Abstract
Taylor segments, as a common feature in two- or multi-phase microflows, are a strong flow pattern candidate for applications when enhanced heat or mass transfer is particularly considered. A thin film that separates these segments from touching the solid channel and the flow fields near and inside the segment are two key factors that influence (either restricting or improving) the performance of heat and mass transfer. In this numerical study, a computational fluid dynamics (CFD) method and dense carbon dioxide (CO2) and water are applied and used as a fluid pair, respectively. One single flowing liquid or supercritical CO2 drop enclosed by water is traced in fixed frames of a long straight microchannel. The thin film, flow fields near and within single CO2 drop, and interfacial distributions of CO2 subjected to diffusion and local convections are focused on and discussed. The computed thin film is generally characterized by a thickness of 1.3~2.2% of the channel width (150 µm). Flow vortexes are formed within the hydrodynamic capsular drop. The interfacial distribution profile of CO2 drop is controlled by local convections near the interface and the interphase diffusion, the extent of which is subject to the drop size and drop speed as well.
Highlights
Fluid segments in microfluidic devices are generally characterized by large surface-to-volume ratios and short transfer distances which enhance heat and mass transfer.As two-phase flows involving gas–liquid and liquid–liquid are considered in a microscale device, they mostly feature an interface that separates one phase from the other
Compared with experimental methods in general, numerical simulations have not been widely employed to study two-phase microflows, which is mainly due to the three-dimensional nature of the flow which results in high cost in computation power and time and limited numerical methods developed for two-phase flows
We focus on understanding CO2 drop profile, thin water film, flow fields near and within CO2 drops, and interfacial profile of CO2 drops subjected to diffusion and local convections at the interface
Summary
As two-phase flows involving gas–liquid and liquid–liquid are considered in a microscale device, they mostly feature an interface that separates one phase from the other. Compared with experimental methods in general, numerical simulations have not been widely employed to study two-phase microflows, which is mainly due to the three-dimensional nature of the flow which results in high cost in computation power and time and limited numerical methods developed for two-phase flows. Rapid developments in computational methods and equipment have promoted the applications of numerical methods in two-phase microfluidic simulations, especially in those interface-involved-and-resolved ones over the last two decades [1,2,3,4,5]
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