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[Display omitted] • The formation and morphological transformation processes of droplets in dripping regime were systematically studied. • Droplets rapidly deformed from nearly-spherical shape to ellipsoidal shape after detaching from nozzles. • The correlations of droplet characteristic parameters were established using dimensional analysis. Achieving the counter-current flow in mini-channel extractor is a challenge. The formation and characteristic parameters of droplets in mini-channel counter-current extractor were systematically investigated to provide a guide for the realization and operation of counter-current extraction. A mixture of P507 diluted with sulfonated kerosene was served as dispersed phase, while 0.2 mol/L LaCl 3 solution was used as continuous phase. Droplets rapidly deformed from the nearly-spherical shape to ellipsoidal shape after detaching from nozzles, eventually floated upwards as monodisperse droplets with same spacing. Sauter mean diameter of droplets decreased with the increase of superficial velocity of organic phase, yet increased with the increase of superficial velocity of aqueous phase. The specific interfacial area of droplets increased with the increasing superficial velocity of organic phase, and slightly decreased with the increasing superficial velocity of aqueous phase. The correlations of droplet characteristic parameters were established using dimensional analysis for further prediction and analysis. [ABSTRACT FROM AUTHOR]

There are several approaches for the calculation of capillary pressure curves in porous media including the centrifuge method. In this work, a new installation of centrifuge test is introduced and compared with the traditional setup. In the first setup, which is a standard approach in labs, the core face closest to the rotational axis is open to the non-wetting phase, while the farthest face is open to the wetting phase where strictly co-current flow is generated in rotations; labeled Two-Ends-Open (TEO). In the second setup, which is proposed as a new approach, only the outer radius surface is open and is exposed to the light non-wetting phase; labeled One-End-Open (OEO). This setup strictly induces counter-current flow. The two systems and their corresponding boundary conditions are formulated mathematically and solved by a fully implicit numerical solver. The TEO setup is validated by comparison with commercial software. Experimental data from the literature are used to parameterize the models. It is mathematically, and with examples, demonstrated that the same equilibrium is obtained in both systems with the same rotational speed, and changing the installation does not influence the measured capillary pressure. This equilibrium state is only dependent on the rotational speed, rock capillary pressure properties, and fluid densities, not the installation geometry, relative permeabilities, or fluid viscosities. However, the dynamic transition trend and saturation profiles were found to be dependent on the applied installation. It was observed that the OEO setup takes almost identical equilibration time as the TEO setup for mixed-wet states, although it needed much longer time in water-wet states. The presence of threshold capillary pressure significantly increased the time scale of the OEO setup. Also, it was found that in contradiction to the TEO setup, the dynamic saturation profile in OEO was rarely influenced by viscosity ratio. To conclude, the performed history matching analysis demonstrated that the OEO setup can be applied for the calculation of counter-current relative permeability from the production data with reasonable accuracy.

The effects of T-shaped fins on the improvement of phase change materials (PCM) melting are numerically investigated in vertical triple-tube storage containment. The PCM is held in the middle pipe of a triple-pipe heat exchanger while the heat transfer fluid flows through the internal and external pipes. The dimension effects of the T-shaped fins on the melting process of the PCM are investigated to determine the optimum case. Results indicate that while using T-shaped fins improves the melting performance of the PCM, the improvement potential is mainly governed by the fin’s body rather than the head. Hence, the proposed T-shaped fin did not noticeably improve melting at the bottom of the PCM domain; additionally, a flat fin is added to the optimal case (Added-Fin case) and compared to the No-Fin, Uniform-Fin, and Optimum T-shaped Fin cases (no added fin). The analysis shows that the total heat storage rate of the Added-Fin case increased by 141.7%, 58.8%, and 47.6% compared with the No-Fin, Uniform-Fin, and the Optimum T-shaped Fin cases, respectively. Furthermore, the total melting time for the Added-Fin case was 1882 s and decreased by 59.6%, 38.4%, and 33.6% compared with those of the No-Fin, Uniform-Fin, and the Optimum T-shaped Fin (Optimum) cases, respectively.

[Display omitted] • Concentration of orange juice by air stripping studied in two rotating contactors. • Highest concentration achieved in a baffled rotating contactor (32.6 °Brix – 2 h). • Volumetric mass transfer coefficient varied between 7 kg/m3s and 20 kg/m3s. • Volume of the conventional evaporators can be reduced by rotating contactor. Simultaneous heat and mass transfer experiments with air–water system were performed in a baffled rotating contactor and volumetric mass transfer coefficient determined towards exploring an alternate strategy for the concentration of fruit juice. The proposed concentration technology is based on the stripping of water from fruit juice by an unsaturated gaseous stream. In the contactor, the phases flowed counter-currently between two rotating circular disks zigzagging across concentric circular baffles fitted in the inner surface of the disks. The volumetric mass transfer coefficient varied between 7 kg/m3s to 20 kg/m3s for the range of operating conditions studied. The evaporation rate of water per unit volume was higher than in falling film type evaporators used conventionally for the concentration of fruit juice. The maximum concentration of orange juice attained in the rotating contactor within two hours with continuous recirculation of the solution was 32.6 °Brix for the operating conditions studied. This was significantly higher than that obtained in a rotating packed bed contactor of similar volume (2.0 L). [ABSTRACT FROM AUTHOR]

Flow mal-distribution in the shell side of the gas-cooled conventional reactor (CR) in the mega methanol plant is responsible for producing gas condensate in the catalytic zone. This phenomenon leads to catalyst agglomeration and efficiency reduction in the reactor. In this study, two novel and viable strategies, possible to be implemented in working reactors, are introduced to prevent condensation. In the first strategy, co-current mode (CCM), the reactant flow changes from counter-current into the co-current. In this regard, the feed inlet is replaced from the bottom of the reactor into the top. In the second strategy, changed-bed mode (CBM), the catalyst particles at the last two meters of the reactor are replaced with non-reactive ceramic balls. The results for three-dimensional computational fluid dynamics (CFD) in CR have been validated against previous study and industrial data, indicating close agreement. The main advantage of CCM and CBM is that the sudden temperature drop fails to occur at the end of the reactor. Consequently, the higher temperature of the products prevents water and methanol condensation. In addition, the CCM leads to a milder temperature profile throughout the shell side, which increases catalyst durability. [ABSTRACT FROM AUTHOR]

