Imbibition Dynamics in a U-Groove Microchannel with Sudden Enlargement

Imbibition dynamics in a rectangular U-groove that is connected to a sudden enlargement and complicated by the presence of Concus-Finn (CF) filaments is investigated using many-body dissipative particle dynamics. For open-ended sudden enlargement, four flow types are identified and depend on the contact angle θ_y, the critical angle θ_f associated with the occurrence of CF filaments, and the critical angle θ_c associated with the occurrence of main flow. First, for θ_y > θ_f and θ_y > θ_c, the corner flow is absent, and the main flow stops at the end of the small U-groove. Second, for θ_c > θ_y > θ_f, the corner flow vanishes, but the main flow occurs. Third, for θ_f > θ_y > θ_c, the corner flow takes place in the large U-groove, but the main flow is still absent. Fourth, for θ_y < θ_f and θ_y < θ_c, both the corner and main flows appear in the large U-groove. Additionally, the flow dynamics is greatly influenced by the length of the large U-groove (l_e). For closed-ended sudden enlargement, similar findings can be obtained. However, the outcome of the third case is altered for sufficiently small l_e, and the sudden enlargement can eventually be filled.