Gas-liquid Interfacial Area Research Articles

Methanogenic activity in water-saturated reservoir analogues for underground hydrogen storage: The role of surface area

The activity of methanogenic Archaea in porous formations is influenced by various pore characteristics, including porosity, surface area, and the gas-liquid interfacial area. This study explores the impact of surface area on methanogenic activity using techniques such as MICP, NMR, SEM, and μCT. The cells of Methanothermococcus thermolithotrophicus, ranging from 1 to 2 μm, indicate that pores smaller than this threshold are not accessible for microbial traversal and colonization. Upon normalization of microbial activities based on pore volume and interfacial area, the findings exhibit strong correlations with specific surface areas of accessible pores in the examined rocks, as determined by MICP, NMR, and SEM. These areas ranged from 0.001 to 0.017 m2/g, 0.003–0.024 m2/g, and 0.012–0.02 m2/g, respectively. The normalized activities increase from 0.19 to 0.44 mM/(h·cm3·cm2) with an increase in the specific surface area, varying by method. Furthermore, an empirical model has been established to quantitatively evaluate hydrogen loss during underground hydrogen storage or the efficiency of bio-methanation, incorporating pore volume, specific surface area, and interfacial area.

Intensifying interfacial oscillations in falling film flows over rectangular corrugations

Unsteady film flows play an important role in intensifying heat and mass transfer processes, with applications, e.g., in falling film absorbers or reactors. In this context, the influence of surface structure modification on the wave dynamics of falling film flows is experimentally investigated based on localized film thickness time series data. Arrays of rectangular ridges oriented perpendicular to the main flow direction are considered, and an optimum ridge distance is identified, at which particularly strong interfacial oscillations are induced in the falling film. These potentially result from the interaction of the flow with a statically deformed base film under resonance-like conditions. The transient destabilization is amplified in the case of narrow ridge sizes, where inertia-driven flow features are particularly pronounced. With regard to mass transfer applications, the structure-induced increase in gas–liquid interfacial area may be of secondary importance compared to changes in internal flow conditions.

Biomimetic fractal pillars for the thermal–hydraulic enhancement of a vapor chamber

Owing to their remarkable thermal–hydraulic performance, vapor chambers have diverse applications, especially for cooling electronic devices. However, the performances of circular and noncircular pillars throughout the entire vapor chamber under identical wick volume conditions have been compared in very few studies. In this study, a series of noncircular pillar arrays featuring biomimetic tree-like fractal networks is introduced. The incorporation of fractal pillars significantly enhances the thermal–hydraulic performance of the vapor chamber because the gas–liquid interface area is extended. Compared to a vapor chamber with circular pillars, the maximum condensation surface temperature difference, total thermal resistance, and liquid pressure drop of this vapor chamber with fractal pillars are reduced by up to 57.8 %, 13.8 %, and 10.9 %, respectively. In particular, with large branch levels and pillar diameters, the fractal structure is pivotal for boosting the overall performance. When the number of pillars is increased, the fractal structure's impact on the thermal performance reaches a limit, whereas its boosting effect on the flow performance weakens. This study is a pioneering exploration of the application of stretched geometries in pillar-type vapor chambers, with fractal pillars utilized in showcase demonstrations.

Computational Fluid Dynamics Modeling of Multiphase Flows in a Side-Blown Furnace: Effects of Air Injection and Nozzle Submerged Depth

The side-blown smelting process is becoming popular in the modern metallurgical industry due to its large potential for dealing with complex materials. To further enhance its efficiency, it is essential to comprehensively understand the complex gas–liquid flow behavior in the smelting bath. In this study, the volume-of-fluid method is employed to establish computational fluid dynamics modeling on a 1:5 scaled model of a side-blown furnace. The simulation was validated against the experimental results. Notably, the influences of the nozzle’s submerged depth, injection velocity, and angle were systematically investigated. The results show that increasing the injection velocity from 29.44 to 58.88 m/s resulted in 52.97%, 116.67%, 500.00%, and 5.88% increases in the interface area, liquid velocity, liquid turbulent kinetic energy, and gas penetration depth, respectively. The maximum gas–liquid interface area, gas penetration depth, velocity, and turbulence of the liquid were found at an injection angle of 30°. Furthermore, increasing the submerged depth increased the interface area and the velocity of the liquid but decreased the turbulent kinetic energy of the liquid. Overall, increasing the injection velocity is considered a more effective measure to strengthen the smelting intensity.

