Conjugate Mass Transfer Research Articles

The role of reactant contact modes in droplet-based microfluidics

Undesired side reactions can significantly impact the efficiency and economic viability of chemical processes. Droplet-based microfluidics(DBM) offers precise control over reaction conditions by isolating reactants in distinct droplets. Each droplet acts as microreactor with high surface-to-volume ratio. This paper comprehensively investigates the role of two reactant contact modes that give rise to droplet flow. The first contact-mode, Conjugate Mass Transfer Mode(CMTM), is characterized by mass transfer of a reactant from Continuous phase(CP) to Dispersed phase(DP). In second mode, Single-Sphere Mode(SSM), both reactants coexist within the dispersed phase, and there is no effect of external mass transfer on performance. The Hadamard-Rybczynski flow field is used to obtain insights into the system behavior. Two reaction networks, Parallel and Series-Parallel reactions, are considered, which arise from side reactions that accompany the primary reaction.This work highlights the importance of choosing an appropriate reactant contact-mode when side reactions occur. The role of two experimentally controllable parameters, diffusivity ratio(Dr) and feed concentration ratio(M), is analyzed to identify the desirable contact mode. Notably, our study showed that, for Parallel reactions, CMTM has a superior performance compared to SSM under some conditions. Whereas for Series-Parallel reactions, SSM exhibits better performance when equal concentrations of reactants are employed.

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.

Finite element simulation of Soret-Dufour and conjugate heating effects on mixed convective heat absorbing hydromagnetic Casson fluid flow with suction/blowing from flat semi-infinite vertical porous plate

The finite element simulations of the Soret-Dufour and angled magnetic field effects on conjugate heat and mass transportation of unsteady heat absorbing hydromagnetic Casson flow across a semi-infinite flat oscillatory plate engrafted in a porous medium with suction/blowing, radiation and chemical reaction is performed. The dimensionless coupled flow guiding nonlinear PDEs of the physical structure is handled numerically by the dynamic Galerkin finite element scheme. The demeanor of the velocity, concentration and the temperature profiles due to the alterations in the regulating flow parameters are examined graphically whereas the wall-friction, mass and heat transfer rates explicated by utilizing the tabular data. The research discovered that radiation; conjugate heat transfer and diffusion thermo effects heighten the temperature and velocity distributions whereas heat absorption has a reverse effect. Likewise, conjugate mass transfer and thermo-diffusion effects intensify the concentration and velocity distributions whereas the chemical reaction display overturns aspect. Increased radiation absorption, inclined magnetic field and porosity parameter stimulate fluid velocity whereas the Casson and magnetic parameters exhibit the converse impact. In the instance of suction, the profiles of concentration, velocity and temperature displayed a downturn nature but for the case of blowing, it was noticed a reversal trend. Further, a comparative analysis between the current findings and existing research works in the literature demonstrates our results are exact and accurate.

A "training-test" method for predicting single capillary evaporation rates using a conjugate mass transfer model based on coefficient fitting

A "training-test" method for predicting single capillary evaporation rates using a conjugate mass transfer model based on coefficient fitting

Deterioration effects of SiO2 nanoparticles on the mass transfer in a single drop system with resistance in both phases

In the present study, it has been shown that the very small amount of Nanoparticles(NPs) has very significant effects on mass transfer deterioration. For the first time, the effects of hydrophilic SiO 2 NPs have been investigated in the system with the resistance in both phases (butanol-succinic acid-water. NPs with four-volume concentrations were added to the dispersed phase, and the transient and terminal velocities of drops were reported using an image processing tool. Results showed that the effects of NPs on the transient velocity of circulating /oscillating drops are insignificant. Experimental results also showed that the maximum and average deterioration effects were 54% and 26%, respectively in the presence of NPs. The addition of only 0.0005 vol% of NPs revealed about 20% deteriorating effect, while after the addition of 0.01 vol% of NPs, slight differences were observed. Accumulation of NPs in the interface area and gradual occupation were the main reason for mass transfer reduction, which has been supported by the calculation results in the present study. At the final stage, for the first time, the new overall mass transfer correlation has been proposed based on conjugate mass transfer resistance. This general form of correlation can be used for any liquid-liquid extraction (LLE) system with the dominant mass transfer resistance in the two phases in the presence of NPs. • Investigation of hydrophilic NPs effects on the mass transfer in systems with the resistance in both phases • Reporting the mass transfer deterioration of about 20% in the presence of 0.0005 vol% of NPs • Proposing a general form of mass transfer correlation for systems with resistance in both phases • confirmation of experimental findings with the calculation results

Simulation of conjugate mass transfer in multiphase flow: A new unified approach based on the phase field method

