Gas absorption into a spherical liquid droplet: Numerical and theoretical study

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.

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

“…the external regime Sh EXT ) are compared in limiting situations where k √ D * 1 (resp. 1), according to the criteria established by Wylock et al [5] . Although the same hydrodynamic and physical-chemical properties were considered, [14] : Re = 100 , μ * = 0 .…”

“…internal Fourier number F D drag force h i internal mass transfer coefficient h e external mass transfer coefficient h INT mass transfer coefficient of the internal problem h EXT mass transfer coefficient of the external problem I identity tensor D * = D i /D e the solute diffusivity ratio, the asymptotic behaviour of the mass transfer regime can be assessed by the value of the dimensionless quantity k √ D * [5] . For internal problems ( k √ D * 1 ), the interface concentration C s is fixed by the external flow, and is supposed constant and uniform.…”

“…Except from these simplified configurations, the derivation of an analytic solution is not straightforward, and a numerical approach is required. Still assuming creeping flow, Juncu [2] , Wylock et al [5] , Brignell [8] solved the mass transfer equation assuming droplet hydrodynamics is following the Hadamard-Rybczynski analytic solution. More recently, Colombet et al [9] considered the effect of higher Reynolds number flows (0.1 ≤ Re ≤ 100) thanks to numerical simulations of both the Navier-Stokes and mass transfer equations.…”

Numerical Model to Analyze the Physicochemical Mechanisms Involved in CO2 Absorption by an Aqueous Ammonia Droplet

“…Juncu [ 22 ] examined the influence of the diffusivity ratio on the mass transfer rate. Wylock et al [ 23 ] studied the interactions between the diffusive and convective mass transports and chemical reactions. Chen et al [ 24 ] compared Selexol, Rectisol, and water as solvents.…”

Liquid Water Scavenging of PEMFC Contaminants

“…Pollutant scavenging by rain drops [18][19][20][21][22][23][24][25][26][27] and gas absorbers 28 such as spray towers, [29][30][31][32] packed columns 33,34 and cables bundle contactors 35 are related cases because a contaminant is removed from a gas stream to a liquid either naturally or purposefully. The penetration model is useful to understand the scavenging process.…”