Additional Flow Resistance Research Articles

Robust well-balanced method with flow resistance terms for accurate wetting and drying modeling in shallow water simulations

Hydrodynamic simulations in shallow water environments require careful consideration of the Wetting and Drying (WD) processes, which poses challenges to accurately modeling moving boundaries. This study introduces a novel method called the flow resistance method (FRM), which builds upon the foundation of the Negative-Depth Method (NDM) to tackle the intricacies of the moving boundary problem. Inspired by the Navier-Stokes/Brinkman (NSB) model from porous media theory, FRM incorporates a continuous function related to additional flow resistance that is proportional to the flow velocity. This approach facilitates a seamless transition between the exposed bed and fluid area wherein the additional flow resistance becomes 0 within the fluid area and approaches infinity in the exposed bed. Consequently, FRM adeptly and implicitly manages the moving boundary problem, causing a rapid decay of flow velocity to 0 in the exposed bed. In order to test the performance of FRM, four typical numerical experiments were conducted, along with an examination of a real-life case. Accuracy, robustness, and computational efficiency were assessed as key performance indicators. The simulations demonstrate that FRM adeptly tracks the moving water front, yielding precise results. Furthermore, when compared to established methods such as the Element Removal Method (ERM) and NDM, FRM exhibits broader applicability and achieves significant enhancements in the key performance indicators. These findings underscore the promising potential and broad applications of FRM in the field.

Reliability-based thermal-fluid-structural topological optimization of three-dimensional coolant channels in proton exchange membrane fuel cells

In order to minimize the flow resistance in designing the cooling multi-channels of proton exchange membrane fuel cells (PEMFCs) under the double constraints of target thermal reliability index and target structural performance, this work proposes a three-dimensional (3D) thermal-fluid-structural reliability-based topology optimization (RBTO) method for the first time. In the RBTO for PEMFCs’ coolant channels, the position uncertainty of the multi-heat loads on the bipolar plates caused by irregular metal foam skeleton is considered, and the multi-heat load positions are treated as the interval uncertain variables within a certain range. To solve the problem of low computational efficiency caused by the coupling of topological parameter optimization and reliability constraint analysis, the RBTO is equivalently decoupled to a sequence of cycles of deterministic topology optimization (DTO) and inverse reliability assessment, and the latter is completed by performance measure approach (PMA) based on the target reliability index. Results show that RBTO introduces more flow resistance cost than DTO, and the additional flow resistance in RBTO increases with the increase of the target reliability index. The heat concentration caused by a smaller fiber diameter of foam skeletons results in more flow resistance cost of RBTO compared to DTO. When the inlet velocity of the coolant channel varies in the region of 0.05–0.3 m/s, the flow resistance of the multi-channel obtained by RBTO is 1.29–0.96 times as that of the straight multi-channel. In addition, the uneven reactant gas concentration in PEMFC gas channels leads to the uneven distribution of heat flow, and it affects the temperature distribution on bipolar plates, which in turn affects the results of RBTO. The above method and findings can be applied to design the cooling channels of PEMFCs with irregular metal foam gas channels.

Study on the self-adaptive process of droplet traffic to a perturbation of flow resistance at the arms of a micro-T-junction

The response of the water–oil droplet flow to a perturbation of flow resistance added at the arms of a bypassed micro-T-junction is studied through a numerical method. The capillary number of the continuous flow varies between 0.007 and 0.034. Once an additional flow resistance is introduced at the arms of the T-junction, the flow self-adapts to the perturbation and droplets show complex dynamics at the junction, including splitting, merging, and reshaping. During the self-adaptive process, the instantaneous splitting ratios of the dispersed flow show positive correlations with that of the continuous flow. The correlation coefficient reduces as the increase in the amplitude of the perturbation. The ensemble splitting ratios of them, however, are independent. It shows a rather simple law that the ensemble splitting ratios of oil anchor at around a constant value while the corresponding parameter of water varies from 0 to 1. It illustrates that the droplet flow splitting at a T-junction resembles a resilient system, the stiffness of which depends on the capillary number of the flow. The energy loss of the system induced by a perturbation of the flow resistance is self-reduced by just redistributing of droplets into the two arms.

Pressure Drop Characteristics of the Reduced NGI Configuration with Several Common Glass Fiber Filters.