[Display omitted] Microchemical technology shows prospect in the process intensification field of carbon capture and storage, however, there remain great challenges in microchemical technology for gas-liquid mass transfer with counter-current flow. In this work, we proposed a micro-apparatus with confined structure for gas-liquid counter-current flow mass transfer. The flow patterns on the confined structure, steady flow and bead flow, were observed, furthermore, the critical flow rate between them was measured. The influences of confined structure geometry, surface tension and viscosity of liquid on the meniscus at the gas-liquid interface were studied. The operation window of micro-apparatus with different types of confined structures was examined. The liquid loading and gas loading of micro-apparatus with S1005 were tested to be 230 μL/min and 500 mL/min, respectively. The system of absorption of pure CO 2 in a 1 M NaOH solution was used to study the mass transfer. The average liquid side mass transfer coefficient of 25.1 × 10−5 m/s was measured at liquid flow rate of 30 μL/min and gas flow rate of 300 μL/min, which proves that the micro-apparatus achieves the process intensification of CO 2 absorption. [ABSTRACT FROM AUTHOR]

• Counter-flow arrangement of Peltier modules increases system efficiency. • Optimal number of modules was calculated as a function of thermal load. • Splitting each stream into parallel channels further improves the COP. • COP of counter-flow arrangement is higher than ideal COP of cascade unit. We evaluate the thermal behavior of a thermoelectric cooler composed of Peltier modules connected in series by two air streams in counter-current flow, i.e., in the so-called horizontal stack configuration. An advantage of this configuration over cascade (pyramid-like, or vertical stack) arrangements to achieve large temperature spans is the comparatively higher coefficients of performance of the former at large values of heating load and temperature span. In the counter-flow configuration, the temperature span per Peltier module is relatively small, giving rise to much higher individual (i.e., per module) coefficients of performance. In this paper, we outline a procedure to determine the optimal number of modules in a counter-current flow unit as a function of the applied thermal load (up to approximately 200 W), considering all relevant loss mechanisms (Joule heating and heat conduction in the semiconductors and fluid friction). Pin-fin heat sinks are employed to reduce the fluid-surface temperature differences on the hot and cold sides of the thermoelectric modules. An assessment of the influence of the number of parallel channels on each stream (hot or cold) was also carried out. [ABSTRACT FROM AUTHOR]

• Systematic investigation is carried out to study the counter-current Taylor bubble shape and rise velocity. • Generating a large numerical database of Taylor bubbles in annular conduits under various flow configurations. • Proposed upscaled surrogate models describing the flow of Taylor bubbles. This study numerically investigates counter-current slug flow by considering the motion of a Taylor bubble in annular conduits with downward-flowing liquids using the Volume-of-Fluid method implemented in the commercial computational fluid dynamics software ANSYS Fluent (Release 19.2). The translational velocity of a counter-current ascending or co-current descending Taylor bubble in vertical concentric annuli and the corresponding distribution parameter (C 0) are analyzed. The latter is correlated in terms of Eötvös number (Eo) and inverse viscosity number (Nf) within the range of Eo between 40 and 400 and Nf between 40 and 320. The proposed correlation provides an accurate fit to the numerical data with an average error of 2.64%, and is successfully compared with published numerical findings. In general, the smooth and stable shape of the bubble is disrupted as the counter-current flow velocity (Fr l) increases above a critical value, leading to the formation of surface waves and the displacement of the bubble tip away from the annular gap center and towards the outer pipe. C 0 increases with Eo and Nf , plateauing at high values of Eo. The effects of annulus inclination (θ) and eccentricity (ε) on bubble rise velocity are examined within the common range of θ and ε encountered during the drilling of oil, gas, or geothermal wells, i.e. 0° ≤ θ ≤ 60° and 0 ≤ ε ≤ 0.7, and their impact on the C 0. The increasing Fr l and θ lead to a streamlined bubble with pointed nose and thus a reduction in the wrap angle (θ wrap), ultimately leading to reduced drag compared to the vertical annulus case and a decrease in C 0. As the ε increases, which is accompanied by an increase in the degree of bubble eccentricity, the corresponding C 0 decreases. For a constant Eo = 100 and Nf = 160 with inclination angle of θ = 40°and eccentricity of ε = 0.5, the C 0 < 1 is observed. [Display omitted] [ABSTRACT FROM AUTHOR]

Cooling system in nuclear reactor is much influenced by counter-current flow. When a leakage is occured, coolant in primary circuit of hotleg and hot steam from reactor will flows in counter-current condition. An experimental investigation has been performed to examine the effect of flooding phenomenon on the pressure drop. It was observed using acrylic complex pipe as hotleg simulator consisting of three parts: horizontal, bend and inclined pipe. Geometrical sizes of pipes was in scale of 1/30 of the actual hotleg geometrical size in the PWR with inner diameter=25.4 mm, the horizontal pipe length L=635 mm, and inclined pipe length was 20 mm with an angle of 50o. Pressure drop was meassured by using differential pressure sensor installed in the lower-tank (RPV simulator) dan upper-tank (SG simulator). Pressure drop was observed before, during and after flooding. Based on the observation, it was found that the change of flow pattern is followed by the change of pressure drop. The results of this study were also compared with some correlations using the dimensionless superficial velocity parameter by Wallis correlation. Wallis correlation can be written as JG*1/2 + 0,3974 JL*1/2 = 0,4832 .

