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Abstract: This work deals with the modeling and the direct numerical simulation of the absorption of a gas component into a spherical liquid droplet in free fall, where the absorbed component takes part to a chemical reaction. This study is realized by computing the flow fields and the concentration fields simultaneously in the gas and liquid phases. The time evolution of the droplet global mass absorption rate is studied for various regimes characterized by the Reynolds and the Hatta numbers. The monitoring of the time evolution of the concentration fields in the droplet enables the understanding of the interactions between the diffusive and convective mass transports and the chemical reaction. The phenomena controlling the mass transfer rate and how they evolve during the mass absorption process can then be identified. In a first stage, the case of the physical absorption is studied. Moreover, analytical expressions are developed to correlate the time evolution of the Sherwood number with the Reynolds number and the absorption time. In a second stage, the influence of the coupling with a chemical reaction is studied. It is observed that several rate-limiting mechanisms successively control the global absorption rate, enlightening the complex interactions between convective and diffusive mass transport and the chemical reaction. [Copyright &y& Elsevier]

Abstract: This work deals with the study of bubble-liquid mass transfer coupled with chemical reactions. The absorption of carbon dioxide in aqueous solution of sodium carbonate and bicarbonate is used as a reference case. The influences of the interface contamination state and of the ellipsoidal shape of the bubble on the mass transfer rate are studied using a two-dimensional (2D) axisymmetric model. On the one hand, the case of a spherical bubble with a partially contaminated interface is investigated. It is assumed that a fixed stagnant cap lies on a part of the bubble surface in the rear. On the other hand, the case of an ellipsoidal bubble with a clean interface is investigated. In a first stage, correlations to estimate the transfer rate without reaction are presented and compared to the 2D model results. In a second stage, the mass transfer rate is computed with chemical reactions for several reaction rates. The influences of the coupling reactions – contamination state and the coupling reactions – ellipsoidal shape are then presented and discussed. These 2D model results are also compared to mass transfer rate estimations based on classical one-dimensional (1D) models. It is shown that 1D approaches are useful to provide a rough estimation of the mass transfer rate but 2D models have to be used when an accurate estimation of the mass transfer rate is required. [Copyright &y& Elsevier]

Abstract: This work deals with the quantification of the bubble-liquid transfer rate coupled with chemical reactions in the liquid phase. A two-dimensional axisymmetrical model is developed. The numerical simulations are validated without chemical reaction. The validated numerical procedure is used to study the enhancement influence of chemical reactions on the bubble-liquid mass transfer rate. Moreover, the results of this study are compared with classical uni-dimensional approaches and excellent comparisons are observed. [Copyright &y& Elsevier]

In this paper, a new comprehensive analysis of a suspended drop of a pure liquid evaporating into air is presented. Based on mass and energy conservation equations, a quasi-steady model is developed including diffusive and convective transports, and considering the non-isothermia of the gas phase. The main original feature of this simple analytical model lies in the consideration of the local dependence of the physico-chemical properties of the gas on the gas temperature, which has a significant influence on the evaporation process at high temperatures. The influence of the atmospheric conditions on the interfacial evaporation flux, molar fraction and temperature is investigated. Simplified versions of the model are developed to highlight the key mechanisms governing the evaporation process. For the conditions considered in this work, the convective transport appears to be opposed to the evaporation process leading to a decrease of the evaporation flux. However, this effect is relatively limited, the Péclet numbers happening to be small. In addition, the gas isothermia assumption never appears to be valid here, even at room temperature, due to the large temperature gradient that develops in the gas phase. These two conclusions are explained by the fact that heat transfer from the gas to the liquid appears to be the step limiting the evaporation process. Regardless of the complexity of the developed model, yet excluding extremely small droplets, the square of the drop radius decreases linearly over time ( R 2 law). The assumptions of the model are rigorously discussed and general criteria are established, independently of the liquid–gas couple considered. [ABSTRACT FROM AUTHOR]

Abstract: This work deals with the experimental characterization of carbon dioxide ( ) absorption in an aqueous solution of N-(2-hydroxyethyl)piperazine, by using of digital holographic interferometry. This method enables visualizing the phenomena taking place in the vicinity of the gas–liquid interface. Thanks to a calibration, the obtained results yield the time evolution of the loading field in the aqueous solution and the gas–liquid absorption rate for various operating conditions. The processing method and the obtained results are detailed. A phenomenological model, highlighting the limiting steps of the gas–liquid absorption, is proposed. A set of experiments is realized and the parameters of this model are estimated for various initial amine concentrations and initial loadings. The results are discussed and correlations are proposed for the model parameters. [Copyright &y& Elsevier]

Abstract: This work deals with the development of a new experimental tool and an original procedure to study the gas–liquid absorption process coupled with chemical reactions in the liquid phase. This absorption is realized inside a Hele-Shaw cell and digital holographic interferometry is used to visualize the formation and the development of the diffusion layer during the mass transport in the liquid phase in the vicinity of the gas–liquid interface. An image processing code is developed to extract quantitative information from the raw experimental results. The experimental results are compared to a mass transfer model in the liquid phase of the Hele-Shaw cell and some physico-chemical parameters of this model are estimated from this comparison using on a non-linear least-square fitting method. The developed procedure is used to study the gaseous CO2 absorption in NaHCO3–Na2CO3 aqueous solution. Calibration curves are determined and experiments are realized for several couples of NaHCO3–Na2CO3 initial concentrations. The estimated values of the physico-chemical parameters for each experiment are presented and they are compared to the values calculated from correlations found in the literature. A reasonable agreement is observed, which tends to show that the methodology is promising and could be applicable to other systems. [Copyright &y& Elsevier]