Background: Measurement of aerodynamic particle size distribution, a clinically relevant in vitro attribute of inhalable drug products, involves multistage cascade impactors and is tedious and expensive. A leading candidate for a quicker method is the reduced NGI™ (rNGI). This method involves placing glass fiber filters on top of the nozzles of a chosen NGI stage, selected often to collect all particles with an aerodynamic diameter smaller than approximately five microns. These filters contribute additional flow resistance that can alter the flow rate start-up curve, potentially affecting the size distribution and mass of the drug product dispensed by passive dry powder inhalers (DPIs). The magnitude of these additional flow resistance measurements is currently unreported in the literature. Materials and Methods: We placed glass fiber filters on top of the stage 3 nozzles of an NGI, along with the necessary support screen and hold-down ring. We measured the pressure drop across NGI stage 3 with the assistance of a delta P lid and a high-precision pressure transducer. With each filter material type and multiple individual filters, we gathered eight replicates at flow rates of 30, 45, and 60 L/min. Results: The filters typically doubled the total pressure drop through the NGI. For example, at a flow rate of 60 L/min, the Whatman 934-AH filters introduced a pressure drop of about 9800 Pa at stage 3, reducing the absolute pressure exiting the NGI to about 23 kPa below ambient, compared with a typical value of 10 kPa for the NGI alone at this flow rate. Conclusions: The pressure drop across typical filters is approximately equal to that through the NGI alone and therefore will affect the flow start-up rate intrinsic to compendial testing of passive DPIs. This change in start-up rate could cause differences between results of the rNGI configuration and those of the full NGI and will increase the required vacuum pump capacity.

Numerical analysis of the performance of proton exchange membrane fuel cell with longitudinal vortex generators

To improve the performance of proton exchange membrane fuel cell (PEMFC), in this study the combination of longitudinal vortex generators (LVGs) and cathode channel is proposed to improve the power density performance and optimize the water-thermal management of PEMFC with a less pressure loss. The effects of the shape, spacing, angle of attack, and number of LVGs on the performance of PEMFC are investigated via numerical simulation. The results show that the current density of the PEMFC improved the most significantly by installing five groups of rectangular plane winglet with a 12 mm spacing and 45° angle of attack in the cathode channel, and that the peak current density increases by 33.3% with additional flow resistance loss of 164.64% than the initial design. The current density of the PEMFC increases with the increase of spacing, angle of attack, and number of vortex generator groups. Moreover, the vortex generator improves the distribution uniformity of temperature, water content, and oxygen content inside the PEMFC. Importantly, it is also observed that the secondary flow intensity of PEMFC channel is positively correlated with the current density of the PEMFC. When the angle of attack is 45°, the vorticity increases the most, i.e., 16.79% higher than that without a VG. Ultimately, the pressure drop and overall performance indicator of PEMFC with LVGs are demonstrated. Compared with the initial design, except the comprehensive performance of the 0° angle of attack has been improved, that of other schemes has been reduced. It is worth noting that, for other published optimization schemes, the research scheme proposed in this paper has certain advantages in terms of lifting current density with lower resistance loss. Therefore, it is still of great significance to improve the energy density of PEMFC.

Numerical study on the drag characteristics of rigid submerged vegetation patches

Aquatic plants play a crucial role in the hydrodynamic and material transport processes within the aquatic environments due to the additional flow resistance induced by vegetation stems. In this study, high-resolution numerical experiments were performed to investigate the drag characteristics of circular vegetation patches fully immersed in a turbulent open channel flow. The submerged vegetation patch was modeled as a rigid cylinder array with a diameter D composed of N cylinder elements with a diameter d. The effects of vegetation density Φ (0.023 ≤ Φ ≤ 1) and relative diameter d/D (d/D = 0.051 and 0.072) were tested. The simulation results show that Φ and d/D affect the flow resistance exerted by the vegetation patch by modifying the bleeding flow intensity. With the increase in Φ, the drag forces acting on the individual cylinder elements decrease, whereas the total drag forces of the patch increase. The oscillation strength of the drag force of individual cylinders depends on Φ and the fixed positions within the patch. The presence of the free end of submerged cylinder array leads to enhanced wake entrainment with the increase in Φ. The drag coefficient of the submerged patch is smaller than that of the emergent patch when the dimensionless frontal area aD > 3. However, the two patches exhibit comparable drag coefficients for smaller aD values.

