Mass Transfer Characteristics Research Articles

Simulation study on heat and mass transfer characteristics within tubular moving bed heat exchangers

In the field of waste heat recovery, tubular moving bed heat exchangers (MBHEs) hold great promise as equipment capable of effectively handling large-sized granular materials with high temperature. To further clarify the heat and mass transfer characteristics within tubular MBHEs, this study firstly conducted detailed investigations on the contributions of different heat transfer mechanisms. The result shows that heat radiation (∼45 %) and gas film heat conduction (∼42 %) control the heat transfer processes involving tube walls, with an inlet particle temperature of 600 °C, tube wall temperature of 50 °C, and particle descent velocity of 2 mm/s. These contributions can be influenced by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. Additionally, for a specific particle, its heat transfer state is highly depended on where it is located. Subsequently, the time-varying and space-varying characteristics of the heat transfer processes involving tube walls are studied. The results suggest that the time-varying and space-varying characteristics are inherent in tubular MBHEs due to the difficulty to achieve complete stability. Meanwhile, temporal fluctuations intensify with an increase in the inlet particle temperature, a decrease in wall temperature, or an increase in particle descent velocity. The result of power spectral density (PSD) indicates that the heat transfer processes exhibit a degree of chaotic behavior due to the nonlinear property of sub-models, as well as the randomness in particle feeding and contacts. The space-varying characteristic is mainly determined by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. This characteristic can be observed in both the axial and circumferential directions, with the circumferential variation being more pronounced than the axial variation. Furthermore, a double-tube MBHE, a topic that has received scant attention in previous research, is investigated in comparison to a single-tube MBHE to explore the differences in heat and mass transfer between the two configurations. It indicates that under the same boundary conditions, there are differences in heat transfer results, which are attributed to the interactions between two vertically arranged tubes. These interactions are reflected in the reconstruction of particle flow patterns and the effect altering the temperature distribution for the particles or fluid surrounding the tubes. The obtained results provide valuable insights into the mass and heat transfer behaviors of particles and fluids within tubular MBHEs, laying a foundation for advancing the development of efficient tubular MBHEs.

Study of electric field-enhanced mass transfer and Li/Mg separation of N, N-bis (1-methylheptyl) acetamide/TBP-NaFeCl4 composite membrane

Using N,N-bis(1-methylheptyl)acetamide (N503) synergized with TBP-NaFeCl4 (TFe), a ternary composite extraction membrane known as TFeN-PIM was created. Under optimum membrane phase conditions, the mass transfer properties of TFeN-PIM-Li(Ⅰ) and its Li/Mg selective separation performance by electric field augmentation were examined, and confirmed the mechanism of TFeN-PIM-Li(Ⅰ) electric field enhanced mass transfer. The findings demonstrate a homogeneous distribution of [FeCl4-] in the TFeN-PIM membrane phase and a decrease in the water contact angle as the TFe content increases. In the TFeN-PIM membrane, the cation binding order of the composite carrier was H+>Li+>Na+>Mg2+, and the mass transfer was carried out at the interface of the two phases of the membrane through the mechanism of "cation exchange-neutralization", in which Li(Ⅰ) was bonded with the carrier in the form of 2N503-LiFeCl4-2TBP, and showed a fixed-site "hopping" mass transfer characteristics under the reinforcement of electric field. The mass transfer process of the TFeN-PIM- Li(Ⅰ) system under electric field enhancement conforms to the first-order kinetic rate equation, and the voltage (5–45 V) is positively correlated with the permeability coefficient PLi(Ⅰ) but decreases the Li/Mg selectivity of TFeN-PIM. The SLi(Ⅰ)/Mg(Ⅱ) of TFeN-PIM was 9.18 at 3 V. After three cycles of 72 h cycling at 40 V, the decrease rate of PLi(Ⅰ) was <7.42 %, which showed good stability.

