Coupled Mass Transfer Research Articles

A numerical study of two identical CO2 bubbles rising side by side in water coupled with mass transfer

ABSTRACT In contrast to the relatively straightforward rising dynamics of single bubbles, the behavior of multiple bubbles involves a more intricate interplay of flow field dynamics, trajectory patterns, morphological changes, and mass transfer phenomena. To reveal the coalescence characteristics and mass transfer effects of CO2 bubbles during the rising process, this study developed a coupled mass transfer numerical model for bubbles. The Volume of Fluid (VOF) method was used in combination with a mass transfer code for solving the model. The effects of bubble pair initial spacing and liquid viscosity on the coalescence and mass transfer were discussed. The numerical simulation results show that as the initial distance between the two bubbles decreases, the interaction force between the bubbles increases, and the possibility of bubble coalescence increases, the coalescence behavior reduces the contact area and thus decreases the amount of CO2 dissolved about 24.07%. When the initial viscosity of the liquid phase is low, there is an oscillation in the bubble velocity, and the two bubbles tend to merge. As the initial viscosity of the liquid phase increases, resistance increases, causing a decrease in bubble velocity. Consequently, the path of bubble ascent shifts from “approach-repulsion-approach” to “continuous repulsion.” The viscous resistance reduces the gas–liquid contact area, resulting in a corresponding decrease in the mass transfer rate, the dissolution amount of carbon dioxide decreased by approximately 24.42% in this case. The exploration of coupled fluid dynamics and mass transfer phenomena at the multi-bubble scale holds paramount importance in guiding the design and exploration of gas–liquid two-phase flow systems.

Light tuning CO/H 2 composition on Ag: Unraveling CO 2 mass transfer and electron-phonon coupling in plasmon-enhanced electrocatalysis

Light tuning CO/H ₂ composition on Ag: Unraveling CO ₂ mass transfer and electron-phonon coupling in plasmon-enhanced electrocatalysis

Evaluating the effectiveness of the modified multi-scale multi-physics coupled model for solid oxide fuel cells: A comparative analysis

A multi-scale multi-physics coupling numerical model serves as an effective tool to study the performance and improve the efficiency of solid oxide fuel cells (SOFCs) and provides the theory and data support for optimizing SOFC structure and operational strategy. To improve the accuracy and reliability of the model, this work established a modified simulation model that considers the effect of operational, structural, and physical parameters of SOFCs. First, the electrochemical kinetics equation, multi-component diffusion lattice Boltzmann (LB) model, and heat transfer LB model are modified by incorporating the reaction gas molar fraction, gas mixture concentration, temperature, and other parameters. Second, a regional hierarchical modeling strategy is proposed, and the multi-scale coupling model is modified by coupling mass and heat transfer. Third, considering the effect of carbon monoxide molar fraction, temperature difference, concentration change and porosity on electrochemical, mass, and heat transfer processes, the effectiveness of modification model is analyzed and validated. Results demonstrate that the modified model considerably improves the numerical simulation to handle the complex operational conditions of SOFCs. The modified model's predictions show better accuracy compared with experimental data, while maintaining consistency with the trends predicted by the original numerical models.

Pore-Scale Study of Diffusion and Adsorption Mechanisms during Capture of Atmospheric Carbon Dioxide

The surge in the global average temperatures has necessitated a decrease in the level of the released carbon dioxide (CO2) from different anthropogenic sources. In addition to curtailing the various emissions, there is a growing demand to remove the CO2 already existing in the atmosphere. As such, there is an impetus for synergistic experimental and modeling studies as it can propel the endeavor toward the development of durable and less energy-intensive CO2 capture systems. In this work, a physics-based numerical model employing the Lattice-Boltzmann Method (LBM) is formulated to simulate the coupled mass transfer and adsorption phenomena occurring during CO2 capture. A modeling workflow integrated with experiments will be presented which aids in the determination of the pertinent reaction order and adsorption rate constant based on a mixed-order kinetic model. The influence of Damköhler number, porosity, and microporosity content of the carbon fiber domain on key metrics such as the adsorption efficiencies and time constants will be further delineated.

