Range Of Volumetric Flow Rates Research Articles

A methodology to reduce the computational effort in 3D-CFD simulations of plate-fin heat exchangers

The analysis of a plate-fin heat exchanger performance requires the evaluation of key parameters such as heat transfer and pressure drop. In this regard, Computational Fluid Dynamics (CFD) can be proficiently adopted, at the design stage, to predict the performance of plate-fin heat exchangers. However, these last are often characterized by a complex geometry, such as in the case of plate exchangers with turbulators, leading to a huge computational effort, which often exceeds the available resources. In this study, a numerical methodology for the simulation of plate heat exchangers is proposed, to bypass the limits imposed by the computational cost. The methodology relies on the simulation of a minimal portion of the exchanger (two plates, one per fluid) characterized by periodic boundary conditions (that mimic the presence of several layers). The total heat exchanged is obtained simply multiplying the calculated heat transfer by the number of plate couples composing the device. Moreover, the two plates allow to calibrate porous media which are adopted to rebuild (in a simplified version) the two fluid circuits of the whole exchanger and obtain the overall pressure drop across the device for both the hot and cold fluids.The proposed approach is validated against experimental data of an oil cooler for automotive application, that is a plate-fin heat exchanger characterized by the presence of turbulators. The numerical outcomes are compared to the experiments in terms of pressure drop and heat transfer for a wide range of volumetric flow rates. Particular attention is devoted to the mesh sensitivity and the adopted computational grid minimizes the number of cells (and, thus, the computational cost), without compromising the accuracy. Moreover, the Reynolds-Stress-Transport turbulence model is accurately selected among the most diffused ones, in order to properly match the test bench data.The proposed methodology allows to reduce of nearly one order of magnitude the total number of cells required for the simulation of the heat exchanger performance. The heat transfer is predicted with high accuracy, i.e. error is always lower than 4%. As for the pressure loss, the deviation compared to the experiments increases up to nearly 15% (for one of the simulated conditions) but it is considered still acceptable.

A foam column system harvesting freshwater algae for biodiesel production: An experiment and process model evaluations

The purpose of this study was to examine the application of the mathematical model of drift flux to the experimental results of the effect of cationic trimethyl-ammonium bromide (CTAB)-aided continuous foam flotation harvesting on the lipid content in Chlorella vulgaris microalgae. An experiment was conducted to determine the effect of the operating conditions on the enrichment factor (EF) and percentage recovery efficiency (%RE), where the flow rates at the inlet and bottom outlet remained constant. Data for the binary system (without algae) and ternary system (with algae) in an equal-area foam column show that the EF decreases linearly with increasing initial CTAB concentrations ranging from 30 to 75 mg/L for three levels of the studied air volumetric flow rate range (1–3) L/min. The percentage harvesting efficiency increased with increasing initial CTAB concentration and air volumetric flow rate to 96 % in the binary systems and 94 % in the ternary systems. However, in the foam column with the riser used in the three systems, a lower volume of liquid foam in the upward outlet stream resulted in a lower RE% than that of the column without the riser. The objective function of EF for the system with algae increased when the initial CTAB concentration was increased from 30 to 45 mg/L in the foam column with a riser for all air flow rates, and after 45 mg/L, a sudden drop in the microalgae EF was observed. In the comparison between the foam column with and without the riser for the system with algae, the optimum EF was 145 for the design of the column with the riser and 139 for the column without the riser.

A 3D Miniaturized Glass Magnetic-Active Centrifugal Micropump Fabricated by SLE Process and Laser Welding