Stagnant liquid layer as “Microreaction System” in submerged plasma Micro-Jet for formation of carbon quantum dots

This study aims to intensify reactivity via bespoke transient hydrodynamics in a plasma-activated three-phase catalyst system. Likewise, three-phase plasma systems in literature are not well designed, understood and commercially available. The synthesised N-doped carbon quantum dots, with application as fertilisers and wastewater treatment was evaluated as a model reaction. A plasma microjet was produced using a commercial plasma system, creating an almost flat, large interface covering a thin stagnant liquid layer with a catalyst bed underneath. In this hydrodynamic regime, plasma can penetrate the catalyst bed via the stagnant thin liquid film and polarise the plasma-liquid interface. The new process regime’s effectiveness is proven by the enhanced reaction rate achieved by raising liquid diffusivity toward the catalyst bed through solvent viscosity reduction. Results indicate that the reaction rate depends on the small surface area interacted with the plasma jet amid an excess of excited species, not the total gas–liquid interface area. The plasma process competes energetically with the best dielectric barrier discharge processes and uses less energy than microfluidic processing in chemical microreactors. High momentum transfer from the plasma jet to the liquid partly evaporates non-water additives, impacting process design and requiring reduction.

Dispersion Behavior of a Droplet Impacting a Single Fiber.

The high-gravity reactor, known for its excellent mass transfer capability, plays a crucial role in the carbon capture process. The wire mesh packing serves as the core structure for enhancing mass transfer performance. Understanding the underlying dispersion mechanism requires a thorough exploration of the dynamics of droplet impact on a single fiber. This work aimed to numerically study the process of a droplet impacting a single fiber by applying the volume of fluid method. The effects of initial velocity (u0), initial diameter (D0), impact eccentric distance (e), and impact angle (θ) on the deformation evolution and dispersion characteristics of a droplet impacting a single fiber were systematically studied. Central or vertical impacts can be categorized into four main stages: splitting, merging, stretching, and breaking. Meanwhile, asynchronous breaking, sliding splitting, and oblique stages were observed during eccentric and nonvertical impacts. Subsequently, dimensionless time (t*) and the rate of increase of the gas-liquid interfacial area (η) were introduced to quantitatively analyze the dispersion characteristics postimpact. Increasing the initial velocity, reducing the droplet diameter, minimizing the impact eccentric distance, and maximizing the impact angle all contribute to enhanced dispersion performance. A correlation for the maximum increase rate of the gas-liquid interfacial area of the droplet was proposed, with errors less than ±15%. Finally, the deformation mechanism of droplet impact on a fiber was summarized by analyzing the influences of differential pressure inside and outside the liquid film, as well as gas vortices.

Thermal-hydraulics performance evaluation of bubble swarms sweeping tube bundles in a direct contact gas-liquid-solid reactor

