat flux is dominant because its magnitude is one order larger than that of conductive heat flux. The convective heat flux accelerates the flow rate of the molten metal, benefits to heat dissipation. The convective heat flux makes the molten pool wider, while the conductive heat flux makes comparably the molten pool deeper and wider. Furthermore, heat accumulation caused by multiple scanning increases convection and conduction heat flux resulting in the increase of the width and depth of the molten pool, but no change of dominant role of convective heat flux to the shape of the molten pool.

Flow rate-pressure drop relation for deformable shallow microfluidic channels

Abstract: Laminar flow in devices fabricated from soft materials causes deformation of the passage geometry, which affects the flow rate–pressure drop relation. For a given pressure drop, in channels with narrow rectangular cross-section, the flow rate varies as the cube of the channel height, so deformation can produce significant quantitative effects, including nonlinear dependence on the pressure drop (Gervais et al., Lab on a Chip, vol. 6, 2006, pp. 500–507). Gervais et al. proposed a successful model of the deformation-induced change in the flow rate by heuristically coupling a Hookean elastic response with the lubrication approximation for Stokes flow. However, their model contains a fitting parameter that must be found for each channel shape by performing an experiment. We present a perturbation approach for the flow rate–pressure drop relation in a shallow deformable microchannel using the theory of isotropic quasi-static plate bending and the Stokes equations under a lubrication approximation (specifically, the ratio of the channel’s height to its width and of the channel’s height to its length are both assumed small). Our result contains no free parameters and confirms Gervais et al.’s observation that the flow rate is a quartic polynomial of the pressure drop. The derived flow rate–pressure drop relation compares favourably with experimental measurements.

Formation of liquid–liquid slug flow in a microfluidic T-junction: Effects of fluid properties and leakage flow

Abstract: Characteristics of liquid–liquid slug flow are investigated in a microchannel with focus on the leakage flow that bypasses droplets through channel gutters. The results show that the leakage flow rate varies in a range of 10.7–53.5% and 8.3–30.9% of the feed flow rate, during the droplet formation (i.e., at T-junction) and downstream flow (i.e., in the main channel), respectively, which highly depends on Ca number and wetting condition. Empirical correlations are proposed to predict them for perfectly and partially wetting conditions. Leakage flow contribution is further used to improve the Garstecki model for size scaling in order to extend its suitability for both squeezing and shearing regimes. The instantaneous flow rates of the immiscible phases are found to fluctuate periodically with the formation cycles, but in opposite behavior. The effect of the presence of leakage flow on such fluctuation are investigated and compared with gas–liquid systems. © 2017 American Institute of Chemical Engineers AIChE J, 2017

Robotic volumetric PIV of a full-scale cyclist

Abstract: A novel approach to the measurement of large-scale complex aerodynamic flows is presented, based on the combination of coaxial volumetric velocimetry and robotics. Volumetric flow field measurements are obtained to determine the time-averaged properties of the velocity field developing around a three-dimensional full-scale reproduction of a professional cyclist. The working principles of robotic volumetric PIV are discussed on the basis of its main components: helium-filled soap bubbles as tracers; the compact coaxial volumetric velocimeter; a collaborative 6 degrees of freedom robot arm; particle image analysis based on Shake-the-Box algorithm and ensemble statistics to yield data on a Cartesian mesh in the physical domain. The spatial range covered by the robotic velocimeter and its aerodynamic invasiveness are characterised. The system has the potential to perform volumetric measurements in a domain of several cubic metres. The application to the very complex geometry of a full-scale cyclist in time-trial position is performed in a large aerodynamic wind tunnel at a flow speed of 14 m/s. The flow velocity in the near field of the cyclist body is gathered through 450 independent views encompassing a measurement volume of approximately 2 m3. The measurements include hidden regions between the arms and the legs, otherwise very difficult to access by conventional planar or tomographic PIV. The time-averaged velocity field depicts the main flow topology in terms of stagnation points and lines, separation and reattachment lines, trailing vortices and free shear layers. The wall boundary layers developing on the body surface hide below the level resolvable by the present measurements.

