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We demonstrate an autonomous, high-throughput mechanism for sorting of emulsion droplets with different sizes concurrently flowing in a microfluidic Hele-Shaw channel. The aqueous droplets of varying radii suspended in olive oil are separated into different streamlines across the channel upon interaction with a shallow (depth ∼ 700 nm) inclined guiding track ablated into the polydimethylsiloxane-coated surface of the channel with focused femtosecond laser pulses. Specifically, the observed differences in the droplet trajectories along the guiding track arise due to the different scaling of the confinement force attracting the droplets into the track, fluid drag, and wall friction, with the droplet radius. In addition, the distance traveled by the droplets along the track also depends on the track width, with wider tracks providing more stable droplet guiding for any given droplet size. We systematically study the influence of the droplet size and velocity on the trajectory of the droplets in the channel and analyze the sensitivity of size-based droplet sorting for varying flow conditions. The droplet guiding and sorting experiments are complemented by modeling of the droplet motion in the channel flow using computational fluid dynamics simulations and a previously developed model of droplet guiding. Finally, we demonstrate a complete separation of droplets produced by fusion of two independent droplet streams at the inlet of the Hele-Shaw channel from unfused daughter droplets. The presented droplet sorting technique can find applications in the development of analytical and preparative microfluidic protocols.

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Windshield wipers were developed to improve visibility during inclement weather and belong to standard safety equipment. A conventional wiping system of a vehicle consists of three components; namely, motor and mechanism, wiper arm and wiper blade. The wiper arm transfers the movement to the wiper blade and cleaning is achieved by wiping water and dirt from the windscreen by a blade rubber. In order to wipe water and dirt from the windscreen, the wiper blade should be forced onto the windscreen with a specified force. The necessary force is obtained by the spring mechanism within the arm. In this study the effect of free-stream velocity, turbulence models on the drag and lifting forces acting on the windshield wiper and spoiler geometry are investigated numerically. The spoiler geometry is modified to reduce the lifting force.

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