Experimental and modeling study of CO2 capture by phase change blend of triethylenetetramine-ethanol solvent

Post combustion Carbon capture based on chemical absorption is the best-known technology to reduce CO2. Recently, attention has been paid to biphasic solvents due to their excellent potential in reducing energy consumption. This study investigated carbon dioxide absorption by biphasic non-aqueous triethylenetetramine (TETA)-ethanol solvent in a T-shaped microchannel. Effect of four parameters including: concentration of TETA (4–8 wt%), liquid flow (2–5 ml/min), inlet CO2 concentration (5–20 vol%) and gas flow (100–175 ml/min) have been examined. Mass transfer characteristics has been assessed by investigation of absorption percentage, molar flux and overall mass transfer coefficient. The results show that increasing the concentration of amine diminishes all three responses by increasing the solution viscosity. As a result, it decreases the penetration of CO2 in the solution and the rate of absorption.Furthermore, the TETA-ethanol phase change solvent has been compared with aqueous monoethanolamine (MEA). The results of this comparison indicated that the efficiency of CO2 absorption and mass transfer coefficient, for TETA-ethanol biphasic solvent are higher than MEA solvent, respectively. Finally, the dimensionless Damköhler number (Da) was utilized in the new correlation to predict KLa for CO2 absorption into TETA-Ethanol solution with acceptable accuracy.

Influence of flight acceleration on heat transfer and carbon deposits of aviation kerosene under supercritical conditions

During the acceleration or escape of the hypersonic vehicle, the flight acceleration will have an important impact on heat and mass transfer characteristics of pyrolytic hydrocarbon fuel in the regenerative cooling channel of scramjet. Based on the detailed pyrolytic mechanism and coking kinetics model, numerical model was established to study the flight acceleration effect on flow field, fuel pyrolysis, heat transfer and carbon deposit of supercritical hydrocarbon fuel in the horizontal cooling channel. Results indicate that the secondary flow is induced in the cross-section of horizontal cooling channels because of the flight acceleration and density gradient. Due to the secondary flow, thermal and fuel conversion stratifications in the radial distribution increase. The bottom wall heat transfer coefficient is higher, while the wall temperature and carbon deposits are lower than that of the top wall. Meanwhile, with the increase of the flight acceleration, the thermal and fuel conversion stratifications become larger. The differences of heat transfer coefficient, wall temperature and carbon deposits between the top and bottom walls rise. The operating pressure enhances the flight acceleration effect on the heat transfer and carbon deposits. In addition, Petukhov’s criterion is proved to be applicable to evaluate the flight acceleration effect quantitatively.

Development of Pseudo-Homogeneous Three-Dimensional Reaction Anode Structure for Proton Exchange Membrane Water Electrolysis

Solid Polymer Electrolyte (SPE) diaphragm such as Nafion🄬 has been applied to proton exchange membrane water electrolysis (PEMWE) due to the high efficiency and response. The structure of PEMWE consists of a catalyst layer, diffusion layer, current collector, flow-field, etc. In addition to the membrane, these elements and structural parameters were adapted from the proton exchange membrane fuel cell (PEMFC) technology due to the time series factors in the development process and are still strongly influenced by that technology today. Although PEMFC technology is applied to these elements in PEMWE, the material composition, structure, and various parameters are not fully optimized, and the basic structure and technology are diverted from various PEMFC conditions, although the main object of fluid has greatly changed from the gas phase to the liquid phase. As the above background, PEMWE technology needs to go back to the basic level of structural design, mainly from the viewpoint of mass transfer, and reconstruct the component structure.In this study, we focused on the mass transfer characteristics that most affect the performance of PEMWE and investigated a new structure for gas-liquid two-phase fluids for the electrode structure, which is the most important element of PEMWE.Figure 1 shows the two and three-dimensional reaction electrode structures in PEMWE. Figure 1(a) is the electrode structure of a conventional general PEMWE, which is the catalyst reaction in the catalyst layer on the rate-limiting electrode side proceeds in a heterogeneous two-dimensional reaction area. In this current method, sufficient diffusion cannot be maintained from the viewpoint of mass transfer, which leads to performance decrease due to the inability to remove obstacles such as bubbles to mass transport to the catalyst layer. Figure 1 (b) shows the pseudo-homogeneous three-dimensional reaction electrode structure developed in this study. The catalyst is supported on the porous current collector itself. This structure dramatically increases the reaction area from two-dimensional to three-dimensional, and it is expected to greatly improve electrolytic performance by optimizing various parameter conditions.The experimental was performed as following. The anode catalyst IrOx was synthesized from H2IrCl6-nH2O and NaNO3 by the Adams method1). Catalyst Ink, which mixed with the synthesized catalyst and Nafion🄬 dispersion solution, was dropped onto a Ti-web current collector and dried. The anode catalyst loading current collector was evaluated in a 1 cm2 component evaluation electrolyzer2).In this development, the essential issue is the establishment of the conditions to support the catalyst in the three-dimensional reaction area and to maintain the supply path of the proton from the SPE membrane efficiently.References T. Saida, S. Hirano, E. Niwa, F. Sato, and M. Maruyama, ECS Trans., 85, 865 (2018). K. Nagasawa, T. Ishida, H. Kashiwagi, Y. Sano, S. Mitsushima, Int. J. Hydrog. Energy, 46, 36619 (2021). Figure 1

