Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Chemical and Biochemical Engineering

Supervisor

Zheng, Ying

2nd Supervisor

Zhu, Jingxu (Jesse)

Co-Supervisor

Abstract

Experimental studies were performed to characterize the development process of orifice-induced cavitation and transitional bubble behaviors. The transition from non-cavitation to fully developed cavitation was carefully studied. Cavitation bubble clouds were observed at orifice, indicating the inception of cavitation. The number of bubbles produced were dramatically increased while the averaged sizes of bubble reduced when cavitation was initiated. Both orifice opening ratio and perimeter can affect the cavitation developing process. A long orifice perimeter promotes the production of fine bubbles. The orifice plates with the smallest opening ratio generated a desired gas-liquid interfacial area at the lowest required pressure. An orifice plate with multiple orifices is recommended in the design of orifice-based cavitation reactor for production of high cavitation intensity.

Summary for Lay Audience

Hydrodynamic cavitation was first observed due to the damage it caused in hydraulic machinery. Cavitation process is related to the formation, growth and collapse of bubbles. The collapse of these bubbles were accompanied with significant energy, which caused the damage. However, making good use of the energy released by cavitation can benefit many industrial processes. To date, cavitation phenomena have been applied in many industrial processes such as wastewater treatment, food and beverage industry, and biomedical applications. The bubble behavior regarding the formation and collision in its transition process along with the effects they brought are not yet fully understood. Therefore, this process was studied from multiple perspectives in the present work.

The research was divided into three sections: (1) how does the bubble behavior changes the inception of cavitation process; (2) can the initiation of cavitation be affected by the addition of surfactant; and (3) how does the geometry of cavitation inducer influence the intensity of generated cavitation.

First, experiments were conducted to characterize hydrodynamic cavitation transition process based on the experimental results generated from high-speed camera, pressure transducers and power spectral analysis. Visualization of bubbles and their pressure fluctuations along with the power spectrums generated based on Fast Fourier Transform were analyzed to correlate each other.

Second, investigations were conducted to study the effects of surface tension on the inception of cavitation in the current set up. Five solutions with known surface tension were treated as the working fluid respectively. The bubble clouds and pressure variations generated were recorded and compared.

In the final part of the study, different geometric designs of cavitation inducers were used to illustrate the impact on the intensity of produced cavitation. The data were analyzed based on three criteria: number of bubbles produced, bubble sizes and their interfacial area created. The results showed that an orifice plate with multiple orifices is recommended for production of high cavitation intensity.

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