Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel
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Date
2018-02-12
Authors
Qin, Ning
Wen, John Z.
Ren, Carolyn L.
Journal Title
Journal ISSN
Volume Title
Publisher
IOP Publishing
Abstract
Hydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width similar to 100). A general form of a mathematical model of the solvent-side mass transfer coefficient (k(s)) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of k(s) is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (L-x, x = 1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, k(s) is calculated mainly based on Lx and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios (Q(LCO2)/Q(H2O)) are generally characterized by higher (nearly three times) ks and Sherwood numbers than those produced by higher Q(LCO2)/Q(H2O), which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (similar to 10(4) m(-1)) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng-Robinson equation of state and initial pressures of drops at the T-junction in experiments, overall pressure drop (Delta P-t) in the straight channel as well as the resulted drop volume change are quantified. Delta P-t from position 1-3 is by average 3.175 kPa with a similar to 1.6% standard error, which only leads to relative drop volume changes of 0.3 parts per thousand to 0.52 parts per thousand.
Description
This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condensed Matter. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-648X/aaa81c
Keywords
equation-of-state, supercritical carbon-dioxide, mass-transfer, gas-liquid, slug-flow, microstructured reactors, interfacial-tension, size distributions, chemical-reactions, cubic equations, droplet microfluidics, liquid carbon dioxide, drop shrinkage, mass transfer across partially miscible interface