Retaining primary wall roughness for flow in rock fractures and implications on heat transfer and solute transport

Wall roughness is often found to have evident influences on flow-related processes in rock fractures. In this work, we first define the primary wall roughness to have dominating effects on the overall flow, whereas the secondary roughness only generates additional flow resistance and have insignificant impacts on the bulk flow. Accordingly, an effective procedure is presented to quantitatively identify primary and secondary roughness, and the validity of the procedure is tested with flow simulations in a two-dimensional rough fracture. The results show that the reconstructed fracture with only primary roughness can still well resemble the general flow behavior in the original fracture with a steady transmissivity increment of 5% for the Reynolds number from 0.01 to 100. We further examine the effects of both primary and secondary roughness on processes associated with heat transfer and solute transport in fracture flow. It is found that the heat transfer and solute transport behaviors are closely related to the flow behavior under the effect of wall roughness. As the flow velocity increases to cause strong flow inertia, larger eddies can occur to affect the heat transfer and solute transport processes. Although the presence of secondary roughness shows limited effects on the overall transport behaviors, secondary roughness is found to give rise to more irregularly-shaped eddies, which result in different local behaviors. The findings in this study can provide new insights into the roughness effect on fracture flow and associated processes. In addition, the roughness quantification presents a straight-forward evaluation of potential deviations when neglecting small-scale secondary roughness, as is often needed when analyzing larger-scale problems.

Effects of wettability on relative permeability of rough-walled fracture at pore-scale: A lattice Boltzmann analysis

Abstract Two-phase flow in fractured geo-material plays a significant role in various subsurface processes. In this study, the realistic issues regarding two-phase flow in rough-walled fractures (RWFs) with different surface wettability are initially investigated with an improved approach based on the free energy multiphase lattice Boltzmann model and a novel rough-walled discrete fracture network model. After validation with analytical solutions, the proposed model is applied to investigate the co-current flow of two immiscible fluids in RWFs at different surface wettability conditions, and the impact of contact angle and fracture aperture on fluid flow distribution, velocity field, and relative permeability curves are further clarified. For fluid initially distributed near the surface, its relative permeability increases monotonically with its saturation. For fluid flowing as the bulk phase, when its saturation is low, its relative permeability decreases with the decrease of its saturation. However, when its saturation is high (about 0.6–0.9), its relative permeability in RWFs exposes instabilities and could be lower than that in smoothed wall fractures, meaning additional flow resistance exists in RWFs. According to our simulation results and theoretical analysis, this phenomenon is mainly caused by the wettability-related microscale fluid distribution. In RWFs with small aperture, the fluid–solid surface interaction dominates, the distribution and flow pattern of fluid flowing near the surface alters the “apparent roughness” of the fracture and further impact the relative permeability curves.

Experimental Study on the Drag Reduction Performance of Clear Fracturing Fluid Using Wormlike Surfactant Micelles and Magnetic Nanoparticles under a Magnetic Field.

This paper examines a new study on the synergistic effect of magnetic nanoparticles and wormlike micelles (WLMs) on drag reduction. Fe3O4 magnetic nanoparticles (FE-NPs) are utilized to improve the performance of viscoelastic surfactant (VES) solutions used as fracturing fluids. The chemical composition and micromorphology of the FE-NPs were analyzed with FT-IR and an electron microscope. The stability and interaction of the WLM-particle system were studied by zeta potential and cryo-TEM measurements. More importantly, the influences of the temperature, FE-NP concentration, magnetic field intensity, and direction on the drag reduction rate of WLMs were systematically investigated in a circuit pipe flow system with an electromagnetic unit. The experimental results show that a suitable content of magnetic nanoparticles can enhance the settlement stability and temperature resistance of WLMs. A magnetic field along the flow direction of the fracturing fluid can improve the drag reduction performance of the magnetic WLM system. However, under a magnetic field perpendicular to the direction of fluid flow, an additional flow resistance is generated by the vertical chaining behavior of FE-NPs, which is unfavorable for the drag reduction performance of magnetic VES fracturing fluids. This study may shed light on the mechanism of the synergistic drag reduction effects of magnetic nanoparticles and wormlike micelles.