A miniaturized pump to manipulate liquid flow in microchannels is the key component of microfluidic devices. Many researchers have demonstrated active microfluidic pumps, but most of them still required additional large peripherals to operate their micropumps. In addition, those micropumps were made of polymer materials so that their application may be limited to a variety of fields that require harsh conditions at high pressures and temperatures or organic solvents and acid/base. In this work, we present a 3D miniaturized magnetic-driven glass centrifugal pump for microfluidic devices. The pump consists of a volute structure and a 3D impeller integrated with two magnet disks of Φ1 mm. The 3D pump structure was 13 mm × 10.5 mm × 3 mm, and it was monolithically fabricated in a fused silica sheet by selective laser-induced etching (SLE) technology using a femtosecond laser. The pump operation requires only one motor rotating two magnets. It was Φ42 mm × 54 mm and powered by a battery. To align the shaft of the motor to the center of the 3D glass pump chip, a housing containing the motor and the chip was fabricated, and the overall size of the proposed micropump device was 95 mm × 70 mm × 75 mm. Compared with other miniaturized pumps, ours was more compact and portable. The output pressure of the fabricated micropump was between 215 Pa and 3104 Pa, and the volumetric flow rate range was 0.55 mL/min and 7.88 mL/min. The relationship between the motor RPM and the impeller RPM was analyzed, and the flow rate was able to be controlled by the RPM. With its portability, the proposed pump can be applied to produce an integrated and portable microfluidic device for point-of-care analysis.

Concurrent characterization of compressibility and viscosity in extrusion-based additive manufacturing of acrylonitrile butadiene styrene with fault diagnoses

Compressibility and viscosity of polymer feedstock are critical to their volumetric flow rate, weld strength, and dimensional accuracy in material extrusion additive manufacturing. In this work, the compressibility and viscosity of an acrylonitrile butadiene styrene (ABS) material is characterized with an instrumented hot end design. Experiments are first performed with a blocked nozzle to characterize the compressibility behavior. The results closely emulate the pressure-volume-temperature (PVT) behavior of a characterized generic ABS. Experiments are then performed with an open nozzle over a range of volumetric flow rates and temperatures. The static pressure data is fit to power-law, Ellis, and Cross viscosity models and the dynamic melt pressure data is then used to jointly fit material constitutive models for compressibility and viscosity. The results suggest that the joint fitting substantially improves the fidelity relative to the separately characterized viscosity and compressibility. The implemented methods support material extrusion process simulation and control including real-time identification of process faults such as (1) limited melting capacity of the hot end, (2) skipping (grinding) of the extruder drive gears, (3) low initial nozzle temperature, (4) varying flow rates associated with the intermeshing gear tooth velocity profile, and (5) delays and reduced melt pressures due to drool prior to extrusion. The ability to monitor the printing process for faults in real time, such as that presented in this work, is critical to born qualified parts. Additionally, these approaches can be used to screen new materials and identify optimal processing conditions that avoid these process faults. • Detailed design of an instrumented hot end is provided. • Two-stage compression is used to characterize compressibility with a blocked nozzle. • Power law, Ellis, and Cross models are fit to apparent viscosity data generated with a stock nozzle having a diameter of 0.4 mm. • Viscosity and compressibility models are fit by minimizing the error between the input mass flow rate and the modeled fluid capacitance and outlet mass flow rate. • Dynamic melt pressure data reveals significant faults occurring during extrusion.

The effect of the volumetric flow rate and endotracheal tube diameter on the pressure distribution in human airways

The comprehension of the fluid flow in the upper airways is of paramount importance when treating patients under clinical conditions that demand mechanical ventilation. Barotrauma and overdistension are related to undesirable pressures and might be responsible for morbidity and mortality. In the current work we use computational fluid dynamics to investigate the pressure field in the upper respiratory airways. We performed a set of simulations varying the volumetric flow rate of mechanical ventilators and we have shown that the pressure profile can be calculated by means of the volumetric flow rate in accordance with a mathematical expression given by Pav=aV˙2, where Pav is the average pressure at selected sections of the upper airways and V˙ is the volumetric flow rate. Numerical findings provide evidence that the constant a varies with the location of the plane in the upper airways. We also show that some particular diameters of endotracheal tubes (ETT) must be used with care for a given range of volumetric flow rates. Overall, we document an important relationship among pressure, volumetric flow rate and selected internal diameters from ETT.

