Channel Flow Research Articles

Numerical Model for Investigating Effects of Cracks and Perforation on Polymer Electrolyte Fuel Cell Performance

The presence of cracks in the microporous layer (MPL) of polymer electrolyte fuel cells (PEFCs), often occurring during the membrane electrode assembly manufacturing process, has a significant impact on cell performance. However, the exact influence of crack presence, density, and patterns within MPLs on cell performance and transport behaviors remains unclear. This study introduces a three-dimensional macroscale model of PEFCs aimed at investigating the effects of MPL cracks and gas diffusion layer (GDL) perforations on cell performance and transport behavior. This model offers several advantages, including the ability to potentially integrate the effects of flow channel design in future. Additionally, the model can seamlessly incorporate electrochemical reactions and explore phenomena within the catalyst layers (CLs), expanding simulation capabilities beyond water transport alone. The findings suggest that MPL cracks contribute positively to performance by facilitating water drainage. Furthermore, when combined with perforations in GDLs, MPL cracks can significantly enhance performance by providing pathways for water transport. Overall, this study provides valuable insights into developing models for optimizing PEFC performance and underscores the need for further research and development in this area.

Numerical modeling of hydro-mechanical processes during hydraulic testing of pre-existing fractures at the Grimsel Test Site, Switzerland

This study presents a fully coupled hydro-mechanical framework for modeling hydraulic shearing in a mesoscale reservoir located at the Grimsel Test Site, Switzerland. The experiment was conducted on a ductile–brittle fault embedded in low-permeable granite. We observe that normal fracture opening increases flow channel recoverably, while fracture sliding locks asperities leading to a non-recoverable increase in flow. To couple these processes, we use a poro-elasto-plastic constitutive framework and employ a permeability function that depends on several parameters, such as dilation angle, in-situ stresses, residual aperture and maximum aperture. Our results capture the recorded pressure responses well, and indicate that the permeability changes by one order of magnitude during the experiment.

Start-up investigation and heat transfer enhancement analysis of a loop thermosyphon with biomimetic honeycomb-channel evaporator

Loop thermosyphon has the ability of heat transfer without external energy input, which has good application potential in many areas. Biomimetic flow channel is an effective way for heat transfer enhancement and resistance optimization, therefore it is a promising method to improve the performance of loop thermosyphon. While currently few studies have been conducted in this field. In this paper, the start-up stages, flow patterns and heat transfer performance of a loop thermosyphon with biomimetic honeycomb-channel evaporator are experimentally investigated, and compared with a loop thermosyphon with parallel-flow evaporator. The results show that the start-up of can be divided into three stages: stage dominated by heat conduction, stage dominated by boiling and stage transited to stable operation; For the steady-state performance, the heating power of the optimal point with the lowest thermal resistance increases from 90 W to 150 W with the increase of the filling ratio from 50% to 70%; Compared to loop thermosyphon with parallel-flow evaporator, loop thermosyphon with biomimetic honeycomb evaporator has lower thermal resistance. The decline of thermal resistance is 4.1%-21.6%, and is more significant under small heating power. This paper provides a simple and affordable method for heat transfer improvement of loop thermosyphon.

Mesoscale modeling on the influence of surfactants on seepage law during water injection in coal

To investigate the mesoscopic influence of surfactants on seepage law during water injection in coal seam, this paper innovatively establishes a fluid transport lattice Boltzmann (LBM) model by incorporating the seepage resistance generated from the porous media and external forces, which embodies the impact of wettability degree resulted from cocamidopropyl betaine (CAB), sodium dodecyl sulfate (SDS), and coconutt diethanol amide (CDEA) reagents at a 0.1% concentration. The main conclusions derived from this investigation are as follows: Firstly, as the lattice number in the X direction increases, the average seepage velocities in coal samples treated by deionized water, 0.1% CAB, 0.1% SDS, and 0.1% CDEA reagents (Nos. 1, 2, 3, and 4) exhibit three distinct stages: rapid decline, slow decline, and steady decline; in comparison to raw coal sample, modified coal samples demonstrate decreases of 20.84%, 33.91%, and 61.70%, respectively. Secondly, the critical values of displacement pressure difference exist during the phenomenon that modified reagents spread out in the entire flow channel, which are 3.5 MPa, 3.5 MPa, and 5.2 MPa, respectively, for coal samples Nos. 2, 3, and 4; this signifies that surpassing these critical values help prevent issues such as blank belts within the wetting range and insufficient dust control. Finally, at a displacement pressure difference of 0.01 (lattice unit), the average velocity ratios for samples (Nos. 2, 3, and 4) are 0.78, 0.56, and 0.37(lattice unit), respectively; notably, the water flow velocities in modified coal samples are lower compared to that in raw coal sample, indicating that the addition of surfactants impede the seepage process of water injection in coal seam. Moreover, when the displacement pressure difference reaches 0.03 (lattice unit), the velocity ratio of CDEA-modified coal sample exceeds 100%; this means that when the displacement pressure difference surpasses 15.6 MPa, the water injection effect of CDEA-modified coal sample begins to be improved. These research findings offer a theoretical basis for enhancing water injection technology in coal mines.

