Thermal effect in the process of surface acoustic wave atomization

Abstract

This paper describes an experiment conducted to investigate thermal distribution during liquid atomization. An infrared camera was used to measure liquid temperature changes over time during atomization. Effects of device frequency, input power, and liquid viscosity on thermal distribution during surface acoustic wave (SAW) atomization were investigated, both experimentally and through simulation. We found that the temperature value of the atomizing area was higher than other areas. These results indicate that liquid heating was due to viscous dissipation of irradiated longitudinal wave energy; it was not caused by inelastic effects in the piezoelectric substrate. In the low-frequency atomization process, the increase of atomization rate was closely related to the thermal effect, but the atomization energy and the efficiency value were very low. Note that for a 30-MHz device with input power of 5.26 W, the atomization energy was 0.397 mW, and the efficiency was 0.00769%. Moreover, the viscosity had a remarkable influence on the thermal effect, not only on temperature changes, but also on the heat transfer mechanism in the liquid. To explain the thermal effect caused by radiated acoustic waves, we conducted a numerical study using finite element software. Based on the corresponding simulation results and experimental comparison with experimental results, we concluded that the energy radiated into the liquid by SAW was mainly dissipated by viscous dissipation, which caused the temperature of liquid to rise, while the energy consumed by atomization constituted a very small fraction. Finally, through the study of different adhesive layer materials, we found that the main reason for the SAW device cracking. The higher the input power, the greater the temperature difference taking place simultaneously. A SAW device using the silver paste can achieve continuous water atomization under an input RF power of 10.49 W for more than 1 h without cracking after many tests. At this input RF power, atomization rate can be achieved 0.57 ml/min. This has important practical significance for commercialization of SAW atomizers.