Theoretical Aspects of Microchannel Acoustofluidics: Thermoviscous Corrections to the Radiation Force and Streaming

We study the effects of the temperature dependence of viscosity and density on the acoustic radiation force and the boundary-driven acoustic streaming in microchannel acoustofluidics. The acoustic streaming slip velocity for the bulk flow is calculated numerically taking these thermoviscous effects into account inside the micrometer-thin acoustic boundary layer and compare the results to recent analytical work in the literature. The acoustic radiation force is calculated for the case of an ultrasound wave scattering on a compressible, spherical particle suspended in a viscous, thermal conducting fluid. Using Prandtl–Schlichting boundary-layer theory, we include the viscosity and the volume thermal expansion coeffcient of the fluid and derive an analytical expression for the radiation force. The resulting force (valid for particle radius and boundary layers much smaller than the acoustic wavelength) is analyzed for microchannel acoustophoresis.