Counter Flows Research Articles

Novel approach to cooling microelectronics with complex fins configuration

This paper presents a numerical simulation and optimisation of a complex microchannel featuring innovative fin designs. The primary objective of the study is to minimise resistance in the heat sink by utilizing intricate fin structures. Three different approaches are explored: firstly, cylindrical solid fins are designed and placed on the heat sink; secondly, the solid fins are drilled halfway (50 %); and in the third scenario, the solid fins are drilled 87.5 % and mounted on the heat sink. In the simulation set-up, the heat sink has a heat load of 250 W imposed on the bottom wall and single-phase water of Reynolds number between 400 and 500 flows in a forced convection laminar condition to remove the heat at the bottom and internally within the fins walls surface area, while an air stream of Reynolds number between 3 and 6 flows convectively across the cylindrical fins to dissipate excess heat externally. The finite volume method and computational fluid dynamic code, are employed to discretise the geometry with heat and fluid fields solved. The optimisation is performed for parallel and counter flows and the outcomes compete favorably. Similarly, the influence of the Reynolds number on minimised temperature and resistance results is discussed. The results show that in parallel flow the integrated heat sink with half hollow fins is best with a minimised resistance of 27.2 %, while in the counter flow the hollow fins are superior with a declined resistance of 19 %. The study is validated with experimental results in open literature.

Instability of steady states with inhomogeneous field in electron–positron plasma diode

Instability features of steady states of the plasma diode with electron and positron counter flows are studied. There are several types of such states for each value of the inter-electrode distance. The case when charged particles moving in the diode plasma are not reflected from potential extrema is considered. We have solved an equation for the amplitude of the electric field perturbation for steady states with an inhomogeneous field distribution. Studying the dispersion equation has shown that all considered solutions are unstable. We have also confirmed this result when simulating small perturbation evolution of a steady-state solution.

The influence of low-permeability geological inclusions on the seepage behavior of ionic rare earth leaching mining: A study using visual microfluidic technology

Ionic rare earth deposits often contain semi-weathered or slightly weathered low-permeability geological inclusions (LPGI), which significantly impact the permeation process and leaching efficiency of in-situ liquid leaching mining. To investigate the influence of LPGI with varying developmental degrees on the seepage process of ionic rare earth leaching mining, we developed six microfluidic chip models using Polydimethylsiloxane (PDMS). A visual experiment was conducted, employing water to drive gas at a rate of 0.5 μl/min, enabling observation of the seepage and displacement process. Using MATLAB image processing technology in conjunction with time-history diagrams, we analyzed the evolution patterns of the infiltration front position and saturation over time. Our findings revealed distinct capillary fingering and side wall flow phenomena during the process of liquid phase displacing gas phase infiltration, accompanied by horizontal and counter flows perpendicular to the solution's direction of advancement. Notably, when the solution traversed the LPGI, we observed significant flow-around phenomena and low saturation of the LPGI. These inclusions hindered solution infiltration, with wider LPGI resulting in greater inhibition. Additionally, the LPGI acted as a protective barrier, preventing solution intrusion into the underlying ore body. However, due to the air discharge is not timely, it was sealed by the outlet solution, forming a substantial leaching blind area near the outlet. This study unveils the seepage laws of ionic rare earth earth leaching mining involving LPGI of various developmental degrees, signifying its vital engineering significance in the efficient extraction of ionic rare earth.

Numerical simulation of hydrodynamics in wet cooling tower packings

Wet cooling towers are used in many industrial processes but hydrodynamic behaviour of air-water counter flows in towers packing remains unknown. Hydrodynamics is directly linked with main operating issues (e.g. packing fouling reducing cooling efficiency). The objective of this work is to use Computational Fluid Dynamics (CFD) simulations to characterize local hydrodynamic parameters such as water film thickness, velocity or wall shear stress and system scale parameters such as wetting rate or interfacial area. After a theoretical study of fluid mechanics, Volume of Fluid (VOF) simulations, with dedicated models for air/water interface capture and solid/liquid contact angle, successfully reproduced water falling films on packing surface. Simulations allowed the calculation of main water flow local and system parameters. The results have pointed out trends of increasing liquid film thicknesses and wetting rates with increasing water flowrate in agreement with experimental observations. A correlation of the interfacial area has been proposed as a function of the hydrodynamic adimensional numbers to characterize transfer phenomena in the considered packing.

