Flow Resistance Coefficient Research Articles

Investigation on flow resistance reduction and EOR mechanisms by activated silica nanofluids: Merging microfluidic experimental and CFD modeling approaches

Activated silica nanofluids (ASN) flooding has been proven to be an effective method to enhance oil recovery. However, due to the variety of nanoparticles and surfactants used for ASN synthesis, the main mechanisms of flow resistance reduction and oil recovery enhancement by ASN are still unclear, and most studies are based on physical experiments, which are too cumbersome and inefficient. In this study, the ASN flooding experiment and CFD modeling are combined based on microscopic visualization experiments. Firstly, three kinds of ASN with different hydrodynamic diameters were synthesized by BS-12 and nano-silica sol, and the basic properties were tested to obtain the modeling parameters. Surface flow experiments were also carried out. Then, a microscopic model based on the real pore-throat size was developed, and combined with image processing technology, the quantitative study and EOR mechanism analysis of the ASN flooding process was carried out. Finally, CFD modeling was carried out based on microscopic visualization experiments to predict the recovery improvement after improving ASN performance. The results show that at the optimal concentration of 1%, the ASN with a smaller hydrodynamic diameter performs better in wettability alteration and reducing interfacial tension and viscosity ratio. ASN can significantly reduce the flow resistance coefficient by 30.36% to 95.43%. The reduction of micro-resistances is the important EOR mechanism of ASN. The results of the microscopic visualization experiment and CFD simulation are compared, and errors ranged from 3.9% to 5.22% for recovery factors in various injection scenarios. The prediction results by CFD simulation show that the viscosity reduction ability has the most significant effect on the recovery factor. The best performance parameters of ASN under the highest recovery factor are also predicted. Simulation results guide the selection of surfactants and nanoparticles in the subsequent ASN synthesis process, which has the advantages of high efficiency and low cost.

Experimental study on the effect of simulated grass and stem coverage on resistance coefficient of overland flow

AbstractVegetation plays a significant role in preventing desertification, conservation of soil and water. However, nowadays, there is still uncertainty regarding the mechanisms of flow resistance caused by dissimilar vegetation covers. To address this gap, a series of these was conducted in this study to investigate the influence of synthetic grass and stems on the variation of resistance on overland flows. Thirty vegetation configurations were selected (combining five synthetic grass coverage options and six synthetic stem coverage ones), and tested against five unit discharges (flow range = 0.28–2.22 L m−1 s−1) and four slope gradients (3.49%–20.78%). The results obtained showed that the unit discharge is the key driving factor for the transition from laminar to transitional flow. Furthermore, the relationship between the resistance coefficient (f) and the Reynolds number (Re) was not monotonically increasing or decreasing, but behaviours observed were specifically linked to each vegetation coverage. However, a critical coverage threshold was identified, and it corresponded to 2.72% when the slope gradient tested was 3.49%. This threshold decreased with the increase of the slope gradient. In addition, when the vegetation coverage was less than the critical threshold, the f was negatively correlated with Re, otherwise if the vegetation coverage was higher than the critical threshold identified the f–Re relation was positively correlated. The total flow resistance under synthetic grass and stem cover was unequal to the linear superposition of grain resistance and form resistance caused by synthetic stem and grass, which meant that the linear superposition approach is not applicable to overland flows. Finally, a model was developed to predict the flow resistance by applying the π‐theorem and the multiple nonlinear regression analysis and it has been validated against the experimental results confirming its accuracy and high performance (adj.R2 = 0.99, NSE = 0.94).

Flow Resistance Analysis of Clinically Significant Portal Hypertension in Patients with Liver Cirrhosis.

