Increase In Interfacial Area Research Articles

Two-group interfacial area concentration model for dispersed gas-liquid flows in large-diameter pipes

Interfacial area concentration (IAC) plays a critical role in heat and mass transfers between gas and liquid phases through the interfaces. As interfacial area increases, mass and heat transfers between phases increase. Hence, a reliable IAC estimation is important for two-phase flow numerical simulations to conduct engineering designs and safety analyses. Gas bubbles show different behavior according to their shapes and sizes. Based on the size, gas bubbles can be classified into two groups that show different characteristics, such as IAC. Hence, two-group modeling helps to achieve a general approach for estimating the IAC in bubbly to beyond-bubbly flow regimes. Available models in the literature use empirical correlations to obtain group one and group two void fractions. These empirical approaches are not reliable for different flow conditions. In addition, these models are usually complex with several empirical constants. This study aims to develop a two-group area-averaged IAC model for upward vertical dispersed flows through large-diameter pipes. In addition, this study proposes using a general approach based on the two-group drift-flux model to calculate two-group void fractions rather than applying empirical correlations. The models are evaluated using 156 two-group measured data points in dispersed flow conditions through large-diameter pipes. The resulting prediction errors for group one and group two IAC models are 24.1 % and 34.2 %, and the errors for group one and group two void fraction predictions are 22.8 % and 25.6 %, respectively.

A numerical study of thermal shrinkage influence on the impact dynamics of alumina droplets thermally sprayed on flat, grit-blasted and laser treated surfaces

Thermal spray splat morphology and its microstructure are of significance to the coating resulting properties. Depending on the material, the changes in density as the droplet solidifies during splat development and solidification could have a substantial role in the particle deformation dynamics, formation of porosity and subsequent adhesion to the flat or rough target surface.In the current study, the effect of shrinkage on the final splat shape is numerically investigated for collisions occurring under several high-speed impact conditions using the Volume-of-Fluid (VOF) method on real surface topography. This influence is also studied for the interaction of two successive impacting particles. The developed models study the splat impact, development and dynamics of heat transfer on flat, laser-patterned, grit-blasted surfaces and numerically designed features. The results of droplet material variable density cases are compared with those assuming constant density. Experimentally obtained single splat depositions are also used to validate the developed models and obtained numerical results.Findings show that micro substrate surface features lead to splat stretching, porosity and limited finger creation subsequent to improved solidification through interfacial contact area increase. Macro surface characteristics, however, lead to splashing and separation from the substrate surface driven by fluid instabilities. Irrespective of the interface topography, shrinkage processes reduce droplet spreading and accentuate splat feature discontinuities such as porosity.

Enhancement of ozonation using microbubbles – Micropollutant removal, mass transfer and bromate formation

Microbubble technology is a promising development in the optimisation of gas–liquid contacting processes. When applied to ozonation, microbubbles have demonstrated significant enhancements to mass transfer, dissolved ozone residual and the speed and extent of compound removal. However, the mechanism by which microbubbles enhance performance over conventional bubbles is not well understood and numerous explanations exist within the literature. To elucidate the critical components that drive such enhancements the performance of microbubbles (Sauter mean diameter 37 µm) and conventional bubbles (5.4 mm) were compared under identical conditions in terms volumetric mass transfer coefficient, steady state dissolved ozone concentration, rate constant for ozone self-decomposition and the rate constant for degradation of two pesticides: mecoprop and metaldehyde. Overall, the improvement observed in performance can be attributed to the increase in the volumetric mass transfer coefficient through the combination of an increase in specific interfacial area and a decrease in the mass transfer coefficient. The increase in area outweighed the decrease in mass transfer coefficient such that an overall improvement factor of 1.6 was observed for microbubbles over conventional bubbles. All other differences were an artefact of the enhanced mass transfer leading to higher dissolved ozone concentrations when operating at a fixed input dose. For the first time it has been shown that when normalised to the amount of ozone transferred to the water, no enhancement in hydroxyl radical production, bromate formation or impact from the background constituents could be observed.