A New Model to Calculate Contributions of the Distributed Power

Besides metering, a more transparent load with known power distribution is valuable to draft energy strategies, especially in a deregulated power market. Thus, the usage-of-transmission can be considered properly. There are many studies published on related subjects and every research tried to solve a particular part of the problem. There are three basic categories for discussing power distributions: (i) the real power distribution, (ii) the reactive power distribution, and (iii) the loss allocation. These categories were very often treated separately, with the mutual coupling terms, counter flows, and line charging largely neglected. However, we know that these entities are non-separable. These are inter-related entities; the change of one entity will cause the change to every other entity. A good method should consider these entities altogether, while satisfying all electrical theories. This study developed a method to solve the above problem, with all electrical entities solved, satisfying all electrical circuit theories. With several matrix formulations, this method is capable of solving and tracing all electrical entities, including the current flow, the real and reactive power, the counter flow, and the couplings between the active and reactive power. The algorithm can also allocate power distributions and loss among participants effectively. Besides, a line usage idea is formed to allocate the loss to each generator, where counter flows are not necessarily penalized. It can be awarded sometimes. The idea can integrate with the existent tariffs in a deregulated market.

Investigating the experimental parameters of a rib triple pipe heat exchanger

In the current research, the triple concentric-pipe heat exchanger is experimentally inspected with regard to the double concentric-pipe heat exchanger. To optimize the design, the thermo-fluid of the heat exchangers has been clarified with respect to several design parameters for a counter and parallel flows. One procedure is to full the inner pipe with chilled water and the inner annulus pipe with hot water, while the outer annulus pipe, the tap water was used. The temperatures of the supplied water measured by thermocouples linked to the computer through a data acquisition unit. The flow rates of the system's water were evaluated by 3 flow-meters while the water's drop pressure were measured using a pre-calibrated digital pulse pressure transmitter. The performed flow patterns were the co-current, counter-current, co-current with counter-current flow and counter-current with co-current. The efficiency, friction factor and Nusselt number have been investigated and compared for both types of exchangers. The results showed that the triple concentric-pipe heat exchanger exhibited high heat exchanging efficiency and lower energy consumption than the double concentric-pipe heat exchanger. By the same token, better efficiency ε (around 50% greater) obtained for both counter and parallel flows. The results also revealed that with various flow arrangements, Nu, and the ε, for the triple concentric-pipe heat exchanger are greater than that for the Double concentric-pipe heat exchanger.

Electrically driven free shear flows in a duct under a transverse uniform magnetic field

A mathematical model of two-dimensional electrically driven laminar plane free shear flows in a straight duct under the action of an applied spanwise uniform magnetic field is considered. The mathematical approach is like that used in the research of Hunt and Williams (J. Fluid. Mech., 31, 705, 1968) and Kolesnikov and Kalis (Magnetohydrodynamics, vol. 57, 2021, no. 2). A system of stationary partial differential equations with two unknown functions of velocity and induced magnetic field is solved. The electric current is injected into the liquid by means of two couples of linear electrodes located vis-à-vis on opposite duct walls, perpendicular to the magnetic field. Three cases are considered. One pair of electrodes is current supplied and, depending on the direction of electric current injection on the electrode pair, two coinciding or two counter flows are also driven. At Hartmann numbers Ha >> 1, quasi-potential cores are formed in these flows, bounded by lateral Shercliff free boundary layers parallel to the field and two Hartmann layers on the walls perpendicular to the field. As a result, almost all of the injected current passes through these layers. An increase of the magnetic field leads only to an internal rearrangement of the potential cores of the flows. The Hartmann number varies in the range from 1 to 100. Figs 15, Refs 11.

Flows and Counterflows of Buddhism ‘South of the West’: Australia, New Zealand and Hawai‘i

Introduction to the JGB Special Focus section, "Flows and Counterflows of Buddhism ‘South of the West’: Australia, New Zealand, and Hawaiʻi." In this special issue, we endeavour to explore horizontal flows and counter flows of Buddhism on ‘paths less travelled’ across the Pacific sea of islands, and ‘South of the West’ (Gibson 1992) rather than the usual ‘from Asia to Europe and the Americas’ story. As such, this special issue fits within the more recent scholarship on the globalisation of Buddhism that seeks to point to a more complex picture of historical and contemporary flows of Buddhist ideas, practices, objects and peoples across the globe.

Mathematical bases of calculation of gas-dispersed flows in vortex dust collectors

Development of numerical methods for calculating the movement of gas-dispersed flows in vortex and inertial separators, creation of devices with counter tangential and flows of increased dust collection efficiency, determination of the optimal profile of corrugated channels in order to minimize the release of droplet moisture from inertial separators.