Understanding the Performance of Flow-Electrodes for Capacitive Deionization through Hydrodynamic Voltammetry

Flow-electrode capacitive deionization is a promising approach to scale up this desalination technology, because of its ability to regenerate the electrodes outside the main cell, and thereby remove a higher amount of salt from the feed water using carbon slurries as flowable electrodes. Previous works have focused on improving the performance by changing the flow-electrode composition or by proposing different cell designs, using a wide range of volumetric flow rates for the electrode, as well as performing mathematical and experimental modelling considering the slurries as Newtonian fluids. In this work, hydrodynamic voltammetry is used to understand the electrochemical behaviour of the carbon slurries, to develop an optimization method that will give an improved electrochemical performance of the slurries. Results show that the apparent viscosity of the slurries must be considered to explain the behaviour of the slurry within the cell, as well as the effect of shear thinning on the migration of activated carbon particles inside the slurry. A dimensionless number is proposed to define a threshold that will ensure a capacitive behaviour of the flow-electrode. Figure 1

Hydrothermal Investigation of a Microchannel Heat Sink Using Secondary Flows in Trapezoidal and Parallel Orientations

Thermal performance enhancement in microchannel heat sinks has recently become a challenge due to advancements in modern microelectronics, which demand compatibility with heat sinks able to dissipate ever-increasing amounts of heat. Recent advancements in manufacturing techniques, such as additive manufacturing, have made the modification of the microchannel heat sink geometry possible well beyond the conventional rectangular model to improve the cooling capacity of these devices. One such modification in microchannel geometry includes the introduction of secondary flow channels in the walls between adjacent mainstream microchannels. The present study computationally models secondary flow channels in regular trapezoidal and parallel orientations for fluid circulation through the microchannel walls in a heat sink design. The heat sink is made of silicon wafer, and water is used as the circulating fluid in this study. Continuity, momentum, and energy equations are solved for the fluid flow through the regular trapezoidal secondary flow and parallel secondary flow designs in the heat sink with I-type, C-type, and Z-type inlet–outlet configurations. Plots of velocity contours show that I-type geometry creates optimal flow disruption in the heat sink. Therefore, for this design, the pressure drop and base plate temperatures are plotted for a volumetric flow rate range, and corresponding contour plots are obtained. The results are compared with corresponding trends for the conventional rectangular microchannel design, and associated trends are explained. The study suggests that the flow phenomena such as flow impingement onto the microchannel walls and formation of vortices inside the secondary flow passages coupled with an increase in heat transfer area due to secondary flow passages may significantly improve the heat sink performance.

Understanding the performance of flow-electrodes for capacitive deionization through hydrodynamic voltammetry

Flow-electrode capacitive deionization is a promising approach to scale up this desalination technology, because of its ability to regenerate the electrodes outside the main cell, and thereby remove a higher amount of salt from the feed water using carbon slurries as flowable electrodes. Previous works have focused on improving the performance by changing the flow-electrode composition or by proposing different cell designs, using a wide range of volumetric flow rates for the electrode, as well as performing mathematical and experimental modelling considering the slurries as Newtonian fluids. In this work, hydrodynamic voltammetry is used to understand the electrochemical behaviour of the carbon slurries, to develop an optimization method that will give an improved electrochemical performance of the slurries. Results show that the apparent viscosity of the slurries must be considered to explain the behaviour of the slurry within the cell, as well as the effect of shear thinning on the migration of activated carbon particles inside the slurry. A dimensionless number is proposed to define a threshold that will ensure a capacitive behaviour of the flow-electrode.

A parametric analysis of the output voltage of all-vanadium redox-flow battery system

Vanadium redox flow battery (VRFB) becomes a global technology used in stationary applications like grid storage. The characteristics of output voltage during the charge-discharge cycles and the resulted power of VRFB are strongly based on solving a multidisciplinary problem. In this paper, a 2 D steady state numerical model for the operation of a single VRFB has been formulated, validated with good agreement, and tested. The output voltage response of VRFB at different state of charges (SOCs) has been investigated under range of volumetric flow rates and current densities. Next, a comprehensive parametric analysis, sensitivity study, for the major electrode and electrolyte material properties is conducted which can improve confidence in model predictions. The results showed that increasing flow rate can help to minimize concentration polarization, however, pumping power would be dominated. A low flow rate can cause some poor covered regions, but would reduce pumping power. Based on the sensitivity results, only cathode reaction rate, specific surface area, conductivity of porous electrode and electrolyte, and carbon felt porosity are input parameters that dominate the simulation results. It is expected that this proposed model would be applicable to most flow batteries architectures and can be extended to stack flow batteries.

