Gas-liquid mass transfer around Taylor bubbles flowing in a long, in-plane, spiral-shaped milli-reactor

A colorimetric technique to characterize mass transfer during liquid-liquid slug flow in circular capillaries

“…Note : Current sliced-calibration strategy is only possible when the capillary has been well straightened. For curved capillaries, pixel-by-pixel calibration would be needed [24] .…”

“…Note that k L theoretically equals to 1/(1/ k L,W +1/ mk L,O ) for liquid-liquid system, where k L,W and k L,O are respectively the mass transfer coefficients from water and organic phases, but k L ≈ k L,W in current case, as explained above. For gas-liquid systems, k L = k L,W (mass transfer resistance in gas phase is usually negligible), and was reported to be in the magnitude of 10 −4 m/s [ 11 , 21 , 23 , 24 ] in gas-liquid microreactors using this resazurin system. Thus, here we assume that the overall mass transfer coefficient k L in our liquid-liquid system is in the same magnitude, leading to Ha = 17.7.…”

A revised 1D equivalent model for the determination of incident photon flux density in a continuous-flow LED-driven spiral-shaped microreactor using the actinometry method with Reinecke’s salt

“…As shown in Fig. 1, this microreactor consisted of FEP tubing fixed in a channel carved in a flat plate of either aluminium or polymethylmethacrylate (PMMA), and wound into an Archimedean spiral [31,32]. Tubing with an internal diameter, d i , equal to either 0.5 mm or 1 mm (the corresponding external diameter being 1.58 mm or 3.2 mm) was used.…”

Effect of mixing on mass transfer characterization in continuous slugs and dispersed droplets in biphasic slug flow microreactors

“…For example, with the same resazurin system, Yang et al [33] reported that the measured k L a was reduced along the channel length as τ = 1-5 s. This is because: (1) the large channel dimension (w = h = 2 mm) abated the intensity of internal circulation; (2) the reaction rate of oxygen with low resazurin concentration (0.1 g/L, corresponding C max = 0.199 × 10 -3 mol/L vs. C*=0.255 × 10 -3 mol/ L) might be smaller than its physical transport rate, especially when resazurin conversion approached 100%, leading to the presence of oxygen molecules at the interface or even in the slug bulk. In a recent work of the same group [34], the time-related k L a was also presented in an FEP circular tube (d = 1 mm, 0.1 g/L resazurin solution) under nonwetting slug flow (i.e., the liquid film was absent), which largely attenuated the internal mixing [51]. In comparison, the wetting slug flow within rectangular microchannel in the current work induced evident leakage flow and intensive internal circulation (will be explained in the following text), together with the low conversion of resazurin (mostly < 60%) allowed us to obtain the intrinsic k L a in the current residence time range.…”

“…slug with blue gradient color), leading to a deviation between the actual concentration difference and the calculated one based on average values. With the expanding of such deviation along the channel, a significant decrease of measured k L a was observed [29,30,[33][34][35]. Under the absolute dominance of diffusion (i.e., absence of convection), Susanti et al [30] considered the entire interface surrounding the droplet as a curved stationary plane and estimated the corresponding contact time by the residence time.…”