Countercurrent Flow Research Articles

3D-CFD Modeling of Hollow-Fiber Membrane Contactor for CO2 Absorption Using MEA Solution.

Membrane technology is considered an innovative and promising approach due to its flexibility and low energy consumption. In this work, a comprehensive 3D-CFD model of the Hollow-Fiber Membrane Contactor (HFMC) system for CO2 capture into aqueous MEA solution, considering a counter-current fluid flow, was developed and validated with experimental data. Two different flow arrangements were considered for the gas mixture and liquid solution inside the HFMC module. The simulation results showed that the CO2 absorption efficiency was considerably higher when the gas mixture was channeled through the membranes and the liquid phase flowed externally between the membranes, across a wide range of gas and liquid flow rates. Sensitivity studies were performed in order to determine the optimal CO2 capture process parameters under different operating conditions (flow rates/flow velocities and concentrations) and HFMC geometrical characteristics (e.g., porosity, diameter, and thickness of membranes). It was found that increasing the membrane radius, while maintaining a constant thickness, positively influenced the efficiency of CO2 absorption due to the higher mass transfer area and residence time. Conversely, higher membrane thickness resulted in higher mass transfer resistance. The optimal membrane thickness was also investigated for various inner fiber diameters, resulting in a thickness of 0.2 mm as optimal for a fiber inner radius of 0.225 mm. Additionally, a significant improvement in CO2 capture efficiency was observed when increasing membrane porosity to values below 0.2, at which point the increase dampened considerably. The best HFMC configuration involved a combination of low porosity, moderate thickness, and large fiber inner diameter, with gas flow occurring within the fiber membranes.

Duox activation in Drosophila Malpighian tubules stimulates intestinal epithelial renewal through a countercurrent flow

The gut must perform a dual role of protecting the host against toxins and pathogens while harboring mutualistic microbiota. Previous studies suggested that the NADPH oxidase Duox contributes to intestinal homeostasis in Drosophila by producing reactive oxygen species (ROS) in the gut that stimulate epithelial renewal. We find instead that the ROS generated by Duox in the Malpighian tubules leads to the production of Upd3, which enters the gut and stimulates stem cell proliferation. We describe in Drosophila the existence of a countercurrent flow system, which pushes tubule-derived Upd3 to the anterior part of the gut and stimulates epithelial renewal at a distance. Thus, our paper clarifies the role of Duox in gut homeostasis and describes the existence of retrograde fluid flow in the gut, collectively revealing a fascinating example of inter-organ communication.

Pengaruh Kenaikan Laju Alir Fluida Panas dan Arah Aliran terhadap Kinerja Plate and Frame Heat Exchanger

Plate and Frame Heat Exchanger (PFHE) is a plate and frame type heat exchanger that is efficient and effective in improving energy efficiency. Research using PFHE aims to determine the effect of increasing the flow rate of hot fluid on heat exchanger performance. This research was conducted at a flow rate variation of 0.7 L/min, 0.9 L/min, 1.1 L/min, 1.3 L/min, 1.5 L/min, 1.7 L/min, and 1.8 L/min with 180 seconds of testing each variation and recording data every 2 seconds. The cold fluid used is tap water and the hot fluid used is distilled water. The results showed that with the increase in hot fluid flow rate, the performance of PFHE also increased because the effectiveness of NTU (Ɛ-NTU) increased. The Ɛ-NTU value of unidirectional flow is 25.37% - 44.87% and in the opposite direction 37% - 68.39%. The largest Ɛ-NTU value in the countercurrent flow indicates that the countercurrent flow is more effective than the unidirectional flow. In addition, increasing the flow rate increases the Reynold's number (Nre) and Nusselt's number (Nu) which indicates the greatest convection heat transfer occurs at the highest flow rate.

Analysis of configurational factors that influence the reversibility of nonstoichiometric countercurrent thermal reduction reactors

Recently, thermodynamic modeling has demonstrated that reduction of nonstoichiometric oxides in a counterflow gas current with a single inlet and exit must result in an equilibrium temperature gradient that deviates from the typically assumed isothermal operation at every single point but one, under assumed mass balance constraints. This necessity for a temperature gradient results in real processes that are near isothermal to deviate from the ideal reversible process, except for the single point where the Gibbs free energy change is zero. In this paper, new configurations with additional inlets and exits that can better approximate reversible and isothermal countercurrent flow reactors are considered and thermodynamically modeled. We show that it is possible to decrease irreversibilities while operating under the same maximum temperature, gas flowrates and initial nonstoichiometry simply by employing two or more exits and/or inlets. Under the most optimal conditions where the normalized irreversibilities are lowest, utilizing either an extra exit or extra inlet and exit show improved results in terms of minimizing the Gibbs free energy and lowering the needed separation work for the gases. Generally, as more irreversibilities are generated within the reactor, the more significant the usage of extra inlets/exits becomes.

