Effect of Bend on Film Thickness in Slug, Slug-Annular, and Annular Flow Regimes in Gas-Liquid Flow in a Microchannel

In this work, gas-liquid two-phase flow in a microchannel with multiple U-bends is studied over a range of gas and liquid flow rates using a high-speed camera for four Newtonian liquids of different viscosities. The flow regime is observed to transition from slug to annular flow regime for the conditions studied. The liquid film formed between the wall and gas core/bubble is observed to be asymmetric in the curved section of the channel due to the centrifugal force. In the slug flow regime, the film thickness on the inner wall of the bend is observed to be thinner than that on the outer wall. On the contrary, the inner film is observed to be thicker than the outer film in the annular flow regime. This transition is possibly caused by the change in the relative importance of gas and liquid centrifugal forces with change in the flow regime. The understanding of the film behavior at the bends will be useful for the efficient design of chemical microprocessing equipment such as compact heat exchangers and microreactors.