Review on Absorption Refrigeration Technology and Its Potential in Energy-Saving and Carbon Emission Reduction in Natural Gas and Hydrogen Liquefaction

With the requirement of energy decarbonization, natural gas (NG) and hydrogen (H2) become increasingly important in the world’s energy landscape. The liquefaction of NG and H2 significantly increases energy density, facilitating large-scale storage and long-distance transport. However, conventional liquefaction processes mainly adopt electricity-driven compression refrigeration technology, which generally results in high energy consumption and carbon dioxide emissions. Absorption refrigeration technology (ART) presents a promising avenue for enhancing energy efficiency and reducing emissions in both NG and H2 liquefaction processes. Its ability to utilize industrial waste heat and renewable thermal energy sources over a large temperature range makes it particularly attractive for sustainable energy practices. This review comprehensively analyzes the progress of ART in terms of working pairs, cycle configurations, and heat and mass transfer in main components. To operate under different driven heat sources and refrigeration temperatures, working pairs exhibit a diversified development trend. The environment-friendly and high-efficiency working pairs, in which ionic liquids and deep eutectic solvents are new absorbents, exhibit promising development potential. Through the coupling of heat and mass transfer within the cycle or the addition of sub-components, cycle configurations with higher energy efficiency and a wider range of operational conditions are greatly focused. Additives, ultrasonic oscillations, and mechanical treatment of heat exchanger surfaces efficiently enhance heat and mass transfer in the absorbers and generators of ART. Notably, nanoparticle additives and ultrasonic oscillations demonstrate a synergistic enhancement effect, which could significantly improve the energy efficiency of ART. For the conventional NG and H2 liquefaction processes, the energy-saving and carbon emission reduction potential of ART is analyzed from the perspectives of specific power consumption (SPC) and carbon dioxide emissions (CEs). The results show that ART integrated into the liquefaction processes could reduce the SPC and CE by 10~38% and 10~36% for NG liquefaction processes, and 2~24% and 5~24% for H2 liquefaction processes. ART, which can achieve lower precooling temperatures and higher energy efficiency, shows more attractive perspectives in low carbon emissions of NG and H2 liquefaction.

Optimization of reaction kinetics on natural convection microfluidic devices by computer simulation

This study presents a novel methodology framework for simulating and optimizing reaction kinetics in natural convection microfluidic devices. The approach involves coupling heat and mass transfer, fluid flow, and chemistry. Visual and regression analyses are performed to evaluate the impact of different operational parameters on reaction speed, aiming to improve microfluidic natural convection systems. The methodology was applied to a practical example of a Polymerase Chain Reaction triangular microfluidic glass device that utilizes natural convection for the required reactions. The findings showed that the fluid flow velocity is significant in determining the reaction speed, which can be controlled by adjusting the temperature cycling differences and the inner diameter of the device. Despite challenges posed by the fluid flow direction, the best reaction times achieved ranged from 18 to 21 minutes. Due to its computational efficiency, the developed methodology allows simulations to be conducted on mid-range computers. Also, the visual and regression analyses offer insights into improving a specific device by measuring the influence of several parameters. Then, the methodology is convenient for selecting the best conditions before developing an experiment.

Component innovations for lower cost mechanical vapor compression

Despite significant capital and operating costs, mechanical vapor compression (MVC) remains the preferred technology for challenging brine concentration applications. This work seeks to assess the dependence of MVC costs on feedwater salinity and desired water recovery and to quantify the value of improved component performance or reduced component costs for reducing the levelized cost of water (LCOW) of MVC. We built a cost optimization model coupling thermophysical, heat and mass transfer, and technoeconomic models to optimize and identify low cost MVC system designs as a function of feedwater salinity and water recovery. The LCOW ranges over 3.6 to 6.1 $/m3 for seawater feed salinities of 25–150 g/kg and water recoveries of 40–80 %. We then perform sensitivity analysis on parameter inputs to isolate irreducible costs and determine high value component innovation targets. The LCOW was most sensitive to evaporator material costs and performance, including the overall heat transfer coefficient in the evaporator. Process and material innovations such as polymer-composite evaporator tubes that reduce evaporator costs by 25 % without reducing heat transfer performance by more than 10 % would result in MVC cost reductions of 8 %.