Countercurrent chemical looping for enhanced methane reforming with complete conversion and inherent CO[formula omitted] separation

Methane reforming is a widely applied chemical process for the production of hydrogen and syngas. It can play an important role in the energy transition, allowing for the production of so called blue hydrogen, or in the processing of biogas for renewable fuel and fertiliser production. This work describes and demonstrates a novel countercurrent chemical looping reforming process, which offers a new mode of reforming with complete conversion of methane, inherent separation of pure CO2, and flexibility in the choice of oxidant allowing for hydrogen or syngas production. The packed-bed chemical-looping reactor operates by storing the favourable oxygen chemical potential inclines of the alternating countercurrent flows using the unique properties of non-stoichiometric oxides. The improvement in chemical equilibrium limitations are illustrated using an analysis of an idealised countercurrent membrane reactor. The concept is experimentally demonstrated in a dry reforming process using the non-stoichiometric oxide CeO2−δ at a temperature of 1203K. The results show complete oxidation of CH4 to CO2 and H2O in the reduction step, and a cumulative CO2-to-CO molar conversion of 86 % during oxidation.

Process intensification of metal solvent extraction studies using a miniaturized solvent extraction plant

This study examines the potential of a miniaturized solvent extraction plant (MSXP) to improve the efficiency and reproducibility of laboratory and pilot-scale metallurgical studies that typically require extended testing periods. The MSXP has been designed to replace conventional solvent extraction (SX) apparatus and aims to reduce start-up time, time to reach equilibrium, and overall test time. Two copper solvent extraction (Cu-SX) research campaigns were conducted to test the functionality, ease of operation, modularity, and reproducibility of the MSXP. The first campaign quantified the extraction efficiency and net copper transfer, while the second campaign operated the MSXP in a semicontinuous countercurrent flow configuration with three extraction and two stripping stages. The main variables studied in the first campaign are the number of stages (1-3), volumetric flow rates (O/A, 1-3), and organic phase residence time in the micro-contactor (0.7-2.4 min). The results demonstrate that the MSXP can work with very low stage efficiencies (48%), while achieving high copper recoveries (> 90%). At the stripping circuit level, we show that the MSXP can operate at superior stage efficiencies (> 100%), with low copper recoveries (30%–55%). The reproducibility evaluation also demonstrates high statistical confidence (< 6% CV) in the obtained process values. The MSXP offers great flexibility in net copper transfer and can be used to benchmark and emulate a wide range of Cu-SX systems. Experimental Cu-SX campaigns can be run in about 60 min while investing roughly US$1.4/h on reagents, which is significantly lower compared to typical campaigns that can last from days to weeks to reach reliable research outcomes and require about US$62/h for reagents. The potential of MSXP extends to more elaborate solvent extraction systems, specifically those designed to purify energy-critical elements like lithium, nickel, cobalt, or rare-earth elements. This study demonstrates the promise of process intensification approaches for improving the efficiency of laboratory and pilot-scale SX studies, which can help in reducing time, reagents, and energy consumption while improving the reproducibility of results.

Numerical study of Taylor bubble breakup in counter-current flow using large eddy simulation

This paper investigates dynamics of Taylor bubble in counter-current flows, leveraging large eddy simulations combined with the volume of fluid method. Utilizing the OpenFOAM framework, we have implemented a high-order Runge–Kutta time-integration scheme, along with a piecewise linear interface calculation method for precise geometric reconstruction of the bubble interface. We examine the performance of algebraic vs geometric capturing techniques in the context of Taylor bubble breakup, focusing specifically on the transitional flow regime with a liquid Reynolds number of 1400. Our results reveal that the geometric capturing technique offers superior accuracy, improving our understanding of the breakup process and providing valuable insight for multiphase flow simulations in various engineering fields. Our study also reveals the emergence of a secondary vortex in the turbulent wake region behind the Taylor bubble, a phenomenon most prominent at finer mesh resolutions. This vortex represents a novel discovery in counter-current Taylor bubble flows.

