Thermoacoustic streaming in a linear temperature gradient

Thermoacoustic effects arise when a temperature gradient is present in a sound field. This work investigates the interplay of orthogonal sound and thermal fields in a water-filled microchannel. We measured the three-dimensional streaming in the water-filled cavity for only sound applied, for only thermal gradient, and for the two fields combined. The resulting thermoacoustic streaming was 30 times faster than natural convection and 15 times faster than acoustic streaming. We also performed two-dimensional simulations of the channel's cross section, reaching good qualitative agreement with the measured streaming data. Moreover, we measured the temperature of the fluid both with and without a sound field, showing that the thermal resistance of the channel decreased when the acoustic field was present, while we could not capture this in the current model. We believe our results can have implications for acoustically aided heat exchangers with liquid media.