Pressure retarded osmosis (PRO) is a novel renewable energy technology that generates electricity from two water sources. Due to the osmotic pressure difference, freshwater permeates across a membrane to the other side, where the high-pressure seawater flows and drives a turbine to generate power. Many mathematic models have been proposed to evaluate the performance of a PRO. However, it was found that most performance of the PRO that have been reported were performance by using freshwater with limited supply (batch) in the model. It is not accurate as, in practice, the supply of freshwater occurs in a continuous manner. In this work, the influence of batch and continuous supply of fresh water on the performance of PRO was demonstrated. The effect of flow direction, i.e., concurrent and counter-current flows, was also examined. The model simulation was performed by using MATLLAB program, and the performance of PRO is expressed in terms of average power density. The results revealed that the batch and continuous supplies of freshwater had a strong impact on the performance of the PRO. However, the performance of concurrent and counter-current flow were not significantly different.

The exact stationary solution of the boundary-value problem that describes the convective motion of an incompressible viscous fluid in the two-dimensional layer with the square heating of a free surface in Stokes’s approach is found. The linearization of the Oberbeck-Boussinesq equations allows one to describe the flow of fluid in extreme points of pressure and temperature. The condition under which the counter-current flows (two counter flows) in the fluid can be observed, is introduced. If the stagnant point in the fluid exists, six non-closed whirlwinds can be observed.

HPR1000 (Hua-long Pressurized Reactor) Nuclear Power Plant is a type of third generation advanced PWR developed in China. In this study, a home-made multi-compartment containment code, ATHROC (Analysis of Thermal Hydraulic Response Of Containment), was developed to analyze the thermal-hydraulics and hydrogen behaviors in HPR1000 containment. Two types of bulk fluids, the atmosphere bulk fluid and the pool bulk fluid, were used to model the transient behaviors of multiphase flow. The atmosphere bulk fluid consists of steam, noncondensables and homogeneously dispersed liquid droplets. The code contains comprehensive models, including flow model, heat and mass transfer model, engineering safety feature model, etc. A plume model was implemented to assess buoyancy driven plume movement inside a compartment. A counter-current flow model was developed to evaluate the buoyancy driven bidirectional exchange flow through the junctions. Also, a film tracking model was developed to simulate film flow on the contiguous walls. Special methods such as using variable time steps and non-uniform nodalization for heat sinks were applied to speed up the computation. Code assessments were carried out by simulating several separated effects tests (Phebus FPT0 test, JAERI tests) and integral effects tests (CVTR tests, NUPEC M-7-1 test). Comparing results between code simulations and experimental data showed that the code was capable of providing reasonable predictions. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) operated in counter-current flow mode is more efficient than in co-current flow mode to extract salinity gradient energy. Knowledge of the performance of counter-current flow PRO under various operating conditions (on equilibrium or off equilibrium) is of paramount importance to understand the potential capacity of the technology and to optimize process design. In this study, a systemic and rigorous numerical procedure was developed for performance simulation of counter-current flow PRO. An optimization technique was used to accurately determine the originally unknown flow rate of the draw solution at the feed entrance of membrane channel so that the procedure could also be used for PRO systems not at equilibrium. With this numerical procedure, new interesting findings were made about the ideal counter-current flow PRO. A characteristic parameter of the PRO, the required membrane area to reach equilibrium for any given operating condition, was determined and reported for the first time. Another exciting finding was that the no-flux zone (dead region) occurs adjacent the draw entrance at the critical feed fraction when the membrane area is greater than the required equilibrium area. Power density and specific energy in PRO under various conditions were investigated with this numerical procedure. [ABSTRACT FROM AUTHOR]

A semi-empirical correlation for CCFL (counter-current flow limitation) in vertical pipes was derived from one-dimensional momentum equations. Available correlations such as the empirical correlations proposed by Wallis (1969) and Zapke and Kröger (1996) can be deduced from the derived fundamental functional form of the semi-empirical correlation in limiting flow conditions. Comparisons between the semi-empirical correlation with available experimental data of CCFL taking place at the sharp-edged lower end of a vertical pipe showed that the correlation is applicable for various fluid properties and pipe diameters. The fundamental functional form of the correlation was also transformed so as to express the characteristics of CCFL occurring at the sharp-edged upper end of a vertical pipe. The present fundamental functional form of CCFL correlation is useful not only to express CCFL data but also to understand how relevant parameters play their roles in the CCFL characteristics. [ABSTRACT FROM AUTHOR]

In this work, we investigate the impact of mobility changes due to flow reversals from co-current to counter-current flow on the displacement performance of water alternating gas (WAG) injection processes. In WAG processes, the injected gas will migrate toward the top of the formation while the injected water will migrate toward the bottom of the formation. The segregation of gas, oil and water phases will result in counter-current flow occurring in the vertical direction in some portions of the reservoir during the displacement process. Previous experimental and theoretical studies of counter-current flow have shown that the relative mobility of each of the phases in a porous medium is considerably less when counter-current flow prevails as compared to co-current flow settings. A reduction of the relative permeability in the vertical direction results in a dynamic anisotropy in phase mobilities. This effect has, to the best of our knowledge, not previously been considered in the modeling and simulation of WAG processes. A new flow model that accounts for flow reversals in the vertical direction has been implemented and tested in a three-phase compositional reservoir simulator. In order to investigate the impact of flow reversals, results from the new flow model are compared to cases where counter-current flow effects on the phase mobilities are ignored. A range of displacement settings, covering relevant slug sizes, have been investigated to gauge the impact of mobility reductions due to flow reversals. Significant differences, in terms of saturation distribution, producing GOR and oil recovery, are observed between the conventional flow model (ignoring mobility reductions due to counter-current flow) and the proposed new model that accounts for reductions in phase mobility during counter-current flow. Accordingly, we recommend that an explicit representation of flow transitions between co-current and counter-current flow (and the related impact on phase mobilities) should be considered to ensure accurate and optimal design of WAG injection processes. [ABSTRACT FROM AUTHOR]

