A focused ultrasound based cooling strategy for small solid heat sources

[Display omitted] •The focused ultrasound based cooling method can targetedly cool small solid heat source in air.•Acoustic streaming at the focal region positively contributes to the cooling effect.•Employing the flexural vibration mode of the acoustic lens is critical in the cooling device design. In this work, a cooling strategy, which employs focused ultrasound in air to cool small solid heat sources, is proposed and its characteristics are investigated. Analyses of the FEM computational and experimental results indicate that the cooling effect results from a forced convective heat transfer generated by the acoustic streaming at the focal region. By this cooling method, the heat flux is increased by 150 % and Nusselt number is doubled approximately for an ellipsoidal heat source made of Pt wire with a surface area of 6.44 mm2 and temperature of 100 °C, compared to natural convection. It is experimentally demonstrated that employing the flexural vibration mode of the acoustic lens is critical in the cooling device design, and increasing the vibration velocity and working frequency properly can further enhance the cooling effect. The method is also effective to a disc heat source with a surface diameter of 9 mm. Compared with the axial-fan cooling, the method proposed in this work does not use a rotary part (thus no dust accumulation, silent operation and ease of miniaturization) and has a faster cooling response.