Numerical simulation of hydrate particle behavior in vertical pipeline gas-liquid flow

During the extraction of deep terrestrial and deep-sea natural gas reservoirs, changes in temperature and pressure in the production well can lead to the formation of natural gas hydrates in the wellbore, blocking the flow channel and posing significant challenges to gas well production and management. To address this, we have established a mathematical model to describe the flow characteristics of hydrate multiphase flow systems in vertical pipelines. We employ Computational Fluid Dynamics simulations coupled with a Population Balance Model to predict the formation and breakage of hydrate particles, taking into account mechanisms such as particle collision, aggregation, and breakage. We have analyzed the impact of gas flow rate, slurry flow rate, and hydrate volume fraction on hydrate particle size in the pipeline. The results indicate that hydrate particles tend to aggregate at the bottom of the pipeline. The larger the hydrate slurry flow rate, the faster the hydrate particle size increases. As the gas phase flow rate increases, the increase in particle size slows down. High gas phase flow rates help form turbulence to suppress particle aggregation, velocity fluctuations contribute to particle aggregation growth, and stable velocities facilitate particle decomposition. The increase in hydrate volume fraction significantly increases the diameter of hydrates in the center of the pipeline. The research results can provide suggestions for wellbore blockage caused by hydrate particle aggregation on the wall and a decline in gas well production during actual natural gas well production.

Study on the influence characteristics of multi-working condition parameters on membrane electrode type CO2 electrolyzer

The electrochemical conversion of carbon dioxide (CO2) into basic chemicals or carbon-based fuels is a promising new strategy for carbon resource utilization. Within this domain, solid-electrolyte CO2 electrolyzer demonstrate significant potential for the continuous production of pure formic acid solutions. This study, leveraging a 4 cm2 visualization electrolyzer, explores the impact of three working condition parameters on performance: working voltage, gas flow rate, and the intermediate chamber water flow rate. It compares the variations in current density, formic acid concentration, and the distribution of liquid water on the cathode side under different working conditions. The results indicate that the working voltage, current density, and formic acid yield are all positively correlated; overly low gas flow rates can lead to CO2 deficiency and diminished electrolyzer performance; concentration control of the formic acid solution is effectively achieved by adjusting the intermediate chamber water flow rate; and during the electrolyzer reaction process, almost all of the liquid water is positioned at the bends downstream of the cathode flow channel.

Flow channel simulation and optimization design of pervaporation membrane pool based on heat-mass-flow coupling

Flow channel simulation and optimization design of pervaporation membrane pool based on heat-mass-flow coupling

Теплоотдача при движении воды в трубе при температурах, близких к температурам кипения в переходном режиме