In the present study, convective motion of an incompressible viscous fluid in the geometrically anisotropic zone with the lower boundary cooled by a localized point source is considered. The existence of closed isolines for the pressure, counter-current flows in the fluid and localization of thermal layer near the free surface is shown. [ABSTRACT FROM AUTHOR]

We characterize the flow of a viscous suspension in an inclined channel where the flow is maintained in a steady state under the competing influences of gravity and an applied pressure drop. The basic model relies on a diffusive-flux formalism. Such models are common in the literature, yet many of them possess an unphysical singularity at the channel centreline where the shear rate vanishes. We therefore present a regularization of the basic diffusive-flux model that removes this singularity. This introduces an explicit (physical) dependence on the particle size into the model equations. This approach enables us to carry out a detailed parameter study showing in particular the opposing effects of the pressure drop and gravity. Conditions for counter-current flow and complete flow reversal are obtained from numerical solutions of the model equations. These are supplemented by an analytic lower bound on the ratio of the gravitational force to the applied pressure drop necessary to bring about complete flow reversal. [ABSTRACT FROM AUTHOR]

We present semianalytical solutions for cocurrent displacements with some degree of countercurrent flow. The solution assumes a one-dimensional horizontal displacement of two immiscible incompressible fluids with arbitrary viscosities and saturation-dependent relative permeability and capillary pressures. We address the impact of the system length on the degree of countercurrent flow when there is no pressure drop in the nonwetting phase across the system, assuming negligible capillary back pressure at the inlet boundary of the system. It is shown that in such displacements, the fractional flow can be used to determine a critical water saturation, from which regions of both cocurrent and countercurrent flow are identified. This critical saturation changes with time as the saturation front moves into the porous medium. Furthermore, the saturation profile in the approach presented here is not necessarily a function of distance divided by the square root of time. We also present approximate solutions using a perturbative approach, which is valid for a wide range of flow conditions. This approach requires less computational power and is much easier to implement than the implicit integral solutions used in previous work. Finally, a comprehensive comparison between analytical and numerical solutions is presented. Numerical computations are performed using traditional finite-difference formulations and convergence analysis shows a generally slow convergence rate for water imbibition rates and saturation profiles. This suggests that most coarsely gridded simulations give a poor estimate of imbibition rates, while demonstrating the value of these analytical solutions as benchmarks for numerical studies, complementing Buckley-Leverett analysis. [ABSTRACT FROM AUTHOR]

Characteristics of counter-current flow limitation (CCFL) inside vertical pipes with sharp-edged upper end (CCFL-P/SE) and with round-edged upper and lower ends (CCFL-P) were evaluated to clarify the dependence of the limiting locations. The CCFL is defined by the relationship between the gas and liquid volumetric fluxes (JG and JL) under a quasi-steady state after onset of flooding. CCFL correlations were constructed for CCFL-P/SE and CCFL-P based on the previous experimental data. The correlations were compared to the characteristics of CCFL at the vertical pipes of the sharp-edged upper end (CCFL-U) and the sharp-edged lower end (CCFL-L). CCFL-P has the highest liquid volumetric flux when CCFL occurs, and the lowest is CCFL-L. For the Wallis correlation, selection of the characteristic length of w = D(1-β)Lβ (where D and L respectively denote the diameter and the Laplace capillary length) is quite important. Our results have indicated that CCFL-P/SE and CCFL-P are also expressed by β ~ 0.5, CCFL-U is expressed by β = 1, and CCFL-L is expressed by β = 0. [ABSTRACT FROM AUTHOR]

An understanding of the bubble properties, size distributions and shapes is of fundamental importance for comprehending flow dynamics and mass transfer phenomena in bubble column reactors. A large number of studies have focused on open tube bubble columns, and the knowledge concerning bubble columns with internals is still limited. This paper contributes to the existing discussion experimentally investigating a counter-current annular bubble column with 0.24 m inner diameter and two internal pipes. The experimental investigation consists in holdup measurements and image analysis. The former is used for identifying the flow regime transition and studying the bubble column hydrodynamics, whereas the latter is used for investigating the bubble shapes and size distributions. The definition of the transition point is important because the size distribution and bubble shapes depend on the operating conditions and a change of the bubble properties is expected near the transition. The image analysis is applied at different superficial gas and liquid velocities, corresponding to a gas holdup between 2.9% and 9.6%. It is difficult to measure bubble size distribution accurately in large-diameter bubble columns owing to the overlapping of bubbles, even at low void fractions, and—in an annular gap bubble column—the fact that cap bubbles have also been reported in the homogeneous flow regime. The use of a bubble image analysis method to study the bubbly flows in a large-diameter annular gap bubble column is described. In the proposed method, each bubble is approximated and reconstructed using an ellipse. The proposed approach is used to quantify the bubble size distribution, as well as to study the bubble shape and orientation as function of the superficial gas and liquid velocities. The experimental data obtained are used to develop a correlation between non-dimensional parameters and aspect ratios. Also, the experimental data are compared with non-dimensional diagrams from the literature, revealing good agreement. Finally, the image analysis is used for supporting the flow regime transition prediction in the stability analysis method: the virtual mass formulation is obtained by using the aspect ratio correlation provided by the image analysis. The stability analysis—supported by the image analysis—was able to predict the transition point in very good agreement with experimental data and performed better than literature correlations. [ABSTRACT FROM AUTHOR]