Conjugate mass transfer phenomena are commonly found in industries and nature. It raises a serious challenge for numerical research, because at interfaces not only the continuity of mass flux but also the concentration jump (i.e. Henry's law) must be guaranteed. A complicated interface will further increase the complexity of numerical research of conjugate mass transfer. The phase field method has an intrinsic advantage over the other available numerical methods to model complicated interfaces, but so far there is no efforts to investigate interphase mass transfer with the aid of phase field method. The challenge is to design an appropriate governing equation for concentration field, which can be coupled with the phase field method and meanwhile can describe conjugate mass transfer in a unified manner. In this study, a new governing equation for concentration field is proposed to address the challenge. A number of benchmark test cases are employed to validate the present approach. The excellent agreement of the present numerical results with the analytical solutions and published data can demonstrate the applicability of the present approach for simulating conjugate mass transfer not only with a flat stationary interface but also with a moving/curved interface.

Study on flow and heat and mass transfer characteristics of cross-flow poly propylene hollow fiber membrane module

ABSTRACT Hollow fiber membrane solution dehumidification technology is a new type of dehumidification technology combining solution dehumidification and membrane separation. It is currently widely used in the field of air conditioning dehumidification. In this study, membrane dehumidification technology was applied to low-temperature flue gas dehumidification, and a model of regularly arranged hollow fiber membrane modules was established on the basis of a conjugate heat and mass transfer model. The accuracy of the model was verified by comparing it with literature and experimental data, applying a random arrangement of components. Numerical simulation is carried out by COMSOL software. The flue gas velocity, temperature and water vapor concentration field in the module are coupled together, and the flue gas flow and heat and mass transfer characteristics are affected by the distance between the membrane filament tubes. The dehumidification and cooling efficiency of the randomly arranged hollow fiber membrane module can reach 68.3% and 39.1%,respectively, which Close to 72.1% and 48.7% of regularly arranged components. And the components can be optimized based on the model.

Conjugate Heat and Mass Transfer on Steady MHD Mixed Convection Flow along a Vertical Slender Hollow Cylinder with Heat Generation and Chemical Reaction Effects

This paper studies the effects of heat generation and chemical reaction on the coupled conjugate heat and mass transfer by MHD laminar mixed convective flow along a vertical slender hollow cylinder. The governing boundary layer equations along with the boundary conditions are first cast into a dimensionless form by a non similar transformation and the resulting equations are then solved by the finite difference method using Matlab@ following the code bvp4c. Numerical results of the velocity, temperature and concentration for different values of the conjugate heat transfer parameter p, the magnetic parameter M, the heat generation Q, and the chemical reaction K are studied. The local skin friction, Nusselt number and Sherwood number are also analyzed and presented graphically. In the numerical ranges of the main parameters, it is found mainly that working with strong conjugate heat transfer or/and all others parameters affects negatively the Nusselt and Sherwood numbers. The same trend is revealed for the skin friction factor.

Numerical Study of the Influence of Spherically Blunted Cone Oscillations during a Supersonic Air Flow around on the Characteristics of Conjugate Heat and Mass Transfer

Numerical Study of the Influence of Spherically Blunted Cone Oscillations during a Supersonic Air Flow around on the Characteristics of Conjugate Heat and Mass Transfer

Mathematical Simulation of the Action of Oscillations of a Blunt-Nosed Conic Body on the Conjugate Heat and Mass Transfer in Its Coating

Mathematical Simulation of the Action of Oscillations of a Blunt-Nosed Conic Body on the Conjugate Heat and Mass Transfer in Its Coating

Effect of suction/blowing on heat-absorbing unsteady radiative Casson fluid past a semi-infinite flat plate with conjugate heating and inclined magnetic field

This article studies the effect of suction/blowing, inclined magnetic field, and chemical reaction on heat-absorbing unsteady radiative Casson fluid past a semi-infinite flat plate in porous medium incorporating the oscillatory plate movement as a linear combination of ‘cosine’ and ‘sine’ functions in time. Further, the mass and heat transfer characteristics are examined under the influence of conjugate mass and heat transfer phenomena at the boundary. The governing equations of the model, viz. the energy, mass transfer, and momentum, are transformed into the non-dimensional form adopting suitable non-dimensional variables and parameters. The exact analytic solutions of the model for species concentration and fluid temperature are obtained using Laplace transform technique whilst, the solution for the fluid velocity has been obtained numerically with the help of the INVLAP routine of MATLAB. The expressions for fluid temperature, species concentration, and velocity are obtained and studied graphically for various physical parameters influencing the fluid flow model taking into account the case of both suction and blowing. Further, the solutions when the Casson fluid parameter $$\alpha \rightarrow \infty $$ are also obtained as special cases. Results for the skin friction coefficient, Sherwood number, and Nusselt number are numerically calculated and put in tabular form. An increment for the inclination angle of the magnetic field enhances the fluid velocity while it has a reverse effect on skin friction. Increasing the Schmidt number Sc leads to a reduction in fluid concentration and increasing the value of thermal radiation accelerates fluid temperature. This fluid flow model has several industrial applications in the field of chemical, polymer, medical sciences, etc.