Direct contact gas-liquid-solid reactor pertains to an extremely high efficiency heat-exchange facility in industrial application. Nevertheless, the scarcity of quantitative analysis data hinders the optimal design of this type of reactor. In the present study, a novel variable bubbles size modeling approach which considers the bubble swarms breakup and coalescence rates, is proposed to evaluate the complex thermal-hydraulics performance of bubble swarms sweeping tube bundles. On the basis of verifying the responsibility of the numerical modelling with published experimental data, the intrinsic link of hydrodynamics and thermodynamics parameters on reactor features, including field characteristics, gas holdup, bubble swarms diameter distribution, gas–liquid interfacial area, temperature difference and heat flux inside different tube bundles regions, are deeply revealed. Results demonstrate that the temperature difference between bubble swarms and tube bundles walls is approximately equal to 2 K. Interestingly, different positions of heat exchanging tubes affect the peak value of circumferential heat transfer coefficient. For typical Tube 1–2, the maximum value of 3146.28 W/m2·K appears around 162°. The presence of tube bundles gives rise to the well-distributed iso-surfaces of bubble swarms which contributes to enhance heat transfer. When superficial gas velocities are respectively 0.09 m/s, 0.12 m/s and 0.14 m/s, the average bubble warms diameters are 13.47 mm, 16.22 mm and 17.24 mm. When initial liquid phase height increases from 342 mm to 378 mm, the corresponding gas–liquid interfacial area decreases by 16.2 % in total. Finally, two new modified dimensionless correlations were developed for the prediction of gas holdup and Nusselt number. The prediction errors are respectively 10 % and 6 %. The findings can improve the awareness for promising applications in design and scale-up processes of direct contact gas-liquid-solid reactor.

Superior Heat and Mass Transfer Performance of Bionic Wick with Finger-like Pores Inspired by the Stomatal Array of Natural Leaf.

The thermal management of electronics has gained significant attention, with loop heat pipes (LHPs) emerging as an attractive solution for heat dissipation. The heat transfer performance of LHPs is influenced by the heat and mass transfer processes within the wick. However, designing the pore diameter of the wick is challenging due to the different requirements of flow resistance and capillary force. Specifically, the working fluid needs large pores to reduce resistance, while the liquid suction requires small pores to provide a large capillary force. To address this issue, we drew inspiration from the stomatal array of natural leaves used for transpiration and developed an alumina ceramic bionic wick with finger-like pores using the phase-inversion tape casting method. The finger-like pores in the wick resemble the straight hole structure of stomata, which increases the gas-liquid interface area within the wick. This design allows for timely discharge of water vapor generated by boiling, thereby reducing mass transfer resistance. Additionally, numerous micrometer-sized small pores surrounding the finger-like pores provide sufficient capillary force to replenish liquid for the gas-liquid evaporation interface. Experimental results demonstrate that the introduction of finger-like pores in the wick increases gas and water permeabilities by 2.4 and 5.2 times, respectively. Furthermore, the superior heat and mass transfer performance of the bionic wick was demonstrated with an LHP. This work effectively addresses the conflicting demands of capillary force and flow resistance, enhancing the heat transfer performance of LHPs, which holds great promise for addressing heat dissipation challenges in high power density electronic chips and has potential applications in aviation, aerospace, and microelectronics for efficient thermal management.

CFD simulation and experimental study of CO2 absorption in a rotating packed bed

The rotating packed bed (RPB), a process intensification equipment, has been widely studied and applied to chemical engineering processes such as gas absorption, nanomaterial preparation, and polymer devolatilization. In this study, we presented a typical RPB model to study the intensification mechanism of high gravity on gas-liquid mass transfer. Based on this, three-dimensional computational fluid dynamics (CFD) simulations and experiments of CO2 physical absorption were conducted to investigate the gas-liquid mass transfer characteristics in the RPB. The predicted and experimental values of CO2 saturation rates of the liquid phase showed good agreement, and the errors were within ± 15 % under various operating conditions. Moreover, detailed flow field and mass transfer information that are difficult to measure experimentally, such as the distribution of CO2 mass fraction in the liquid, liquid holdup, turbulent kinetic energy dissipation rate, and gas-liquid interfacial area, were analyzed by CFD simulation results. These results provide a solid foundation for the further development and application of RPB.

Pore-scale Simulation of Two-phase Flow in Foamed Porous Materials

This paper establishes a pore cell model of foamed silicon carbide material based on a tetradecahedron structure, and uses FLUENT software to numerically study the flow rate and pressure drop changes in the porous structure at different flow rates and the gas-liquid two-phase flow state of the channel. The research results show that the porous skeleton structure has a great influence on the velocity and pressure distribution in the calculation domain; the inlet flow velocity has a certain impact on the gas-liquid mixing zone and gas-liquid interface area in two-phase flow. The application of tetradecahedral porous media increases the thickness of the gas-liquid mixing zone and the phase interface area are increased, with a maximum increase of 11.5%, thus promoting gas-liquid heat and mass transfer.