Bubble columns are frequently studied without considering internals (open tube bubble columns). However, in most industrial applications, internal devices are often added to control heat transfer, to foster bubble break-up or to limit liquid phase back mixing. These elements can have significant effects on the multiphase flow inside the bubble column reactor and the prediction of these effects is still hardly possible without experimentation. In this paper, we study experimentally a counter-current gas–liquid bubble column in the open tube and annular gap configurations. In the annular gap bubble column, two vertical internal tubes are considered. The column has an inner diameter of 0.24 m, and the global and local hydrodynamic properties are studied using gas holdup measurements and a double-fiber optical probe. The gas holdup measurements are compared with the literature and used to investigate the flow regime transition. A double-fiber optical probe is used to acquire midpoint data and radial profiles of the local properties to study the flow properties and to further investigate the flow regime transition. The counter-current mode is found to increase the holdup, decrease the bubble velocity and cause regime transition at lower superficial gas velocity. The holdup curves in the annular gap and open tube configurations are similar in shape and values, suggesting that the presence of internals has a limited influence on the global hydrodynamic. In addition, it is found that the presence of the internals stabilizes the homogeneous regime in terms of transition gas velocity and holdup. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of solution film flow with counter-current air flow, especially the two phase contact area, are important for the optimal design and operation of LDD (liquid desiccant dehumidifier). However, the unsteady interfacial information, including the interfacial pressure, velocity and film thickness, is hardly to be examined accurately by theoretical prediction or experimental measurement due to its complexity. In this study, CFD (computational fluid dynamic) models for the counter-current flow of the LDD were established based on the VOF (volume of fraction) and RNG (Renormalization group) k-ε turbulence model. Experimental research had been conducted to validate the liquid film thickness and typical interfacial waves obtained in simulation. With the established model, the dynamic formation process of unsteady counter-current flow is evaluated. Moreover, the effects of various parameters on the liquid film waves, pressure drop, liquid film thickness and interfacial information were obtained and analyzed by the built models. With the increase of liquid flow rate, the roll waves appear and the wave amplitudes are increased significantly, which may obviously enhance the performance in the LDD absorption and regeneration process due to the increased contact area. [ABSTRACT FROM AUTHOR]

Drying and salt precipitation in geological formations can have serious consequences for upstream operations in terms of injectivity and productivity. Here we investigate the consequences of supercritical CO 2 injection in sandstones. The reported findings are directly relevant for CO 2 sequestration and acid–gas injection operations, but might also be of interest to a broader community dealing with drying and capillary phenomena. By injecting dry supercritical CO 2 into brine-saturated sandstone, we investigate the drying process and the associated precipitation of salts in a capillary-pressure-dominated flow regime. Precipitation patterns were recorded during the drying process by means of μCT scanning. The experimental results and numerical simulations show that under a critical flow rate salt precipitates with an inhomogeneous spatial distribution because of brine and solutes being transported in counter-current flow upstream where salt eventually precipitates. A substantial impairment of the absolute permeability has been found, but despite high local salt accumulation, the effective CO 2 permeability increased during all experiments. This phenomenon is a result of the observed microscopic precipitation pattern and eventually the resulting K ( ϕ ) relationship. The findings in this paper are related to unimodal sandstone. In a companion paper ( Ott et al., 2014 ) we present data on the distinctly different consequences of salt precipitation in dual- or multi-porosity rocks. [ABSTRACT FROM AUTHOR]

Rotating spiral channels enable any two immiscible fluid phases to flow counter-currently in parallel layers allowing independent control of phase flow rates and layer thicknesses. This opens the possibility of application over the full range of fluid contacting operations, including distillation, absorption, extraction and multiphase reaction with separation. A device has been developed that enables wide-ranging experimental studies to support model refinement and design of first-generation applied devices. In this first work with the new device hydrodynamic characteristics are studied for gas–liquid systems as functions of phase flow rates, rotation rate and liquid viscosity. Measurement of the heavy phase layer thickness, using image analysis based on the Young–Laplace theory for interface shape, and measurement of volume flow rate of each phase and pressure and temperature in the spiral channel allows rigorous comparisons with an existing ‘wide-channel’ model relating flow rates and layer thicknesses to phase properties, geometry and rotation rate. The measured thickness of the heavy-phase layer is predicted well by the wide-channel model at high rotation and phase flow rates, where the deviation from a uniform layer thickness due to menisci at the channel end walls and interface tilt from gravity are small. At low rotation rates, where significant meniscus height and tilt develop, the layer thickness is over-predicted by the wide channel model. The sub 20 µm heavy-phase layer thicknesses measured suggest operation at optimum thickness is possible with the rotating spiral over a wide range of phase and solute systems. [ABSTRACT FROM AUTHOR]

The optimal design and operation of a liquid desiccant dehumidifier needs the understanding of the flow mechanism. However, the study in this aspect is still limited. In the present work, a model has been established on the basis of computational fluent dynamics (CFD) software. With the model, the counter-current gas–liquid flow process is evaluated microscopically and dynamically. The impacts of various parameters on the velocity profiles, the minimum liquid flow rate for wetting the whole surface, interfacial area, and film thickness are analyzed. The critical advantage of the model lies in that it can predict the dynamic and local performance of the dehumidifier microscopically. [ABSTRACT FROM AUTHOR]

• The experiment was conducted during the liquid–gas counter-current two-phase flow in a 1/30 scaled-down of PWR hot leg. • The liquid thickening on the upper edge of the hydraulic jump triggers the liquid blockage to initiate the CCFL. • The statistical characterizations were investigated on the basis of both the locus and the flow parameters. • The time-domain and frequency-domain analyses implies a good agreement with the visual observations, while the wavelet analysis is able to differ the obtained flow regimes. The present work investigates the statistical characteristics of the fluctuations of the liquid film thickness obtained by resistive-conductance probe signals of a complex geometry representing a 1/30 down-scaled of a PWR hot leg. Here, four locations at the horizontal part of the test section were assessed, while the flow development was investigated through a close observation by using a high-speed video camera. Next, the normalized voltages, indicating the liquid film thickness fluctuations, are shown in the time-series. From the fluctuations, the amplitudes representing the film thickness were recorded. Hence, such statistical diagnostic tools were applied on the basis of time-domain, frequency-domain and also time–frequency domain analyses. From the probability density function, the distributions of the fluctuations were assessed, whereas the power spectral density function describes the dominant frequencies. In addition, the Kolmogorov entropy denotes the chaotic level of the signal, meanwhile the wavelet energy corresponds to several details on the wavy interfaces on the basis of its frequency scales. Next, those parameters were statistically employed to elaborate the interfacial behaviors due to the signal characteristics. The results indicate that the low dominant frequency corresponds to the occurrence of either liquid blockage or slugs during the acquisition, meanwhile the largest scale fluctuations reveal the wave movements. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops a two dimensional Green element simulator based on a “compatibility-equation” algorithm for simulation of counter-current spontaneous imbibition (COUCSI) process. The Green element method is a novel computational approach based on the boundary integral theory, which is regarded as a hybrid combination of both boundary and finite element methods. The superiority of the Green element method in modeling of two phase water/oil flow is at the core of this paper. The developed simulator within the context of this proposition is explored to predict the oil recovery from a one dimensional single matrix block. The results are then compared with the experimental data, and they demonstrate the method׳s accuracy at all times of the process. Moreover, the amount of oil recovered from two dimensional matrix block by counter-current imbibition is well predicted by the Green element method. A sensitivity analysis is eventually conducted which reflects the fact that the Green element method uses considerably fewer number of elements in order to obtain converged solutions in comparison with those of the traditional simulation methods. [Copyright &y& Elsevier]