Energy Efficiency of Steady DC and Half Sine Pulsed DC in the High Voltage Pre-Plasma and Plasma Alkaline Water Electrolysis

The research addresses the contrasting views on the energy efficiency of alkaline water electrolysis using the regular DC vs the pulsed DC. We compare the high voltage steady DC electrolysis with the high voltage half-wave rectified (HWR) AC (or the half Sine pulsed DC, an unexplored form of the pulsed DC) across a wide range of voltage regimes, with a particular focus on the less explored Plasma electrolysis (PE) regime. In addition, the current-voltage characteristics are mapped across the voltage regimes (NE to PE) using a novel high-voltage 3-electrode circuit, which allows better control over the working electrode potential. The experimental design considers critical parameters such as energy efficiency, Faradaic efficiency, and current density, providing a comprehensive evaluation of the regular DC Vs. the half-wave rectified AC electrolysis.Pulsed electrolysis can facilitate bubble removal and ensure timely replenishment of reactant during the low-bias phase and this is expected to diminish over potential losses due to mass transfer resistance. However, the preliminary energy efficiency assessment suggests that the regular DC is ~13% higher at 33 V bias and ~24% higher at 26.5 V bias than the half sine pulsed DC(50 Hz) electrolysis. This suggests that for these particular reaction conditions, the fluctuations in the current leading to reactive losses in the circuit and other internal losses overwhelm any enhancement in the mass transfer characteristic of pulsed electrolysis. The study also points to regimes where significant thermal decomposition results in a significant increase in the apparent Faradaic efficiency.

An efficient technology for dye intermediate production: Process intensification of catalytic hydrogenation of aromatic nitrocompounds in a rotating packed bed reactor

AbstractThe rotating packed bed (RPB) is suitable for catalytic hydrogenation of aromatic nitrocompounds whose reaction rate is limited by the mass transfer rate. However, the matching mechanism between the mass transfer rate and intrinsic reaction rate in the RPB reactor is still unclear. In this work, the matching relationship in the RPB reactor is studied by combining the characteristics of mass transfer and reaction in detail. Effects of various operating conditions on the gas–liquid mass transfer coefficient up to 0.31/s, under working conditions were studied and the mass transfer correlation was proposed. The hydrogenation of p‐nitroanisole was used as a probe reaction to analyze the matching mechanism. Various aromatic nitrocompounds in the RPB and stirred tank reactors were investigated. The reaction efficiency of the former is 5–20 times that of the latter, which further explained the universality of the matching mechanism in the RPB reactor.

Inverse design of V-shape feed spacer for batch and semi-batch reverse osmosis

In recent years, batch and semi-batch reverse osmosis (RO) processes have received wide attention because of their internal staging feature. However their performance is severely compromised by salt retention induced by incomplete flushing, which leads to elevated salt concentration, uplifted peak pressure, and extra power consumption. Herein we adopt transient three-dimensional computational fluid dynamics to systematically analyze the effect of the V-shape feed spacer geometries on hydrodynamics and mass transfer characteristics. After a sensitivity analysis of all geometric parameters, a heuristic optimization framework is proposed for inverse design of the feed spacer. Using the optimized feed spacer, flushing efficacies after one displacement volume are 0.936, 0.962, 0.969 and 0.974 respectively for one, three, five and seven membrane elements connected in series (whereas 0.884, 0.926, 0.942 and 0.952 for commercial spacers), which help to mitigate membrane scaling and fouling. Moreover, the optimized spacer has a pressure drop per meter 73 % lower than that of the commercial spacer. If used in conjunction with high permeability membranes, batch RO and semi-batch RO could save 29.9 % and 24.1 % specific energy consumption relative to conventional one-stage seawater RO.