Sound reduction in heat exchanger modules by integrating plate absorbers with sub-millimeter openings

In air conditioning systems heat exchangers are frequently installed upstream of ventilators. These modules are part of the daily life of humans and should therefore create an environment that is as quiet as possible. The heat exchanger generates increased turbulence, which leads to increased sound emissions of the ventilator. Due to installation space limitations, it is not possible to connect silencers to the heat exchanger module. A novel concept is presented, which allows to reduce the sound emissions of heat exchanger due to plate absorbers without the need of additional installation room. The plates contain sub-millimeter openings. They are integrated into the heat exchanger housing together with back volumes. This arrangement guarantees compactness and generates no additional flow resistance. The emitted sound could be reduced by up to 2.9 dB in the partial load range. The main advantages of the concept presented are individual adjustment, cost-effective design and simple installation.

Shape optimization for a tube bank based on the numerical simulation and multi-objective genetic algorithm

This paper presents an optimal shape design for a tube bank in turbulent flow to enhance the thermal and hydraulic performance, where the multi-objective genetic algorithm (MOGA) and computational fluid dynamics (CFD) software is coupled in the optimization procedure. Five tubes in the tube bank could have different shapes, and twenty-five polar radii are selected as design variables accordingly. After the optimization, the initial circular tube bank is compared with two optimal solutions with the same pressure drop Δp or the same average heat flux q. Results show that the optimal solution could increase q by 7.6% without additional flow resistance or reduce Δp by 27% without heat transfer deterioration. Furthermore, the best compromise solution is determined by a decision-making approach, TOPSIS (technique for order preference by similarity to an ideal solution), where three different weighting factors are tested. It is found that all the selected solutions are located in the low pressure drop area, which indicates reducing the flow resistance may better improve the comprehensive performance of staggered arrangement tube banks.

A porous medium model for simulating conjugate heat transfer between wire-wrapped fuel bundles under forced and mixed convection

Wire-wrapped fuel bundles have been widely used in SFRs, and the conjugate heat transfer between wire-wrapped fuel bundles plays a key role in safety characteristics of SFRs. However, due to the existence of helical wire spacers, the geometry of fuel bundle becomes quite complicated, bringing challenges to realistic CFD modeling. A porous medium model for simulating conjugate heat transfer between fuel bundles have been proposed in this study. The geometries of fuel rods and wrapper tubes are preserved and helical wire spacers are treated as solid body of porous medium in this model. The flow resistance induced by helical wire spacers is considered by adding additional flow resistance source terms to momentum equation and the transverse mixing effects caused by wire spacers and thermal plumes are accounted by modifying diffusion terms in energy equation of porous medium model. The sodium experiment of 19-pin wire-wrapped fuel bundle under forced convection performed by ORNL and sodium experiments of multi-bundle systems named CCTL-CFR and PLANDTL-DHX under mixed convection conducted by JNC were selected as benchmark. Comparison results show that under both forced and mixed convection, this model could attain considerable accuracy in the prediction of conjugate heat transfer between fuel bundles with relatively low computational cost and have the potential to simulate core-wide temperature distribution of SFR.

Preparation and migration study of graphene oxide-grafted polymeric microspheres: EOR implications

Through an inverse emulsion polymerization technique, graphene oxide-grafted polymeric microspheres (RGO-PMSs) with superior suspension properties, thermostability, hydration swelling, elasticity and strength were developed for in-depth profile control and displacement. RGO-PMSs undergo migration and adsorption in large pores; capture by means of single plugging, coincidence plugging and bridging plugging; and elastic deformation-recovery in small pores to increase seepage resistance. When matching coefficient was 2.11, RGO-PMSs particles could not enter the porous media. However, RGO-PMSs particles entered core samples smoothly and perform plugging when the matching coefficient ranged from 0.78–1.44, while RGO-PMSs particles could not effectively block the pores when the matching coefficient was 0.67. An increase in the injection rate improved RGO-PMSs injectivity while weakening plugging efficiency. Additionally, the increase in the RGO-PMSs concentration and strength enhanced the plugging efficiency. Moreover, RGO-PMSs had a favorable anti-outwash property with a retention ratio of 88.7%, maximum additional flow resistance of 7.12 kPa and additional flow resistance of 4.53 kPa during migration. All the results indicated that RGO-PMSs could be an applicable candidate for in-depth profile control and displacement.