Effect of the axial gap on the energy consumption of a single-blade wastewater pump

The effect of the axial gap on the energy consumption of a single-blade wastewater pump (Sulzer XFP PE-2 150E CB1.1) is assessed using unsteady Reynolds-averaged Navier–Stokes simulations with ANSYS Fluent. The numerical model was compared to experimental data with a nominal design configuration (i.e. gap size) to provide confidence in the modeling approach. The global performance of the pump was evaluated in terms of pressure-discharge, torque, and efficiency for a range of volumetric flow rates (110 m3ċh−1 to 254 m3ċh−1) and gap sizes (0.3 mm to 1.15 mm). While it is found that the power consumption at a given flow rate is reduced with increased gap, this is at the expense of a drop in outlet pressure, and hence the efficiency of the pump drops significantly. At the largest volumetric flow rate considered (254 m3ċh−1), the sensitivity of the efficiency to the gap size is −13.5%ċmm−1 and the sensitivity of the reduction in mechanical power consumption to gap size is 0.58 kWċmm−1. These results emphasize the importance of active maintenance during the lifetime of a wastewater pump to avoid a reduction in the energy performance caused by increased gap size.

The Effect of a Conical Inner Electrode on the Mass-transfer Behavior in a Cylindrical Electrochemical Reactor under Single-Phase and Two-Phase (Gas-Liquid) Swirling Flow

The influence of a continuous change in the cross-section area on mass-transfer performance is analyzed in an electrochemical reactor under swirling flow. Thus, a conical frustum is used as an inner electrode in a cylindrical arrangement. A convergent flow is obtained by placing the conical frustum with its smaller base at the bottom of the reactor, or conversely, it produces a divergent flow. Experimental local mass-transfer coefficients along the electrode length are reported using the reduction of ferricyanide as a test reaction. The mass-transfer distribution as well as the global mass-transfer coefficient are both discussed in three geometric arrangements, i.e. constant interelectrode gap, convergent and divergent cases under single-phase and two-phase (gas-liquid) flow. The highest global mass-transfer coefficients are obtained for the convergent arrangement in the middle range of volumetric flow rates, giving out values 7.6% higher than those for the constant interelectrode gap case. Divergent geometry presents, as its main asset, the most uniform mass-transfer distribution in comparison with the other two configurations. The presence of the gas phase also has little influence on the mass-transfer performance of the reactor. Computational fluid dynamics calculations are in good agreement with experimental measurements.

Experimental characterization of a micro cross-junction as generator of Newtonian and non-Newtonian droplets in silicone oil flow at low Capillary numbers

In this paper the generation of Newtonian and non-Newtonian droplets in a continuous silicone oil flow through a micro cross-junction has been studied experimentally. The results obtained by using, as dispersed phase, pure water, water with Tween 20 and different concentrations of Xanthan gum aqueous solutions with the addition of Tween 20 are presented and discussed with the aim to put spotlight on the effect of properties of the involved immiscible liquids on the droplet regimes. A commercial micro cross-junction based on two glass microchannels having a stadium-shaped cross-section and inner hydrophobic walls has been employed. A wide range of volumetric flow rates of the continuous and dispersed phase has been imposed at the inlets of the micro cross-junction by two independent syringe pumps. The main droplet regimes have been correlated to the Capillary number linked to the continuous phase (Cac) and the volumetric flow rate ratio (α). The role of the viscosity ratio (λ) and of the shear-thinning nature of Xanthan gum aqueous solutions on the droplet regime is discussed. The results evidence that the tested micro cross-junction is able to generate very uniform monodispersed droplets with low polydispersity values (P < 6%) at low Capillary numbers (Cac < 0.02) in presence of both Newtonian and non-Newtonian dispersed phases.

Multi-component mathematical model based on mass transfer coefficients for prediction of the Zn and Cd ions biosorption data by E. densa in a continuous system

The objective of this study was to evaluate the biosorption dynamics of heavy metals by the dead macrophyte Egeria densa in fixed bed column. Experiments were conducted with mono- and bi-component solutions of Cd(II) and Zn(II) at pH 4.0, temperature of 30 °C and volumetric flow rate range between 2 and 6 cm3 min−1. A mass transfer mathematical model was applied for describing the mono-component biosorption dynamics. In this model, the equilibrium was represented by the batch Langmuir isotherm, and intraparticle diffusion was considered as the rate-limiting step for the mass transfer. The mass transfer coefficient (KS) was estimated by the downhill simplex optimization method for each volumetric flow tested, while the axial dispersion coefficient was calculated by empirical correlations. The KS coefficients and the equilibrium parameters obtained in a mono-component batch system were validated using data from the breakthrough curves of the Cd(II) and Zn(II) binary mixture obtained for different volumetric flows and initial concentrations of each metal ion.

