Showing papers on "Volumetric flow rate published in 2020"

Quantification of water transport in a CO2 electrolyzer

Abstract: A sufficient supply of water at the catalyst layer is needed to mediate the CO2 reduction reaction (CO2RR), yet too much water favours the competing hydrogen evolution reaction (HER) and lowers the efficiency of CO2 electrolysis. It is therefore important to quantify water at the cathode, but CO2 electrolyzers are typically enclosed systems where only the inputs and outputs can be readily measured. We report herein an analytical CO2RR electrolyzer with sensors in the cathode chamber to directly measure the relative humidity (RH) and temperature during electrolysis. These measurements enable the flow of water to be tracked inside the flow cell, and provide the boundary conditions necessary for a 3D model of mass transport and fluid flow in the cathode chamber. We developed a 3D model which showed that the molar fraction of water at the cathodic GDE/membrane interface, xH2O,mem, is constant under a range of applied current densities (25–200 mA cm−2) and CO2 flow rates (25–200 sccm), and does not change as a function of humidification of the CO2 feed. The value of xH2O,mem is held at parity because more water is drawn across the membrane (from the liquid-fed anode) when insufficient water is supplied to the cathode from the CO2 feed. This result points to a higher flux of water across the membrane when using drier CO2 feedstocks at higher flow rates and higher current densities. Consequently, undesirable anolyte crossover (which causes salt precipitation at the cathode) can be suppressed by maintaining a humidified CO2 feed. This 3D model can be used for a range of operating conditions, materials, and flow fields to help with CO2RR electrolyzer design and optimization.

A review of respiratory anatomical development, air flow characterization and particle deposition

Abstract: The understanding of complex inhalation and transport processes of pollutant particles through the human respiratory system is important for investigations into dosimetry and respiratory health effects in various settings, such as environmental or occupational health. The studies over the last few decades for micro- and nanoparticle transport and deposition have advanced the understanding of drug-aerosol impacts in the mouth-throat and the upper airways. However, most of the Lagrangian and Eulerian studies have utilized the non-realistic symmetric anatomical model for airflow and particle deposition predictions. Recent improvements to visualization techniques using high-resolution computed tomography (CT) data and the resultant development of three dimensional (3-D) anatomical models support the realistic representation of lung geometry. Yet, the selection of different modelling approaches to analyze the transitional flow behavior and the use of different inlet and outlet conditions provide a dissimilar prediction of particle deposition in the human lung. Moreover, incorporation of relevant physical and appropriate boundary conditions are important factors to consider for the more accurate prediction of transitional flow and particle transport in human lung. This review critically appraises currently available literature on airflow and particle transport mechanism in the lungs, as well as numerical simulations with the aim to explore processes involved. Numerical studies found that both the Euler–Lagrange (E-L) and Euler–Euler methods do not influence nanoparticle (particle diameter ≤50 nm) deposition patterns at a flow rate ≤25 L/min. Furthermore, numerical studies demonstrated that turbulence dispersion does not significantly affect nanoparticle deposition patterns. This critical review aims to develop the field and increase the state-of-the-art in human lung modelling.

Unsteady electro-osmotic flow of couple stress fluid in a rotating microchannel: An analytical solution

Abstract: In this work, we present the theoretical investigation of the transient rotating electro-osmotic flow of a couple stress fluid in a microchannel, through the Laplace transform technique. The analysis is dependent on the Debye–Huckel linear approximation for electrical potentials. The governing equations of the couple stress fluid are taken to address the flow field in a rotating environment. The mathematical formulation of these governing equations provides a system of ordinary differential equations, which are then solved to achieve analytical solutions for electrostatic potential, axial and transverse velocity distribution, and volumetric flow rate. A comparison was made for the present analytical solution with data available in the literature. There was excellent matching. The characteristics of different influential parameters on axial and transverse velocity distributions, volume, and angle flow rates are pictorially deliberated. The study reveals that the rise in the couple stress parameter accelerates the axial electro-osmotic flow velocity inside the electrical double layer.