Investigation of hydrodynamic performance in a staggered multistage internal airlift loop reactor

The multistage internal airlift loop reactor (MIALR) has shown promising application prospects in gas–liquid–solid reaction systems. However, traditional MIALRs have a global circulation with strong interstage liquid-phase exchange. This paper proposes a staggered multistage internal airlift loop reactor (SMIALR) that incorporates special guide elements to create a staggered flow. Both experiments and computational fluid dynamics-population balance model simulations were conducted to investigate the hydrodynamic performances of MIALR and SMIALR. The results demonstrate that SMIALR exhibits a local circulation at each stage. Bubbles have a longer residence time in SMIALR, resulting in a 28.35%–55.54% increase in gas holdup and a 7.27%–13.69% increase in volumetric mass transfer coefficient. The gas–liquid mass transfer coefficient of SMIALR was improved by increasing the gas–liquid interfacial area. Additionally, the radial distribution of solids was found to be more uniform. This study offers insights for optimizing MIALR and provides a theoretical foundation for the design and scale-up of SMIALR.

Effects of viscosity on hydrodynamics and mass transfer under a wire mesh-coupled solid particles method

Many practical industrial processes require gas–liquid mass transfer in highly viscous liquids, and liquid viscosity affects bubble characteristics and gas–liquid mass transfer. The current study investigated the effects of liquid viscosity on bubble dynamics and gas–liquid mass transfer via shadow imaging and dynamic oxygen dissolution methods, and the influence of fluid viscosity on the hydrodynamic effect when using a wire mesh-coupled solid particles method. The coupling strategy was associated with a bubble size regulation effect, with greater viscosity increasing the gas–liquid interface area by 27%–55% compared with unreinforced gas–liquid flow, which was superior to embedded wire mesh and added solid particles methods. Increased viscosity weakened the mass transfer enhancement effect of the coupling method, but the coupling method still effectively enhanced the gas–liquid mass transfer process, increasing the volumetric mass transfer coefficient (KLa) by 80%–130% compared to non-enhanced gas–liquid flow. Novel empirical KLa correlation equations were developed to predict the effects of the coupling method on gas–liquid mass transfer processes, and those equations exhibited good reliability and predictive capacity.

Efficient conversion of propane in a microchannel reactor at ambient conditions

The oxidative dehydrogenation of propane, primarily sourced from shale gas, holds promise in meeting the surging global demand for propylene. However, this process necessitates high operating temperatures, which amplifies safety concerns in its application due to the use of mixed propane and oxygen. Moreover, these elevated temperatures may heighten the risk of overoxidation, leading to carbon dioxide formation. Here we introduce a microchannel reaction system designed for the oxidative dehydrogenation of propane within an aqueous environment, enabling highly selective and active propylene production at room temperature and ambient pressure with mitigated safety risks. A propylene selectivity of over 92% and production rate of 19.57 mmol mCu−2 h−1 are simultaneously achieved. This exceptional performance stems from the in situ creation of a highly active, oxygen-containing Cu catalytic surface for propane activation, and the enhanced propane transfer via an enlarged gas-liquid interfacial area and a reduced diffusion path by establishing a gas-liquid Taylor flow using a custom-made T-junction microdevice. This microchannel reaction system offers an appealing approach to accelerate gas-liquid-solid reactions limited by the solubility of gaseous reactant.

