Efficient microextraction process exploiting spontaneous interfacial convection driven by Marangoni and electric field induced instability: A computational fluid dynamics study

Abstract

The present study focuses on the component transfer from one liquid phase to another liquid phase, commonly known as the extraction process, performed in a microchannel in the presence of spontaneous interfacial convection, driven by either an interfacial tension gradient or an applied external electric field. Marangoni instability occurs as a result of a lateral gradient of interfacial tension existing along the interface of the two fluids. Nonequilibrium phenomena associated with factors such as temperature imbalance, a nonuniform distribution of surface-active components at the interface, evaporation, etc. can lead to the interfacial Marangoni instability. In the present study, first, we have explored temperature gradient driven Marangoni instability, which deforms the interface with significant acceleration and induces local convective mass transfer along with the conventional diffusion mode. Next, we have explored the same phenomenon in the presence of an external electric field, which can also deform the liquid-liquid interface almost instantaneously to a considerable extent. The relative strength of the mass transfer rate for different cases, such as temperature driven instability, in the presence of uniform and nonuniform electric fields has been reported in detail. It has also been observed that, due to the larger mass transfer area, the annular flow offers an enhanced rate of mass transfer compared to the stratified flow. Additionally, this article reports that the nonuniform electric field could influence the process of interfacial instability more strongly compared to the uniform electric field. The effect of the nonuniform electric field with different spatial periodicity on the extraction process has been studied in detail.

Utilizing Low-Voltage Pulsed Electric Fields for Mass Transfer Intensification of Drops in Liquid–Liquid Extraction

“…According to their findings, accumulation of induced charges at the interface causes electrical stress and amplifies interfacial instability. More recently, a pronounced effect of an electric field (within 100–350 V) on microfluidic extraction was reported by Mitra et al…”

“…According to their findings, accumulation of induced charges at the interface causes electrical stress and amplifies interfacial instability. More recently, a pronounced effect of an electric field (within 100−350 V) on microfluidic extraction was reported by Mitra et al 28 Utilizing a high-voltage electric field in columns encounters economic and safety problems. Here, low-voltage pulsed electric fields with a controllable frequency have been employed for mass transfer intensification of drops.…”

“…This instability improves the mass transfer between phases. 28 Figure 1 depicts a schematic of the charge distributions around a drop exposed to a bipolar pulsed electric field.…”

“…By applying a bipolar pulsed electric field, the interfacial stresses are evolved because of displacement of charges through switching the positive and negative poles and also due to permittivity and conductivity contrast of the fluids. This instability improves the mass transfer between phases Figure depicts a schematic of the charge distributions around a drop exposed to a bipolar pulsed electric field.…”