Controllable generation of multi-row bubbly flow in coupled microstructures and its boosting of photocatalytic decarboxylative carbonylation

Continuous-flow microreactor technology has emerged as a powerful driver of process innovation in photocatalysis. However, microfluidic schemes that are ideal for gas–liquid photoreactions are still limited by the low specific interfacial area. Herein, we invent for the first time a coupled microstructure comprising sudden contraction, shearing, and sudden expansion parts, which can generate microbubbles with smaller sizes under lower flow rates compared with the conventional T-junction. Based on bubble dynamics studies, a predictive model for the bubble size, with prediction errors of less than 10%, is established. Interestingly, the generated microbubbles can be induced by the expansion flow to form a multi-row bubbly flow. Additionally, predictive models for the row number are proposed to guide its controlled production. Computational fluid dynamics simulations show a 22.8-fold increase in specific interfacial area for the five-row bubbly flow compared to the segmented flow. Moreover, the average dissolved oxygen concentration at a given time increases by 34.0 times. Further, photocatalytic decarboxylative carbonylation limited by oxygen mass transfer is employed as the model reaction, demonstrating the excellent performance of multi-row bubbly flow in enhancing the gas–liquid photocatalysis, and the stronger enhancement at higher row number. Subsequently, the phototransformation achieves 96.3% yield within 19 min at a six-row bubbly flow, and the space–time yield reaches 6.82 gL–1 h−1, thus indicating the high efficiency of the developed microdevice. The multi-row bubbly flow enabled by this coupled microstructure provides a new process window for continuous, efficient, and controllable gas–liquid photocatalysis.

Fabrication of Biodegradable Poly(Lactic Acid) Composites with High Toughness via In Situ Fibrillation Method and Facile Annealing Process

Elastomer-toughened biodegradable poly(lactic acid) (PLA) composites have been extensively studied; however, improving the toughening efficiency of elastomers with low costs while maintaining the biodegradability of composites remains challenging. In this work, biodegradable PLA/poly(propylene carbonate) polyurethane (PLA/PPCU) composites with high toughness were successfully prepared by the in situ fibrillation method followed by a facile annealing treatment. The chain extender (CE) was added to alter the viscosity ratio of the dispersed phase to the matrix, thereby tailoring dispersed phase morphology. PPCU fibers were observed when the CE content is greater than 0.5 wt %. Due to the increase in interfacial area, the impact strength increased from 5.1 ± 1.1 kJ/m2 for PLA/PPCU/CE blends with droplet-like dispersed phase morphology to 8.3 ± 1.0 kJ/m2 for PLA/PPCU/CE blends with fibrous dispersed phase morphology. Furthermore, when the CE content was 1.5 wt %, the impact strength of PLA/PPCU/CE blends increased sharply to 30.5 ± 3.9 kJ/m2 after a facile annealing treatment, which could be attributed to the greatly increased interfacial area and interfacial strength. This work provides a viable way to improve the toughness of PLA-based blends without sacrificing their degradability, which will facilitate the large-scale practical application of PLA.

CO2 absorption and desorption enhancement by nano-SiO2 in DBU-glycerol solution with high viscosity