Numerical simulation of all-vanadium redox flow battery performance optimization based on flow channel cross-sectional shape design

This paper numerically investigates optimizing trapezoidal flow channel cross-sectional shapes to improve all‑vanadium redox flow battery performance. A 3D steady-state multiphysics model coupling fluid dynamics, mass transfer, and electrochemistry was developed in COMSOL. Eight trapezoidal and one rectangular cross-section serpentine flow fields were simulated at varied flow rates. Results showed the TCS-T06 design reduced pressure drop by 12 % and pump power by 12 % versus the RCS. The concentration distribution of VO2+ was also improved, enhancing mass transfer. At 60 mA/cm2, TCS-T06 achieved 0.9 % higher pump power-based voltage efficiency. The optimized trapezoidal cross-section was proven to minimize losses, improve electrolyte distribution, and enhance VRFB performance. This work provides guidance for optimizing trapezoidal flow channel cross-sections to improve VRFB performance via enhanced mass transfer and reduced pressure drop.

Morphological changes and color development during cookie baking-Kinetic, heat, and mass transfer considerations.

Color and shape are important quality attributes in baked goods, particularly cookies. Composition and processing conditions determine and influence color development and morphological changes in these baked goods. The objective of this study was to systematically evaluate the evolution of color and shape during baking to determine useful correlations that can be implemented during the assessment and modeling of the baking process. Cookies (AACC-I standard protocol 10-53.01) were baked at 185, 205, and 225°C. Moisture content, water activity, surface temperature, characteristic dimensions (radius and thickness), and color indexes (lightness, redness, blueness, and browning index [BI]) were monitored at different locations on the cookie surface and baking times. Relationships among the tested conditions were explored using correlation analysis. The cookies' dimensions and color indexes were strongly correlated with changes in moisture content over time, and those relationships were characterized using empirical models. The temperature dependence of the kinetic parameters of the changes in lightness and BI was also described and deemed independent of the location on the cookie surface. This study provides insights into the influence of heat and mass transfer on the physical and physicochemical changes of cookies during baking. The kinetic and secondary models developed in this study can serve as important components for establishing a comprehensive approach for coupling heat transfer, mass transfer, and reaction kinetics to estimate and optimize cookie-baking processes. PRACTICAL APPLICATION: The findings from this study provide valuable information for better understanding the morphological changes and color developments during the cookie-baking process. The quantitative data and models generated in this study will allow identifying baking conditions for better quality development.

Performance optimization of non-isothermal endoreversible chemical pump via Lewis analogy

By considering heat and mass transfer (HMT) coupling, an endoreversible non-isothermal chemical pump cycle model is established and the optimal performance is studied herein. Assuming that the HMT follows Lewis analogy (heat transfer (HT) process obeys Newton's HT law and mass transfer (MT) process obeys diffusion MT law), rate of energy-pumping (Σ) and its corresponding vector coefficient of performance (χT and χμ, which are defined herein) are deduced analytically. Based on the general optimization results, the special examples of endoreversible Carnot heat pump with Newton's HT law and the endoreversible isothermal chemical pump with diffusion MT law are further deduced. The effects of heat flux rate (q1) and mass flux rate (g1) on the optimization results are analyzed. The Σ increases with the increases of q1 and g1. The surface of Σ to [χT,χμ] is a monotonically decreasing plane, and the Σ decreases with the increases of χT and χμ. The special cases of endoreversible Carnot heat pump with Newton's HT law and endoreversible isothermal chemical pump with diffusion MT law are further obtained. The Σ and χμ obtained by endoreversible non-isothermal chemical pump are larger than those obtained by endoreversible isothermal chemical pump. Coupling effect of HMT increases Σ and χμ, but correspondingly decreases χT.

