Numerical Analysis Of Bubble Floating Process Under Mechanical Stirring And Ultrasonic Vibration

Aluminum alloys are widely used in aerospace,rail transit,housing frame and other fields because of their low density,strong corrosion resistance,high strength and easy processing.The presence of dissolved hydrogen in aluminum melt may be cause defects such as blowhole and inclusion in ingot and its service life is shorten due to the reaction of aluminum melt with water vapor,so it is very important to study efficient purification technology of aluminum melt.This paper presents a compound degassing method combining rotary stirring blowing method and power ultrasonic degassing method.In this method,the hydrogen in melt is removed mainly by the adsorption function of bubbles blown out,so as to achieve the purpose of purification.The shape and distribution law of bubbles are closely related to the dehydrogenation efficiency of melt.However,because of the high temperature and opacity of the aluminum melt,it is very difficult to directly study the shape and distribution law of bubbles in the composite field,so FLUENT software is used to analyze the problem.Firstly,the influence of the stirring parameters on the bubble distribution and internal flow field behavior in the process of stirring and blowing are discussed,and the best combination of stirring parameters is found out.Then,the influence of the ultrasonic parameters on the bubble distribution and internal flow field behavior are discussed under the condition that other parameters remain unchanged.The numerical simulation results show that the rotation speed of impeller has a strong impact upon bubble chain under rotating flow field and the chains mainly presents a linear shape,“S” shape and concave shape with increasing of rotation speed.Besides,the gas flow rate plays a dominant role in bubble sizes and the model prediction shows that the bubble size increases with the increase of gas flow rate.The rotation speed is the main factor in influencing the flow field of internal stirring.The liquid phase velocity,turbulence intensity and pressure gradient increase with the increase of rotation speed.The gas flow rate is detrimental to liquid phase velocity,but it has little impact on the pressure gradient and turbulence intensity.Ultrasonic has a certain effect on the bubble distribution and internal flow field behavior under original mixing field.In the aspect of bubbles,ultrasound can break the bubble in a limited area that near the ultrasonic end-face and the broken bubbles can be dispersed,but it has little effect on bubbles far away from the ultrasonic end-face.In the aspect of flow fields,the positive and negative static pressure are formed near the ultrasonic end-face.In addition,the velocity and turbulence intensity of liquid phase here are higher than those of the original flow field.In the other regions,the pressure difference is small and it has a little difference on the velocity and turbulence intensity of liquid phase.Finally,the ultrasonic amplitude,ultrasonic length and ultrasonic position have important effects on the breakup and dispersion of bubbles.