Discharge and mass transfer characteristics of atmospheric pressure gas-solid two-phase gliding arc

In this work, a gas-solid two-phase gliding arc discharge (GS-GAD) reactor was built. Gliding arc was formed in the gap between the blade electrodes, and solid powder was deposited on the sieve plate positioned beneath the blade electrodes. A range of experimental parameters, including the inter-electrode spacing, gas flow rate, applied voltage, and the type of the powder, were systematically varied to elucidate the influence of solid powder matter on the dynamics of gliding arc discharge (GAD). The discharge images were captured by ICCD and digital camera to investigate the mass transfer characteristics of GS-GAD, and the electrical parameters, such as the effective values of voltage, current, and discharge power were record to reveal the discharge characteristics of GS-GAD. The results demonstrate that powder undergoes spontaneous movement towards the upper region of the gliding arc due to the influence of electric field force. Increasing the discharge voltage, decreasing relative dielectric constant of the powder and reducing the electrode-to-sieve-plate distance all contribute to a greater involvement of powder in the GAD process, subsequently resulting in an enhanced powder concentration within the GAD region. Additionally, powder located beneath the gliding arc experiences downward resistance caused by the opposing gas flow and arc. Excessive gas flow rate notably hampers the powder concentration within the discharge region, and the velocity of powder motion in the upper part of the GAD region is reduced. Under the condition of electrode-to-sieve-plate distance of 30 mm, gas flow rate of 1.5 L/min, and peak-to-peak voltage of 31 kV, the best combination of arc gliding and powder spark discharge phenomena can be achieved with the addition of Al2O3 powder.

Effect of surfactant type and concentration on the gas-liquid mass transfer in biotrickling filters used for air pollution control

Volatile organic compounds (VOCs) emitted into the atmosphere negatively affect the environment and human health. Biotrickling filtration, an effective technology for treating VOC-laden waste gases, faces challenges in removing hydrophobic VOCs due to their low water solubility and therefore limited bioavailability to microorganisms. Consequently, the addition of (bio)surfactants has proven to be a promising strategy to enhance the removal of hydrophobic VOCs in biotrickling filters (BTFs). Yet, up to now, no single study has ever performed a mass transfer characterization of a BTF under (bio)surfactants addition. In this study, the effect of (bio)surfactant addition on the gas-liquid mass transfer characteristics of two BTFs was measured by using oxygen (O2) as a model gas. Through an empirical correlation, the mass transfer coefficients (kLa) of two hydrophobic VOCs, toluene and hexane, which are of industrial and environmental significance, were estimated. One BTF was filled with expanded perlite, while the other with a mixture of compost and wood chips (C + WC). Both BTFs were operated under different liquid velocities (UL: 0.95 and 1.53 m h−1). Saponin, a biological surfactant, and Tween 80, a synthetic surfactant, were added to the recirculating liquid at different critical micelle concentrations (CMCs: 0–3 CMC). The higher interfacial and surface area of the perlite BTF compared to the C + WC BTF led to higher kLaO2 values regardless of the operational condition: 308 ± 18–612 ± 19 h−1 versus 42 ± 4–177 ± 24 h−1, respectively. Saponin addition at 0.5 and 1 CMC had positive effects on the perlite BTF, with kLaO2 values two times higher compared to those at 0 CMC. Tween 80 exhibited a neutral or slightly positive effect on the mass transfer of both BTFs under all conditions. Overall, the CMC, along with the physical characteristics of the packing materials and the operational conditions evaluated explained the results obtained. This study provides fundamental data essential to improve the performance and design of BTFs for hydrophobic VOCs abatement.

Biodegradation of carbon disulfide and hydrogen sulfide using a moving bed biofilm reactor coupled with sulfur recycling: Performance, mechanism, and potential application