Kriging surrogate model for optimizing outlet temperature distribution in low-emission combustors without dilution holes

Designing advanced combustors that operate at high temperatures and produce little pollution, especially in the absence of primary and dilution holes, is a difficult task that may bring significant challenges. In this regard, this paper introduces a Kriging surrogate model approach to optimize the outlet temperature distribution of the combustor to achieve such advanced low-pollution combustors. Building upon previous research, this study explores the effects of the swirler blade installation angle on the outlet temperature distribution of the combustor without primary or dilution holes. Traditional methods, such as the control variable method using computational fluid dynamics (CFD) for numerical simulation, are limited in application due to the complex coupling of flow, heat transfer, mass transfer, and combustion processes. In contrast, surrogate models, especially the Kriging model, offer a rapid and efficient alternative to extensive CFD simulations that provide accurate predictions and error estimates for the solution of the problem. In summary, this paper details the process of generating sample points through three-dimensional numerical simulations, develops a Kriging surrogate model through Latin hypercube sampling, and optimizes the model to identify the most uniform outlet temperature distribution achievable by adjusting the installation angle of the swirl blade. The optimal design parameters, which are quickly obtained through the Kriging model, showed a significant reduction in the overall temperature distribution function and the radial temperature distribution function by 21% and 27.14%, respectively.

A between-wall heat transfer simulation approach based on the lattice Boltzmann method and its application in tube heat transfer analysis

Between-wall heat transfer is a fundamental physical process. As a typical coupling heat and mass transfer process, between-wall heat transfer-based problems can be solved conveniently on the basis of advanced computation methods among which the lattice Boltzmann method (LBM) has been widely used in the analysis of simple heat and mass transfer cases. To investigate the applicability of LBM in more complex solid-fluid coupling heat transfer analysis, a 3D fluid-solid-fluid model was established in this work to carry out between-wall heat transfer simulations using the doubled-population LBM. Three independent simulation regions were coupled in the heat transfer model, and the heat flux was taken as the physical quantity that transferred from the region at high temperature to that at low temperature through solid wall. The simulation results satisfactorily agree with that obtained using the commercial code FLUENT. Furthermore, an equivalent fluid-wall-fluid heat transfer model was established for simulation of heat transfer between internal and external fluids through a circular tube. All the boundaries are complete quadrilaterals on which heat transfer boundary conditions can be conveniently applied. The proposed between-wall model based on LBM can be easily established and applied in cases with internal heat source or mass force.

Study on heat transport analysis and improvement method in a single CaCO3 pellet for thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) pellets have significant advantages in bulk energy storage density, transport, and utilization. However, severe heat transport limitations within the milli-sized CaCO3 significantly affect the TCES efficiency and economy. Currently, investigations on the effect of initial porosity, bulk gas flow velocity, and reaction rate on heat transport and methods of enhancing the heat transport inside the pellet are lacking. In this paper, we developed a mathematical model coupling calcination reaction, mass transfer, and heat transfer to reveal the effects of pellet parameters and operating conditions on heat transport and reaction conversion rate within a CaCO3 pellet. The results show that the size of the CaCO3 pellet, bulk gas temperature, and reaction rate generate the most pronounced impacts on heat transport in a single CaCO3 particle during the TCES process. Furthermore, the heat transport inside the CaCO3 pellet can be improved by appropriately increasing the bulk gas flow velocity. Finally, this paper first numerically investigates the addition of SiC as a thermal conductivity enhancer to improve the heat transport performance inside a CaCO3 pellet. This study can guide the design of high-performance CaCO3 composite pellets and inform the selection of operating conditions for subsequent reactor applications.