Viscous Dissipation and Apparent Permeability of Gas Flow in Nanoporous Media

AbstractThe nanopore confinement effect can increase the mobility for gas flow in shale rocks, and the apparent permeability is usually adopted to account for this effect. However, most of the apparent permeability calculation models are derived based on straight channels (capillaries) and neglect the influence of end effect. The end effect is caused by the bending of streamlines which yields more viscous dissipation and additional flow resistance for gas flow in nanoporous media. In this paper, for the first time the viscous dissipation for gas flow in nanoporous media is analyzed. In addition, an improved apparent permeability calculation model is proposed based on the Beskok‐Karniadakis (B‐K) model by introducing the influence of end effect, which is characterized by the ratio of the length to the width of a short channel (L/H). The accuracy of this model is validated by lattice Boltzmann simulations of gas flow in three different geometries: an infinite‐length straight channel, a finite‐length straight channel, and nanoporous media. For the infinite‐length straight channel, there is no end effect therefore both the B‐K model and the improved model can well predict the apparent permeability. However, for the finite‐length straight channel and nanoporous media, the original B‐K model overestimates the gas apparent permeability as it neglects the influence of end effect, while the improved model can still well predict the gas apparent permeability. In summary, the improved apparent permeability calculation model is more reasonable in predicting gas mobility in nanoporous media.

Numerical simulation of gas flow in porous structures of various geometries

Optimization of the porous material geometry is caused by engineering needs in reducing the value of the pressure drop in the gas or liquid flow through a complex structure. Computer models of porous media in various configurations are constructed, the pressure drop is calculated depending on the flow rate for the created models. The geometry of the packing of randomly located intersecting spheres gives a nonlinear change in pressure, whereas the ordered packing of spheres and the structure of randomly arranged cylinders and spheres yield results close to the Darcy model. For a model of randomly spaced spheres with the same porosity of the medium as for other models, the resistance coefficient has a maximum value, which is due to a multitude of channels of complex geometry that create additional flow resistance. The experimental data of the pressure drop calculation agree well with the results of the numerical simulation, which indicates the validity of using such models for studying hydrodynamics in highly porous cellular materials. A detailed study of the material structure influence on the hydrodynamic calculation using computer simulation will allow creating samples of porous media with improved characteristics.

Comparison of direct numerical simulation with volume-averaged method on composite phase change materials for thermal energy storage

Melting heat transfer in open-cell metal foams embedded in phase-change materials (PCMS) predicted by the volume-averaged method (VAM) was systematically compared with that calculated using direct numerical simulation (DNS), with particular attention placed upon the contribution of natural convection in the melt region to overall phase change heat transfer. The two-temperature model based on the assumption of local thermal non-equilibrium was employed to account for the large difference of thermal conductivity between metallic ligaments and PCM (paraffin). The Forchheimer extended Darcy model was employed to describe the additional flow resistance induced by metal foam. For the DNS, a geometric model of metal foam based on tetrakaidehedron cells was reconstructed. The DNS results demonstrated significant temperature difference between ligament surface and PCM, thus confirming the feasibility of local thermal non-equilibrium employed in VAM simulations. Relative to the DNS results, the VAM combined with the two-temperature model could satisfactorily predict transient solid-liquid interface evolution and local temperature distribution, although pore-scale features of phase change were lost. The presence of natural convection affected significantly the melting front shape, temperature distribution and full melting. The contribution of natural convection to overall phase change heat transfer should be qualitatively and quantitatively given sufficient consideration from both macroscopic (VAM) and microscopic (DNS) point of views. Besides, practical significance and economic prospective using metal foam in TES unit for WHR system to provide residential heating or hot water is discussed and analyzed.

A comprehensive investigation of polymer microspheres (PMs) migration in porous media: EOR implication

A type of polymer microspheres (PMs) with superior dispersity, swelling, elasticity, and saline and temperature resistance was prepared in this work through inverse emulsion polymerization. It was observed that these PMs experienced elastic deformation and obstructed micro-pores by means of complete, single and bridge plugging, and thus causing additional flow resistance. The migration modes of the PMs in porous media could be defined as smooth pass, elastic plugging-remigration incorporating low-efficiency and high-efficiency plugging, and complete plugging, on the basis of matching coefficients between the PMs and pore geometry. The plugging capability of the PMs was largely dependent on the matching coefficients. Interestingly, it was found that if appropriate matching coefficients was obtained, the PMs with higher elastic modulus showed an enhanced plugging capability even with smaller particle size. In addition, the results of adsorption and desorption behaviors of the PMs implied that the adsorbed PMs partially detached as a result of caused flow fluctuation and decline/disappearance of secondary adsorption potential well. It is believed that the proposed PMs could be a viable, robust and promising candidate for conformance control and oil recovery improvement.