Currently, there is a problem of developing effective methods to calculate heat and mass transfer processes during steam condensation from a vapor-gas mixture in industrial devices. This is due to the need to create new reliable and highly efficient designs of heat exchangers for various purposes. The finite element method has been used in the ANSYS Fluent software package during the numerical simulation. An experimental plant is tested in the pipeline of an industrial enterprise at the production site of the Technopolis KHIMGRAD industrial park (Kazan-city). The applicability of the Lee model to solve problems of water flow in a pipeline with partial evaporation is proved. This model allows you to accurately account for the processes of evaporation and condensation, which is important for the design of cooling and air conditioning systems. The authors have designed a three-dimensional model of the flow area of the experimental module and a CFD model to calculate temperatures, phase velocities and their concentrations, considering the peculiarities of the ongoing processes of heat and mass transfer. A slight effect on the heat flow of a 180° rotation during the flow of a liquid medium in the range of the Reynolds numbers 1800–2600 is shown. The developed model is verified with the results obtained at the experimental plant. It is established that the model reproduces experimental data well. An analysis of studies of heat and mass transfer processes during the fluid flow in channels in the presence of phase transitions is carried out. The problems of calculating the parameters of heat transfer during the movement of a fluid in a transient mode are revealed, especially at values of the Reynolds number close to 2000. The experimental plant diagram is presented. It is found that in the range of Reynolds numbers of 2600–3600, the calculated temperature values differ from the temperature values obtained experimentally by less than 0,42 %. During the partial transition of water into steam in the range of Reynolds numbers of 1800–2600, the deviations were less than 6 %, which confirms the adequacy of numerical modeling of calculating the heat transfer process in a pipe. It is shown that considering the influence of temperature on surface tension, the coefficient of thermal conductivity of water and the coefficient of dynamic viscosity of water is important to obtain accurate results. The proposed approach can be used to optimize the operating parameters of condensers and evaporators, as well as to accurately calculate the heat transfer coefficient and determine the areas of vapor formation. It will improve the energy efficiency of industrial installations and reduce the cost of equipment operation.

Direct calculation of the eddy viscosity operator in turbulent channel flow at Re τ = 180

This study aims to quantify how turbulence in a channel flow mixes momentum in the mean sense. We applied the macroscopic forcing method (Mani & Park, Phys. Rev. Fluids, 2021, 054607) to direct numerical simulation (DNS) of a turbulent channel flow at $Re_\tau =180$ using two different forcing strategies that are designed to separately assess the anisotropy and non-locality of momentum mixing. In the first strategy, the leading term of the Kramers–Moyal expansion of the eddy viscosity is quantified, revealing all 81 tensorial coefficients that essentially characterise the local-limit eddy viscosity. The results indicate the following: (1) the eddy viscosity has significant anisotropy, (2) Reynolds stresses are generated by both the mean strain rate and mean rotation rate tensors associated with the momentum field and (3) the local-limit eddy viscosity generates asymmetric Reynolds stress tensors. In the second strategy, the eddy viscosity is quantified as an integration kernel revealing the non-local influence of the mean momentum gradient at each wall-normal coordinate on all nine components of the Reynolds stresses over the channel width. Our results indicate that while the shear component of the Reynolds stress is reasonably reproduced by the local mean gradients, other components of the Reynolds stress are highly non-local. These results provide an understanding of anisotropy and non-locality requirements for closure modelling of momentum transport in attached wall-bounded turbulent flows.

Experimental Study for Wave Overtopping Volume Estimation of Rubble-Mound Structure Using Pressure-Current Speed Relationship

In this study, a new method for wave overtopping measurement was proposed. The proposed method utilize the pressure-current speed relationship and the wave overtopping height. The relationship between pressure and current speed was studied using a flow channel, and the validity of the method for measuring wave overtopping was examined using a two-dimensional wave flume. After installing a pressure gauge in the current channel, the change in pressure according to the increase in current speed was measured, and the relationship between pressure and current speed was derived. The proposed method showed high accuracy when the incident angle was normal condition, and it was confirmed that the accuracy decreased somewhat as the incident angle increased. The reason that the accuracy is somewhat lower under oblique incidence conditions is because the sensitivity to pressure and current speed is high. In addition, when the amount of wave overtopping was large, the relative error increased, but the correlation coefficient between the measured and the estimated overtopping volume was relatively high. It was confirmed that the proposed method was possible as a method for wave overtopping measurement in the field.

Design of Shape Forming Elements for Architected Composites via Bayesian Optimization and Genetic Algorithms: A Concept Evaluation.

