Ultrasound induced cavitation and resonance amplification using adaptive feedback Control System

University essay from Blekinge Tekniska Högskola/Institutionen för tillämpad signalbehandling

Abstract: Acoustic cavitation in fluids using high powered ultrasound has been of great interest in industries and biomedical engineering. The need for high-intensity focused ultrasound (sound with frequencies between 20 kHz to 10 MHz) and modeling of such systems has drawn great attention in engineering. Ultrasound excitation has found recent application in terms of replacing the existing dynamic mechanical systems that use high energy with low levels of efficiency. The proposed thesis work focuses on an application of acoustic cavitation and on adaptive control of resonance amplification to be used in the paper pulp industry. The primary objective is to keep a system of coupled and tuned resonances stable, and by that obtain high cavitation intensity in a water filled beaker. The secondary aspect is to numerically model and experimentally evaluate a prototype beaker, where the adaptive control scheme is implemented to attain high and stable cavitation intensity. The characteristic control parameters (excitation frequency and amplitude) can be adjusted to the fluid condition in the beaker (reactor) by a feedback control from a pressure sensor inside the beaker. The aim of this feedback loop is to keep the resonance phenomena stable with respect to an adaptable frequency. In this application, the resonance amplification is mainly used to generate and control cavitation at a frequency that corresponds to a range of beaker natural frequencies. The results of the development process show that high cavitation intensity can be achieved by ultrasound induced power. The electric power input required to achieve high cavitation intensity is relatively low and resulted in high energy efficiency. The results of the study will be used for an application for fibrillation of cellulose fibers to further improve energy efficiency in paper pulp industry.

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