Modeling and simulation absorption of CO2 using hollow fiber membranes (HFM) with mono-ethanol amine with computational fluid dynamics

Abstract: In these papers, the computational fluid dynamics technique is used to simulation a Hollow fiber membrane contactor to absorb carbon dioxide from the air by absorbing Mono-ethanol amine. The governing equations of this process include the equations of continuity, momentum and mass transfer in areas related to the shell membrane and tube and taking into account the relevant boundary conditions and assumptions, using the software COMSOL were solved. By examining and comparing the results with experimental data presented in the papers, the accuracy of simulation results was confirmed. The influence of important parameters in the process including wetness of membrane, the volumetric flow rate of gas, liquid volumetric flow rate and temperature effects were studied. The results showed that by increasing the volumetric flow rate of liquid absorption 73–83, the mass transfer rate of carbon dioxide to absorption increases because of the carbon dioxide concentration gradient in the gas phase and liquid increases. Because of the reduced residence time 86 to 20 in the membrane contact, by increasing the volumetric flow rate of gas the amount of removed CO2 in contact reduced so that by increasing the gas flow rate 0.6–1.4, the CO2 removal rate will be only 18 % decreased. The CO2 concentration is decreased along the tube since it penetrates the tube where the highest concentration of carbon dioxide is in the contact surface of the membrane and absorbent solution. In doing so, due to the reactions done in the tube between Carbon dioxide and Monoethanolamine, the CO2 concentration is decreased and reaches zero at the center of the tube. The other factors are the solvent temperature and wetness. With increasing the absorption solvent temperature, carbon dioxide removal efficiency is significantly increased. Wettability has a strong negative effect on the efficiency of the membrane contactor. So with increase wettability, the efficiency of the membrane suddenly finds a sharp decrease. In some cases with increased wettability efficiency is close to zero.

Theoretical analysis of two-layered electro-osmotic peristaltic flow of FENE-P fluid in an axisymmetric tube

Abstract: This article presents the theoretical analysis of two-dimensional peristaltic transport of two-fluids in a flexible tube under the influence of electro-osmotic force. The flow domain is composed of two regions, namely, the core region and the peripheral region. The Newtonian and the FENE-P models are used to describe the rheology of fluids in the peripheral and the core regions, respectively. Governing flow equations corresponding to each region are developed under the assumption of long wavelength and low-Reynolds number. The interface between the two regions is computed numerically by employing a system of non-linear algebraic equations. The influence of relevant controlling parameters on pressure gradient, interface, trapping, and reflux is highlighted graphically and explained in detail. Special attention is given to estimate the effects of viscoelastic parameter of the core region fluid in the presence of electro-osmotic environment. Our investigation indicates an augmentation in the pressure loss at a zero volumetric flow rate with growing the viscoelastic and occlusion parameters. Moreover, trapping, reflux, and pumping efficiency are found to increase by increasing the electro-osmotic and viscoelastic parameters. The analysis presented here may be helpful in controlling the micro-vascular flow during the fractionation of blood into plasma (in the peripheral layer) and erythrocytes (core layer). This study may also have potential applications in areas such as electrophoresis, hematology, design, and improvement of bio-mimetic electro-osmotic pumps.

Analysis of entropy generation for MHD flow of viscous fluid embedded in a vertical porous channel with thermal radiation

Abstract: The present article describes the fully developed natural convective flow on a conducting viscous fluid towards a vertical parallel porous plates channel Furthermore, the velocity slip and temperature jump conditions are implemented on both the vertical walls of the channel Besides, the effects of the applied magnetic field along with thermal radiation are also considered We employ the entropy generation method (EGM) to discuss the thermodynamic optimization To model the flow equations, the Cartesian coordinates system is used Closed-form solutions of the resulting coupled differential equations describing the flow behavior are obtained for velocity and temperature distribution The obtained exact form solution is also validated to examine the accuracy by two different numerical approaches namely, Keller- box and shooting method, and found in good agreement A comprehensive analysis of the influence of velocity slip and temperature jump condition in the presence of the magnetic field, thermal radiation and suction or injection parameters on the velocity field, volumetric flow rate, temperature distribution, skin friction coefficients, and the rate of entropy generation was carried out The obtained results reveal that by taking the specific value of the velocity slip and temperature jump conditions, change in the magnetic and suction or injection parameter affects the fluid velocity at the solid–fluid interface