Generation of Newtonian and non-Newtonian droplets in silicone oil flow by means of a micro cross-junction

In this paper the generation of non-Newtonian and Newtonian droplets in a continuous silicone oil flow through a micro cross-junction has been studied experimentally by focusing the attention on the behavior of the device at values of continuous Capillary number (Cac) larger than 0.01. Different liquids have been used as dispersed phase: (i) pure water; (ii) water with Tween 20; (iii) Xanthan gum aqueous solutions. A wide range of volumetric flow rates of the continuous and dispersed phase have been imposed at the inlets of the micro cross-junction with the aim to correlate the main droplet regimes (squeezing, dripping and jetting) to the continuous and dispersed Capillary number (Cac, Cad) and to the volumetric flow rate ratio (α). The role of the viscosity ratio of the immiscible liquids (λ) on the droplet regime is discussed. The experimental results confirm that the transition between squeezing and dripping depends mainly on the Capillary number associated to the continuous phase and not on the viscosity ratio. On the contrary, larger viscosity ratio values tend to reduce the Capillary number in correspondence of which the transition between dripping and jetting is observed. In addition, it has been observed that an increase in the viscosity of the dispersed phase tends to reduce the range of the operative conditions in correspondence of which monodispersed emulsions can be generated.

Easy-to-perform and cost-effective fabrication of continuous-flow reactors and their application for nanomaterials synthesis

The translation of continuous-flow microreactor technology to the industrial environment has been limited by cost and complexity of the fabrication procedures and the requirement for specialised infrastructure. In the present study, we have developed a significantly more cost-effective and easy-to-perform fabrication method for the generation of optically transparent, continuous-flow reactors. The method combines 3D printing of master moulds with sealing of the PDMS channels’ replica using a pressure-sensitive adhesive tape. Morphological characterisation of the 3D printed moulds was performed and reactors were fabricated with an approximately square-shaped cross-section of 1 mm2. Notably, they were tested for operation over a wide range of volumetric flow rates, up to 20 ml/min. Moreover, the fabrication time (i.e., from design to the finished product) was <1 day, at an average material cost of ∼£5. The flow reactors have been applied to the production of both inorganic nanoparticles (silver nanospheres) and organic vesicular systems (liposomes), and their performance compared with reactors produced using more laborious fabrication methods. Numerical simulations were performed to characterise the transport of fluids and chemical species within the devices. The developed fabrication method is suitable for scaled-up fabrication of continuous-flow reactors, with potential for application in biotechnology and nanomedicine.

High‐resolution ecological niche modelling of threatened freshwater mussels in east Texas, USA

Abstract Unionid freshwater mussels are one of the most imperilled groups in North America. They play an important role in freshwater ecosystems, both as a food source and as filter feeders. Their priority conservation status has generated interest in unionid research. Here, data from the US Geological Survey was used to produce predictive models of mussel habitat affinities at a resolution of 100 m2 across an area of thousands of square kilometres. This approach correctly identifies areas that are more suitable for threatened mussel species beds as compared with less suitable areas (&gt;97% of the time) Stream segments were identified that are forecast to have high suitability for threatened mussels. Potamilus amphichaenus differed from other threatened mussel species by being associated with a wider range of volumetric flow rates and by not being restricted by the clay content of the soils. Of the species examined, it was the most large‐river oriented in habitat use and distribution. These methods can help conservation planners and land‐use managers make rational decisions about where to focus their efforts in lotic habitats without the need for intensive environmental measurements while still providing high‐resolution information.