In this work, a moving bed biofilm reactor (MBBR) was equipped for simultaneous biodegradation of CS2 and H2S. MBBR was started up and operated with different inlet concentrations and retention time; results indicated that approximately 81.9% CS2 and 93.9% H2S could be degraded, and the maximum elimination capacities of 209.3 g/(m3·h) and 138.5 g/(m3·h) were achieved for CS2 and H2S, respectively. The biodegradation mechanisms, including mass transfer, kinetics, and electron transfer, were then investigated. The mass transfer fraction and the maximum degradation rate per unit filter volume were calculated for evaluating the characteristics of mass transfer in MBBR. The variations of extracellular polymeric substances secretion, electron transport system activity and ATP enzyme activity showed that MBBR had an excellent performance for waste gas purification. Subsequently, the recovery of sulfur was explored via morphology, crystal structure, and generation kinetics, indicating that a modified Gompertz model could precisely describe the kinetics of sulfur recovery, and the product selectivity of 51.7% was achieved for sulfur. The microbial community analysis suggested that the dominant genera for biodegradation and sulfur recovery were Acidithiobacillus and Mycobacterium. Finally, MBBR system was validated for treatment of actual waste gas; results indicated that maximum elimination capacities of 134.1 g/(m3·h) and 117.1 g/(m3·h) were obtained for CS2 and H2S, respectively, suggesting that MBBR had the potential for application.

Recent Advances in Regulating Ceramic Monolithic Catalyst Structure for Preferential Oxidation of CO in H2.

Preferential oxidation of CO (CO-PROX) has tremendous significance in purifying hydrogen for fuel cells to avoid catalyst poisoning by CO molecules. Traditional powder catalysts face numerous challenges, including high pressure drop, aggregation tendency, hotspot formation, poor mass and heat transfer efficiency, and inadequate thermal stability. Accordingly, ceramic monolithic catalysts, known as their excellent thermal stability, high surface area, and superior mass and heat transfer characteristics, are gaining increasing research attention. This review examines recent studies on ceramic monolithic catalysts in CO-PROX, placing emphasis on the regulation of active sites (e.g., precious metals like Pt and Au, and non-precious metals like CuO and CeO2), monolith structures, and coating strategies. In addition, the structure-catalytic performance relationships, as well as the potential and limitations of different ceramic monolithic catalysts in practical application, are discussed. Finally, the challenges of monolithic catalysts and future research prospects in CO-PROX reactions are highlighted.

Analysis of Darcy–Forchheimer flow of magnetized hybrid nanofluid (MoS 2+ZnO/E) with non-linear heat source and quartic autocatalytic chemical reaction

In this article, an effort is made to analyze the 3 − D flow of hybrid nanofluid over a rotating stretching sheet. The hybrid nanofluid contains engine oil as a base fluid amalgamated with nano-particles Mo S 2 and ZnO . The flow is assumed to pass through a Darcy–Forchheimer medium subjected to the influence of an inclined magnetic field. In addition, heat radiation, Joule heating, viscous dissipation, nonlinear heat source, and quartic autocatalytic chemical reaction are applied to discourse heat and mass transfer features. The PDEs representing the physical problem are converted to ODEs with the introduction of similarity transformations. The solution of the problem is determined numerically by using MATLAB built-in bvp4c method. The proposed mathematical model’s validation is ascertained by comparing it with an earlier study in limiting case. In this regard, an excellent consensus is accomplished. The current investigation reveals that the flow along axial direction gets retarded by enhancing the values of rotational parameter, inertial parameter, and magnetic parameter, whereas the flow along radial direction gets accelerated. The increasing value of angle of inclination admirably resists the motion of nanofluid and hybrid nanofluid. The concentration profile gets decreased under the increasing influence of inclination angle and Schmidt number while it enhances for homogeneous reaction parameter. The enhancing values of rotational parameter, solid volume fraction and temperature, and exponential dependent heat generation parameters enhance the value of Nusselt number.

Enhancing the permeability and selectivity of graphene oxide membrane through polyhedral oligomeric silsesquioxane intercalation for textile wastewater treatment

Graphene oxide-based loose nanofiltration membranes have shown significant potential in nanofiltration processes due to their unique 2D mass transfer nanochannels. However, they still suffer from poor structural stability and overly compact laminar stacking. To address these issues, a novel AP-POSS was intercalated into GO-based membrane to construct a tuned interlayer structure and mass transfer characteristics. The aromatic ring structure of aminophenyl groups on AP-POSS act as hydrophobic side walls of the mass transfer channels between adjacent GO nanosheets, reducing the interaction between water molecules and channel structure. With an optimal amount of AP-POSS as an intercalator, the permeation flux of the prepared POSS-GO membrane could be improved by 30 wt% while maintaining nearly complete rejection of Congo Red (CR). Moreover, the prepared membrane exhibited enhanced structural stability, long-term stability, and a separation factor above 91.0 for CR/NaCl in binary solutions. Our study highlights the excellent performance of the POSS-GO membrane and demonstrates its potential application in dye/salt wastewater treatment.

