Effect of microchannel junction angle on two-phase liquid-gas Taylor flow

Two-phase liquid-gas Taylor flow triggered by blocking-squeezing mechanism was studied with different junction angle theta microchannels, i.e. 20 degrees, 45 degrees, 90 degrees, 135 degrees and 160 degrees, at various liquid (ethanol) and gas (He) flow rates. We experimentally investigated the effects of flow rates and theta on the gas bubble V-B and liquid slug V-S volumes. A theoretical model was formulated for the quantitative predictions of bubble and slug sizes for different theta and flow rates. Good agreements were obtained between theoretical predictions and experimental observations. The unit cell volume V-U (V-B + V-S) decreased pronouncedly for the 20 degrees channel with decreasing liquid or increasing gas flow rate, due to the slight increase in V-B and large decrease in V-S. In comparison, for the 45 degrees, 90 degrees, 135 degrees and 160 degrees channels with increasing liquid or decreasing gas flow rate, V-U were less sensitive to fluid flow rate changes, due to the approximate cancellation between V-B decrease and V-S increase. For the 20 degrees and 45 degrees channels, it produced larger V-U, due to larger V-B and V-S, when compared to the 90 degrees channel. This is caused by the larger gas bubble throat width D-N at the junction when theta < 90 degrees. As for the 135 degrees and 160 degrees channels (theta > 90 degrees), D-N is approximately equal to the gas channel width, with V-B, V-S and V-U approximately the same as the 90 degrees channel. With theta >= 90 degrees (i.e. 90 degrees, 135 degrees and 160 degrees channels), as evident from the smaller V-U, higher gas bubble density can be obtained when compared to theta < 90 degrees (i.e. 20 degrees and 45 degrees channels). Hitherto, this observation has not been realized, and the mechanics is first investigated here with the employment of extreme theta (i.e. 20 degrees and 160 degrees). A thorough understanding of the underlying mechanics affecting Taylor flow can facilitate its exploitation for controlled gas bubble and liquid slug generation. Our theoretical model facilitates the tuning of the channel designs and fluid flow rates to achieve the desired gas bubble and liquid slug sizes for specific applications. (C) 2019 Elsevier Ltd. All rights reserved.