Gas-liquid Interfacial Mass Transfer Research Articles

Computational fluid dynamics modeling and mass transfer study of an in situ gas production process

AbstractThe oxidation of cyclohexanone with nitric acid in microreactors, as a representative chemical reaction with in situ gas production, was selected as the model reaction for computational fluid dynamics (CFD) modeling. The reaction kinetics was coupled with the CFD model by user‐defined functions (UDFs) to obtain the velocity field of liquid phase, the concentration field of products, and the temperature field of gas–liquid phases during the reaction process. The simulation results were then validated by the experimental data. Based on the established model, the fluid flow behavior and mass transfer characteristics during the in situ gas production process in a microreactor were further analyzed. Finally, the effects of channel diameter and bubble velocity on gas–liquid interfacial mass transfer were investigated. This work provides an effective method for studying in situ gas production processes through modeling and simulation, which is valuable in the design and optimization of tubular reactors.

Enhancement and mechanism of adsorptive particles on gas-liquid interfacial mass transfer

The aim of this paper is to study the enhancement mechanism of adsorptive particles on gas-liquid interfacial mass transfer. A quantitative model for predicting enhancement factor is proposed based on film model and interfacial non-equilibrium model, in which the enhancement factor depends mainly on the surface fractional coverage θ and the solute bulk concentration Cb, the interfacial concentration of liquid CI is dependent of the mass transfer coefficient kl and Cb, and usually is far from the equilibrium concentration with gas phase at the interface. The surface fractional coverage θ is a function of particle property and operating condition. The present model divided the enhancement into two regimes: particle-transport-controlled regime and surface-adsorption-controlled regime. The increase of gas-liquid mass transfer rate in the presence of adsorptive particles could mainly attributed to the surface adhesion of particles, the enhancement factor is an increasing function of surface fractional coverage θ but a decreasing function of the solute bulk concentration Cb, which well explains the effects of particles concentration and stirring intensity on enhancement factor. The prediction values of present model are at considerably good agreement with experimental data.

Three-dimensional numerical simulation of gas-liquid interfacial mass transfer with Rayleigh convection using hybrid LBM-FDM and its mass transfer coefficient model

Rayleigh convection has a significant effect on gas-liquid interfacial mass transfer. However, its intensified mechanism has not been clarified so far. In the present work, three-dimensional hybrid Lattice Boltzmann Method-Finite Difference Method (LBM-FDM) was employed to simulate the Rayleigh convection emerging in the CO2-ethanol absorption process. A gas phase random disturbance model was applied to represent the disturbances on the gas-liquid interface which effectively induces Rayleigh convection. Then the front view images obtained by three-dimensional simulation were compared to the Schlieren observations for validation. Finally, a theoretical mass transfer coefficient model based on dissipation rate of concentration variance was proposed, by analyzing the overhead view of concentration contour and dissipation rate of concentration variance contour. Compared to the small eddy model and surface divergence model, the proposed model shows its strength in determining molecular diffusion stage and convective mass transfer stage of Rayleigh convection process, as well as eliminating the phase difference in model prediction.

Modeling the transport and capture of analytes in a two-phase heterogeneous microfluidic immunosensor

In a typical heterogeneous microfluidic immunosensor, the carrier fluid transports the target analytes to the antibodies immobilized on the channel surfaces with a thin liquid layer where they are captured. While single-phase systems (the carrier fluid being a liquid) are well studied, two-phase systems (the carrier fluid being a gas) are less explored. There in particular, the effect of transport parameters on the capture efficiency (a critical performance parameter) has not received much attention, and thus is the subject of study here. Hence, we have investigated the transport and capture of analytes in a two-phase heterogeneous microfluidic immunosensor wherein the target analytes in the gaseous phase are transported to the immobilized antibodies via gas–liquid interfacial mass transfer which strongly depends on flow variables of the gas phase flow. Parametric studies on capture efficiency using the properties of trinitrotoluene (TNT) were used to obtain the effects of important transport parameters on the capture of analyte molecules. The highlight of this work is the development of an empirical correlation between the capture efficiency and the gas-side non-dimensional interfacial mass transfer coefficient (Sherwood number, Shg). This could help design of a two-phase microfluidic device with improved performance parameters to capture gaseous analytes.