Flow analysis in a return channel of a multi-stage centrifugal pump

Flow recirculation is an unpleasant and even hazardous phenomenon that can cause mechanical damage in turbomachinery and has to be prevented during their operations. We numerically studied the effects of return channel blade curvature on reducing the recirculation of flow inside the return channel vanes of a multi-stage centrifugal pump. Computational fluid dynamics (CFD) analyses were performed for a wide range of volumetric flow rates. The standard k-e turbulence model was adopted as the turbulence model, and the impeller rotation simulated employing the Multiple reference frames (MRF) method. First, a baseline model together with five different modified geometries for return channel was studied and compared using a two-stage pump framework. The results reveal that decreasing the curvature of the return channel blade makes smooth streamlines and eliminates the flow recirculation inside the return channels. As the second part, two return channels with the highest pump performance were selected to be used in the simulation of a multistage pump. The simulations of the multi-stage pump show that the flow inside the baseline return channel includes considerable areas of flow recirculation, while the modified return channels again have attached flow stream. It is concluded that the return channels with the smooth curvatures and outlet blade angles above 90° remove the flow recirculation inside the return channels, resulting in higher pump efficiencies.

Biosensor Enhancement Using Grooved Micromixers: Part II, Experimental Studies.

In this study we examine the experimental use of the staggered herringbone mixer (SHM) for the signal enhancement of a microfluidic surface plasmon resonance imaging (SPRi) affinity-based biosensor. We define the signal enhancement (Emix) as the ratio of the time-dependent slope of the sensor response of a SHM-based microfluidic channel and that of an unmixed channel; Emix is directly proportional to changes in the sensor sensitivity and inversely proportional to changes in the sensor limit of detection (LOD). Measurements were carried out for three SHM designs under a wide range of volumetric flow rates for two analytes: high diffusivity ssDNA and low diffusivity Escherichia coli bacteria. The experimental data collected in this study was found to exhibit a good match to that predicted by the numerical methods discussed in part I of this study. We found that Emix is dependent on the SHM groove geometry, the Péclet number Pe, and the overall microchannel length L; these dependencies are discussed in detail. For realistic experimental conditions, the enhancement that the SHM can provide is in the range of 1 < Emix < 5 (0% < improvement < 400%).

Modification of the Local Cubic Law of fracture flow for weak inertia, tortuosity, and roughness

AbstractThe classical Local Cubic Law (LCL) generally overestimates flow through real fractures. We thus developed and tested a modified LCL (MLCL) which takes into account local tortuosity and roughness, and works across a low range of local Reynolds Numbers. The MLCL is based on (1) modifying the aperture field by orienting it with the flow direction and (2) correcting for local roughness changes associated with local flow expansion/contraction. In order to test the MLCL, we compared it with direct numerical simulations with the Navier‐Stokes equations using real and synthetic three‐dimensional rough‐walled fractures, previous corrected forms of the LCL, and experimental flow tests. The MLCL performed well and the effective errors (δ) in volumetric flow rate range from −6.7% to 13.4% with an arithmetic mean of |δ| (&lt;|δ|&gt;) equal to 3.7%. The MLCL is more accurate than previous modifications of the LCL. We also investigated the error associated with applying the Cubic Law (CL) while utilizing modified aperture field. The δ from the CL ranges from −14.2% to 11.2%, with a slightly higher &lt;|δ|&gt; = 6.1% than the MLCL. The CL with the modified aperture field considering local tortuosity and roughness may also be sufficient for predicting the hydraulic properties of rough fractures.

Numerical Studies on the Performance of Saccardo Ventilation System in Emergency Fire Scenarios

In this study, the influence of volumetric flow rate and inclination angle of air jet is evaluated on the performance of a Saccardo ventilation system in a straight rectangular tunnel in case of fire. Simultaneous effects of volumetric flow rate and inclination angle of jet exiting the Saccardo nozzle on the behavior of smoke plume is considered by studying the structure of velocity profile before the fire source. It is found that this factor has a remarkable influence on the behavior of smoke plume and therefore, on the temperatures experienced near the fire. Besides, the influence of tunnel slope on the performance of the Saccardo system to sweep the plume is investigated. It is shown that the slope effect on the behavior of smoke plume and temperature profiles is completely different for locations before and after the fire, in both negative and positive slopes. Finally a range of volumetric flow rates and inclination angles is proposed as the optimized range of performance in an emergency fire scenario.