Nano-SiO2 was used to enhance the performance of CO2 absorption and desorption in viscous DBU-glycerol solution with a viscosity of about 60 mPa·s. The effects of ultrasonic time in the preparation of nanofluids, solids loading and particle/cluster size of SiO2 on absorbent properties and absorption performance were investigated. Meanwhile, the enhancements of heat transfer and mass transfer with nanoparticles in the desorption of CO2-loaded DBU-glycerol solutions were also analyzed. Proper ultrasonic vibration time and nano-SiO2 loading can both decrease the average particle size in the system which can improve the absorption. The increase of interfacial area between gas and liquid with the addition of nano-SiO2 dominates the enhancement of absorption and it has little effect on the enhancement factor when the nano-SiO2 size is 102 nm or below. But when the particle size is higher than 102 nm, the enhancement factor decreases with the increase of particle/cluster size. The addition of 0.10 wt% SiO2 nanoparticle with a particle size of 16 nm can increase the absorption rate by 31 % compared with base liquid. In desorption process, the desorption rate for CO2-loaded DBU-glycerol solutions can increase 18 % with the addition of 0.10 wt% nano-SiO2 with a particle size of 32 nm. The main reason could be that nano-SiO2 can improve the heating rate of the base fluid and supply plenty of nucleation sites for the formation of bubbles to improve the desorption rate. It shows that nano-SiO2 can be used to enhance both the absorption and desorption processes in solutions with high viscosity.

Unprecedented Triboelectric Effect of Lignin on Enhancing the Electrical Outputs of Natural-Rubber-Based Triboelectric Nanogenerators (TENGs)

Because of a lack of electron donor/acceptor groups, TENGs fabricated from natural rubber (NR) usually produce low electrical outputs. The present study demonstrated that the electrical outputs of NR TENGs could be enhanced by the presence of lignin. Lignin with an unanticipated triboelectric property became a triboelectric active material upon subjecting to ultrasound in a basic solution. Physically, lignin irradiated with ultrasound would undergo particle size reduction from tens of micrometers down to a micrometer in diameter, leading to an increase of interfacial area for triboelectric charge generation. Accompanying the size reduction was a partial depolymerization of lignin arising from the chemical bond cleavage via the nucleophilic attack of hydroxide ions. This event caused an increase of polar functional groups on lignin that benefited the charge generation and transfer. TENGs from the NR/lignin composite generated a power output density up to 500% larger than that produced from NR TENG. However, NR/lignin TENGs suffered from the aggregation of lignin leading to a compromise of the electrical outputs. Therefore, NR was grafted with polyacrylamide (NR-g-PAM) to inhibit lignin aggregation as well as to promote an even distribution of lignin particles in the NR matrix. As a result, NR-g-PAM/lignin TENG was capable of enhancing the power output density to 260 and 1300% compared with that of NR/lignin and NR TENGs, respectively.

Improvement of interfacial adhesion of CuO nanostructured carbon fiber reinforced polymer composites

AbstractHydrothermal technique was used to deposit copper‐oxide (CuO) nanostructures on woven carbon fibers (WCF) to produce a nanostructured interphase that increased the interfacial strength with an epoxy resin matrix. In order to create laminated hybrid composites, CuO‐modified WCF was reinforced with mixture of bisphenol‐A epoxy resin and dimethyl aniline hardener as matrix using the vacuum bagging approach. Enhanced mechanical qualities are the result of increased volume fraction of CuO nanostructures, where the void content is minimal. The mechanical characteristics such as impact strength and tensile strength of CuO‐coated WCF reinforced epoxy resin composite samples were assessed using drop‐down impact test and universal material testing system. The outcomes demonstrate a considerable improvement in impact energy absorption (74.8%), elastic modulus (52%) tensile strength (42%) and in‐plane shear strength (32%) for the CuO‐coated WCF reinforced epoxy resin composites. This work demonstrates that the development of CuO nanostructures can lessen composite delamination and enhance composite performance because of the increase in interfacial surface area between the matrix and the fiber by CuO nanostructures potentially expanding the spectrum of structural applications for these materials.

Failure Mechanisms at the Interfaces between Lithium Metal Electrodes and a Single-Ion Conducting Polymer Gel Electrolyte.