Modeling of microfluidic solvent extraction: Evaluation of different flow regimes and cascade configurations

ABSTRACT Solvent extraction using a microfluidic platform is one of the process intensification tools. It may involve different two-phase flow regimes that have different physical and mass transfer characteristics. Therefore, this study focuses on the selection of a better flow regime, flow conditions and cascade configuration (cross or counter-current) using mathematical modeling for a typical high-throughput application (1000 L/day). The mathematical model is based on a plug flow model. The liquid–liquid system considered is a water–acetone–toluene system. The different flow regimes such as slug flow (SF), slug-droplet flow (SDF) and core-annular flow (CAF) in different cascade configurations are compared on the basis of parameters like specific extraction rate (SER), solvent extraction process effectiveness (SEPE) and modified merit index (MMI). Among the different flow regimes and cases studied, CAF is found to offer lesser parallel paths, total extraction length, total pressure drop and residence time. The best case of CAF has higher SER (3.6 times), SEPE (3.6 times) and MMI (21.8 times) than the best case of SF in both cascades. SDF shows the results between SF and CAF. For a specific flow regime, higher values of parameters are obtained at higher flow rates. Counter-current cascade is found to be better than cross-current cascade.

Optimization of passive micromixers: effects of pillar configuration and gaps on mixing efficiency

Chemical bioreactions play a significant role in many of the microfluidic devices, and their applications in biomedical science have seen substantial growth. Given that effective mixing is vital for initiating biochemical reactions in many applications, micromixers have become increasingly prevalent for high-throughput assays. In this research, a numerical study using the finite element method was conducted to examine the fluid flow and mass transfer characteristics in novel micromixers featuring an array of pillars. The study utilized two-dimensional geometries. The impact of pillar configuration on mixing performance was evaluated using concentration distribution and mixing index as key metrics. The study explores the effects of pillar array design on mixing performance and pressure drop, drawing from principles such as contraction–expansion and split-recombine. Two configurations of pillar arrays, slanted and arrowhead, are introduced, each undergoing investigation regarding parameters such as pillar diameter, gap size between pillar groups, distance between pillars, and vertical shift in pillar groups. Subsequently, optimal micromixers are identified, exhibiting mixing efficiency exceeding 99.7% at moderate Reynolds number (Re = 1), a level typically challenging for micromixers to attain high mixing efficiency. Notably, the pressure drop remains low at 1102 Pa. Furthermore, the variations in mixing index over time and across different positions along the channel are examined. Both configurations demonstrate short mixing lengths and times. At a distance of 4300 μm from the inlet, the slanted and arrowhead configurations yielded mixing indices of 97.2% and 98.9%, respectively. The micromixers could provide a mixing index of 99.5% at the channel’s end within 8 s. Additionally, both configurations exceeded 90% mixing indices by the 3 s. The combination of rapid mixing, low pressure drop, and short mixing length positions the novel micromixers as highly promising for microfluidic applications.

Breaking the limits of ambient air conditions in evaporative cooling with vacuum-assisted hollow fiber membrane technology

Conventional direct evaporative cooling systems suffer from persistent issues like air–water cross-contamination, mold growth, and scaling of paddings. Moreover, their widespread application in humid climates is hindered by ambient air conditions. This research presents a promising solution in the form of a vacuum-assisted hollow fiber membrane-based evaporative water cooler (VMEWC). It shifts from relying on air state to vacuum pressure for cold water production. A numerical model was established to reflect the coupled heat and mass transfer characteristics, employing Knudsen diffusion to describe water vapor migration within membrane pores. Experimental tests were performed on the constructed VMEWC system, revealing strong alignment between simulation and measured data, with a 2.2 % error in outlet water temperature predictions. Numerical studies explored the effects of six parameters (inlet water temperature, water velocity, shell-side pressure, fiber length, fiber inner diameter, and overall membrane structure parameter) on VMEWC’s outlet water temperature (Tw2), cooling capacity per unit volume (Qv), and coefficient of performance (COP). The results emphasized that elevated inlet water temperature, reduced shell-side pressure, and a large overall membrane structure parameter effectively enhanced the overall performance of VMEWC. Under specific conditions, Qv and COP reached impressive values of 3753.1 kW/m3 and 13.6, respectively. This work provides a novel and practical perspective, offering references for advancing efficient and sustainable refrigeration technologies.

