Papers by Keyword: Acoustic Streaming

Abstract: The megasonic cleaning efficiency is evaluated as a function of the angle of incidence of acoustic waves on a Si wafer. Acoustic Schlichting streaming alone is not able to remove nanoparticles smaller than 400 nm. It is shown that oscillating or collapsing behavior of bubbles are responsible for removing nanoparticles smaller than 400 nm during a cleaning process with ultrasound. Optimal particle removal efficiency is obtained around the angle of acoustic transmission of the silicon wafer.

Abstract: This study investigated on cooling characteristics of thermoelectric cooling system using thermoelectric materials as Bi-Te alloy. The thermoelectric module used as thermoelectric materials of thermoelectric cooling system can achieve heating and cooling by change of electricity direction. When thermoelectric module and cooling fan received 12V from DC power source, the cooling region was occurred in thermoelectric cooling system. Also, the piezoelectric actuator was applied to improve the cooling effect and investigate the heat transfer phenomenon. The temperature distribution of cooling region was measured to investigate cooling characteristics of thermoelectric cooling system. The flow phenomenon of cooling region was visualized using visualization device such as He-Ne laser, optical lens, image grabber and CCD camera. When the piezoelectric actuator was applied to the heat transfer process of thermoelectric cooling system, acoustic streaming was occurred in the cooling region. The acoustic streaming was occurred forced convection flow, and was regularly formed the temperature distribution in the cooling region. In the end, the results clearly show that the acoustic streaming is one of the prime effects to enhance the convection heat transfer and cooling effect.

Abstract: Cavitation erosion is predominant in pipelines for liquid transportation, causing damage to pipe wall, impeller and their accessories. The present study is focused on development of cavitation -wear resistant nano-ceramic particle-reinforced polymer matrix material; and on study of its feasibility to be used as lining material in hydraulic transportation. The polymer/nano composite is fabricated using power ultrasound in all three process steps: synthesis of nano-dimensional particles of white fused alumina (WFA) from micron size particles, optimized blending and finally reinforcement into poly methyl methacrylate (PMMA) matrix. The effect of ultrasonic parameters on nanocomposite/ virgin polymers (like polyethylene and polypropylene) is studied by measuring mass loss of the materials and suspension turbidity during exposure time. At low frequency (20-60 kHz), cavitation intensity is predominant; this effect is utilized for fabricating sub-micron particles, and for performing accelerated cavitation erosion tests. At high frequency, acoustic streaming is predominant; this effect is utilized for blending and reinforcing of the nano ceramic particles into polymer matrix. The size and quantity of the particles generated by cavitation erosion was analyzed by Laser Particle Size Analyzer (20 nm-1400 micron range). The nano-composite coupons were analyzed before and after the ultrasonic erosion test using SEM. It is concluded that lowfrequency sonication is a viable option for cavitaton erosion testing of ceramic/polymer composites.

Abstract: This study focused on observing the melting phenomena and investigated a principle factor of enhanced heat transfer in phase change material when the ultrasonic vibrations were applied during the melting process. For visualization, particle image velocimetry and thermal-vision camera for observing the flow phenomenon was used. Also, experiments were performed to obtain the experimental results such as melting time and temperature distribution. Besides, structural vibration simulator which is applying a coupled finite element-boundary element method (Coupled FE-BEM) was used for calculation of acoustic pressure occurred by ultrasonic vibrations in liquid region. The results of experimental and numerical observations show that acoustic streaming induced by ultrasonic vibrations is one of the prime effects acoustically enhanced phase change heat transfer and help to accelerate the melting of phase change material. Also, the application technique of visualization and computational simulation introduced in this study is very useful and important to analyze the mechanical behavior of material in a fast fluid dynamic or acoustic field.

Abstract: The present study is investigated the causes of enhanced heat transfer during the melting process of solid-liquid PCM (Phase Change Material) using an ultrasonic vibration. Paraffin (noctadecane) was selected as a PCM and experimental studies were performed as following. Heat transfer coefficient and enhancement ratio of heat transfer was measured, acoustic streaming induced by ultrasonic waves observed using a PIV (Particle Image Velocimetry) and thermally oscillating flow phenomenon observed using an infrared thermal camera during the melting process. For the numerical study, a coupled FE-BEM (Finite Element-Boundary Element Method) was applied to investigate acoustic pressure occurred by acoustic streaming in a medium. And then, the profiles of pressure variation compared with the enhancement ratio of heat transfer. The results of this study revealed that ultrasonic vibrations accompanied the effects like acoustic streaming and thermally oscillating flow. Such effects are a prime mechanism in the overall melting process when ultrasonic vibrations are applied. Also, as the acoustic pressure occurred by acoustic streaming increases, the higher enhancement ratio of heat transfer is obtained.