Electroosmotic flow of Phan-Thien-Tanner fluids at high zeta potentials: An exact analytical solution

Abstract: We present a mathematical model to study the electroosmotic flow of a viscoelastic fluid in a parallel plate microchannel with a high zeta potential, taking hydrodynamic slippage at the walls into account in the underlying analysis. We use the simplified Phan-Thien–Tanner (s-PTT) constitutive relationships to describe the rheological behavior of the viscoelastic fluid, while Navier’s slip law is employed to model the interfacial hydrodynamic slip. Here, we derive analytical solutions for the potential distribution, flow velocity, and volumetric flow rate based on the complete Poisson–Boltzmann equation (without considering the frequently used Debye–Huckel linear approximation). For the underlying electrokinetic transport, this investigation primarily reveals the influence of fluid rheology, wall zeta potential as modulated by the interfacial electrochemistry and interfacial slip on the velocity distribution, volumetric flow rate, and fluid stress, as well as the apparent viscosity. We show that combined with the viscoelasticity of the fluid, a higher wall zeta potential and slip coefficient lead to a phenomenal enhancement in the volumetric flow rate. We believe that this analysis, besides providing a deep theoretical insight to interpret the transport process, will also serve as a fundamental design tool for microfluidic devices/systems under electrokinetic influence.

Hydrogen production by biomass gasification in a supercritical water fluidized bed reactor: A CFD-DEM study

Abstract: In this study, we used CFD-DEM model to simulate glucose gasification in a supercritical water fluidized bed reactor (SCWFBR). Simplified reaction kinetic model, including glucose decomposition, water gas shift reaction and methanation reaction, was used. Particle distributions, gas composition and reaction rate profiles were analyzed. Moreover, the influence of chemical reaction on flow behavior, and the effects of operation parameters, such as wall temperature, flow rates and initial bed height were investigated. The results show that high wall temperature, low flow rate and high initial bed height are in favor of gasification. However, lower H 2 yield, gasification efficiency (GE) are found at flow rate below the minimum fluidization velocity. The simulation results show good agreement with the experimental results, demonstrating the validity of this model. The information obtained by the numerical study is useful for the operation and optimization of the gasification reactor.

Experimental investigation on the Effect of Using Nano fluid (Al 2 O 3 - Water) on the Performance of PV/T System

Abstract: In the following, a work was conducted to evaluate the performance of PV/T system when using Nano fluid as working fluid. The used Nano fluid consists of Al2O3 50 nm suspended in water as base fluid. Firstly, Tests were performed with different flow rates of water as a cooling agent, and then volume concentrations ratios (0.05, 0.075, 0.1, 0.2, .03) were used as a working fluid at the highest flow rate. The results showed that using Nano fluid increases the combined performance of PV/T by 74 and 56% at volume concentration 0.1% V Concentration. The optimum flow rates achieved in the experiment was 1.2 l/mini. Finally using Nano fluid increases the efficiency of PV/T system significantly.

Analysis of Crystal Size Dispersion Effects in a Continuous Coiled Tubular Crystallizer: Experiments and Modeling

Abstract: Continuous processing gains importance in the fine chemical and pharmaceutical industries where crystallization is an important downstream operation Seeded cooling crystallization of the l-alanine/water system was investigated under similar conditions, ie, temperature interval, cooling rate, and seed material, both in a stirred batch vessel and in a continuous plug flow crystallizer in the coiled flow inverter (CFI) design with horizontal helical tube coils (ID = 4 mm) and frequent 90° bends of the coils Short-cut calculations based on characteristic time scales and the Damkohler number allow for comparing the batch and continuous crystallization processes The experimental results reveal crystal growth and growth rate dispersion to be dominating on the product crystal size distribution (CSD) However, at low flow rates of approximately 31 g min–1, a moving sediment flow of the slurry was present in the CFI crystallizer, resulting in further size dispersion effects Elevated flow rates of approximatel