Cirrhosis-induced clinically significant portal hypertension (CSPH) is a fatal disease. Early detection of CSPH is vitally important to reduce the patients' mortality rate. In this study, combined with three-dimensional image construction technology and computational fluid dynamics (CFD), an image-based flow resistance analysis was proposed. The flow resistance analysis was performed for nine cirrhosis patients with CSPH and ten participants without liver diseases, respectively. The results showed that the flow resistance coefficient of the portal vein system in CSPH patients was significantly lower than that in the control group (0.97 ± 0.11 Pa/(mL/s) for CSPH patients; 1.80 ± 0.40 Pa/(mL/s) for the control group; P = 0.028). In contrast, although main portal vein dilation was found in CSPH patients, the cross-sectional area enlargement was not statistically significant (186.01 ± 57.48 mm2 for CSPH patients; 166.26 ± 33.74 mm2 for the control group; P = 0.39). The research outcomes indicated that the flow resistance analysis was more sensitive than the commonly used vessel size measurement in the detection of CSPH. In summary, we suggest using flow resistance analysis as a supplementary noninvasive method to detect cirrhosis patients with CSPH.

CFD Modeling and Simulation of the Axial Dispersion Characteristics of a Fixed-Bed Reactor.

In this study, the axial dispersion characteristics of a fixed-bed reactor with different packed structures were investigated via computational fluid dynamics (CFD) simulation. The discrete element method was employed to develop the physical model of a fixed bed. Then, CFD simulations were performed to investigate the flow resistance coefficient under different Reynolds numbers. The prediction values were in fair agreement with those calculated by the Carman equation, thereby validating the proposed CFD model. The tracer pulse method and the step method were employed to evaluate the residence time distribution characteristics in the fixed-bed reactors where the mean residence time and axial dispersion coefficient were calculated. The distribution characteristics of the tracer concentration and fluid velocity were also obtained and used to explain the mixing performance of the fixed bed. This simulation study can contribute to the optimization design and scaling up of reactors with porous packed structures.

Pore-scale numerical simulations of flow and convective heat transfer in a porous woven metal mesh

• The fluid dynamics through the woven mesh were studied from the pore scale. • The numerical model was verified in comparison with experimental data. • The flow patterns inside the pores of the woven mesh were studied in detail. • Difference between the numerical and the analytical results of friction factor is 5%. • A new correlation of the Nusselt number was proposed. Woven metal meshes have received considerable attention in several engineering applications owing to their excellent physical properties. Macroscopic parameters, such as flow resistance and heat transfer coefficient through the porous structure, have been extensively investigated. However, the microscale mechanism requires further analysis. In this study, a numerical model was developed to evaluate the fluid dynamics and heat transfer characteristics of a porous woven mesh at the pore scale. The accuracy of the model was verified by comparing the simulated results with experimental data. Flow patterns were comprehensively studied in terms of velocity, helicity, and vorticity. The effects of the fluid properties on the flow behavior were examined. The flow reversal region downstream of the mesh expanded as the Reynolds number increased. Based on the pore-scale numerical results, a Nusselt number correlation was derived for convective heat transfer in the porous woven mesh. This study provides insights into the flow physics within a woven mesh and a framework to optimally design related devices.

Numerical Simulation of the Flow and Heat Transfer Characteristics of Sweeping and Direct Jets on a Flat Plate with Film Holes

The internal heat transfer performance and flow structures of a sweeping jet and film composite cooling on a flat plate were numerically studied. Sweeping jet and film composite cooling consists of a fluidic oscillator and 20 cylindrical film holes; the direct jet is formed by removing the feedback from the fluidic oscillator, which is different from the traditional cylindrical nozzle. Four different mass flow rates of coolant were considered, and the inclination angle of the film hole was 30°. The Conjugate Heat Transfer method (CHT) and Unsteady Reynolds Averaged Navier Stokes equation (URANS) were employed. The results indicated that the flow resistance coefficients of the sweeping jet were larger than those of the direct jet, and the Nusselt number monotonously increased with the increase in the mass flow rate. Compared to the direct jet, the sweeping jet had a more spatially uniform heat removal rate, and the area-averaged Nusselt number was slightly lower. Therefore, the sweeping jet and film composite cooling caused the distribution of the flat plate heat transfer to be more uniform. It is worth noting that the novel direct jet nozzle in the present work had considerable area-averaged impingement cooling effectiveness.