Hydrodynamics of CH4-Sn molten-metal bubble columns under electromagnetic field using computational fluid dynamics

The use of molten metal bubble column reactors (MMBCRs) for CO2-free H2 production via non-oxidative CH4 pyrolysis has gained attention due to little catalyst deactivation and simple downstream processing. Maintaining a small size of bubbles is crucial to enhance CH4 decomposition rates in MMBCRs. In this study, the effect of electromagnetic field on the hydrodynamics of MMBCRs was investigated using volume-of-fluid computational fluid dynamics (VOF-CFD) coupled with a large-eddy simulation (LES) model for turbulence and a magnetohydrodynamic (MHD) model for the electromagnetic field. Hydrodynamic parameters such as the gas holdup (αG), mean bubble size (d32), and gas–liquid interfacial area (as) were obtained from the validated VOF-CFD model in the bench-scale CH4-Sn system at 900 °C. A horizontal electromagnetic field with alternating current (AC) at an electromagnetic field strength of 1.0 T promoted bubble breakup and increased as from 8.6 to 18.2 m2/m3 compared to the MMBCR without electromagnetic field.

Characteristics analysis of multi-channel ceramic membranes for dilute gas absorption in falling film operation

Capturing dilute gases has posed a significant challenge due to the extremely low mass transfer driving force associated with them. Falling film-based absorption using porous membranes emerges as a promising technology for gas separation, offering a substantial gas–liquid interface area while simultaneously eliminating mass transfer resistance within pores that is inherent in hydrophobic membrane-based absorption processes. In this study, we investigated the mass transfer performance of multi-channel ceramic membranes in falling film-based dilute CO2 absorption under various gas and liquid operating conditions. Experimental tests and computational fluid dynamics (CFD) simulations were conducted to examine the effects of pore size and geometrical configuration on the distribution of liquid and gas flows across different channels. Simulations indicated that the optimization of multi-channel ceramic membranes for the falling film-based dilute gas absorption should prioritize achieving a more rational distribution of gas–liquid flows. When the disparity between liquid and gas distribution in the outermost channels exceeded 40%, as opposed to cases where the difference was within 20%, there was a reduction of over 50% in mass transfer performance.

Effect of surfactant frequently used in soil flushing on oxygen mass transfer in micro-nano-bubble aeration system

In-site soil flushing and aeration are the typical synergetic remediation technology for contaminated sites. The surfactant presented in flushing solutions is bound to affect the aeration efficiency. The purpose of this study is to evaluate the effect of surfactant frequently used in soil flushing on the oxygen mass transfer in micro-nano-bubble (MNB) aeration system. Firstly, bio-surfactants and chemical surfactants were used to investigate their effects on Sauter mean diameter of bubble (dBS), gas holdup (ε), volumetric mass-transfer coefficient (kLa) and liquid-side mass-transfer coefficient (kL) in the MNB aeration system. Then, based upon the experimental results, the Sardeing’s and Frössling’s models were modified to describe the effect of surfactant on kL in the MNB aeration. The results showed that, for the twenty aqueous surfactant solutions, with the increase in surfactant concentration, the value of dBS, kLa and kL decreased, while the value of ε and gas–liquid interfacial area (a) increased. These phenomena were mainly attributed to the synergistic effects of immobile bubble surface and the suppression of coalescence in the surfactant solutions. In addition, with the presence of electric charge, MNBs in anionic surfactant solutions were smaller and higher in number than in non-ionic surfactant solutions. Furthermore, the accumulation of surfactant on the gas–liquid interface was more conspicuous for small MNB, so the reduction of kL in anionic surfactant solutions was larger than that in non-ionic surfactant solutions. Besides, the modified Frössling’s model predicted the effect of surfactant on kL in MNB aeration system with reasonable accuracy.

Mass transfer enhancement and hydrodynamic performance with wire mesh coupling solid particles in bubble column reactor

It is of vital significance to investigate mass transfer enhancements for chemical engineering processes. This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas–liquid mass transfer process in a bubble column. Particle image velocimetry (PIV) technology was employed to analyze the flow field and bubble motion behavior, and dynamic oxygen absorption technology was used to measure the gas–liquid volumetric mass transfer coefficient kLa. The effect of embedding wire mesh, adding solid particles, and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared. The results show that the gas–liquid interface area increases by 33% to 72% when using the wire mesh coupling solid particles strategy compared to the gas–liquid two-phase flow, which is superior to the other two strengthening methods. Compared with the system without reinforcement, kLa in the bubble column increased by 0.5–1.8 times with wire mesh coupling solid particles method, which is higher than the sum of kLa increases with inserting wire mesh and adding particles, and the coupling reinforcement mechanism for affecting gas–liquid mass transfer process was discussed to provide a new idea for enhancing gas–liquid mass transfer.