Conjugate mass transfer from a spherical moving droplet: Direct numerical simulations of enhancement by a chemical reaction

Chemical reactions can have a significant impact on the overall rate of mass transfer in fluid–fluid applications (such as gas absorption in a liquid or liquid–liquid extraction). However, as for non reacting systems, the rate at which a solute is exchanged between the two fluids is difficult to predict accurately. Yet from a theoretical point of view, most studies address uniform diffusion transport or creeping flow, i.e. conditions enabling the derivation of analytical or simple numerical solutions of the solute transport equation, therefore neglecting the effect of convection in the case of coupled mass transfer problems. On the other hand, experimental investigations available in the literature provided correlations corresponding to flow conditions, shape and contamination of the interface which are extremely difficult to control precisely.Direct numerical simulation (DNS) is therefore a powerful tool to investigate the coupling of hydrodynamics with transfer and reaction. It was recently applied to model the internal and external resistances (or Sherwood numbers, Shi and She) prevailing during the transfer of a non reacting solute, in the general case of conjugate mass transfer from a moving spherical droplet (Godé et al., 2023; 2024). This study is complemented by considering a first order reaction that consumes the transferred solute in the continuous phase. The results indicate that the double film model, based on these last correlations for Shi and She, with She corrected by an enhancement factor allows obtaining accurate predictions of the overall mass transfer coefficient in the case of a reactive conjugate problem, thus extending the work of Juncu (2002) to flows at moderate or even high Re, as long as the droplet remains spherical and the flow axisymmetric.

Experimental study on flow characteristics of falling film over horizontal tubes under countercurrent gas flow

Open-absorption heat pump serves as an important means of industrial waste heat recovery, and the overall performance of the heat pump system depends on the absorber’s performance. Horizontal-tube–falling-film absorption refers to a complex process involving the coupling of fluid flow, heat transfer, and mass transfer. For the complete understanding of the intertube flow characteristics of horizontal-tube falling film under countercurrent gas flow (We), Visual experimental studies on falling-film flow were conducted using high-speed photography. The critical Reynolds number (Re) was quantitatively characterized to represent the transition of different flow patterns between tubes. The experiment was conducted to investigate the variation in the critical Re under the coupling effects of various factors and establish an experimental prediction correlation formula for the critical Re and solution properties, We, s, and d with an error margin of less than 10%. The influence of single factors was characterized qualitatively and then subjected to sensitivity analysis. The factors affecting the critical Re in descending order of magnitude were as follows: solution mass fraction > s > d > countercurrent gas flow (We). A reduction of approximately 50% in the critical Re for every 10% increase in the solution mass fraction.

Numerical Simulation Technologies in Solar-Driven Interfacial Evaporation Processes.

Solar interfacial evaporation technology has the advantages of environmentally conscious and sustainable benefits. Recent research on light absorption, water transportation, and thermal management has improved the evaporation performance of solar interfacial evaporators. However, many studies on photothermal materials and structures only aim to improve performance, neglecting explanations for heat and mass transfer coupling or providing evidence for performance enhancement. Numerical simulation can simulate the diffusion paths and heat and water transfer processes to understand the thermal and mass transfer mechanism, thereby better achieving the design of efficient solar interfacial evaporators. Therefore, this review summarizes the latest exciting findings and tremendous advances in numerical simulation for solar interfacial evaporation. First, it presents a macroscopic summary of the application of simulation in temperature distribution, salt concentration distribution, and vapor flux distribution during evaporation. Second, the utilization of simulation in the microscopic is summed up, specifically focusing on the movement of water molecules and the mechanisms of light responses during evaporation. Finally, all simulation methods have the goal of validating the physical processes in solar interfacial evaporation. It is hoped that the use of numerical simulation can provide theoretical guidance and technical support for the application of solar-driven interfacial evaporation technology.