Experiments and computations of microfluidic liquid–liquid flow patterns

Abstract: We study two-phase liquid–liquid flow patterns in a 500 μm capillary microchannel for four biphasic systems: ethyl acetate/water, 2-pentanol/water, methyl isobutyl ketone/water, and heptane/water. Flow visualization experiments using laser induced fluorescence (LIF) reveal a total of 7 different flow patterns for all solvent pairs, namely slug flow, droplet flow, slug-droplet flow, parallel, annular, dispersed, and irregular flow. A map of different flow patterns was built to delineate the origin of their formation. We find conventional dimensionless groups are insufficient to uniquely identify the flow patterns. Computational fluid dynamics (CFD) modeling in OpenFOAM shows agreement with the experimental flow patterns for most of the two-phase flows. Principal component analysis reduces the dimensionality of potential descriptors of flow patterns and, unlike prior work using two dimensionless numbers, determines six important features that describe >95% of the variance of the experimental flow patterns. These include the total flow rate, the flow rate ratio between the two phases, the capillary and Ohnesorge numbers of the aqueous phase, and the Weber number and velocity of the organic phase. We build a decision-tree model to further regress the data and identify the critical features and demonstrate an accuracy in predicting the flow patterns of up to 93%.

Investigation of inhalation and exhalation flow pattern in a realistic human upper airway model by PIV experiments and CFD simulations

Abstract: In this study, flow field characteristics in the trachea region in a realistic human upper airway model were firstly measured by particle image velocimetry (PIV) in the air under three constant inhalation and exhalation conditions: 36 L/min, 64 L/min and 90 L/min, representing flow rates of 18 L/min, 32 L/min and 45 L/min in real human airway (the model was twice the size of a human airway). Computational fluid dynamics (CFD) analyses were performed on four turbulence models, with boundary conditions corresponding to the PIV experiments. The effects of flow rates and breathing modes on the airflow patterns were investigated. The CFD prediction results were compared with the PIV measurements and showed relatively good agreement in all cases. During inhalation, the higher the flow rates, the less significant the “glottal jet” phenomenon, and the smaller the area of the separation zone. The air in the nasal inhalation condition accelerated more dramatically after glottis. The SST-Transition model was the best choice for predicting inhalation velocity profiles. For exhalation condition, the maximum velocity was much smaller than that during inhalation due to the more uniform flow field. The exhalation flow rates and breathing modes had little effect on the flow characteristics in the trachea region. The RNG k − e model and SST k − ω model were recommended to simulate the flow field in the respiratory tract during exhalation.

Experimental characterization of a hybrid impinging microjet-microchannel heat sink fabricated using high-volume metal additive manufacturing

Abstract: A high-performance water-cooled micro heat sink for the thermal management of high heat flux microelectronics was designed, fabricated, and tested. The heat sink design leverages a multi- metal electrodeposition additive manufacturing process to produce complex flow which are impossible to fabricate with traditional processes. A previous study employed simulation-driven design to develop and optimize micro heat sinks and is a hybrid of microchannels with an array of integrated microjets. In the present investigation, a prototype heat sink was fabricated and tested at heat fluxes up to and exceeding 1000 W/cm2. The results demonstrate reasonable agreement between the numerical predictions and experimental results, considering the complex geometry flow and conjugate heat transfer within the device. From a thermal–hydraulic performance standpoint, the heat exchanger achieved an estimated overall thermal conductance of ~330 kW/m2K with a pressure drop of 160 kPa (23 psi) for a flow rate of 0.5 L/min. For inlet water at 20 °C, this corresponded to a measured base temperature of 54 °C at an applied heat flux of 1000 W/cm2. The hybrid microchannel–microjet heat sink further exhibited an enhancement ratio of 6 when compared with a microchannel heat exchanger of commensurate design. To the extent of our knowledge, this microfluidic heat exchanger has achieved one of the highest effective thermal conductance levels reported in the literature and has done so at moderate pressure drop and flow rate.