(414a) Acoustothermal Heating in a Surface Acoustic Wave Driven Microchannel

Pradipta Kr. Das^*‡, Arthur David Snider^† and Venkat R. Bhethanabotla^‡

^‡Department of Chemical & Biomolecular Engineering, University of South Florida, Tampa, Florida 33620, United States

†Department of Electrical Engineering, University of South Florida, Tampa, Florida 33620, United States

^*Email: pradipta@mail.usf.edu

Abstract:

Surface acoustic waves (SAWs) are of significant importance due to their applications in non-invasive manipulation of microparticles, detection and trapping of biological cells, fluid mixing etc. The surface acoustic waves, when propagating along the surface of the piezoelectric substrate loaded with fluid, refract energy into the fluid due to mismatch between the propagation velocity in the solid and the fluid. This refracted energy is converted into heat via acoustic damping caused by the fluid. Significant heat generation in SAW-driven microfluidic systems containing Newtonian fluids has been reported in the literature. We present a theoretical model for the temperature rise in such systems for Newtonian and non-Newtonian fluids. Difficulties in modeling such systems arise due to differences in timescales corresponding to fast oscillatory flow and slow steady streaming flow. A perturbation approach is employed to separate the timescales and the resulting equations are implemented in a finite element method using weak form partial differential equations. The zeroth order is trivial and expresses the stagnant flow and temperature field before applying the SAW whereas first order equations represent the fast oscillatory flow at the frequency of the SAW. The second order equations are expressed in time-averaged form to account for the steady streaming flow and temperature distribution. We investigated the acoustothermal heating for a variety of Newtonian and power-law fluids, SAW powers, and excitation frequencies. The results have applications in microreactors, SAW-based biosensors, and microfluidic heating.