Boiling is presumed to be a well-known simple process of heat transfer where a liquid is heated to its boiling point. In reality, it is a complex liquid-vapor phase change phenomenon at the micro level. The boiling process has always been an active area of research for applications such as food processing, chemical industry, materials and manufacturing, power generation and space industry. A number of experimental investigations have been performed using pool boiling to study the hydrodynamics of bubbles and improve boiling heat transfer performance parameters, such as the critical heat flux and the heat transfer coefficient.
It is important to understand bubble behavior because the boiling performance parameters are intricately linked to the bubble ebullition process i.e. bubble growth and departure. However, it is significantly challenging to study bubble behavior with current techniques due to the following reasons: First, bubble ebullition is a fast and short-timescale process requiring the use of advanced imaging techniques. Second, bubble behavior is dictated to a big extent by the behavior of the contact line microlayer, which is difficult to capture due to the small length scale involved. Third, it is quite difficult to achieve proper visualization of a single bubble under actual boiling circumstances due to the statistical nature of boiling. Research in the past has usually been performed by generating multiple random bubbles on a heated substrate, where it is difficult to predict the location of and, therefore, focus on a single bubble. Further, neighboring bubbles often block the view path to the bubble being observed, in addition to affecting its overall behavior.
In this study, we focus on a laser-based approach for controlled single bubble generation. An experimental setup is built in which a single bubble can be nucleated in various fluids, and the hydrodynamics of these bubbles can be studied by using high-speed optical and infrared imaging. Single bubble generation is achieved using a combination of a Titanium heater as a heat source and a high-power laser pulse to generate a microscale bubble nucleation site. High-speed optical data is collected and analyzed for a controlled thermal transient. Bubble growth characteristics are studied using numerical simulation and experimental data. The effect of laser parameters such as pulse amplitude and pulse width on bubble ebullition is studied. The techniques and findings from this research can be further used to investigate and elucidate precise bubble behavior for various fluids.
|Advisor:||Dhillon, Navdeep Singh|
|Commitee:||Torabzadeh, Jalal, Roy, Surajit|
|School:||California State University, Long Beach|
|Department:||Mechanical and Aerospace Engineering|
|School Location:||United States -- California|
|Source:||MAI 81/4(E), Masters Abstracts International|
|Subjects:||Mechanical engineering, Engineering, Fluid mechanics|
|Keywords:||Bubble growth, Laser, Pool boiling, Pulse power, Pulse width, Vapor bubbles|
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