Study on Micro-Pump Using Boiling Bubbles

By making use of boiling and condensation in a micro channel, a micro pump was developed. The length and the diameter of the half-circle cross-section micro-channel which had two open tanks at both ends were 26 mm and 0.5 mm, respectively. A 0.5×0.5 mm patch electrically heated was located at the offset location from the center between both ends of the micro channel; at 8.5 mm from the one end and at 17 mm from the other end. The micro channel and the two open tanks were filled with distilled water. The heating patch was heated periodically to cause periodical formation of a boiling bubble and its condensation. By this procedure, flow from the short side (8.5 mm side) to the long side was created. The flow rate increased as the heating rate was increased. The average flow velocity and flow rate obtained were approximately ∼ 12 mm/s and ∼ 3 mm³/s, respectively. The velocity of a interface between the bubble and liquid during the condensation period was much faster than that during the boiling period. During the condensation period, the velocity of the interface at the short channel side (8.5 mm side) was faster than that at the long channel side (17 mm side). The equation of motion of liquid in the flow channel was solved to calculate the traveling of liquid in the flow channel. Predicted velocities agreed well with the experimental results. The velocity differences between the short side and the long side as well as between the boiling period and the condensing period were expressed well by the calculation. Liquid began to move from the stationary condition during both boiling and condensing periods. Liquid in the inlet side (short side) moves faster than that in the outlet side (long side) during the condensation period because of less inertia than that in the long side. Since the condensation was much faster than boiling, this effect is more prominent during the condensation period. By iterating this, the net flow from the short side to the long side was created.