ABSTRACT
The heat transfer in the ultrasonic processing of stainless steel melt is studied in this thesis. The temperature field is simulated when the metal melt is treated with and without ultrasound. In order to avoid the erosion of high temperature melt, ultrasound was introduced from the bottom of melt. It is found that the temperature of melt apparently increases when processed with ultrasound, and the greater the ultrasonic power is, the higher the melt temperature will be; ultrasonic processing can reduce the temperature gradient, leading to more uniform temperature distribution in the melt. The solidification speed is obviously brought down due to the introduction of ultrasound during solidification, with the increasing of ultrasonic power, the melt temperature rises and the solidification speed decreases; as without ultrasound, the interface of solid and mushy zone is arc-shaped, so is the interface of liquid and mushy zone, with ultrasound, the interface of solid and mushy zone is still arc-shaped, but the interface of liquid and mushy zone is almost flat. The simulation results of temperature field are verified in experiment, which also indicates that the dendrite growth direction is in accord with thermal flux direction. The effect of ultrasonic treatment, which improves with the increase of treating power, is in a limited area due to the attenuation of ultrasound.
ABSTRACT
The effect of ultrasonic treatment of the melts is mainly ultrasonic streaming and cavitation. In this paper, the ultrasonic streaming in water, aluminum and steel melts was numerically simulated and compared. And the simulated results of streaming in water were validated by experimental results. In the experiment, the ultrasonic booster was immersed vertically into water, the ultrasonic streaming phenomenon was observed by high-speed CCD (Charge-coupled Device) system, then the streaming velocity and streamlines were obtained. The cavitation area and threshold in aluminum and steel melts were compared. The results show that the effective streaming and cavitation area in steel melt is smaller than that in aluminum melt, and far smaller than that in water. A symmetrical vortex forms both in water and aluminum melt by the drive of downward ultrasonic streaming caused by the booster tip. However, in steel melt, a double-vortex structure, including a vortex in the upper part and a vortex with reverse cycling in the lower part appears in the flow field. As a result, inclusions and air bubbles may be trapped in steel melt. The density and viscosity of the fluids are the main factors influencing ultrasonic streaming and cavitation. The results provide references for the application of ultrasonic treatment in metal melts.
