Droplets coalescence at microchannel intersection chambers with different shapes*

The~influence~of~microchannel~intersection~chamber~shape~on~droplets~coalescence~process~is~investigated~in~this~study.~Three~kinds~of~chamber~shapes~(half-round,~triangle~and~camber)~are~designed~to~realize~head-on~droplets~coalescence.~The~coalescence~processes~are~visualized~with~high-speed~camera~system~and~the~internal~flow~patterns~are~resolved~with~micro-PIV~system.~Experimental~analyses~on~droplets~coalescence~position,~coalescence~time~and~the~critical~conditions~are~discussed.~Both~direct~coalescence~and~late~coalescence~can~be~observed~in~the~camber~junction~while~only~the~late~coalescence~is~present~for~the~half-round~and~the~triangle~junction. The~critical~capillary~number~Ca*~varies~for~different~working~systems~or~intersection~shapes.~Ca*~in~the~camber~junction~is~larger~than~that~in~the~other~two~junctions~for~each~working~system~and~it~decreases~with~the~increase~of~the~viscosity~ratios~for~each~intersection~shape.~Moreover,~the~characteristics~of~the~velocity~fields~for~different~coalescence~cases~are~analyzed~for~in-depth~understanding~of~the~process.