Quality of Mixedness Using Information Entropy in a Counter-Current Three-Phase Bubble Column

Knowledge of mixing phenomena is of great value in the mineral and other chemical and biochemical industries. This work aims to analyze the quality of mixedness (QM), the intrinsic mass transfer (MT) number, and the MT efficiency based on information entropy theory in the counter-current microstructured slurry bubble column. A thorough analysis is conducted to assess the effects of particle loading, gas and slurry velocity, and axial variation on the QM. The range of gas velocity, slurry velocity, particle size, and particle loading was 0.011–0.075 m/s, 0.018–0.058 m/s, 242.72–408.31 μm, and 15.54–88.94 kg/m3, respectively. QM is a time-dependent parameter, and the concept of contact time has been used for scale-up purposes. The maximum QM was achieved at dimensionless times of 0.40 × 10−3, 0.15 × 10−3, and 0.85 × 10−3 for the maximum superficial gas velocity, particle loading, and axial height, respectively. The gas velocity positively influenced both the intrinsic MT number and its efficiency. In contrast, the slurry velocity and particle loading had a negative effect. The present theoretical analysis will pave the path for industrial process intensification in counter-current flow systems.

Utilization of unrejected ammonium for fouling prevention in a forward osmosis process tested with real primary wastewater from Hong Kong

Forward osmosis (FO) process is known to have high rejection towards foulants and ions. However, the polyamide surfaces of FO membranes are usually designed to be negatively charged, which results in low ammonium rejection. This study proposes to utilize the unrejected ammonium in the draw solution (DS) of FO processes by adding OCl− to generate monochloramine, which can diffuse back towards the feed side and prevent. Tests were performed to identify the optimal FO operating conditions, such as DS concentration, crossflow velocity, and flow direction. Optimal conditions were determined to be a DS concentration of 1.0 M, a crossflow velocity of 5.4 cm/s and counter-current flow mode. A 72 h fouling tests were also conducted with real wastewater from the Siu Ho Wan Sewage Treatment Works in Hong Kong as the feed. The existence of monochloramine alleviated membrane fouling. The novelty of this study lies on the fact that the chloramine is generated using the unrejected ammonia, and consequently utilizing the generated chloramine that is reversely diffusing towards the feed to prevent the fouling formation. Findings from this study suggest that the generation of monochloramine from unrejected ammonium ions can lengthen membrane life while endowing self-cleaning abilities that prevent severe fouling.

A novel microchannel heat sink with staggered inlet and outlet to improve base surface temperature uniformity

Non-uniform temperature distribution can lead to performance degradation and thermal failure of electronic devices. So as to improve the base surface temperature uniformity, we proposed a novel microchannel heat sink with staggered inlet and outlet. This arrangement divides a complete flow channel into three regions, and the flow direction in each channel can be changed to form different flow modes. The effects of flow mode, the inlet and outlet spacing, Reynolds number and channel length on the temperature uniform performance of base heating surface are investigated numerically. It is found that the microchannel heat sink with staggered inlet and outlet has more uniform fluid distribution and can ensure the same highest temperature in each region to improve the base surface temperature uniformity. The optimal spacing between middle inlet and outlet decreases as Reynolds number decreases for optimal flow mode, and the improving effect of temperature uniformity becomes worse with increasing channel length. Within the calculation parameter range, compared with the straight microchannel unit, the base temperature difference and the pumping power of staggered microchannel unit with countercurrent flow in each region are reduced by 77.6% to 81.3% and 56.1% to 68.8%, respectively.

Molecular insights into mass transfer and adsorption behaviors of hydrocarbon and CO2 in quartz multiple-nanopore system

Exploitating liquid hydrocarbons from unconventional reservoirs is playing an ever-increasing role in addressing global energy supply issues. CO2 huff-and-puff is an environmental and effective method to enhance hydrocarbon recovery and achieve CO2 geo-sequestration simultaneously, playing an important role in carbon capture, utilization, and sequestration (CCUS) projects. The optimization of huff-n-puff operations requires clarifying the adsorption state and migration behaviors of hydrocarbons and CO2 in unconventional reservoirs dominated by nanopores. In this paper, we used molecular dynamics (MD) simulation to investigate adsorption behaviors and mass transfer of CO2and n-decane (nC10) molecules in multiple quartz nanopores by carefully considering pore size and structure effects. It shows that the adsorption behaviors and replacement efficiency of oil molecules are closely related to pore aperture. Interestingly, we found that the surface adsorption of nC10 demonstrates a non-monotonic trend of rising after falling as the pore size decreases from 5 nm to 0.7 nm. Specifically, when the pore size is reduced to ∼ 1 nm, nC10 molecules exhibit a pseudo-double layered distribution state. In such a nanopore, the surface adsorption of nC10 is significantly weakened but thesurface adsorption of CO2 is enhanced, leading to the maximum oil recovery efficiency. Although the reduction of pore width adversely affects the extraction speed of oil, it is generally favorable for improving final oil recovery. In a double-nanopore system, the exchange between nC10 and CO2presents a counter-current flow pattern. By contrast, in the triple-nanopore systems, nC10 and CO2form their respective dominant migration paths and the large pores dominates the equilibrium time. These observations provide a more in-depth understanding of CO2-enhanced oil recovery (CO2-EOR) mechanisms from the molecular level, and reveal new insights into CO2and oil adsorption and migration behaviors in complex nanopores, thus aiding in the efficient implementation of CO2-EOR project.