Highlights: [•] t m is the crucial factor for governing the hydrodynamic and mass transfer properties. [•] The configuration provided an effective counter-current flow in downcommer. [•] The geometry provided significant decrease in P/V compared to other configurations. [ABSTRACT FROM AUTHOR]

Abstract: Lubricant oil return to compressor in household refrigerator is controlled by oil-refrigerant two-phase flow behavior in the suction pipe. Conditions of flooding and flow reversal were considered as a conservative bound for the oil return. Phenomena associated with counter current flow limitation (CCFL or flooding) and flow reversal were experimentally investigated using small diameter tubes with vertical, inclined and crank-type configurations. Flooding and flow reversal phenomena were visually observed. Both flooding and flow reversal points were measured using various shapes of test section in a wide range of liquid flow rate. The gas velocities for flooding were found to be inversely proportional to the liquid flow rates and independent of the tube configurations. The gas velocities for the flow reversal point appeared to be at a similar level over a certain range of liquid flow rate but strongly depend on the inclination angle, horizontal length and kind of liquid. [Copyright &y& Elsevier]

Abstract: The infiltration of liquid into a gas saturated porous network is investigated. Particular attention is paid to the situation in which a pressure gradient in the porous medium drives a gas flow upwards, while a more dense liquid infiltrates down into the reservoir due to gravity. There are two flows in opposite directions. A model is proposed, based upon a compressible gas phase and an incompressible liquid phase. The volume fluxes in each phase are assumed to be governed by Darcy type flow laws, modified to include the permeability caused by both the solid matrix and the impeding of the gas flow by the liquid phase. Isothermal flows are examined in the absence of phase changes. The proposed model is an extension of the traditional Buckley–Leverett model and is used to consider a variety of flows, including carbon sequestration in a porous medium below the seabed and rainfall infiltration into a lava dome. [Copyright &y& Elsevier]

Detailed study of the gas-solid flow in FCC reactor was performed using Euler-Euler two-fluid model. Two distinct regions were identified in the reactor vessel based on differences in catalyst void fraction and fluid flow: the dilute phase congested disengager region and dense phase congested stripper region. Velocity profile revealed an inert yet random flow pattern in the disengager and a counter-current type of flow with a pronounced radial unevenness in the stripper. Residence time distribution proved that a small portion of oil vapour could linger over 5 min before exiting despite that the apparatus may have a significantly shorter average residence time. [ABSTRACT FROM AUTHOR]

There are several approaches for the calculation of capillary pressure curves in porous media including the centrifuge method. In this work, a new installation of centrifuge test is introduced and compared with the traditional setup. In the first setup, which is a standard approach in labs, the core face closest to the rotational axis is open to the non-wetting phase, while the farthest face is open to the wetting phase where strictly co-current flow is generated in rotations; labeled Two-Ends-Open (TEO). In the second setup, which is proposed as a new approach, only the outer radius surface is open and is exposed to the light non-wetting phase; labeled One-End-Open (OEO). This setup strictly induces counter-current flow. The two systems and their corresponding boundary conditions are formulated mathematically and solved by a fully implicit numerical solver. The TEO setup is validated by comparison with commercial software. Experimental data from the literature are used to parameterize the models. It is mathematically, and with examples, demonstrated that the same equilibrium is obtained in both systems with the same rotational speed, and changing the installation does not influence the measured capillary pressure. This equilibrium state is only dependent on the rotational speed, rock capillary pressure properties, and fluid densities, not the installation geometry, relative permeabilities, or fluid viscosities. However, the dynamic transition trend and saturation profiles were found to be dependent on the applied installation. It was observed that the OEO setup takes almost identical equilibration time as the TEO setup for mixed-wet states, although it needed much longer time in water-wet states. The presence of threshold capillary pressure significantly increased the time scale of the OEO setup. Also, it was found that in contradiction to the TEO setup, the dynamic saturation profile in OEO was rarely influenced by viscosity ratio. To conclude, the performed history matching analysis demonstrated that the OEO setup can be applied for the calculation of counter-current relative permeability from the production data with reasonable accuracy., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

Rotary kiln reactors are frequently equipped with an axial burner with which solid burden material is directly heated. The burner flame provides the heat required for the vaporization of the water and the reaction of the solid phase. Lifters are commonly used along the length of the system to lift particulate solids and increase the heat transfer between the solid bed and the combustion gas. The material cascading from the lifters undergoes drying and reacting through direct contact with the gas stream. In this study, volume distribution of materials held within lifters was modeled according to the different lifter configuration and appropriate configuration was used for the design purpose. This was applied to the simplified one-dimensional heat balance model of a counter-current flow reactor, which contributes to the increase of the effective contact surface, and thereby enhances the heat transfer. [ABSTRACT FROM AUTHOR]