This article presents the first use of shape forming elements (SFEs) to produce architected composites from multiple materials in an extrusion process. Each SFE contains a matrix of flow channels connecting input and output ports, where materials are routed between corresponding ports. The mathematical operations of rotation and shifting are described, and design automation is explored using Bayesian optimization and genetic algorithms to select fifty or more parameters for minimizing two objective functions. The first objective aims to match a target cross-section by minimizing the pixel-by-pixel error, which is weighted with the structural similarity index (SSIM). The second objective seeks to maximize information content by minimizing the SSIM relative to a white image. Satisfactory designs are achieved with better objective function values observed in rectangular rather than square flow channels. Validation extrusion of modeling clay demonstrates that while SFEs impose complex material transformations, they do not achieve the material distributions predicted by the digital model. Using the SSIM for results comparison, initial stages yielded SSIM values near 0.8 between design and simulation, indicating a good initial match. However, the control of material processing tended to decline with successive SFE processing with the SSIM of the extruded output dropping to 0.023 relative to the design intent. Flow simulations more closely replicated the observed structures with SSIM values around 0.4 but also failed to predict the intended cross-sections. The evaluation highlights the need for advanced modeling techniques to enhance the predictive accuracy and functionality of SFEs for biomedical, energy storage, and structural applications.

CFD Modeling of Film Condensation from a Steam-Air Mixture in Vertical Channels

Steam condensation in the presence of a noncondensable gas is of vital importance for passive cooling containment systems. The noncondensable gas causes a significant reduction in the condensation rate and heat transfer across the containment, which is important for postulated loss-of-coolant accidents in a nuclear reactor. In this work, computational fluid dynamics models of condensation and the adjacent single-phase steam-air mixture flow are developed for laminar and turbulent flow in vertical channels by two distinct wall condensation modeling approaches using the commercial code STAR-CCM+. The first is the fluid film model available in STAR-CCM+, which solves liquid layer governing equations with connections to the adjacent gas mixture flow. The second is a user-defined wall condensation model that neglects the fluid film and instead accounts for mass, momentum, and heat transfer via user-defined volumetric sink terms adjacent to the cold wall. The condensation models are assessed by first comparing the calculated results with the numerical solution of laminar flow, solved using a complete two-phase model that solves parabolic equations based on conservation of mass, momentum, energy, and species for each phase. Next, the results of a two-dimensional analysis are compared with COPAIN experiments and existing numerical solutions from three-dimensional analyses. The comparisons include new, detailed results that have not been reported in previous analyses of a COPAIN case. These new results include local field profiles of velocity, temperature, and air mass fraction, and local mass flux.

Orientation of inertialess spheroidal particles in turbulent channel flow with spanwise rotation

The orientation dynamics of inertialess prolate and oblate spheroidal particles in a directly simulated spanwise-rotating turbulent channel flow has been investigated by means of an Eulerian–Lagrangian point-particle approach. The channel rotation and the particle shape were parameterized using a rotation number Ro and the aspect ratio λ, respectively. Eleven particle shapes 0.05 ≤ λ ≤ 20 and four rotation rates 0 ≤ Ro ≤ 10 have been examined. The spheroidal particles retained their almost isotropic orientation in the core region of the channel, despite the significant mean shear rate set up by the Coriolis force. Irrespective of channel rotation rate Ro, rod-like spheroids tend to align in the streamwise direction, while disk-like particles are oriented in the wall-normal direction. These trends were accentuated with increasing departure from sphericity λ = 1. The changeover from the isotropic orientation mode in the centre to the highly anisotropic near-wall orientation mode commenced further away from the suction-side wall with increasing Ro, whereas the particle orientations on the pressure side of the rotating channel remained essentially unaffected by Ro. We observed that the alignments of the fluid rotation vector with the Lagrangian stretching direction were similarly unaffected by the imposed system rotation, except that the de-alignment set in deeper into the core at high Ro. This contrasts with the well-known substantial impact of system rotation on the velocity and vorticity fields. Similarly, slender rods and flatter disks were aligned with the Lagrangian stretching and compression directions, respectively, for all Ro considered, except in the vicinity of the walls. The typical near-wall de-alignment extended considerably further away from the suction-side wall at high Ro. We conjecture that this phenomenon reflects a change in the relative importance of mean shear and small-scale turbulence caused by the Coriolis force. Preferential particle alignment with Lagrangian stretching and compression directions are known from isotropic and anisotropic turbulence in inertial reference systems. The present results demonstrate the validity of this principle also in a non-inertial system.

