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A focused ultrasound field is set up in a heat transfer cavity with an elliptical cross section. A sound source and a heat source are designed at the two focus points where the sound intensity is reinforced based on the interference and standing wave criteria. The sound intensities and heat transfer coefficients of the cavity with a focused ultraso...
Citations
... The focused ultrasonic transducer can direct sound energy towards a specific location, resulting in a higher acoustic streaming velocity compared to other types of ultrasonic fields due to the increased Reynolds stress gradient [23,24]. Traditionally, focused ultrasound has been employed for the ablation of solid tumors at its focal area [25,26]. This study introduces a novel focused ultrasound-based cooling method that can effectively cool a heating element situated in the focal region through acoustic streaming generated using a focused ultrasonic radiator. ...
In this work, a focused ultrasonic radiator is proposed for cooling the electrical heating elements in the focal region, and its working characteristics are investigated. The analyses of the FEM compu-tational and flow field visualization test results indicate that focused ultrasound can generate forced convective heat transfer by the acoustic streaming in the focal region, which can cool the heating elements effectively. Experiments show that when the input voltage is 30Vp-p and the ambient temperature is 25 °C, the focused ultrasonic radiator can cause the surface temperature of the heating element (high-temperature alumina ceramic heating plate with a diameter of 5 mm) in the focal region to drop from 100 °C to about 55 °C. When the diameter of the electrical heating element is changed from 5 mm to 30 mm, the cooling effect is similar in the focal region. Compared with a fan, the focused ultrasound radiator has a shorter cooling time and a more concentrated cooling area. The focused ultrasonic radiator proposed in this work is suitable for some special environments.
... Setareh et al. 12 presented experimental and numerical studies of the heat transfer enhancement of water in a ring under ultrasonic waves and fluid flow. Wang et al. 13 exploited a focused ultrasonic field to enhance heat transfer. Bartoli et al. 14 used ultrasound as a heat transfer promoter to promote natural convection in dielectric fluids for thermal control of electronic equipment. ...
In this paper, a three‐dimensional (3D) numerical study of thermal convection and acoustic waves is presented using a hybrid method. This method consists of two computational approaches: the lattice Boltzmann method (LBM) with multiple relaxation times for the study of the fluid behavior and the finite difference method (FDM) for the description of the thermal exchange. The two approaches have been validated by studying two benchmark problems reported in the literature. The LBM was validated by simulating the flow induced by a lid‐driven cavity. The FDM was checked by simulating natural convection in a differentially heated cubic cavity filled with air. After this validation, the main focus was on the study of enhancement of the heat transfer in a 3D cavity using a vibrating acoustic source. The numerical study is performed for different values of the wave amplitude, the Rayleigh number ( Ra ${Ra}$), and the sound source size. It shows that the heat transfer is significantly improved for a low Ra ${Ra}$. However, for high Ra ${Ra}$ values, natural convection cannot be neglected in front of forced convection. The transfer is also influenced by the variation of the source size. This allows obtaining the optimal size corresponding to the maximum heat exchange.
The Lattice Boltzmann Method (LBM) is applied in this thesis to study acoustic waves propagation and heat transfer in fluids. The work can be summarized in five parts:
The first two sections deal with the basic mathematical formulations of the kinetic theory of gases and the numerical lattice Boltzmann approach. Numerical simulations are started in the third part. This part first presents the basic principles of acoustics and then gives a two-dimensional (2D) study of acoustic waves propagation in water. The waves are generated by a rectangular acoustic source vibrating at 200 kHz. The objective is to calculate the acoustic pressure and force produced in the near field, and then to inject the numerically calculated force into the LBM code used to produce the acoustic streaming flow.
Given the importance of numerical studies used as data to perform experiments, the simulation of physical problems in three dimensions (3D) becomes a necessity to visualize the physical phenomenon much better than in 2D. Therefore, the three-dimensional lattice Boltzmann method is used in the fourth section to study the propagation of acoustic waves in water. The main objective of this numerical study is to show how waves generated by a point source and square and circular shaped sources propagate instantaneously in 3D, to calculate the acoustic pressure and to highlight the performance of LBM simulations. A comparison of the numerical results found with the analytical data is performed to validate the numerical approach used.
The fifth part presents a 3D numerical study of the physical phenomena of ultrasound propagation in air, thermal convection and their interaction. Considering its advantages in terms of accuracy and computational efficiency over the pure LBM method, the hybrid method based on the LBM approach for the description of the hydrodynamic behavior of the fluid and the finite difference technique for the temperature calculation is introduced in this last part to investigate the improvement of the heat transfer by the ultrasound.