Diffusion coefficients of polycyclic aromatic hydrocarbons in supercritical carbon dioxide: A molecular dynamics simulation study

Supercritical carbon dioxide (SC-CO2) extraction technology is an effective way to deal with soil contamination problems. Among them, polycyclic aromatic hydrocarbons (PAHs) are one of the main pollutants in soil. Studying the diffusion coefficients of PAHs in SC-CO2 can help us better understand the mass transfer characteristics during the SC-CO2 extraction process. Molecular dynamics simulation was applied in this work to study the diffusion behavior of PAHs in the SC-CO2 environment. Under different SC-CO2 thermodynamic states (temperature: 313–373 K, pressure: 10–30 MPa) and molecule sizes, the diffusion coefficients of PAHs were calculated. The trend of the interaction energy between PAHs and SC-CO2 molecules as temperature, pressure, and molecule size changed was also investigated. The findings demonstrated that compared to heavy PAHs, light PAHs had a higher diffusion coefficient in SC-CO2. Changes in the system’s temperature and pressure have an important effect on the diffusion coefficients of PAHs in SC-CO2. The high-temperature and low-pressure conditions had a promoting effect on the diffusion behavior of PAHs molecules. The van der Waals energy accounts for the largest proportion of the intermolecular interaction energy, which was about 80 %. It can be concluded that the van der Waals interaction energy played an important impact on the diffusion process of PAHs molecules in SC-CO2.

Analytical and numerical study of thermo-solutal convection in pulsating flows between two coaxial cylinders

This research reports an analytical and numerical study of thermo-solutal convection in pulsating flows between two coaxial cylinders under a pressure gradient and subject to Dirichlet-type boundary conditions for temperature and concentration along the vertical walls of the annulus. The numerical procedure used in this work is mainly based on the solution of the momentum equations and coupled with the energy and concentration equations. The finite difference method is adopted to solve governing equations using the implicit Crank-Nicolson time marching scheme in the fluid domain and the alternating direction implicit method inside the inner cylinder. The effect of the various parameters such as the fluid-solid conductivity ratio, thermal diffusivity ratio, buoyancy ratio, Lewis number, Richardson number, aspect ratio, and radius ratio on the heat and mass transfer characteristics and the flow structure is presented and discussed. The governing equations are solved analytically after separating into a steady case and an oscillatory case, where an analytical solution for velocity profile, temperature, and concentration distributions is obtained in terms of Bessel’s functions, while the analytical solutions of temperature and concentration profiles are keeping symmetry with the increase of the radius ratio. The results show that the analytical profile can reproduce the three fields obtained numerically and thus for the whole range of parameters.

Evaluation of Effective Interfacial Area in a Rotating Packed Bed Equipped with Dual Gas Inlets

This study investigates the effective interfacial area in a novel rotating packed bed (RPB) equipped with dual gas inlets instead of the conventional single-gas-inlet RPB. The aim is to enhance the mass transfer efficiency of gas-liquid contacting processes in RPBs by increasing the number of gas inlets to improve the spread of gas supply into the packing. The RPB is a promising gas-liquid contactor configuration known for its intensified mass transfer characteristics. However, the impact of additional gas inlets on the effective interfacial area of the packing remains unexplored. An experimental method assessed the interfacial area under varying operational conditions which include a liquid flow rate of 0.30-0.60 m3/h, a gas flow rate of 100-300 Nm3/h, and a rotation speed of 600-1000 rpm. At operating conditions covering the maximum rotation speed of 1400 rpm, gas flow and liquid flow rates of 300 Nm3/h and 0.60 m3/h respectively, the results showed that on average, 55 to 97% of the 2400m2/m3 specific packing area can be effectively utilized for gas-liquid mass transfer during separation operations using the RPB. Compared to results reported for single-gas-inlet RPBs using similar packings, the RPB with double gas inlet proved to provide higher utilization of the packing. By simply doubling the number of gas inlets, the findings provide valuable insights into optimizing RPB designs and operations which could enhance mass transfer efficiency for various chemical and environmental applications.