Analysis and experimental investigation on the flow rate controller for PWR accumulator

During the large break loss coolant accident (LBLOCA), the emergency safety injection system is used to inject the safety water into the reactor pressure vessel (RPV) via the primary circuit or direct vessel injection (DVI) to avoid any uncovering of the core. The accumulator (ACC) is an important device to act as a water supplier during the safety injection. A flow rate controller (FRC) was designed to provide the large-flow-rate injection to reflood core quickly at the beginning of the injection and then turn to the small-flow-rate injection later. It makes the safety injection longer than those normal ACCs with large flow rate only and improve the efficiency of the safety injection. A FRC concept was evaluated with computational fluid dynamics (CFD) software in the paper. The fluid flow pattern of the fast mode and slow mode were investigated to reveal the mechanism of the FRC operation. To perform the experiment on a small test section, a scaling analysis was done to find the criteria between the model and the prototype. Then a test facility was established to simulate the operation condition of the FRC based on the scaling results. A test section was tested in transient condition with 1/4 diameter and equal height of the prototype. The results show the flow rate ratio was 3.57:1 at the critical point of the flow rate. The paper also presents the thermal hydraulic parameters such as pressure, injection rate, liquid level, temperature of the gas and water in transient during the injection. The flow resistance coefficients of the two modes were obtained in the experiment too.

Modeling of Lateral Flow in CFD for Subchannel Analysis

This paper is aimed at the application of computational fluid dynamics (CFD) calculations for lateral flow modeling in rod bundles of Russian-type pressurized water reactors with hexagonal fuel rod lattice by subchannel analysis under a constant temperature. The subchannel code SUBCAL and CFD code ANSYS Fluent with the Reynolds stress turbulence model, which is capable of solving the anisotropic flow present in rod bundles, are used. Both methods are compared in terms of calculations in rod bundles. The literature review of available experiments of rod bundles suitable for CFD calculation validation follows. This paper describes the created CFD models on a triangular lattice, which are subsequently validated on selected experimental data in a wide range of Reynolds numbers and geometry (pitch-to–rod diameter ratio) together with mesh sensitivity analysis. The main part of this work is to develop a new equation for the lateral flow resistance coefficient for the subchannel code based on CFD calculations. Within these calculations, the turbulent mixing coefficient β for hydraulically smooth rod bundles, which is related to the geometry, and the momentum-energy transfer analogy correction factor ε are also evaluated and for which the equation is subsequently proposed.

Numerical simulation of heat transfer and flow of Al2O3-water nanofluid in microchannel heat sink with cantor fractal structure based on genetic algorithm

The heat generated during operation of microelectronic devices often adversely affects product performance. A remedy for this problem can be through the incorporation of nanofluidic microchannel heat sinks. Advanced working fluids and channel structures can be used to improve the heat transfer performance of the microchannel heat sink. First, thermal resistance is treated as a single objective function, the geometry of the microchannel was optimized using a genetic algorithm. The flow and heat transfer characteristics of the optimized microchannel are analyzed. The effect of different nanofluid volume fractions and geometric parameters on the inlet and outlet pressure drop, flow resistance coefficient, substrate temperature, Nusselt number (Nu), and system thermal resistance in the fractal microchannel are investigated. The thermal resistance of Al2O3 nanofluid with a volume fraction of 5% is 12.5–14.7% lower than that of deionized water, and the microchannel substrate temperature is 6.26 °C lower than that of deionized water.

Evaluation of flow and heat transfer performance of spiral coil jacket with different cross sections

The flow and heat transfer performance of the spiral coil jacket for a reactor with five different cross-section shapes was evaluated. The comprehensive performance of five jacket models was analyzed through PEC and JF evaluation factors, which provided a basis for jacket design in industrial application. The results showed that at certain Reynolds number, the Nusselt number of the arcuate cross-section jacket was lower than that of the half-pipe jacket, but the flow resistance coefficient was lower and the resistance loss was smaller. The secondary flow generated by the half pipe jacket made the temperature gradient in the corner of the cross section far less than that of the center, thus affecting the heat transfer of the jacket. The vortex structure analysis showed that the edges and corners of the inner wall of the jacket were prone to generate vortex structure. The comprehensive evaluation factors of PEC and JF showed that the arcuate jacket of 140° had the best comprehensive performance.