An experimental investigation on CCFL characteristics during gas/low surface tension liquid counter-current two-phase flow in a small-scaling PWR hot leg typical geometry

A sharp increase in world energy demands which further results in another large progress in the development of nuclear energy establishes comprehensive developments on corresponding mitigation studies. Therefore, as a scenario of accident called LOCA is fundamentally considered, the related phenomena, i.e., the counter-current flow followed by flooding in the primary circuit of PWR, is of a great importance. The present work investigates characteristics of the flooding during a pair of gas/low surface tension liquid counter-current two-phase flow in a complex conduit representing a down-scaled of PWR hot leg typical geometry. Visual observations were obviously carried out to observe the flow phenomenology, while flow parameters were frequently varied. A typical result reveals that the gas flow rate to initiate the flooding decreases with the increase of liquid flow rate. Moreover, exhibiting locations of the onset called locus, a front flooding tends to occur during relatively low liquid flow rates while the higher liquid flow rates exhibit another flooding namely rear flooding. Accordingly, the present investigation provides a package of valuable information on a particular understanding towards the flooding characteristics to overcome the efforts on promoting safety managements on the operation of nuclear power plants..

TOPOGRAPHY AND TIDAL VARIATIONS: IMPACT ON COUNTER-CURRENT FLOW AT THE CONFLUENCE AREA OF TANINTHARYI RIVER ESTUARY

TOPOGRAPHY AND TIDAL VARIATIONS: IMPACT ON COUNTER-CURRENT FLOW AT THE CONFLUENCE AREA OF TANINTHARYI RIVER ESTUARY

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

The effect of the radial heat loss, upper reservoir temperature, and corrugated wall channel on the flooding critical heat flux

This study measured the flooding critical heat flux (flooding CHF) for two vertical annular channels with different channel gaps. The experiments were conducted at atmospheric pressure and with no flow. The effects of the upper reservoir temperature within 30–80 °C and radial heat loss have been studied. It was found that the upper reservoir temperature has a small effect on the flooding CHF values, and it varied in the range of up to 10% compared to the saturated conditions. On the other hand, a significant effect of the radial heat loss was observed on the measured flooding CHF values (up to 100%). The flooding CHF experimental results were compared with numerous empirical correlations from the literature, some initially based on air-water counter-current flow experiments (flooding experiments with no heating). It was found that based on the onset flooding velocity experiments, the flooding CHF results can be successfully predicted. The effect of the wall corrugation on the flooding CHF was also examined in the simple air-water counter-current flow setup. This study shows that the air flooding velocity in a corrugated channel is higher than in a smooth channel with the same cross-section geometry and dimensions. Therefore, using a smooth channel flooding CHF value for a corrugated one guarantees a conservative result.

Experimental and numerical investigation of a counter-current flow bubble column

Bubble columns are gas–liquid contactors that are used in many process-engineering applications. A counter-current liquid flow is frequently imposed to adjust the bubbles’ residence-time and thus optimize mixing and mass-transfer. The present work describes measurements in such a device together with corresponding computational fluid dynamics simulations based on the Eulerian two-fluid framework. Bubble-size and -velocity are measured by shadow-imaging for a large range of gas and counter-current liquid flow rates, as well as different nozzle sizes. The corresponding liquid flow-fields are characterized by Particle Image Velocimetry. From the large experimental database, a few cases are selected to analyze the flow structure and effects of the bubble-size. In the simulations, different models for the drag- and lift-force acting on the bubbles are evaluated. While good agreement between experiments and simulations could be achieved for the gas-fraction and gas-velocity, differences are found for the liquid-velocity, which is generally overestimated in the calculations.

