A series of experiments was conducted to investigate nucleate boiling behavior of subcooled liquids on very fine heating platinum wires having diameters of 0.1 mm and 0.025 mm. Both high-speed photography and PIV technology were used to observe boiling dynamic processes. Sweeping bubbles were experimentally observed sliding downward against buoyancy along inclined and vertical wires. The interaction between the bubbles and the thermal conditions of the wire played important roles in bubble sweeping processes. A sweeping bubble would grow when it accelerated and shrink when it decelerated, and also could suck hot liquid from the wire. The heat transfer was accomplished by this pumping mode.