  The fundamental action of the bubble-driven inertial micropump is
investigated. The pump has no moving parts and consists of a thermal resistor
placed asymmetrically within a straight channel connecting two reservoirs.
Using numerical simulations, the net flow is studied as a function of channel
geometry, resistor location, vapor bubble strength, fluid viscosity, and
surface tension. Two major regimes of behavior are identified: axial and
non-axial. In the axial regime, the drive bubble either remains inside the
channel or continues to grow axially when it reaches the reservoir. In the
non-axial regime the bubble grows out of the channel and in all three
dimensions while inside the reservoir. The net flow in the axial regime is
parabolic with respect to the hydraulic diameter of the channel cross-section
but in the non-axial regime it is not. From numerical modeling, it is
determined that the net flow is maximal when the axial regime crosses over to
the non-axial regime. To elucidate the basic physical principles of the pump, a
phenomenological one-dimensional model is developed and solved. A linear array
of micropumps has been built using silicon-SU8 fabrication technology, and
semi-continuous pumping across a 2 mm-wide channel has been demonstrated
experimentally. Measured variation of the net flow with fluid viscosity is in
excellent agreement with simulation results.