Polymer electrolytes have the potential to enable rechargeable lithium (Li) metal batteries. However, growth of nonuniform high surface area Li still occurs frequently and eventually leads to a short-circuit. In this study, a single-ion conducting polymer gel electrolyte is operated at room temperature in symmetric Li||Li cells. We use X-ray microtomography and electrochemical impedance spectroscopy (EIS) to study the cells. In separate experiments, cells were cycled at current densities of 0.1 and 0.3 mA cm-2 and short-circuits were obtained eventually after an average of approximately 240 cycles and 30 cycles, respectively. EIS reveals an initially decreasing interfacial resistance associated with electrodeposition of nonuniform Li protrusions and the concomitant increase in electrode surface area. X-ray microtomography images show that many of the nonuniform Li deposits at 0.1 mA cm-2 are related to the presence of impurities in both electrolyte and electrode phases. Protrusions are globular when they are close to electrolyte impurities but are moss-like when they appear near the impurities in the lithium metal. At long times, the interfacial resistance increases, perhaps due to additional impedance due to the formation of additional solid electrolyte interface (SEI) at the growing protrusions until the cells short. At 0.3 mA cm-2, large regions of the electrode-electrolyte interface are covered with mossy deposits. EIS reveals a decreasing interfacial resistance due to the increase in interfacial area up to short-circuit; the increase in interfacial impedance observed at the low current density is not observed. The results emphasize the importance of pure surfaces and materials on the microscopic scale and suggest that modification of interfaces and electrolyte may be necessary to enable uniform Li electrodeposition at high current densities.

A Geometrically Well-Defined and Systematically Tunable Experimental Model to Transition from Planar to Mesoporous Perovskite Solar Cells.

A series of perovskite solar cells with systematically varying surface area of the interface between n-type electron conducting layer (TiO2) and perovskite are prepared by using an ordered array of straight, cylindrical nanopores generated by anodizing an aluminum layer evaporated onto a transparent conducting electrode. A series of samples with pore length varied from 100 to 500 nm are compared to each other and complemented by a classical planar cell and a mesoporous counterpart. All samples are characterized in terms of morphology, chemistry, optical properties, and performance. All samples absorb light to the same degree, and the increased interface area does not generate enhanced recombination. However, the short circuit current density increases monotonically with the specific surface area, indicating improved charge extraction efficiency. The importance of the slow interfacial rearrangement of ions associated with planar perovskite cells is shown to decrease in a systematic manner as the interfacial surface area increases. The results demonstrate that planar and mesoporous cells obey to the same physical principles and differ from each other quantitatively, not qualitatively. Additionally, the study shows that a significantly lower TiO2 surface area compared to mesoporous TiO2 is needed for an equal charge extraction.

Oxygen transfer of microbubble clouds in aqueous solutions – Application to wastewater

This study aims at improving the knowledge on the effects of gas injection, bubbles sizes and contaminants on oxygen transfer in microbubble clouds. First the effects of gas injection on oxygen transfer are studied and linked to several parameters that change together with changes in flow rate, namely bubble sizes and rise velocities. Oxygen transfer is then studied in the presence of contaminants that are shown to affect bubble size distribution, modify bubble dynamics and interfacial mass transfer. Oxygen transfer efficiencies are also measured in wastewater and compared with those obtained in aqueous solutions. The agreement between contaminated water in the lab (Triton X100) and wastewater experiments is emphasised as this offers the possibility to develop fundamental understanding relevant to wastewater under laboratory conditions. The role of the surfactants on the volumetric oxygen transfer coefficient is further analysed in terms of specific interfacial area and transfer coefficients, respectively. Interestingly, this shows that the increase in oxygen transfer efficiency as the concentration in Pentanol increases is due to the increase in interfacial area while the transfer coefficients decrease.

