In a T-junction, flow pulsation in one limb and continuous flow on the other limb lead to an enhanced mass transfer in the extraction limb. We experimentally and theoretically establish that introduction of a captive air column (air-damper) in combination with pulsating flows at the modified T-junction leads to drastic benefits in terms of interliquid mass transfer per unit power input to the system. Acetic acid is the diffusing species, which is transferred from the organic phase (toluene) in pulsatile flow to an aqueous phase in a continuous flow after they merge together at the cross-junction (T-junction with the fourth limb filled with air). It is found that smaller lengths of the extraction column with the same length of air damper deliver a comparatively higher rate of species extraction compared to longer columns for the same power input.
Marangoni effect plays an important role in many industrial applications where a surface tension gradient induces fluid flow, e.g., the cleaning process of silicon wafers and the welding process of melted metal. Surface tension gradient can also be caused by a spatially varying temperature field which, in the absence of gravity, is solely responsible for driving a large scale convective flow. NASA STDC-1 (Surface Tension Driven Convection) experiments performed on USML-1 Spacelab missions in 1992 were designed to study thermocapillary flows in microgravity. Since then these experiments have become a benchmark in thermocapillary studies in the absence of gravity. However, interpretation of results of the original STDC-1 experiments remains challenging due to the low resolution of the available data. Analysis of the velocity field in those experiments was limited to a single tracking method without systematic and comparative studies. In the present study, we utilize multiple state-of-the-art Particle Image Velocimetry and Particle Tracking Velocimetry tools to extract the flow field from NASA STDCE-1 videos and compare the experimental data to the numerical results from COMSOL Multiphysics® v5.6. Finally, we discuss how our findings of temperature-driven Marangoni flow in the microgravity setting can improve future experiments and analysis.
The work in this manuscript presents liquid‐liquid extraction augmentation and optimization due to flow pulsations on a continuous flow. The mass transfer is achieved via a transfer species (acetic acid) that diffuses in the aqueous phase (water), which is in a continuous flow, from the organic phase (toluene), exhibiting pulsed flow pattern. It is observed through experiments that the incorporation of pulsation leads to enhanced extraction/mass transfer compared to continuous flows. Also, an increase of the pulsation parameters, such as amplitude and frequency, increases the mass transfer, but when the process is evaluated in terms of economy, it is found that the rate of extraction per unit power is maximum for moderate frequencies and amplitudes. Based on the experiments, a Linton and Sherwood‐like correlation for determining extracted concentration at the exit of the test section in semi‐pulsatile flow conditions is proposed. During the course of experiments, it is found that the flow pattern changes from dispersed‐type flow pattern of the organic phase to slug and then slug dispersed with an increase of superficial velocity of toluene, at a particular superficial velocity of the water. Also, the total power consumed during the extraction process increases with an increase in the product of amplitude and frequency. With the experimental approach presented in this paper, one will be able to optimize semi‐pulsatile liquid‐liquid mass transfer operations.
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