Thermal management of lithium-ion batteries based on the coupling of liquid cooling and composite phase change materials

ABSTRACT Effective thermal management techniques for lithium-ion batteries are crucial to ensure their optimal efficiency. This paper proposes a thermal management system that combines liquid cooling with composite phase change materials (PCM) to enhance the cooling performance of these lithium-ion batteries. A numerical study was conducted to examine the impact of various factors on the battery module’s thermal management performance, including the number of flow channels, the distance between these flow channels and the upper and front surfaces, fluid flow rate, coolant inlet temperature, and material’s phase change temperature. The simulation results indicate that at a discharge rate of 6C and a flow channel count of 5, the maximum temperature and the maximum temperature difference of the battery module decrease by 6.44% and 34.35%, respectively, when PCM is coupled with liquid cooling, compared to the pure liquid cooling. However, as the flow rate increases, the rate of temperature reduction slows down, while the pressure drop increases. When the flow rate reaches 0.4 m/s, the maximum temperature only drops by 0.57°C while the pressure drop increases by nearly two times. Furthermore, an increase in the PCM’s melting temperature leads to a larger maximum temperature difference in the battery module. This effect is more pronounced with higher coolant inlet temperatures. Therefore, careful consideration of both flow rate and coolant inlet temperature is essential for designing an effective thermal management system for batteries.

Hydrodynamic Structure of Secondary Polymer Melt Flows in Channels with Changing Geometry

Hydrodynamic Structure of Secondary Polymer Melt Flows in Channels with Changing Geometry

Evaluation of Flow Resistance Increase Due to Fouling in Cooling Channels: A Case Study for Rapid Injection Molding

Abstract After certain time of operation, the cross-section of cooling channels in injection molds may decrease due to fouling, i.e. the formation and growth of a layer of sediment on the walls of the channels. This phenomenon can decrease heat transfer or ultimately completely block the flow of coolant in the channel. The build-up of the sediment layer increases the temperature of the mold, which may consequently reduce the quality of the plastic products. In the paper, the pressure drop in a typical cooling channel of an injection mold is investigated, as well as the effect of the sediment layer on the coolant flow in an example channel with a diameter of 10 mm. A novelty is the developed analytical model that allows determining the pressure drop in the case when two perpendicular channels do not intersect centrally due to manufacturing inaccuracies that often happen when drilling long channels in hard materials. The proposed hydraulic model allows for calculation of the coolant pressure drop in real injection molds and can be an alternative to time-consuming CFD simulations. The presented results of measurements and the hydraulic model calculations show that the thickness of the sediment layer in the tested channel of the actual injection mold can be up to 1.7 mm. The hydraulic model proposed in this work allows for the estimation of the thickness of the sediment layer and the identification of places of local increase in the coolant velocity, where self-cleaning of the channels in injection molds may take place.

The comprehensive analysis of magnetohydrodynamic Casson fluid flow with rectangular porous medium through expanding/contracting channel

PurposeThis study examines fluid flow within a rectangular porous medium bounded by walls capable of expansion or contraction. It focuses on a non-Newtonian fluid with Casson characteristics, incompressibility, and electrical conductivity, demonstrating temperature-dependent impacts on viscosity.Design/methodology/approachThe flow is two-dimensional, unsteady, and laminar, influenced by a small electromagnetic force and electrical conductivity. The Hybrid Analytical and Numerical Method (HAN method) resolves the constitutive differential equations.FindingsThe fluid’s velocity is influenced by the Casson parameter, viscosity variation parameter, and resistive force, while the fluid’s temperature is affected by the radiation parameter, Prandtl number, and power-law index. Increasing the Casson parameter from 0.1 to 50 results in a 4.699% increase in maximum fluid velocity and a 0.123% increase in average velocity. Viscosity variation from 0 to 15 decreases average velocity by 1.42%. Wall expansion (a from −4 to 4) increases maximum velocity by 19.07% and average velocity by 1.09%. The average fluid temperature increases by 100.92% with wall expansion and decreases by 51.47% with a Prandtl number change from 0 to 7.Originality/valueUnderstanding fluid dynamics in various environments is crucial for engineering and natural systems. This research emphasizes the critical role of wall movements in fluid dynamics and offers valuable insights for designing systems requiring fluid flow and heat transfer. The study presents new findings on heat transfer and fluid flow in a rectangular channel with two parallel, porous walls capable of expansion and contraction, which have not been previously reported.