Numerical simulation of two-phase flow in a multi-gas channel of a proton exchange membrane fuel cell

Understanding the two-phase distribution characteristics within the multi-gas channel of a fuel cell is important for improving fuel cell performance. In the paper, the volume of fluid model is used to predict the dynamic behaviour of water in the multi-gas channel, analyze the pressure drop, velocity distribution, and flow resistance coefficient between different channels, and investigate the influence of operating conditions, surface wettability and channel structure on the two-phase distribution characteristics in the channel. The results show that water undergoes the processes of growth, separation, single droplet transport, wall impact, droplet collision, liquid film formation, and liquid film transport in the multi-gas channel. Inlet velocity and surface wettability significantly affect the pressure drop, water saturation, and surface water coverage. As the inlet velocity and gas diffusion layer surface wettability increase, the flow resistance coefficient and unevenness of the distribution decrease, indicating that the in-channel flow distribution homogeneity is enhanced. The rectangular channel has better water removal and flow distribution uniformity than the tapered channel, and the unevenness of distribution decreases significantly with decreasing rectangular width, from 0.15715 to 0.00315. The research work is a guide to understanding water transport in multi-gas channels, accelerating water removal, and improving inter-channel flow distribution uniformity.

Numerical method for determining the coefficient of hydraulic resistance two-phase flow in a gas lift well

The process of stationary movement of a gas-liquid mixture in the lifting pipe of a gas-lift well is considered. To describe this two-phase flow, a mathematical model is proposed that includes the equation of flow motion and the continuity equation for each phase. The presented model is transformed to a single nonlinear ordinary differential equation with respect to pressure. Within the framework of the obtained model, the task is set to determine the hydraulic resistance coefficient of a two-phase flow according to an additionally specified condition with respect to pressure. An additional condition, presented in the form of a nonlinear algebraic equation, is transformed into an ordinary differential equation with respect to an unknown coefficient of hydraulic resistance by applying the method of differentiation by parameter. The solution of the resulting Cauchy problem is determined by the finite difference method. Based on the proposed computational algorithm, numerical experiments were carried out for model data. Keywords: gas lift; two-phase flow; hydraulic resistance coefficient; parameter differentiation method; finite difference method.

Aerodynamic coefficients of irregular non-spherical particles at intermediate Reynolds numbers

In industrial processes such as those related with paper industry, coal or biomass combustion, particles can take irregular non-spherical shapes. However, in related numerical computations the assumption of spherical particle is customary, mainly because the fluid dynamic forces acting on such irregular particles are unknown to a large extent. This contribution aims to generate new information about the flow resistance coefficients (forces and torques) experienced by non-spherical irregular-shaped particles with three different degrees of sphericity ψ (0.7, 0.8 and 0.89) immersed in a uniform flow at intermediate Reynolds numbers (i.e. Re = 1–200). For this purpose, Particle Resolved Direct Numerical Simulations (PR-DNS) are carried out by means of the Ansys-Fluent code using body fitted meshes where the irregular particle is well resolved. The flow coefficients are computed for a set of different particles belonging to the same sphericity group, considering a large number of orientations, which allows the construction of the corresponding distribution functions. Such distributions depend on Reynolds number and particle sphericity and can be reasonably well approximated by Gaussian distributions, which are determined by a mean value and a standard deviation. The obtained drag, lift and torque coefficients display expectedly a scattering around the mean values with a high sensitivity to the irregularity of the surface and particle intrinsic aspect ratio (φ). Additionally, the distribution of the angle formed between the transverse lift force and the transverse torque in the plane orthogonal to the flow direction is computed. The generated information will be used to further pursue a novel statistical model for the fluid dynamic forces and torques acting on irregular particles in the frame of the Lagrangian approach.