Gas absorption in a hydraulic air compressor. Part I: Simultaneous hydrodynamic and mass transfer bubbly flow model

The formulation of a one-dimensional model for the simultaneous evaluation of hydrodynamics and mass transfer in bubbly flow is presented in detail. The mass transfer due to the solubility kinetics and psychrometric aspects of the process is evaluated while accounting for the effects of process temperature and salinity of the liquid phase. While developed for downward co-current bubbly flow, the predictions of the model show good agreement with experimental data found in the literature for co-current upward bubble column. Using the model, the predicted profiles of pressure, temperature, liquid velocity, slip velocity, species’ gas-phase molar flow rate along the axis of the pilot HAC downcomer under selected scenarios are presented. Modelling of the pilot and demonstrator scale HAC downcomers suggest that the psychrometric aspects of the compression process will be the determining factor for selecting HAC operating temperatures. Modelling of gas absorption in aqueous electrolyte solutions suggest that an intent to reduce gas solubility may be defeated due to the reduction of bubble size and the resulting increase in interfacial area. Initialisation of liquid phase concentrations of gas species are discussed with simulations showing the diminishing absorption rate with repeated cycles of gas compression when no gas is removed. The potential impacts on the applications of compressed air production and carbon capture are also discussed.

Foams Stabilized by AquivionTM PFSA: Application to Interfacial Catalysis for Cascade Reactions

AbstractFoams are attractive platforms for engineering gas–liquid–solid catalytic microreactors with enhanced triphasic contact. In this study, the foaming properties of surface‐active AquivionTM perfluorosulfonic acid resin (AquivionTM PFSA) are unraveled. Stable aqueous and non‐aqueous foams are prepared driven by hydrogen bond interactions between AquivionTM PFSA and protic solvents (e.g., benzyl alcohol, aniline, water). In light of these unique properties, a catalytic foam system for one‐pot cascade deacetalization–hydrogenation reactions is designed. As proof of concept, benzaldehyde dimethyl acetal is converted into benzyl alcohol with 84% overall yield at room temperature in a foam system in the presence of AquivionTM PFSA and Pd/SiO2 catalysts, whereas the yield is halved in a non‐foam system. The enhanced reaction efficiency is attributed to a marked increase in interfacial area of the foam system and preferential location of catalytic acid centers at the gas–liquid interface.

Enhancement of thermal conductivity in polymer composites by maximizing surface-contact area of polymer-filler interface

Abstract In this article we discuss in detail the effective approaches to enhance the thermal conductivity in polymer composites. Numerical simulations show that maximizing interfacial area between filler and polymer enhances very significantly the effective thermal conductivity in composites. We show that among the different geometries thermal conductivity is high for those geometries for which the ratio of surface-area to volume is high. For fillers of a particular geometry, by maximizing its surface area without changing the volume fraction of the metallic filler, the effective thermal conductivity increases. Thus, the interfacial area between filler and polymer plays an important role in the enhancement of thermal conductivity. It is also observed that as this interfacial area increases, increase in effective thermal conductivity follows from linear to the logarithmic growth. It should be noted that to inherit the polymer properties there is a restriction on the upper bound of volume fraction of the fillers. The current study brings out an important step in this direction. Our results are technologically very important in designing composite polymers for better heat conduction and are very cost-effective. This study also provides a connection between the bulk and the surface area in effective determination of the thermal conductivity.

Chaotic advection in a recirculating flow: Effect of a fluid-flexible-solid interaction.

The present work is on laminar recirculating flow-induced deformation as well as motion of a neutrally buoyant flexible elliptical solid, resulting in Lagrangian chaos in a two-dimensional lid-driven cavity flow. Using a fully Eulerian and monolithic approach-based single-solver for the fluid flow and flexible-solid deformation, a chaotic advection study is presented for various aspect ratios β ( =0.5-1.0) and a constant volume fraction Φ=10% of an elliptical solid at a constant Ericksen number Er=0.05 and Reynolds number Re=100. Our initial analysis reveals maximum chaotic advection at β=0.5 for which a comprehensive nonlinear dynamical analysis is presented. The Poincaré map revealed elliptic islands and chaotic sea in the fluid flow. Three large elliptic islands, apart from certain smaller islands, were identified near the solid. Periodic point analysis revealed the lowest order hyperbolic/elliptic periodic points to be three. Adaptive material tracking gave a physical picture of a deforming material blob revealing its exponential stretch along with steep folds and demonstrated unstable/stable manifolds corresponding to lowest order hyperbolic points. Furthermore, adaptive material tracking demonstrates heteroclinic connections and tangles in the system that confirm the existence of chaos. For the transient as compared to the periodic flow, adaptive material tracking demonstrates a larger exponential increase of the blob's interfacial area. The finite-time Lyapunov exponent field revealed attracting/repelling Lagrangian coherent structures and entrapped fluid zones. Our work demonstrates an immersed deformable solid-based onset of chaotic advection, for the first time in the literature, which is relevant to a wide range of applications.

