Bubble-driven inertial micropump

Abstract

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.

Interactions between two oscillating bubbles in a rigid tube

“…This separation relies on the calculation of the momentum induced by the collapse, similar to the pumping effect of a single oscillating bubble in a tube. Based on the past studies on the one-dimensional model of pumping effect [9,10], a simplified estimation could be proposed. We suppose an equal constant pressure at the two ends of the tube, and a phase difference of zero.…”

“…Ory [8] developed the calculation using incompressible viscous N-S equation, finding that a net flow developed when the bubble was not located at the midpoint of the tube. Lately, this pumping effect was studied by Yin [9], Torniainen [10] and Kornilovitch [11], focusing on the development of a one-dimensional model to predict the net flow rate. Besides the pumping effect, researchers were also interested in the bubble deformation and the jet produced by the collapse.…”

Microfluidic switchboards with integrated inertial pumps

“…Care had to be taken to not trap air in the system -especially in the central section of the H. Hydrostatic pressure on two sides of the H had to be equalized by establishing a macroscopic fluidic connection between the two bulk reservoirs away from the channels; otherwise, the pressure difference caused a constant flow through the side legs of the H. The printheads were operated in a reservoir-up/die-down orientation to prevent the fluids from dripping out. TIJ technology allows varying the Si die operating temperature between 28 • C and 85 • C with ±1 • C accuracy [19]. In the present work, temperature was set at (28±1) • C. However, local fluid temperature can change in response to pump frequency, resulting in some variation of fluid viscosity.…”

Single-pulse dynamics and flow rates of inertial micropumps

“…Some of them utilize asymmetric nozzle-diffuser geometries [6,7] while others use multiple heaters to create asymmetric heating [8,9] or a traveling vapor plug [10,11,12,13,14]. A more recent development is the inertial pump that relies on dynamic asymmetry of the bubble's expansion-collapse cycle when a microheater is located close to one end of a channel [15,16,17,18,19,20]. Such pumps have characteristic sizes from several microns to hundreds of microns.…”

“…Even without intricate details of bubble generation and interaction in solid-wall tubes [20,22,23], the physics of inertial pumping is complex. Net flow is a result of a subtle imbalance of mechanical momenta of two fluidic columns colliding when the vapor bubble collapses [16,17,18]. The imbalance is caused by unequal fluid inertia during bubble expansion and asymmetry of vortex formation near channel-reservoir interfaces [17].…”