Modeling of Rayleigh convection in gas–liquid interfacial mass transfer using lattice Boltzmann method

Interfacial Rayleigh convection can be generated by concentration gradient near the interface in mass transfer processes. In the present study, a 2D time-dependent lattice Boltzmann method (LBM) with a double distribution model was established for simulating the liquid-phase Rayleigh convection in the mass transfer process of CO2 absorption into various solvents. Two random parameters P and CD denoting respectively the possibility and the magnitude of concentration perturbation at interface were introduced to model the interfacial disturbance, which is known as one of the necessary conditions of onset of Rayleigh convection. The values of the parameters were identified (0.05≤P<0.3 and 0<CD≤10−9kgm−3) by comparing simulated critical onset times of the Rayleigh convection with the experimental result from Blair and Quinn (1969) and theoretical predictions proposed by Kim et al. (2006) and Tan and Thorpe (1992, 1999). The maximum penetration depths, maximum transient Rayleigh numbers, and critical times for the onset of Rayleigh convection were obtained by the proposed model. The simulations captured the detailed information of the onset and the temporal–spatial evolution of Rayleigh convection, and gave the concentration contours of typical plume convection patterns which were well consistent with literatures. Enhancement of mass transfer by the Rayleigh convection was also demonstrated by comparing the simulated instantaneous mass flux across the interface with that predicted by penetration theory.

Hydrodynamics and mass transfer behavior in multiple draft tube airlift contactors

The draft tube configuration significantly affected the performance of an airlift contactor. The multiple draft tube configuration was demonstrated to give a better gas-liquid mass transfer when compared with a conventional one-draft-tube system. The airlift with a larger number of draft tubes allowed a higher level of bubble entrainment, which rendered a high downcomer gas holdup. This resulted in a higher overall gas holdup in the contactor. Liquid velocity was also enhanced by increasing the number of draft tubes. The ratio between downcomer and riser cross sectional areas, Ad/Ar, had a great effect on the system performance, where a larger Ad/Ar led to a lower downcomer liquid velocity and smaller quantity of gas bubbles being dragged into the downcomer. This resulted in low gas holdup, and consequently, low gas-liquid interfacial mass transfer area, which led to a reduction in the overall volumetric mass transfer coefficient. The presence of salinity in the system drastically reduced the bubble size and subsequently led to an enhancement of gas entrainment within the system. As a result, higher gas holdups and gas-liquid interfacial area were observed, and hence, a higher rate of gas-liquid mass transfer was obtained.

Gas–liquid interfacial mass transfer in trickle-bed reactors: state-of-the-art correlations

The state-of-the-art of the gas-liquid mass transfer characteristics in trickle-bed reactors was summarized and its quantification methods were reevaluated based on a wide-ranging data base of some 3200 measurements. A set of three unified whole-flow-regime dimensionless correlations for volumetric liquid- and gas-side mass transfer coefficients, and gas–liquid interfacial area, each of which spanned four-order-of-magnitude intervals, were derived. The correlations involved combination of artificial neural networks and dimensional analysis. The dimensionless interfacial area, Sh L and Sh G were expressed as a function of the most pertinent dimensionless groups: Re L , Re G , We L , We G , Sc L , Sc G , St L , X G , Mo L , Fr L , Eo m , S b .

Toxicity of dibenzothiophene to thermophile Sulfolobus acidocaldarius grown in sucrose medium

Sulfolobus acidocaldarius had been found earlier to grow and desulfurize dibenzothiophene (DBT) in a tryptone medium. Its characteristics were investigated in a cheaper sucrose medium in this study. In DBT-free systems the growth at 70°C and pH 2.5 proceeded with a specific rate of 0.14 h −1 and a cell yield of 0.35 g dry cells g sucrose −1. The maximum cell concentration attainable in the fermentor (3.5 l) was only 0.4 g l −1 under the agitation speed of 600 rpm and aeration rate of 1 l min −1. It increased to 2.0 g l −1 with higher agitation (700 rpm) and aeration (2 l min −1). The strong dependency on agitation and aeration suggested that the growth limitation be related to the gas–liquid interfacial mass transfer, presumably for oxygen supply. As for the study of DBT desulfurization, immediate cessation of cell growth and rapid cell death were observed when an oil phase (2% in volume) containing 10 g l −1 DBT was added to the culture grown in the sucrose medium. Further experiments confirmed that DBT was responsible for the toxicity. Normal cell growth, however, could be obtained by employing gentle mixing to keep the oil and aqueous phases as rather separate layers. The water-soluble DBT was therefore not the cause of the toxicity and the contact frequency of the cells with the oil–water interface might play an important role. Under high agitation, the cells could also overcome the toxicity if a lower DBT concentration (2 g l −1) was involved. Nonetheless, no appreciable DBT transformation could be detected in any of the above systems. Sucrose was shown unsuitable as the substrate for the desulfurization process.