Oxygen transfer and bubble sizes occurring in a pilot‐scale cultivation of Bacillus velezensis 83 for the production of poly(γ‐glutamic acid) under two schemes of power drawn

AbstractBACKGROUNDThe influence of power consumption on oxygen transfer during non‐Newtonian and surfactant‐producing microbial fermentations has been scarcely reported. In this work, we study the oxygen transfer and bubble size distributions in a real 100 L fermentation (producing poly(γ‐glutamic acid)) occurring under constant stirring speed (N) and under constant retrofitted power drawn (Pg/V).RESULTSFor constant N fermentations, Pg/V and the volumetric mass transfer coefficient (kLa) decreased 40% and 70% during cultivation, respectively. Fermentations at constant Pg/V showed a decrease similar to that observed for constant N fermentations. Bubble size distributions were also similar for both operational conditions. Although an increase in bubble size was expected at constant N cultivations due to the increasing viscosity of the medium, the Sauter mean diameter (d32) decreased 65%. This singular behavior of d32 was likely caused by surfactin and bacillomycin, metabolites with strong surfactant activity produced by Bacillus velezensis 83 in the cultivations. The use of a constant Pg/V did not counteract the decrease in kLa due to the increase in viscosity. Although the presence of biosurfactants leads to an increase of interfacial transfer area by decreasing d32, the presence of these molecules and the increase in the medium viscosity affected kLa.CONCLUSIONSAn atypical behavior of this system was found, especially in d32, different to that based on common correlations found in the literature. A complex interaction among the multiple factors involved in a real bioprocess for poly(γ‐glutamic acid) production was evidenced. © 2022 Society of Chemical Industry (SCI).

Influence of multiwall carbon nanotubes and styrene acrylic acid on morphology and thermal properties relationship of 80/20 PA6/ABS blends

ABSTRACT Polyamide-6 (PA6), acrylonitrile-butadiene-styrene (ABS), and its blends with compatibiliser (styrene acrylic acid: SAA, multiwall carbon nanotubes: MWNT, and a combination of MWNT and SAA, respectively) have been investigated. It was found that compatibiliser SAA, MWNT, and the combination of MWNT and SAA help refine the morphology. It includes the decrease in the diameter of the droplets, decreases in interparticle ligament thickness (IPDC), and increase in interfacial area per unit volume (Ai) of the dispersed phase (ABS) in the PA6 matrix. In addition, the morphology crystallinity and thermal stability correlations reveal the behaviour of the blend. Crystallinity and thermal stability of combinations will be maximum when the droplet diameter and critical inter-particle distance must be minimum and interfacial area per unit volume must be foremost.

Modification effect of macroporous comb-like polymeric pour point depressants on the flow behavior of model waxy oils