Abstract: The study investigates a counter-current gravity separation in a downwards-flowing mixture of (up to 3%) oil in water. At much higher oil fraction, the separation is a basis for the conventional downhole oil–water separation (DOWS) where the whole oil and water separate in the well. In contrast, the counter-current separation of a very small oil content is needed in the new “downhole water loop” technique (DWL) prior to injecting the oil-free water in-situ. In the DWL triple-completed wells, the top completion produces oil and only trace of the oil contaminates the water drained by the lower “water sink” completion and is re-injected in-situ using the (third) bottom completion. A drift-flux concept was used to develop an empirical model for predicting the oil droplets raise velocity at different water flow velocities. The model was derived from experiments using seven different oils with a wide range of density, viscosity and interfacial tension values. The experiments monitored oil droplets ejected from a single perforation into the stream of water flowing downwards at various velocities. The results show that the oil–water interfacial tension is the most important factor in the separation process, as it controls the oil droplet size. This observation significantly simplifies the model by replacing the droplet size (most difficult to measure) with a correlation based on interfacial tension developed using the experimental results. The new model also considers the effect of oil viscosity that has been ignored in the co-current separation studies. (Our results reveal over 10% contribution of the viscosity effect to the counter-current separation process.) A practical finding in this study is the 0.33ft/s (0.1m/s) value of critical maximum water velocity for counter-current oil separation. In a real DWL well, this value corresponds to a point in the perforated well section above which separation takes place. It is also shown how oil separation could be predicted from a given water sink completion length and drainage–injection rate. [Copyright &y& Elsevier]

Abstract: In this work, we investigate the impact of co-current to counter-current flow reversals on the migration dynamics of a non-wetting phase plume in a porous medium. The presented results and observations have direct application to CO2 injection into saline aquifers where a less dense CO2-rich plume migrates during and following the injection period. Counter-current gravity segregation experiments were performed in a vertical glass-bead pack with brine and iC8 as analog fluids to mimic the behavior of a CO2/brine system of relevance to CO2 sequestration processes. Four-electrode resistivity measurements were used to monitor the migration of the non-wetting phase (iC8) by relating the resistivity index (RI) to the brine saturation. The observations are compared with numerical calculations to demonstrate that standard co-current relative permeability measurements are inadequate to reproduce the experimental observations. A reduction in the relative permeability of both phases, in particular for the non-wetting phase, is required to improve the agreement between experimental observations and numerical calculations. Numerical calculations based on co-current input data predicts a much faster migration of the non-wetting phase to the top of the column than what is observed in the segregation experiments. Our findings demonstrate that counter-current flow affects the phase''s mobilities, because of interfacial coupling, and should therefore be considered in the modeling of injection/storage of CO2 in saline aquifers: simulation of CO2/brine dynamics based on co-current relative permeability measurements is likely to render estimates of migration time/distance in significant error. [Copyright &y& Elsevier]

Abstract: Carbon dioxide (CO2) injection into saline aquifers is one of the promising options to sequester large amounts of CO2 in geological formations. During as well as after injection of CO2 into an aquifer, CO2 migrates towards the top of the formation due to density differences between the formation brine and the injected CO2. The time scales of CO2 migration towards the top of an aquifer and the fraction of CO2 that is trapped as residual gas depends strongly on the driving forces that are acting on the injected CO2. When CO2 migrates to the top of an aquifer, brine may be displaced downwards in a counter-current flow setting particularly during the injection period. A majority of the published work on counter-current flow settings have reported significant reductions in the associated relative permeability functions as compared to co-current measurements. However, this phenomenon has not yet been considered in the simulation of CO2 storage into saline aquifers. In this paper we study the impact of changes in mobility for the two-phase brine/CO2 system as a result of transitions between co- and counter-current flow settings. We have included this effect in a simulator and studied the impact of the related mobility reduction on the saturation distribution and residual saturation of CO2 in aquifers over relevant time scales. We demonstrate that the reduction in relative permeability in the vertical direction changes the plume migration pattern and has an impact on the amount of gas that is trapped as a function of time. This is to our best knowledge the first attempt to integrate counter-current relative permeability into the simulation of injection and subsequent migration of CO2 in aquifers. The results and analysis presented in this paper are directly relevant to all ongoing activities related to the design of large-scale CO2 storage in saline aquifers. [Copyright &y& Elsevier]

This research investigated the effects of co- and counter-current flow patterns on oil-water-solid separation efficiencies of a circular separator with inclined coalescence mediums. Oil-water-solid separations were tested at different influent concentrations and flowrates. Removal efficiencies increased as influent flowrate decreased, and their correlationship can be represented by power equations. These equations were used to predict the required flowrate, Qss50, for a given influent suspended solids concentration Ciss to achieve the desired effluent suspended solids concentration, Cess of 50 mg/L, to meet environmental discharge requirements. The circular separator with counter-current flow was found to attend removal efficiencies relatively higher as compared to the co-current flow. As compared with co-current flow, counter-current flow Qss50 was approximately 1.65 times higher than co-current flow. It also recorded 13.16% higher oil removal at influent oil concentration, Cio of 100 mg/L, and approximately 5.89% higher TSS removal at all influent flowrates. Counter-current flow's better removal performances were due to its higher coalescing area and constant interval between coalescence plate layers. [ABSTRACT FROM AUTHOR]

Abstract: We carried out a set of experiments on the direct-contact condensation of atmospheric steam for subcooled water flowing co-currently and counter-currently in a circular pipe. The condensation heat transfer coefficient was evaluated both for co-current and counter-current steam–water flow cases in a horizontal circular pipe. In the current experiment the dependency of the liquid Nusselt number on the gas Reynolds number is higher in the counter-current than in the co-current experimental data. The dependency of the liquid Nusselt number on the steam Reynolds number is stronger in the rectangular channel than in the circular pipe. The overall heat transfer characteristics are better in the co-current flow than in the counter-current flow with the same injection flow rates of the steam and the water. The present co-current experimental data were used to assess four existing correlations. However, there are few reliable correlations existing to predict co-current experimental data. The comparisons of the present counter-current experimental data with the existing correlations show that Chu’s (Chu, I.C., Yu, S.O., Chun, M.H. 2000. Interfacial condensation heat transfer for counter-current steam–water stratified flow in a circular pipe, J. Korea Nucl. Soc., 32 (2), 142–156) correlation predicts the experimental data well. [Copyright &y& Elsevier]