Numerical study of conjugate mass transfer from a spherical droplet at moderate Reynolds number

Hydrodynamics and conjugate mass transfer from a spherical droplet at low to moderate Reynolds number have been investigated by direct numerical simulation. The study particularly focuses on the coupling between the internal and external flows, and their respective effects on the resulting mass transfer of a solute under 2D axi-symmetric configuration. The influence of the viscosity, density, and diffusivity ratios (μ*, ρ* and D* respectively) between the two phases, as well as that of the equilibrium constant k (or Henry’s number) characterizing thermodynamic equilibrium at the interface, has been studied in a range of flow Reynolds numbers relevant for solvent extraction processes (up to Reynolds number 100).The temporal evolution of the Sherwood number has been analyzed and a general correlation is proposed for its steady state regime. Interestingly, simulation results show that correlations available in the literature in the limiting cases kD*≪1 and kD*≫1, referred to as internal and external mass transfer regimes, are not always appropriate in the context of conjugate mass transfer. This limits the use of the addition rule of transfer resistances, which reflects the flux continuity in the double stagnant film model. Indeed, a significant discrepancy is observed under specific configurations, especially at low Péclet number (Pe ≤ 500) where non uniform interface concentration prevails.

Non-axis-Symmetric Transport Characteristics of an Evaporating Water Droplet Sessile on Heated Horizontal Superhydrophobic Substrates

Abstract Evaporation of sessile droplets is an important fundamental problem. The present three-dimensional numerical model considers various effects including vapor diffusion, buoyancy-driven flow, and evaporative cooling, with conjugate heat and mass transfer solved throughout the computational domain. Evaporation of a sessile water droplet with an initial volume of 3 μL is investigated on heated horizontal superhydrophobic substrates. A non-axis-symmetric rolling flow is presented inside the droplet rather than the axis-symmetric recirculation flow predicted by a two-dimensional axisymmetric model. This is because the axis-symmetric flow is not stable on heated superhydrophobic substrate and sensitive to any perturbations. The evaporative cooling along the droplet interface is observed, but the coolest point appears on the one side of the droplet instead of the droplet top owing to the rolling flow inside the droplet. Influence of relative humidity is also discussed and it indicates a stronger impact on substrates with relatively lower temperature. The present numerical study reveals the important underlying transport characteristics, which provides new insights into evaporation of water droplets resting on heated horizontal superhydrophobic substrates.

CONJUGATE MASS TRANSFER FOR THE REMOVAL OF HYDROGEN SULFIDE GAS CIRCULATING IN A SLIT MICROCHANNEL ON A HOMOGENEOUS BIOFILM UNDER THE INFLUENCE OF THE DAMKÖHLER NUMBER

CONJUGATE MASS TRANSFER FOR THE REMOVAL OF HYDROGEN SULFIDE GAS CIRCULATING IN A SLIT MICROCHANNEL ON A HOMOGENEOUS BIOFILM UNDER THE INFLUENCE OF THE DAMKÖHLER NUMBER

Unsteady conjugate mass transfer of a 2D deformable droplet in a modest extensional flow in across‐slot

AbstractThis work aims to investigate the unsteady conjugate interphase mass transfer between a stationary deformed drop and the modest extensional flow in a cross‐intersected 2D channel. It is very difficult to accurately quantify the transient mass transfer rate of solute in such a geometry. Therefore, we established a mathematical model on the basic of the Stokes equation and solved it by the boundary element method, which could deal precisely with a two‐phase flow system with a deformable interface; meanwhile, the convection‐diffusion equation was solved by the finite difference method to calculate the unsteady conjugate interphase mass transfer. The simulation results showed that the mass transfer rate, analyzed and characterized in terms of mean concentration variation and Sherwood number Sh, was affected by capillary number Ca, Peclet number Pe, viscosity ratio λ, interior‐to‐exterior diffusivity ratio K, distribution coefficient m, and wall effect factor W.