Polyoctadecyl acrylate (POA) is a commonly used pour point depressant (PPD) for waxy crude oil, and its modification to further improve the fluidity of waxy crude oil is a hot research topic. In this paper, using the octadecyl acrylate (OA) as monomer and the divinylbenzene (DVB) as cross-linker, the macroporous polyoctadecyl acrylate (MP-POA) monoliths with a different cross-linking degrees were prepared by high internal phase emulsions template (HIPEs) method. After drying, the monoliths were ground into micron-scale MP-POA PPD and then characterized by FT-IR, SEM, BET, DSC, and XRD. The influence of the MP-POA PPD on the rheology of a model waxy oil was investigated through rheological tests, DSC analysis, and microscopic observation. The results showed that the crystallinity of MP-POA gradually deteriorated with increasing the cross-linking degree, while the rheological improving effect of the MP-POA first enhances and then reduces. We consider that the performance of the MP-POA PPD is influenced by two factors, that is, the crystallization ability and the nucleation template effect. With the increase of the cross-linker dosage, the crystallization ability of the MP-POA deteriorates, which will weaken the performance of the MP-POA PPD; meanwhile, the porosity of the MP-POA increases with increasing the cross-linking degree and then the waxy oil/MP-POA interfacial area increases, which will facilitate the nucleation template effect of the MP-POA PPD and then strengthen the performance of the MP-POA PPD. As a result, When the dosage of crosslinker was 0.5 wt%, MP-POA can best balance the crystallization ability and the nucleation template effect, resulting in the most excellent modification effect on the low-temperature rheology of model waxy oil, which further decreased its pour point by 3 °C and the yield value (10 °C) by 22.4 Pa. (compared with traditional POA).

A Similarity Solutions Approach to Forced Convection via a Porous Medium Attached to Flat Plate

In the present study, a porous medium adjoining a heated flat plate was modelled by a similarity approach to determine the effect of porosity on the heat transfer phenomena. The momentum and energy equations for porous media transport were transformed using an appropriately determined similarity parameter. The solutions to the momentum equations proved to depend only on the porosity and not the material used. The energy equation however was additionally dependent on the combinations of fluid type and metal matrix used and was solved for four combinations; water/aluminum, air/aluminum, air/copper and SAE 20W-50/stainless. The results show that replacing the clear fluid control volume with a porous matrix altered both the velocity profiles and temperature distribution profiles at all Reynolds numbers. As the porosity of the medium decreased, it resulted in an increase in interfacial area as well as thermal diffusion in the direction normal to the plate, both of which was seen to enhance the heat transfer coefficients. Decreasing porosity also resulted in an increase in thermal storage as well a reduction in volume flow rate going through the medium, which on the other hand tend to inhibit convection. Thus, changing the porosity triggered effects on the heat transfer coefficient. This opposing trend favored convection at porosity greater than 0.5 for low Prandtl number fluids. The clear fluid condition has the lowest heat transfer coefficient and the values increased steeply as porosity changed from 0.99 through 0.7. The heat convection curve reached its maximum turning point at a porosity of 0.5 and then reversed in trend. The dimensionless heat transfer coefficient was found to fit the equation hLL/ReL0.5kfPrf=aebPrmc ( a= 0.51966;b=0.54683;c=-0.665349) . Using Stanton number representation, the relation is StReL>1/2=1/3 aebPrmc , which portrays in relative terms how the convection enhancement and the opposing thermal storage effects vary with porosity. This study concluded that implementing a porous structure in a medium is feasible for enhancing heat transfer performance.

Gas–liquid mass transfer in the gas–liquid–solid mini fluidized beds

The gas–liquid–solid mini fluidized bed (GLSMFB) combines the advantages of fluidized bed and micro-reactor, and meets the requirements for safety and efficiency of green development of process industry. However, there are few studies on its flow performance and no studies on its mass and heat transfer performance. In this paper, the characteristics of gas–liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application. Using CO2 absorption by NaOH as the model process, the gas–liquid mass transfer performance of GLSMFB was investigated. The results show that the liquid volumetric mass transfer coefficient and the gas–liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity. At the same ratio of superficial gas to liquid velocity, the liquid volumetric mass transfer coefficient increases with the increase of the superficial liquid velocity. Fluidized solid particles strengthen the liquid mass transfer process, and the liquid volumetric mass transfer coefficient is about 13% higher than that of gas–liquid mini bubble column.