Steady states stability features of the electron–positron plasma diode

Stationary states stability features of a planar geometry diode with electron and positron counter flows are studied. Such a diode may be considered as a model to elucidate the nature of the pulsar radio emission. The equation for the electric field perturbation amplitude is derived. The exact solution of this equation for the homogeneous stationary field is found. On the basis of the plasma dispersion relation, the stability threshold in terms of the electron current density is found above which the stationary solutions become unstable. This threshold turned out to be 2 times higher than the known Pierce threshold. It can be expected that the development of the detected instability will lead to the electric field oscillations that induce electromagnetic radiation.

Self-organisation phenomena in pedestrian counter flows and its modelling

We implement avoidance and following behaviour in a force-based model (AFFM) to develop realistic simulations of pedestrian counter flows. Using this innovative approach, we summarise an accelerate-then-decelerate lateral movement mode for pedestrians that minimised their required effort to avoid collisions with oncoming pedestrians travelling in the opposite direction. Then, we use the transfer entropy (TE) method to determine the spontaneous following behaviour of pedestrians to align their motion with a leading pedestrian moving towards the same destination. We also introduce a new parameter, lane entropy, to measure the motion smoothness of pedestrians and explain the quantitative characteristics of the lane formation phenomenon. The performance of the proposed model is compared with that of two other force-based models in terms of their ability to replicate the experimentally observed pedestrian flow patterns in a mock corridor, as designed by Feliciani and Nishinari in 2016. The results show that the AFFM performs well at reproducing microscopic behaviours observed in the experiments while consistently presenting the empirically observed lane formation phenomenon with quantitatively self-organised features (e.g., the order parameter and lane entropy). The proposed model is an efficient tool for future applications that can realistically model pedestrian counter flows under varying conditions.

Electrically driven cylindrical free shear flows under an axial uniform magnetic field

We consider a mathematical model of two-dimensional electrically driven laminar axisymmetric circular free shear flows in a cylindrical vessel under the action of an applied axial uniform magnetic field. The mathematical approach is based on the studies by J.C.R. Hunt and W.E. Williams (J. Fluid. Mech., 31, 705, 1968). We solve a system of stationary partial differential equations with two unknown functions of velocity and induced magnetic field. The flows are generated as a result of the interaction of the electric current injected into the liquid and the applied field using one or two pairs of concentric annular electrodes located apart on the end walls. Two lateral free shear layers and two Hartmann layers on the end walls and a quasi-potential flow core between them emerge when the Hartmann number Ha >> 1. As a result, almost all injected current passes through these layers. Depending on the direction of the current injection, coinciding or two counter flows between the end walls are realized. The Hartmann number varies in a range from 2 to 300. When a moderate magnetic field (Ha = 50) is reached, the flow rate and the induced magnetic field flux cease to depend on the magnitude of the applied field but depend on the injected electric current value. Increasing magnetic field leads only to inner restructuring of the flows. Redistributions of velocities and induced magnetic fields, electric current density versus Hartmann number are analyzed. Figs 18, Refs 21.

Manipulating Microvolumes of Fluids By Redox-Magnetohydrodynamics for Applications in Chemical Analysis

Magnetohydrodynamics (MHD) is a unique approach for pumping fluids on a microscale and is highly suitable for enabling multiple functions for chemical analysis on a chip. An ionic current, j, is established in the fluid between selectively-activated electrodes in the presence of a magnetic field, B, that is perpendicular to the current, to generate a force, FB , orthogonal to j and B, through the right hand rule. FB is a body force that propels the liquid in the same direction through momentum transfer. We use microelectrodes, which are patterned into different, individually-addressable geometries on chips. Those electrodes are modified with poly(3,4-ethylenedioxythiophene), PEDOT, a conducting polymer, that converts the applied electronic current in the external circuit to ionic current in the liquid [1] via redox (R) processes and charging. A small NdFeB permanent magnet is placed under the chip to provide B. By strategic activation of the electrodes, fluid flow can be programmed. For example, we previously demonstrated that R-MHD can start, stop, reverse, adjust speed, and alter profiles of the fluid flow. We have also shown recently that R-MHD fluid flow can be diverted in a contactless way by magnetic field gradients when paramagnetic species are present [2]. In our presentation, we will discuss recent studies on using R-MHD to control the paths of individual microvolumes of fluids for different applications, which include chemical separations of mixtures of small biologically-relevant molecules as well as fluorescence imaging [3] and identification of cyanobacteria responsible for algal blooms in fresh water samples. Fluid manipulation and flow profiles under different experimental conditions and solvent and solution compositions will be described. These involve sustained and redirection of flow, adjacent counter flows, transverse paths, sampling, and injection. Acknowledgements: We are grateful for financial support from the National Science Foundation (CMI-1808286) and Arkansas Bioscience Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

