Liquid pumping in a microchannel driven by a vapor-rich bubble

We experimentally investigated liquid pumping in a microchannel driven by a vapor-rich microbubble. A closed-loop microchannel filled with an ethanol/water mixture was positioned on an FeSi2 thin film with photothermal conversion properties. By focusing a laser beam onto the thin film, a vapor-rich bubble with a diameter of 14 μm was generated through photothermal heating. The flow direction induced by the bubble was aligned parallel to the channel wall by controlling the temperature distribution around the bubble through simultaneous multispot laser irradiation. Consequently, unidirectional flow was established within the closed-loop channel with a thickness of 100 μm and a width of 400 μm. Notably, when bubbles were generated near regions with locally reduced cross-sectional areas, the vortices around the bubbles were suppressed, and the flow speed was approximately 4.4 times higher than that observed in the channel without such constrictions. At the position farthest from the bubble—approximately 5 mm away—the flow speed exceeded 440 μm/s. These results demonstrate the strong fluid pumping capability of a single vapor-rich bubble as small as 14 μm, underscoring the potential of bubble-based pumping for microchannel cooling systems.