In this paper the attention was focused on the characterization of the slug flow generated by twofluids upstream (air–water) in serpentine micro-channels with squared sections and widths of {640,320} lm. The curved geometries and the channels width greater than 100 lm increase the complexityof the microfluidic process due to a weak presence of turbolence and inertial effect. All that producesthe flow speed up and the enhancement of the mixing, but at the same time, a loss in the process control.The results presented are related to the changes in the slug flow pattern due to the differentgeometries varying the input flow rates and the investigated channel positions. A wide experimentalcampaign of a total of 69 experiments, divided in three experimental sets {set-1, set-2, set-3} wascarried out.Two-phase microfluidic processes were monitored optically acquiring signals related to the light intensityvariations in a selected channel position. Two flow patterns, slow and fast, were identified and thesignals analysis procedure used has allowed their association to specific dynamical features both in timeand in frequency domains. Four indicators were introduced for a quantitative evaluation of these featuresin the different operative conditions. The results have provided a characterization of the dynamics eventhough the nonlinearity of the process. In experimental set-1, comparing the flow patterns in two microchannelswith straight and serpentine geometries and width 320 lm, it was proved the drastic changesinduced in the flow displacement by the curves in terms of number of slugs and air/water presence. Inexperimental set-2, using a serpentine micro-channel with width 640 lm, it was investigated the roleof the input flow rate in the pattern formation and stabilization in terms bubbles length, frequencyand inter-distance variability. Regarding to the experimental set-3, changing the investigated positionin the micro-channel, the effects that the proximity to the inlet and the outlet leads in the segmentedflow patterns were considered. From all the results, a great variability in the flows behaviours and a highsensitivity to the different operative conditions were evident, nevertheless, the wide potentialities in theuse of serpentine geometries, for example to enhance the robustness to the input variations or to generatefast slug train at an established frequency, were proved. Moreover the low cost optical setting usedintegrated with the signal processing procedure could be easily adaptable to on-chip analysis for the processesinvestigations.
Experimental study on the slug flow in a serpentine microchannel
S. Gagliano;BUCOLO, MAIDE ANGELA RITA
2016-01-01
Abstract
In this paper the attention was focused on the characterization of the slug flow generated by twofluids upstream (air–water) in serpentine micro-channels with squared sections and widths of {640,320} lm. The curved geometries and the channels width greater than 100 lm increase the complexityof the microfluidic process due to a weak presence of turbolence and inertial effect. All that producesthe flow speed up and the enhancement of the mixing, but at the same time, a loss in the process control.The results presented are related to the changes in the slug flow pattern due to the differentgeometries varying the input flow rates and the investigated channel positions. A wide experimentalcampaign of a total of 69 experiments, divided in three experimental sets {set-1, set-2, set-3} wascarried out.Two-phase microfluidic processes were monitored optically acquiring signals related to the light intensityvariations in a selected channel position. Two flow patterns, slow and fast, were identified and thesignals analysis procedure used has allowed their association to specific dynamical features both in timeand in frequency domains. Four indicators were introduced for a quantitative evaluation of these featuresin the different operative conditions. The results have provided a characterization of the dynamics eventhough the nonlinearity of the process. In experimental set-1, comparing the flow patterns in two microchannelswith straight and serpentine geometries and width 320 lm, it was proved the drastic changesinduced in the flow displacement by the curves in terms of number of slugs and air/water presence. Inexperimental set-2, using a serpentine micro-channel with width 640 lm, it was investigated the roleof the input flow rate in the pattern formation and stabilization in terms bubbles length, frequencyand inter-distance variability. Regarding to the experimental set-3, changing the investigated positionin the micro-channel, the effects that the proximity to the inlet and the outlet leads in the segmentedflow patterns were considered. From all the results, a great variability in the flows behaviours and a highsensitivity to the different operative conditions were evident, nevertheless, the wide potentialities in theuse of serpentine geometries, for example to enhance the robustness to the input variations or to generatefast slug train at an established frequency, were proved. Moreover the low cost optical setting usedintegrated with the signal processing procedure could be easily adaptable to on-chip analysis for the processesinvestigations.File | Dimensione | Formato | |
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