Analysis Tool for the Evaluation of Measurements of the Single Bubble and Bubbles Structures Dynamic

Runer Shiloh Salonga

Master's thesis

Abstract:

Cavitation is a phenomenon that is commonly observed in turbines, water pumps, and other similar mechanisms which involve the high-speed and high-pressure movement of fluids, as it is the change in state of a material due to a fast pressure change, in particular from the liquid to the solid state. As a result, bubbles of water vapor form within the fluid, which interact with solid surfaces in a short span of time, particularly the creation of jets during the collapse of these bubbles. These jets inflict force on these solid "walls", and this interaction between bubble and solid wall may cause positive or negative effects, which may be harnessed when better understood. This project aims to develop an analysis tool, developed in C++, that will aid in the understanding of the dynamics of the cavitation bubble in the context of a dynamic flow system with water as the medium. Investigations are made with the tool on an experimental setup consisting of a spark generator for creating the cavitation bubbles, monitored by a high-speed camera and measured by a polyvinylidene fluoride (PVDF) piezoelectric sensor. The camera is used to observe the development of the bubble and determine its size through image processing of the resulting images that are taken, while the PVDF sensor is a low cost option for measuring pressure on a flat surface, as it can convert pressure into voltage. In this study, the differences between the single- and double-bubble spark generated setups are observed and analyzed through the optical and acoustical measurement methods. From these comparisons, the project aims to set a baseline for continued study of further specialized measurement and analysis tools of cavitation behavior.

Abstract:

Cavitation is a phenomenon that is commonly observed in turbines, water pumps, and other similar mechanisms which involve the high-speed and high-pressure movement of fluids, as it is the change in state of a material due to a fast pressure change, in particular from the liquid to the solid state. As a result, bubbles of water vapor form within the fluid, which interact with solid surfaces in a short span of time, particularly the creation of jets during the collapse of these bubbles. These jets inflict force on these solid "walls", and this interaction between bubble and solid wall may cause positive or negative effects, which may be harnessed when better understood. This project aims to develop an analysis tool, developed in C++, that will aid in the understanding of the dynamics of the cavitation bubble in the context of a dynamic flow system with water as the medium. Investigations are made with the tool on an experimental setup consisting of a spark generator for creating the cavitation bubbles, monitored by a high-speed camera and measured by a polyvinylidene fluoride (PVDF) piezoelectric sensor. The camera is used to observe the development of the bubble and determine its size through image processing of the resulting images that are taken, while the PVDF sensor is a low cost option for measuring pressure on a flat surface, as it can convert pressure into voltage. In this study, the differences between the single- and double-bubble spark generated setups are observed and analyzed through the optical and acoustical measurement methods. From these comparisons, the project aims to set a baseline for continued study of further specialized measurement and analysis tools of cavitation behavior.

Keywords

Cavitation, High-speed camera, PVDF sensor, Measurement tool, Bubble dynamics, Image recognition, C++

Language used: English

Date on which the thesis was submitted / produced: 3. 5. 2019

Thesis defence

• Supervisor: Ing. Miloš Müller, Ph.D.

Technical University of Liberec

Faculty of Mechanical Engineering

Master programme / field:
Mechanical Engineering / Machines and Equipment Design