Membrane Fouling for Produced Water Treatment: A Review Study From a Process Control Perspective

The offshore oil and gas industry is experiencing increasing water cuts as the reservoirs mature. The increase in produced water stresses the currently deployed deoiling technologies, resulting in more oil in the discharged water. Deploying membrane filtration to reduce the hydrocarbon concentration inherits additional complications related to fouling of the membranes: A process where the accumulation of material within and on the membrane surface adds additional flow resistance. This paper reviews and analyses the fouling detection, removal, prevention, dynamical and static modeling, with emphasis on how the membrane process can be manipulated from a process control perspective. The majority of the models rely on static descriptions or are limited to a narrow range of operating conditions which limits the usability of the models. This paper concludes that although the membrane filtration has been successfully applied and matured in many other industrial areas, challenges regarding cost-effective mitigation of fouling in the offshore deoiling applications, still exist. Fouling-based modeling combined with online parameter identification could potentially expand the operating range of the models and facilitate advanced control design to address transient performance and scheduling of fouling removal methods, resulting in cost-effective operation of membrane filtration systems. With the benefits of membrane filtration, it is predicted that membrane technology will be incorporated in produced water treatment, if the zero-discharge policies are enforced globally.

Lattice Boltzmann simulation of liquid flow in nanoporous media

In this paper, a multi-relaxation-time lattice Boltzmann (LB) model for nanoscale liquid flow is established to investigate the liquid flow characteristics in nanoporous media. The slip length and effective viscosity obtained by molecular dynamics (MD) simulations are adopted to account for the nanoscale effect. First, the LB model for water flow in nanopores is built and water flow characteristics in nanoporous media are investigated. The fluid-solid interaction force shows significant influence on water flow in nanoporous media. The water flux through nanoporous media increases with the decrease of fluid-solid interaction force. In hydrophobic nanoporous media, the nanoscale effect can decrease the gap between water flow resistance in large pores and that in small pores, making the velocity distribution more uniform. In addition, the end effect caused by the bending of streamlines can induce significant additional flow resistance. Neglecting the end effect can greatly overestimate water flow ability. The pore structure also has significant influence on water flow in nanoporous media. With the increase of specific interfacial length, the nanoscale effect increases. Finally, the LB model for oil (octane) flow in quartz nanopores is also established by incorporating the MD simulation results. Oil flow simulation in quartz nanoporous media shows that the conclusions obtained for water flow are also applicable for oil flow.

The Effect of Wettability Heterogeneity on Relative Permeability of Two‐Phase Flow in Porous Media: A Lattice Boltzmann Study

AbstractRelative permeability is a critical parameter characterizing multiphase flow in porous media and it is strongly dependent on the wettability. In many situations, the porous media are nonuniformly wet. To investigate the effect of wettability heterogeneity on relative permeability of two‐phase flow in porous media, a multi‐relaxation‐time color‐gradient lattice Boltzmann model is adopted to simulate oil/water two‐phase flow in porous media with different oil‐wet solid fractions. For the water phase, when the water saturation is high, the relative permeability of water increases with the increase of oil‐wet solid fraction under a constant water saturation. However, as the water saturation decreases to an intermediate value (about 0.4–0.7), the relative permeability of water in fractionally wet porous media could be lower than that in purely water‐wet porous media, meaning additional flow resistance exists in the fractionally wet porous media. For the oil phase, similar phenomenon is observed. This phenomenon is mainly caused by the wettability‐related microscale fluid distribution. According to both our simulation results and theoretical analysis, it is found that the relative permeability of two‐phase flow in porous media is strongly related to three parameters: the fluid saturation, the specific interfacial length of fluid, and the fluid tortuosity in the flow direction. The relationship between the relative permeability and these parameters under different capillary numbers is explored in this paper.