Fig. 1.

Schematic of a passive pumping device. A. Flowing fluid in the channel is effectuated by adding a drop to the port opposing the large drop. The subsequent increase of pressure due to the small curvature of the added drop provokes its flow towards the large drop until curvatures match. This happens in seconds to minutes. B. During the storage of the channel, as evaporation occurs both at the large and small drop, a decrease in volume will provoke more decrease in curvature in the small drop, and thus an unbalance of pressure in its favor. A flow will be generated from the large to the small drop, thus ensuring constant wetting of the port.