Fundamentals of bubble transport in an ultrasonically assisted separation process.

摘要

Previous research endeavors resulted in a process to recover solid particles and oil droplets from aqueous suspensions. This process involves applying a one-dimensional resonant ultrasonic field to the suspension while it is flowing through or resting in a rectangular chamber. The same process has been utilized here for gas bubbles in an aqueous medium. Bubbles in this system move to the acoustic pressure antinodes, based on the density and compressibility of the bubble and the surrounding fluid as well as the driving frequency and the radius of the bubble.; To obtain a fundamental understanding of the movement of a single bubble within the acoustic chamber, a balance of the relevant physical forces was completed: primary acoustic force, buoyancy force, and drag force. The resulting equations could be used to determine the position of a single bubble within the chamber and the velocity at which that bubble would be moving toward those positions.; A microscopic mathematical model was developed to predict the relative trajectory of a bubble pair in an acoustic field. This model not only took into account the primary forces previously discussed, but also inter-bubble effects: secondary acoustic force, van der Waals force, hydrodynamic interactions, and Brownian diffusivity. The trajectory analysis was used to track the movement of the bubble pairs under a variety of operating conditions and the results were compared to experimental data. This data was then used to calculate volume cleared by the collision of different bubble pairs, thus describing the kinetics of the collision process.; The results from the models were then compared to experimental data obtained by injecting small numbers of bubbles into an acoustic chamber. This comparison was done by taking video of bubbles colliding, mapping their path, and comparing this to the trajectory determined from the bubble pair model. The projected trajectory and the experimental trajectory were shown to be in good agreement. The model can then be used to calculate the collision time for a variety of energy densities at experimental conditions. This relationship can then be used to determine the energy density of the experimental system based on the observed collision time.