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8. Improvement of ultrasonic heat transfer enhancement using acoustical focusing and resonance properties

Author

Zhong Guisheng, Zhenping Wan, Yong Tang, Chen Boqian, and Gong Chen

Subjects
Natural convection, Materials science, 020209 energy, General Chemical Engineering, Heat transfer enhancement, Acoustics, 02 engineering and technology, Heat transfer coefficient, Dissipation, Condensed Matter Physics, 01 natural sciences, Sound intensity, Atomic and Molecular Physics, and Optics, 010406 physical chemistry, 0104 chemical sciences, Physics::Fluid Dynamics, Computer Science::Sound, Heat transfer, 0202 electrical engineering, electronic engineering, information engineering, Intensity (heat transfer), Acoustic resonance
Abstract

This paper is aiming to improve the ultrasonic heat transfer enhancement by controlling the sound intensity distribution and constructing an acoustic focusing field, which can reduce energy dissipation and dramatically enhance the local sound intensity of heat transfer surface. Two design criteria are proposed to construct the acoustic focusing field by utilizing acoustic interference and acoustic resonance. Correspondingly, an elliptical acoustic focusing tank is designed and fabricated. Two-dimensional simulation and experimental tests of sound intensity distribution in the elliptical acoustic focusing tank are performed to verify the theoretical conception and design. In addition, the heat transfer coefficients are measured at different locations in the elliptical tank under natural convection, using a square tank as a control. The experimental results show that the elliptical acoustic focusing tank can promote the intensity of the whole sound field, especially the focus region compared with the square tank. The heat transfer coefficient and heat transfer enhancement rate anywhere in the elliptical tank is higher than that in the square tank. The maximum heat transfer enhancement rate of the elliptical tank is 55.3% in natural convection, which is 47.1% higher than that of the square tank under the same condition.

Published
2019

13. Dynamic performance of a membrane-based variable focus lens with a large aperture.

Author

Duan Z, Wang L, Li Z, Fu J, Fu S, Chen B, Chen Y, and Zhao Y

Abstract

Dynamic performance is one of the most important characteristics of a variable focus lens. However, there are few studies investigating the dynamic response of a membrane-based variable focus lens. In this paper, we present a mathematical model to describe spring-damping phenomena in theory. The first order natural frequencies with different scales were confirmed via finite element analysis. We also built a dynamic response experiment platform with changeable optical apertures, which was driven by a high-speed piezo stack actuator. A photodiode module was placed behind the lens to measure the variation of light luminance as the lens changed, and a laser displacement sensor was used to measure the deformation of the membrane. A series of data was collected with different optical apertures (20 mm, 30 mm, 50 mm) and different pre-stretching ratios (200%, 300%) under different driving frequencies (from 5 Hz to 25 Hz in every 5 Hz step). The experimental results were consistent with the mathematical model, which showed that the first order natural frequency increased as the aperture decreased or the membrane stiffness increased. This frequency-dependent characteristic of the variable focus lens provides a basis for further research on its dynamic performance.

Published
2023
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