Supplementary material from "Mitigating viscous heat generation from the attenuation of acoustic waves in thin fluid films"

Gradients and changes in temperature have long been used in microfluidics to drive flows and perform useful tasks, and have also been associated with adverse effects when uncontrolled. A key example of the latter are acoustic wave devices, where the rapid flows and interfacial phenomena together with the ability to manipulate cells and particles are hampered by viscous heating effects. We examine acoustically driven heating—acoustothermal heating—in thin fluid films and how it develops in the presence of acoustic streaming and adjacent heat sinks, in a configuration similar to many applications of acoustofluidics. We identify the importance of the heat-dissipating substrate in the overall heating phenomenon, particularly its thermal conductivity and the finish of the surface in contact with the acoustic device. Through careful control of these aspects, the heating generated from acoustic wave attenuation in thin fluid films can be mitigated.