Acoustic mixing at low Reynold’s numbers

Abstract

In microfluidic devices, hydrodynamic flow is usually governed by very low Reynold’s numbers. Under these conditions, only laminar flow is possible. Hence, mixing in microfluidics occurs by diffusion only. Interaction of small fluid volumes and acoustic waves in a solid leads to pronounced streaming effects in the fluid inducing mixing and stirring even at low Reynold’s numbers. We demonstrate the applicability of such acoustically induced mixing in a variety of different microfluidic geometries, including planar and conventional three-dimensional microfluidic devices.

Surface-enhanced Raman scattering microfluidic sensor

“…These are rapidly rotated within the fluid by applying a rotating external magnetic field, which results in reasonably effective mixing. Srithanan et al 57 described a micromixing concept based on acoustic streaming, in which surface acoustic waves generated by a piezoelectric transducer induced transversal mixing flow patterns. Glasgow and Audry 59 proposed an active mixer concept by applying sinusoidal pressure pulses to the microchannel through the channel inlets for active mixing.…”

“…More recently, Cecchini proposed an ultrafast and highthroughput droplet-based SERRS method that can make an efficient analysis at the submillisecond scale. 47 As shown in Active micromixers that use the disturbance generated by external field forces for the mixing process, such as electrical fields, 54,55 magnetic fields, 56 acoustic waves 57 and even electrostatic fields, 58 have been used to overcome the mixing problem in microfluidic channels. Active mixers show an excellent mixing performance and the flow control can be switched on or off, but it is relatively difficult to integrate it into a total microfluidic system because of the requirement of an external power source and controller.…”

Acoustic driven flow and lattice Boltzmann simulations to study cell adhesion in biofunctionalized μ-fluidic channels with complex geometry

“…We have shown that this additional layer does not significantly affect the capability of acoustic streaming. 16 Due to the optical transparency of the piezoelectric material employed, we are able to mount the microfluidic chip onto an inverted microscope ͑Zeiss Axiovert 200, Zeiss, Göttingen, Germany͒ to study the dynamics of protein stretching and recoiling under different shear conditions. 8…”

“…The method meets the expectations for flexible design which can be used to mimic various two-and three-dimensional geometries encountered in our microcirculatory system, and can handle extremely small volumes of liquid ͑ l-pl͒. The technique, which has been successfully employed in multiple research areas within our laboratories, [13][14][15][16] is based on the interaction of SAWs with a liquid at the surface at which the waves propagate. The planar arrangement not only allows for controlled microfluidic flow ͑ϳ10 l͒ in complex geometries, such as bifurcations and stenotic conditions, but enormously facilitates surface biofunctionalization with proteins or even confluent cell layers in these small volumes.…”

The Effect of Inertia on the Flow and Mixing Characteristics of a Chaotic Serpentine Mixer

“…A passive mixer utilizes no external actuation except for a pressure head or pump, which is used to drive flows into the microfluidic device. In active micromixers, however, active controls over the flow field are introduced to manipulate fluids to be mixed by using moving parts, varying pressure gradients, acoustic waves or electro-magnetic fields [18][19][20][21][22][23][24]. For more information on this topic, we refer to review articles on micromixers [2][3][4].…”