Model of the Dynamics of Disperse Fractions in Counter Flows of a Metal Powder and Polymer in the Formation of a Composite Material

Model of the Dynamics of Disperse Fractions in Counter Flows of a Metal Powder and Polymer in the Formation of a Composite Material

The Role of Migration in the Formation of Regional Labour Markets Amidst the Second Wave of Depopulation in Modern Russia

The article reflects the results of a study of the impact of migration on regional labour markets amidst a decline in the working-age population in Russia. After substantiating the relevance of the issues under consideration, the authors propose a methodological analysis toolkit, the author’s own methodology for calculating the coefficients of permanent long-term external and internal labour migration in regional labour markets, and the coefficient of total migration burden. In addition, the authors provide an overview of the information and statistical base of the study. According to current migration records, data of Rosstat sample surveys on Russian labour migrants leaving for employment in other regions, regional labour resources balance sheets based on the calculated coefficients of labour market pressures, the authors analyzed the impact of migration on the Russian regional labour markets over the past decade. It revealed an increasing role of internal labour migration in many regions, primarily in the largest economic agglomerations and oil and gas territories. At the same time, the role of external labour migration remains stable and minimum indicators of the contribution of permanent migration to the formation of regional labour markets continue to decrease. It has been established that irrational counter flows of external and internal labour migration have developed, which indicates not only an imbalance in labour demand and supply but also a discrepancy between the qualitative composition of migrants and the needs of the economy. It is concluded that the state does not effectively regulate certain types of migration, considering its impact on the labour market. The authors justified the need for conducting regular household sample surveys according to specific programs to collect information about labour migrants and the conditions for using their labour. In addition to the current migration records, using interregional analysis, this information allows making more informed decisions at the federal and regional levels to correct the negative situation that has developed in the regional labour markets even before the coronavirus pandemic had struck.

Ion exchange properties of natural titanium silicate caryochroite (Na,Sr)3{(Fe,Mg)2+10(OH)6[TiO(Si6O17)(OH)0.5]2}·8H2O with a 1D system of parallel wide channels: Experimental study and theoretical analysis of the topochemical mechanisms

Ion-exchange properties of natural caryochroite (Na,Sr) 3 {(Fe,Mg) 2+ 10 (OH) 6 [TiO(Si 6 O 17 )(OH) 0.5 ] 2 }·8H 2 O, a microporous heterophyllosilicate with a one-dimensional system of broad zeolytic channels, related to nafertisite Na 3 {Fe 2+ 10 (OH) 6 [TiO(Si 6 O 17 )F 0.5 ] 2 }·2H 2 O, were studied in reactions with 1 N aqueous solutions of Rb, Cs, Ag, and Pb nitrates at 50 °C. In reactions with Rb + , Cs + , and Pb 2+ , sodium is partly replaced by nearly equivalent amounts of larger cations. In reactions with Pb 2+ and Ag + , additional processes involving H 2 O molecules take place: replacement of two H 2 O molecules with Pb 2+ + 2OH − and replacement of H 2 O molecule with Ag + + OH − , respectively. The geometrical-topological analysis of ion migration pathways in the nafertisite-type structures carried out using an approach based on the Voronoi-Dirichlet partition has shown that only Na + cations occurring at the centers of wide channels can take part in reactions with large alkaline cations proceeding in counter flows. In the reaction with Ag + , additional Na + ions are involved. Li + cations having a smaller radius can pass through the window between the channels, forming a 2D conducting layer. • Ion-exchange properties of natural titanosilicate caryochroite, a microporous heterophyllosilicate with a one-dimensional system of broad zeolytic channels, were studied in reactions with 1 N aqueous solutions of Rb, Cs, Ag, and Pb nitrates at 50 °C. • Three kinds of Na + cations in the caryochroite structure play different role in ion migration processes. • Li + cations having a smaller radius can pass through the window between the channels, forming a 2D conducting layer.