An Experimental Study of Pressure Drop Characteristics and Flow Resistance Coefficient in a Fluidized Bed for Coal Particle Fluidization

Liquid–solid fluidized beds have a wide range of applications in metallurgical processing, mineral processing, extraction, and wastewater treatment. Great interest on their flow stability and heterogeneous fluidization behaviors has been aroused in research. In this study, various fluidization experiments were performed by adjusting the operating conditions of particle size, particle density, and liquid superficial velocity. For each case, the steady state of liquid–solid fluidization was obtained, and the bed expansion height and pressure drop characteristics were analyzed. The time evolution of pressure drop at different bed heights can truly reflect the liquid–solid heterogeneous fluidization behaviors that are determined by operating conditions. With the increase in superficial liquid velocity, three typical fluidization stages were observed. Accordingly, the flow resistance coefficient was obtained based on the experimental data of bed expansion height and pressure drop. The flow resistance coefficient experiences a decrease with the increase in the modified particle Reynolds number and densimetric Froude number.

Flow resistance and convective heat transfer by elastic turbulence in 1D/2D/3D geometries

Inducing elastic turbulence is a promising method to intensify flow and heat transfer at low Reynolds number Re. Different geometries shall have great impacts on the occurrence of elastic turbulence and its heat transfer effect, which are however seldom investigated especially for flow in 3D geometry. This work conducts a comparative experimental study of the dimension effect on elastic turbulence on 3D, 2D and 1D geometries with similar hydraulic diameters. Polyacrylamide is used to induce elastic turbulence and the corresponding flow resistance and heat transfer performance are obtained for different geometries under laminar flow conditions. The results provide strong evidence that curvatures are necessary for the onset of elastic turbulence in 1D geometry as shown by similar flow resistance and heat transfer coefficient between the Newtonian and viscoelastic fluids. Comparing to the 2D geometry, flow in 3D geometry achieves both reduced pressure drop gradient and increased heat transfer at the same time due to the unique interaction of elastic stress with the torsion and rotation effects. New correlations of Nusselt number Nu and Weissenberg number Wi are proposed in curved geometries as Nu∝Wi2.2 and Wi1.9 for the 3D and 2D flow structures, respectively, under the boundary condition of constant heat flux. The mechanisms of flow and heat transfer of elastic turbulence in different geometries are also discussed to help further optimization.

A framework for detecting stage-discharge hysteresis due to flow unsteadiness: Application to France’s national hydrometry network

A generic framework is proposed to evaluate the relative discharge error made when ignoring stage-discharge hysteresis due to transient flow over large gauging station networks. The diagnosis is conducted using the Jones equation, a simple hydraulic concept relating discharge to stage and its time-gradient. The input data used for the method are the flow resistance coefficients, the temporal stage gradients, and the bed slopes. The hysteresis effect is quantified for each gauging station and mapped using the relative discharge error. The method was applied to 2618 gauging stations of France’s national hydrometry network using data extracted from the national hydrological archive and from Digital Terrain Models. The diagnostic results highly depend on slope estimates used as inputs. Substantial hysteresis effects were found at stations with low bed slope combined with a fast flood regime. The application to France shows the difficulty of drawing a firm conclusion about stations prone to hysteresis due to the slope data uncertainty. This issue is not specific to France; slope estimates over a network of hydrometric stations are difficult to obtain in many countries. The use of local bed slope estimates is recommended to approach the slopes of the reaches controlling the station stage-discharge relation.

Preliminary study on thermal–hydraulic behavior of loss-of-flow accident in deep pool-type nuclear reactor

Deep pool nuclear reactor (DPNR) is a novel pool-type reactor, which has shown great potential in seawater desalination and district heating. In this paper, the thermal–hydraulic behavior of loss-of-flow accident (LOFA) in DPNR were investigated by RELAP5. The parametric analyses were also carried out to reveal the effects of flow resistance coefficient (FRC) in connection pipe and flap valve opening criteria on thermal–hydraulic behavior of LOFA in DPNR. The results showed that the LOFA process could be divided into coast-down phase, oscillation phase and natural circulation phase, and two peaks of clad peak temperature appeared. Besides, the parametric analysis showed that increasing FRC in connection pipe and failure of flap valve can make the first and second peak of clad peak temperature larger, respectively. The decrease of flap valve opening criteria made flap valve open earlier, and inertia tank performance was weakened when flap valve opened in coast-down phase.