Mechanism of bubble cutting by fibers: Experiment and simulation

Bubble fragmentation plays a crucial role in plenty of industrial applications. The incorporation of fiber mechanism enhances fluid turbulence and facilitate bubble fragmentation in gas–liquid flows. However, the bubble cutting mechanism associated with fibers is not fully understood. Here, we sought to elucidate the underlying mechanisms and characteristics of bubble fragmentation by varying solution type, bubble impact velocity, fiber diameter, and surface wettability. Based on the experimental outcomes observed under these varied conditions, a mathematical model describing the bubble fragmentation pattern was developed. Further analysis of velocity, gas–liquid interfacial area liquid film, and dissipation energy by CFD simulations proved instrumental in explicating the results observed in our visual experiments. The interface area of bubble increases from 0.8 × 10-4 m2 to 1.45 × 10-4 m2 with the enhancement of fiber hydrophilicity. This investigation enriches our understanding of bubble fragmentation facilitated by fibers, thereby guiding the optimal design of fibers for enhanced gas–liquid interface interactions.

CFD simulation of geometrical parameters effects on the hydrodynamic characteristics and CO2 absorption efficiency of Arc-RPB

The Computational Fluid Dynamics (CFD) technique was used to study the effect of the geometrical parameters on the intensification of hydrodynamic parameters and Carbon dioxide (CO2) absorption efficiency by Mono-Ethanol-Amine (MEA) solution in a novel Arc-blade Rotating Packed Bed reactor (Arc-RPB). The VOF multiphase approach and RNGk-ε turbulent model were used to study the multiphase and turbulent behavior of the flow field in the computational domain, respectively. The effects of liquid flow rate, the bed wire mesh diameter, and number of the mesh layers were studied on the liquid holdup (αL), gas-liquid interfacial area (Aint) and liquid dispersion index (Id). Considering the Arc-RPB bed wire mesh diameter from 0.2 mm to 1.6 mm showed that αL, Aint and Id decrease 20%, 29% and 11%, respectively. By examining the effect of the bed layers enhancement, the liquid holdup αL decreased by about 36% but, Aint and Id reached a maximum value at 16 bed layers. Finally, with study the effect of the bed geometrical parameters on CO2 absorption efficiency, results showed the efficiency reduces about 7.5% with increase in the bed mesh diameter and shows a maximum at 16 bed layers.

Investigation of surfactant effect on ozone bubble motion and mass transfer characteristics

The low solubility and low mass transfer efficiency of ozone (O3) in water are important reasons for limiting the application of ozone oxidation technology and advanced ozone oxidation technology. Low-dose surfactants were introduced to affect the behavior of ozone bubbles, influencing the ozone mass transfer efficiency. The motion of ozone bubbles in three different types of surfactant solutions (polyoxyethylene lauryl ether (Brij35), sodium dodecylsulfate (SDS), and cetyltrimethylammonium bromide (CTAB)) was observed. The decrease in surface tension led to a decrease in bubble size, a tendency to spherical shape, an increase in gas content and residence time, a decrease in lateral displacement of a single bubble, and a more stable trajectory. The effect of surfactants on ozone mass transfer was further investigated. The addition of surfactant was found to increase the gas-liquid interface area but decrease the liquid phase mass transfer coefficient, and the extent of the two opposite effects varied for different surfactants. The analysis combined with the removal of pollutant p-Nitrophenol (PNP) showed that the addition of the nonionic surfactant Brij35 and the anionic surfactant SDS inhibited ozone mass transfer, while low concentrations of the cationic surfactant CTAB enhanced ozone mass transfer. When the CTAB concentration was 3 mg L−1, the ozone volume mass transfer coefficient reached a maximum of 0.2902 min−1.