The effect of the centrifugal field on the reaction-diffusion-convection processes in a two-layer system of immiscible solvents

Abstract

The presence of a chemical reaction in a liquid medium can lead to changes in some physicochemical parameters of the system and, as a consequence, a number of hydrodynamic instabilities can develop. Studying the conditions of their occurrence in various force fields is an important task, given that the appearance of a convective mechanism of heat and mass transfer can increase the reaction rate by several orders of magnitude. This article presents the results of an experimental study of the effect that a centrifugal field has on the conditions of occurrence, intensity and structure of convective motion arising during a neutralization reaction occurring between reagents initially located in different layers of a two-layer system of immiscible solvents. The upper layer was a solution of hydrochloric acid in n-pentanol, the lower layer was an aqueous solution of sodium hydroxide. The use of inorganic reagents excludes the development of capillary types of instability, bringing to the fore gravity-dependent mechanisms of the convective motion formation. We studied the spatial-temporal distribution of the reagents and reaction product, the structure of the resulting flow by means of interferometric methods and by adding an acid-base indicator. The studies were conducted in parallel in the gravity field and in the centrifugal field. The influence of the centrifugal field leads to a radical change in the flow structure with a slight increase in the reaction rate due to convective motion, compared with experiments in the gravity field. Convective motion in a centrifugal field develops even under conditions when the system remains hydrodynamically stable in a constant gravity field. It is suggested that the reason for the change in the flow structure is the Coriolis force, the manifestations of which are traditionally neglected in theoretical studies due to, as it is believed, its smallness in comparison with the centrifugal force.