Evaluation of temperatures and flow areas of the Phebus Test FPT0

The cladding temperatures and axial mass distribution computed by MAAP5 were compared with their measured values in the test bundle of the Phebus Test FPT0. The computed cladding temperatures were in good agreed with the measured values in the pre-transient phase. In the transient heat-up phase, the computed temperatures were overestimated by the Baker-Just correlation in MAAP5, but the computed temperatures could simulate the subsequently measured values. The computed mass distribution in the axial direction was in qualitative agreement with the measured one for post-test fuel damage observations. The calculated flow areas of inner and outer regions in the test bundle were compared with the photographic observations. MAAP5 computed them at the height of 0.2 m where the molten pool formed was in qualitative agreement with the photographic observations. It was found that the remaining steam flow paths might be caused by the gas-liquid two-phase flow counter-current flow limitation.

Development of a heat-penetration criterion to characterize steam chamber growth and propagation dynamics during a steam-assisted gravity drainage (SAGD) process

Steam chamber growth and propagation dynamics dictates the success of a steam-assisted gravity drainage (SAGD) process, which is an enhanced oil recovery (EOR) method for effectively and efficiently exploiting the enormous heavy oil and bitumen reserves. To set the baseline, this work is focused on the SAGD process with pure steam. After numerous trials and errors, a heat-penetration criterion has been developed and integrated into a reservoir simulator for the first time to characterize steam chamber growth and propagation dynamics conditioned to the production profiles during a steam-assisted gravity drainage process. More specifically, based on the heat transfer principle, a pore-scale heat-penetration criterion has been developed with respect to both heat conduction and convection for calibrating the temperature distributions ahead of the steam chamber interface (SCI). Subsequently, such a heat-penetration criterion has been upscaled to a grid-scale for its integration with a commercial reservoir simulator (i.e., CMG STARS), allowing us to pragmatically and accurately quantify the dynamic temperature field during a steam-assisted gravity drainage process. Furthermore, three sets of multiphase relative permeabilities are employed to evaluate comprehensive impacts of the thermally sensitive co/counter-current flows. Finally, such a heat-penetration criterion has been verified by reproducing the experimentally measured steam chamber during a steam-assisted gravity drainage process from a large-scale 3D physical model. With such an integrated method, good agreements between the measured and simulated data including production profiles and temperature distributions have been found, whereas the dynamics of production profiles and corresponding steam chamber propagations cannot be well reproduced solely with a commercial reservoir simulator. Sensitivity analysis has been performed to examine the effects of thermal-sensitive properties, steam chamber configuration, boundary, multiphase flow behaviour (e.g., co-current and counter-current flow), and gridblock dimension. In practice, the newly developed heat-penetration criterion can be seamlessly integrated with a commercial reservoir simulator. Such an integrated method can significantly reduce the model complexities and uncertainties, providing a simple and convenient way to dynamically and accurately characterize the steam chamber growth and propagation dynamics within a unified, consistent, and efficient framework.

Experimental Studies on Two-Phase Flow with a Novel Slotted Plate Internal in an Air Pulsed Column

ABSTRACT A novel air pulsed column plate internal featuring plates having concentric circular slots of fixed width (3 mm) is conceptualized, tested, and compared against standard sieve plate internal for counter-current two-phase flow. This new plate design (slotted plates) offers significant intensification in terms of specific interfacial area by as much as ~ 50% vis-à-vis standard sieve plates. The studies are carried out in a 3 inch diameter air pulsed column with tap water as the continuous phase and 30% (v/v) tributyl phosphate in dodecane as the dispersed phase. A high-speed imaging system is used to quantify the state of dispersion and obtain drop size distribution along with Sauter mean drop diameter. The effects of pulsing velocity, dispersed phase velocity and continuous phase velocity on dispersed phase holdup, drop size and consequentially specific interfacial area have been systematically studied for both internals. In all cases, slotted plates are characterized by generation of smaller drops and a higher holdup leading to significant improvement in specific interfacial area. Previously reported correlations for estimating dispersed phase holdup and Sauter mean diameter in pulsed sieve plate columns are found to be inadequate for slotted plate internals. Therefore, new correlations for prediction of holdup and drop diameter have been proposed for the new plate design.

Investigation of Taylor bubble dynamics in annular conduits with counter-current flow

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 (C0) 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 (Frl) 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. C0 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 C0. The increasing Frl and θ lead to a streamlined bubble with pointed nose and thus a reduction in the wrap angle (θwrap), ultimately leading to reduced drag compared to the vertical annulus case and a decrease in C0. As the ε increases, which is accompanied by an increase in the degree of bubble eccentricity, the corresponding C0 decreases. For a constant Eo = 100 and Nf = 160 with inclination angle of θ = 40°and eccentricity of ε = 0.5, the C0 < 1 is observed.