Separation of pedestrian counter flows with an array of obstacles

In the present paper, we investigate pedestrian counter flows in a straight corridor by means of a molecular dynamics approach with the social force model. We demonstrate that the flow rate of two groups of people walking in the opposite directions is improved by means of an array of geometrically asymmetric obstacles, as a result of flow separations. That is, the obstacles separate groups of pedestrians walking in the opposite directions so that they spontaneously keep to their right or left. In addition, we show that even geometrically symmetric obstacles possess the same ability to induce the self-organization of pedestrian flow if the interaction force between the people and the obstacles is asymmetric. The appropriately designed geometry or interaction force is fully capable of controlling the filtering direction. The present results potentially provide a guideline for industrial design to improve daily human mobility.

Performance of counter flow membrane-based annular pipe liquid desiccant air conditioner

The present study comprises an experimental and numerical simulation of a counter flow membrane-based annular pipe liquid desiccant air conditioner (AP_LDAC) system. The experimental rig was constructed by using DuPont™ Tyvek® Solid as semi-permeable membrane and it has simplier structure compared to other types of membrane-based dehumidifiers. To validate the numerical data, experiments were carried out at different air side Reynolds (Re) number. The 3D numerical simulation of counter flows of the AP_LDAC system presented good agreement (R-square: 0.9659) with experimental data, as a result of the validation. Once the reliability of numerical data were verified, the mass transfer coefficient of counterflow obtained by designed system was revealed and optimized numerically by investigating for various aspect ratios, Reynolds (Re) and Schmidt (Sc) numbers. The derived Sh model was predicted over COMSOL Sh numbers with error interval from 0.1% to 10%. The effect of air inlet temperatures on temperature, concentration distributions and efficiency of the optimized AP_LDAC system were also investigated. The dehumidification efficiency was found as 99% for the maximum aspect ratio and the lowest Re number.

Simulation of pedestrian counter flow with conflicting preference using a lattice-based simulation model

Pedestrian counter flows widely exist in public pedestrian facilities such as corridors, sidewalks, signalized crossings and so on. There is one specific flow in real life, namely counter flow with conflicting walking preference which often occurs in the case of presence of one-sidedly asymmetry due to shadows, light, snow and so on. It is often overlooked in practice and the related studies are still limited. In this study, to better understand the flow dynamics of pedestrian flow with various walking preference, a simple lattice-based model was proposed in which position exchange and walking preference were simultaneously considered. Specifically, simulations including pedestrian counter flow with preference (Case A), with conflicting preference (Case B), and without preference (Basic case) were performed. Results show that the presented model can capture some essential features of pedestrian counter flow with various walking preference. It is not always necessary to intervene the behavior of pedestrians ’ conflicting preference, since appropriate degree of preference is sometimes beneficial to movement of pedestrians. In addition, with the significant influence of position exchange, the flow in Case A with more orderly motion is more efficient in the context of low density, while the flow in Case B with more frequent interactions is more efficient in the case of high density. The findings in this study will be helpful in crowd management as well as the design and operation of pedestrian facilities.

Manipulating Microvolumes of Fluids in Different Paths By Magnetohydrodynamics

Magnetohydrodynamics (MHD) is a unique approach for pumping fluids on a microscale and is highly suitable for enabling multiple functions for chemical analysis on a chip. An ionic current, j, is established in the fluid between selectively-activated electrodes in the presence of a magnetic field, B, that is perpendicular to the current, to generate a force, FB , orthogonal to j and B, through the right hand rule. FB is a body force that propels the liquid in the same direction through momentum transfer. We use microelectrodes, which are patterned into different, individually-addressable geometries on chips. Those electrodes are modified with poly(3,4-ethylenedioxythiophene), PEDOT, a conducting polymer, that converts the applied electronic current in the external circuit to ionic current in the fluid [1]. A small NdFeB permanent magnet is placed under the chip to provide B. By strategic activation of the electrodes, fluid flow can be programmable. For example, we previously demonstrated that MHD can start, stop, reverse, adjust speed, and alter profiles of the fluid flow. We have also shown recently that MHD fluid flow can be diverted in a contactless way by magnetic field gradients when paramagnetic species are present [2]. In our presentation, we will discuss how MHD can control the paths of individual microvolumes of different fluids for mixing, sampling, and injection. We will describe the conditions that lead to and the resulting flow profiles that result from adjacent counter flows, transverse paths, and different solvent compositions. Acknowledgements: We are grateful for financial support from the National Science Foundation (CMI-1808286) and Arkansas Bioscience Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.