Numerical Modelling of Coupled Heat and Mass Transfer in Porous Materials: Application to Cinder Block Bricks

Numerical Modelling of Coupled Heat and Mass Transfer in Porous Materials: Application to Cinder Block Bricks

Improving the bioactive content in honeydew melon by impregnation with Hibiscus extract/sucrose solutions: A coupled mass transfer analysis

This study investigated the bioactive content enrichment of honeydew melon cuts (hemispheres) immersed into Hibiscus extract/sucrose solutions (HESS). A face-centered design (FCD) was initially conducted to explore the effect of time (30–210 min), solution concentration (20–60°Bx) and temperature (40–60 °C) on water loss (WL), solids gain (SG), as well as in the increase of anthocyanins (ANT), phenolics (PHE), and antioxidant capacity (AXC) of melon. WL and SG were also investigated with pure sucrose syrups (SS) for comparison purposes. Processing conditions were further optimized by a Pareto approach to maximize both WL and bioactive content enrichment with minimal SG. Then, impregnation kinetics, conducted around the optimal experimental conditions, were analyzed with a 2D diffusive model, considering the anisotropic shrinkage of melon and solved under four complexity levels to examine coupled mass transfer (including constant diffusivities, main plus cross diffusion terms or nonlinear diffusivity functions of local water content). HESS favored a higher WL and lower SG than SS during FCD. The optimal condition occurred at 30 min, 20°Bx and about 50 °C, where melon gained ANT not originally present in it, and PHE and AXC increased by factors of 4.5 and 6.1 in comparison with untreated fruit, respectively. No evidence of significant coupling among WL, SG and bioactive transfer was found (p>0.05), with diffusivities for ANT, PHE, AXC, water and solids ranging from 3.26 to 3.45, 12.8–14.4, 1.24–5.19, 0.82–1.36, and 1.19–4.26 (×10−10) m2/s, respectively.

Coupled heat and mass transfer mathematical study for lubricated non-Newtonian nanomaterial conveying oblique stagnation point flow: A comparison of viscous and viscoelastic nanofluid model

Abstract The lubrication phenomenon plays a novel role in the chemical industries, manufacturing processes, extrusion systems, thermal engineering, petroleum industries, soil sciences, etc. Owing to such motivated applications, the aim of the current work is to predict the assessment of heat and mass transfer analysis for non-Newtonian nanomaterial impinging over a lubricated surface. The flow is subject to the oblique stagnation point framework. The lubricated phenomenon is observed due to viscoelastic nanofluid. The impacts of chemical reaction are also endorsed. The fundamental conservation laws are utilized to model the flow problem and similarity transformation are used to transform the governing system of partial differential equations into ordinary differential equations. A thin layer of power law lubricant is used to enhance the lubrication features. The numerical object assessment regarding the simulation process is captured by implementing the Keller Box scheme. The physical characterization endorsing the thermal fluctuation with flow parameters is inspected.

Modeling the distribution characteristics of vapor bubbles in cavitating flows

Dispersed vapor bubbles are the dominant rheology in cloud cavitation, and their size distribution is directly associated with cavitation noise and erosion. However, the numerical resolution of large numbers of dispersed bubbles remains a challenge. In this work, we establish a new cavitation model based on the population balance equation (PBE) that can predict the size distribution and spatiotemporal evolution of bubbles within cloud cavitation under different cavitation numbers. An expression for the phase transition source term without empirical parameters is derived based on the bubble size distribution (BSD) function, enabling the coupling of mass transfer in the governing equations with the PBE cavitation model. The cavitation model is solved alongside the Eulerian homogeneous mixture flow. The mass transfer between water and vapor, and the bubble coalescence and breakup under turbulent flows, are modeled to determine the BSD. The numerical model is carefully validated through comparisons with experimental results for cavitation flows on a wedge-shaped flat plate, and good agreement is achieved with respect to the pressure distribution, void fraction, and BSD. This confirms that our proposed cavitation model can accurately predict the void fraction and BSD within the cloud cavitation region.