A two-phase flow configuration in which the gas phase flows upwards while the liquid phase flows downwards is referred to as a counter-current flow pattern. This flow configuration cannot be preserved if any flow rate exceeds a criterion known as the counter-current flow limitation (CCFL) or flooding. Since the CCFL is important to chemical engineers, it has long been studied via experimental and analytical approaches. Most of the previous CCFL experiments in annular channels have been carried out with a small diameter annulus and large gap-to-diameter ratio annulus. The present experiment examines the CCFL in narrow annular channels having gap sizes of 1, 2, 3, and 5 mm. The outer diameter of the annular passage is 500 mm. At a gap size of 1 mm, it was visually observed that a CCFL locally occurred in some region of the periphery while the other region remained in a counter-current flow configuration. The region under partial CCFL condition expanded with an increase in the air flow rate, finally reaching a global CCFL. The air flow rate for the global CCFL was roughly 15% larger than that for initiation of a partial CCFL. This difference in air flow rate between the initiation of a partial CCFL and the global CCFL was reduced as the gap size increased. When the gap size was 5 mm, the partial CCFL was not observed, but onset of flooding led to a global CCFL. Because of the existence of a transient period, the CCFL was experimentally defined as the situation where net water accumulation is sustained. The measured CCFL data are presented in the form of a Wallis’ type correlation. Two length scales, hydraulic diameter and average circumference, were examined as the characteristic length scale. The average circumference appeared to better fit the experimental data, including results reported elsewhere. A new correlation using the average circumference as the characteristic length scale is suggested based on the experimental measurements of the present work and previous reports. [ABSTRACT FROM AUTHOR]

Abstract: A new method has been developed to analyse the mobility of elements within soils employing counter-current flow soil contacting in a fluidised bed (FB) column. This method alleviates the problem of irreproducible peaks suffered by state-of-the-art micro-column techniques as a result of particle compaction. Reproducible extraction profiles are produced through the leaching of soil with a linear gradient of 0.05molL−1 ammonium sulphate to 0.11molL−1 acetic acid using a high pressure liquid chromatography (HPLC) quaternary pump, and the continuous monitoring of the elements in the leachate with inductively coupled plasma mass spectrometry (ICP-MS). Quantification of the procedure is achieved with an external flow injection (FI) calibration method. Flow rate and FB column length were investigated as critical parameters to the efficiency of the extraction methodology. It was found that an increase in the column length from 10 to 20cm using a flow rate of 0.15mLmin−1 produced the same increase in extracted elemental concentration as an increase in flow rate from 0.15 to 0.30mLmin−1. In both examples, the increase in the concentration of elements leached from the soil may be ascribed to the increase in the concentration gradient between the solid and liquid. The exhaustive nature of the technique defines the maximum leachable concentration within the operationally defined leaching parameters of the exchangeable phase, providing a more accurate assessment of the risk associated with the elements in the soil for the phase providing the greatest risk to the environment. The multi-elemental high sensitivity nature of the on-line detector provides an accurate determination of the associations present between the elements in the soil, and the identification of multiple phases within the exchangeable phase through the presence of multiple peaks in the extraction profiles. It is possible through the deconvolution of these extraction profiles that the concentration corresponding to the peaks identified can be defined. [Copyright &y& Elsevier]

Abstract: In an effort to explore a novel approach to monitoring solids uptake during osmotic dehydration, the combination of product coating with alternative scenarios of product/solution contacting (“flow”) was investigated. Potato was used as a model plant material for short term (i.e. 3h) osmotic treatment in a series of sucrose solutions with decreasing or increasing concentrations to simulate co-current or counter-current product/solution contacting (flow), respectively. A mixed-level full factorial experimental design was used. Data were analyzed using multiple linear regression procedures. Counter-current product/solution contacting contributed to faster water loss and slower solids uptake. In both flow-types, initial solids had a significant impact on both water loss and solids uptake. Sodium alginate coating yielded significantly decreased solids uptake, without negatively affecting water removal. Overall, “dehydration efficiency” was drastically improved (up to 77%) by combined coating and counter-current contacting. Regression models were developed to predict mass exchange (i.e. water loss and solids uptake) under alternative treatment scenarios, considering initial product solids. [Copyright &y& Elsevier]

Abstract: The objective of this work is to investigate characteristics of counter-current bubbly flow in a circular pipe with an inner diameter of 50mm by using wire mesh tomography (WMT). The accuracy of WMT on void fraction measurement is also clarified by comparing the result with a non-intrusive optical method. The accuracy is within ±10%. Local void fractions of many flow conditions are reported. Local void fraction profile affected by superficial liquid velocity and bubble size is shown and discussed. Furthermore, intrusive effects, including bubble break-up and bubble deceleration, are also investigated. Bubbles passing a transparent wire mesh sensor (WMS) are investigated by the optical method. It is shown that bubbles are broken and decelerated by wires of the sensor. It can be concluded that the bubble break-up rate increase with increasing of bubble velocity. However, the bubble deceleration is not depending on the bubble velocity. [Copyright &y& Elsevier]

Abstract: Solid foam materials combine high voidage and high surface area. These two properties are advantageous for use in chemical reactors due to the low frictional pressure drop and relatively high surface area that may be used for catalyst deposition. Hydrodynamic parameters such as liquid holdup, pressure drop, and flow regimes similar to those for packed beds, have been obtained for the gas and liquid flows through these solid foam packings. The open-celled solid foam packings used were in the range of 5–40 pores per linear inch (ppi). The regimes studied are two high liquid holdup regimes and a low liquid holdup regime (trickle flow regime). Also the flooding points for counter-current flow have been determined. [Copyright &y& Elsevier]