Mechanism study of bubble removal in narrow viscous fluid by using ultrasonic vibration

The mechanism of bubble removal in a narrow viscous fluid by using ultrasonic vibration is analyzed in this study. Experimental studies were performed on the adhesive bonding between a carbon fiber reinforced plastic (CFRP) laminate and an aluminum plate. After applying ultrasonic vibration on the CFRP laminate, it was found that the high-frequency vibration could induce an oscillating flow of the adhesive in the narrow bonding layer. Such a flow caused the entrapped bubbles to move and break until all of them were eliminated from the viscous adhesive. A fluid–solid coupling simulation and fluid tracer analysis were performed to analyze the underlying principle of bubble motion. The results reveal that because of the internal pressure of the bubble and the asymmetric characteristic of the fluid resistance around the bubble, the oscillating fluid induced by ultrasonic vibration drove the bubble to move in the direction closest to the edge. The reduction of the gas volume fraction in the adhesive resulted in an improved bonding between the CFRP laminate and aluminum plate.