Study on Micropump Using Boiling Bubbles

A micropump was developed using boiling and condensation in a microchannel. The length and hydraulic diameter of the semi-half-circle cross-section microchannel having two open tanks at both ends were $26mm$ and $0.465mm$⁠, respectively. A $0.5×0.5mm2$ electrically heated patch was located at the offset location from the center between both ends of the microchannel, at a distance of $8.5mm$ from one end and at a distance of $17mm$ from the other end. The microchannel and the two open tanks were filled with distilled water. The heating patch was heated periodically to cause cyclic formation of a boiling bubble and its condensation. By this procedure, flow from the short side (⁠$8.5mm$ side) to the long side was created. The flow rate increased as the heating rate was increased. The obtained maximum average flow velocity and flow rate were $10.4mm∕s$ and $2.16mm3∕s$⁠, respectively. The velocity of an interface between the bubble and the liquid plug during the condensing period was much faster than that during the boiling period. During the condensing period, the velocity of the interface at the short channel side (⁠$8.5mm$ side) was faster than that at the long channel side (⁠$17mm$ side). The equation of motion of liquid in the flow channel was solved in order to calculate the travel of liquid in the flow channel. The predicted velocities agreed well with the experimental results. The velocity differences between the short side and the long side, as well as those between the boiling period and the condensing period, were expressed well by the calculation. Liquid began to move from the stationary condition during both the boiling and the condensing periods. The liquid in the inlet side (short side) moved faster than that in the outlet side (long side) during the condensing period because the inertia in the short side was lower than that in the long side. Since the condensation was much faster than boiling, this effect was more prominent during the condensing period. By iterating these procedures, the net flow from the short side to the long side was created.