Flowloop investigation into hydrate formation and slurry flow in the presence of micron-sized sand particles

Hydrate flow assurance is critical to the exploitation of natural gas hydrate reservoirs. So far, hydrate formation and slurry flow behaviors in the presence of micron-sized sand particles are still unclear. Therefore, experiments of hydrate formation and slurry flow in the presence of micron-sized sand particles were performed in a high-pressure flow loop. The induction time and formation subcooling during hydrate formation process with micron-sized sand particles were studied, and cumulative formation probability under different formation subcooling with micron-sized sand particles was explored. Coupled with a semi-empirical hydrate formation kinetics model, hydrate formation kinetics parameters with micron-sized sand particles were calculated. The influence mechanism of micron-sized sand particles on hydrate formation was revealed. The calculation method for hydrate slurry viscosity under conditions of constant volume fraction and variable shear rate was derived. Combined with viscosity of hydrate slurry with micron-sized sand particles, the importance of the fractal dimension to the accuracy of slurry viscosity prediction was emphasized. Considering hydraulic factors, collision between hydrates or micron-sized sand particles and pipe wall, and friction between hydrates or micron-sized sand particles and pipe wall, the calculation method of flow resistance coefficient of hydrate slurry with micron-sized sand particles was established.

Microstructure modeling of microfiber sound absorbers and investigation of improvement of sound absorption coefficient

In the automotive industry, various studies have been conducted to reduce cabin noise. Currently, it is common to use sound-absorbing materials in door panels and front panels to reduce low-frequency noise such as road noise and wind noise. Porous materials such as glass wool and urethane foam are used as sound-absorbing materials, but they currently have problems such as low sound absorption performance at low frequencies. Therefore, this study focused on fiber-based sound-absorbing materials consisting of multiple diameters. A microstructural model was created based on data obtained from microstructural observations of this fiber material. Using this model, flow resistance and sound absorption coefficient were calculated by the homogenization method. The results of the calculations using the model with bundled fibers showed that the effect of changes in the flow path area was significant.

Numerical investigation of hydraulic and heat transfer characteristics of two-phase ice slurry in helically coiled tubes

The helically coiled tubes (HCT) with ice slurry as the cooling medium plays an essential role in reducing the energy consumption of heating, ventilation, air-conditioning, and refrigeration (HVAC&R) systems. However, the hydraulic and heat transfer behavior of ice slurry in HCT has not been fully understood. Therefore, the thermo-fluidic characteristics of ice slurry in HCT are numerically investigated in this study based on Eulerian-Eulerian model. The research revealed that the velocity near the outer wall is larger than that near the inner wall due to the presence of secondary flow, and the high ice concentration region shifts towards the inner wall. As increasing the inlet ice volume fraction and velocity, the ice concentration distribution in vertical radius direction of the cross-section gradually tends to be uniform. The pressure drop increases with increase of the coil radius, while the coil pitch has little influence on the pressure drop. During heat transfer process, the secondary flow causes the ice volume fraction near the inner wall to decline faster than that near the outer wall. At the entrance section, the local heat transfer coefficient decreases sharply from 9320.05 W/(m2·K) to 3002.11 W/(m2·K) and then increases slowly along the flow direction. With increasing Reynolds number, the local heat transfer coefficient enhances linearly. The increase of ice particle diameter and coil radius leads to the enhanced local heat transfer coefficient. In contrast, increasing coil pitch does not bring a significant change of local heat transfer coefficient. In addition, the correlation of local Nusselt number and flow resistance coefficient is proposed.