Mathematical Model of Conjugate Heat and Mass Transfer at Film Condensation

A mathematical model for calculating the thermohydrodynamic situation during film condensation based on the equations of conservation of mass, momentum and energy for the refrigerant in a limited area, the condensate film flowing and the gas phase in a two-dimensional formulation is constructed. The dependence of the viscosity of the working medium on the temperature is taken into account. The boundary conditions of conjugation are specified on the inner wall of the refrigerant flow region, the outer wall through which the condensate film flows, and also at the film-gas interface. The obtained boundary value problem is solved by approximate and numerical methods together with the condition for determining the unknown film thickness, which allows the calculation of all characteristics of the condensation process.

Conjugate heat and mass transfer model for predicting thin-layer drying uniformity in a compact, crossflow dehydrator

A conjugate heat and mass transfer model was implemented into a commercial CFD code to analyze the convective drying of corn. The Navier–Stokes equations for drying air flow were coupled to diffusion equations for heat and moisture transport in a corn kernel during drying. Model formulation and implementation in the commercial software is discussed. Validation simulations were conducted to compare numerical results to experimental, thin-layer drying data. The model was then used to analyze drying performance for a compact, crossflow dehydrator. At low inlet air temperatures, the drying rate in the compact dehydrator matched the thin-layer drying rate. At higher temperatures, heat losses through the external walls resulted in temperature and moisture variations across the dehydrator.

Unsteady conjugate mass and heat transfer from/to a prolate spheroidal droplet in uniaxial extensional creeping flow

The unsteady conjugate mass/heat transfer from/to a prolate droplet suspended in uniaxial extensional creeping flow was numerically investigated. Based on the Stokes velocity field of a prolate droplet at small Reynolds numbers, a numerical algorithm combined with the finite difference method, the concentration transformation method and the level set approach was adopted to solve the convection-diffusion transport equations. The effects of Peclet number (1 ≤ Pe ≤ 1000), capillary number (0 ≤ Ca ≤ 0.1), viscosity ratio (0.01 ≤ λ ≤ 1), diffusivity ratio (0.1 ≤ K ≤ 10) and distribution coefficient (0.1 ≤ m ≤ 10) on interphase transport process were examined in terms of numerical simulation. The results show that the conjugate mass transfer from/to a single prolate droplet in the uniaxial extensional flow is significantly influenced by these five parameters, and the local and total mass transfer rates of a deformable droplet are slightly different from that of a spherical one. Given Pe, Ca, λ, K and m, an empirical correlation with an average relative deviation of 12.01% was proposed to predict Sh1,∞ of the prolate and spherical droplets suspended in uniaxial extensional creeping flow.

Analysis of Henry’s law and a unified lattice Boltzmann equation for conjugate mass transfer problem

The most challenging problem for simulating conjugate mass transfer problem is the variable concentration jump described by the double film theory at the phase interface. In the present paper, the physical mechanism of Henry’s law is analyzed, and it is found that Henry’s law can be expressed as a relation between two constant weight coefficients in lattice Boltzmann method (LBM). As a consequence, a unified multi-relaxation-time (MRT) lattice Boltzmann equation (LBE) for conjugate mass transfer is proposed. The asymptotic analysis proves that the interface conditions, including the concentration jump determined by the double film theory and mass flux continuity, can be ensured with second-order accuracy. Five test cases containing both transient and steady conjugate mass transfer problems with straight or curved interfaces are calculated to validate the present method. The results show that the proposed MRT LBE has both simplicity and good accuracy. It is capable of simulating conjugate mass transfer at both steady and transient periods, with a stationary or moving interface. Especially, it has a good numerical stability at large distribution coefficient and diffusivity coefficient ratio.

Modelling mass transfer in liquid-liquid slug flow in a microchannel

Liquid-liquid slug flow regime is characterised by the presence of strong internal circulation which enhances mass transfer. In this work, we develop a mathematical model for conjugate mass transfer in the liquid-liquid slug flow regime in a microchannel. A Lagrangian approach is adopted where the behaviour of a unit cell in the channel is analysed in a moving reference frame. The system is analysed for two cases when (I) the slug is in direct contact with the channel wall and (II) there is a thin film of continuous fluid surrounding the slug. A novel contribution of this work is the extension of the stream function formulation to determine the flow structures in multiply connected domains made up of two liquids in a pressure driven flow. The primary objective of the work is to understand the influence of the flow patterns (which is determined by fluid properties and operating conditions) on the mass transfer of a solute from the slug to the continuous phase. Towards this, the species transport equation is solved numerically using the velocity field obtained. The reliability of the model developed is validated with experiments reported in the literature. This study gives us insights on the influence of the film on the hydrodynamics and its contribution to mass transfer. A key finding of this study is that the rate of mass transfer can be enhanced if the continuous phase has higher viscosity than the slug phase.