Vertical Carbon Export During a Phytoplankton Bloom in the Chukchi Sea: Physical Setting and Frontal Subduction

AbstractIn order to quantify pelagic‐benthic coupling on high‐latitude shelves, it is imperative to identify the different physical mechanisms by which phytoplankton are exported to the sediments. In June–July 2023, a field program documented the evolution of an under‐ice phytoplankton bloom on the northeast Chukchi shelf. Here, we use in situ data from the cruise, a simple numerical model, historical water column data, and ocean reanalysis fields to characterize the physical setting and describe the dynamically driven vertical export of chlorophyll associated with the bloom. A water mass front separating cold, high‐nutrient winter water in the north and warmer summer waters to the south—roughly coincident with the ice edge—supported a baroclinic jet which is part of the Central Channel flow branch that veers eastward toward Barrow Canyon. A plume of high chlorophyll fluorescence extending from the near‐surface bloom in the winter water downwards along the front was measured throughout the cruise. Using a passive tracer to represent phytoplankton in the model, it was demonstrated that the plume is the result of subduction due to baroclinic instability of the frontal jet. This process, in concert with the gravitational sinking, pumps the chlorophyll downwards an order of magnitude faster than gravitational sinking alone. Particle tracking using the ocean reanalysis fields reveals that a substantial portion of the chlorophyll away from the front is advected off of the northeast Chukchi shelf before reaching the bottom. This highlights the importance of the frontal subduction process for delivering carbon to the sea floor.

Effects of droplet dynamical behavior in flow channel of proton exchange membrane fuel cell under vibration conditions on cell performance

Proton exchange membrane fuel cells are subjected to severe vibration in aerospace applications. Understanding the droplet transport characteristics in the flow channelunder vibration conditions is essential for improving cell performance. However, the underlying patterns and mechanisms of the vibration effects on cell performance and its internal water transport remain unclear, and there is a lack of improvement methods for drainage under vibration conditions. This study experimentally investigates the effect of vibration on cell performance. Experimental results indicate that vibration predominantly affects cell performance through its modulation of water transport. Therefore, the droplet dynamic behavior in the flow channel is further studied using the volume of fluid method. The results indicate that vibrations can enhance the average performance of the fuel cells, with the largest increase of 8.30 %. This is attributed to vibrations promoting the detachment of droplets from the gas diffusion layer surface and reducing the water coverage ratio on said surface. Under conditions of low gas velocity, high surface hydrophobicity, and large droplet size, droplets exhibited oscillatory and jumping behavior in the flow channel due to vibration, resulting in the largest 53.5 % increase in peak water coverage ratio on the gas diffusion layer surface compared to no-vibration conditions. Furthermore, enhancing the hydrophobicity of the gas diffusion layer and the hydrophilicity of the channel walls promotes droplet detachment and discharge compared to no-vibration, as well as contributing to the improvement of vibration effects on the drainage process.

Novel Fluidic Oscillator Evaluation Considering Dimensional Modifications

Although flow mixing and cooling can be greatly enhanced when considering the use of fluidic oscillators (FOs), they are more commonly employed in active flow control (AFC) applications where the injected pulsating flow interacts with the boundary layer, usually in order to delay its separation. In fact, prior to any FO implementation in a given application, it is essential to study the range of frequencies and amplitudes it can generate as a function of the incoming mass flow and its dimensions. This is what is being performed in the present manuscript for a rather novel FO configuration. A numerical study of a standard three-dimensional (3D) FO configuration, and also using a two-dimensional (2D) approach, is initially presented. After comparing the 3D and the 2D results and analyzing the main differences, we modified some of the internal dimensions of the FO in order to evaluate the variation in its dynamic performance. The present results clarify which internal dimensional modifications are more effective in generating larger output frequencies and velocity field variations. Care is taken to analyze the origin of self-sustained oscillations. This paper links, for the first time, the origin of the pressure force oscillations at the feedback channel’s outlet, with the interaction of the mixing chamber central jet and the reverse feedback channel flow at the mixing chamber’s converging walls. A novel equation relating the FO outlet mass flow frequency with the time-averaged FC reverse flow is presented and discussed. In fact, the present study needs to be seen as the continuation of a former one, recently published by authors, where the effects of several Reynolds numbers as well as some different internal dimensions were considered.