The effect of geometry and flow conditions on the microbubble formation in venturi microbubble generator / Niellambare A/p Nadumaran

Faculty of Mechanical and Automotive Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2024

Includes bibliographical references

The Venturi microbubble generator (VMBG) is a device that creates microbubbles (MBs) using a simple structure and mechanism. Its effectiveness is determined by the size distribution of the generated bubbles (BSD) to meet specific application requirements. Two key parameters affecting VMBG performance are its geometric configuration and flow conditions. Most research had focused on their impact on BSD, but it is also important to consider their relationship to the mechanism of bubble formation and bubble formation characteristics. Despite many recent experimental visualizations, the relationship between key parameters and bubble formation in VMBG has been underdiscussed due to the challenges in studying MB formation mechanisms through experimental visualization. Thus, this study extensively investigated the effect of the two key parameters, geometry configuration and flow conditions of VMBG on the bubble’s formation characteristics. An ideal VMBG and nine additional VMBGs were designed by varying the angle of divergent section, the diameter and length of throat. Particle Image Velocimetry (PIV) setup is used to observe bubble formation and flow velocity distribution between the throat and divergent section of the VMBG. The flow condition varied with three flow rates (50LPM, 60LPM, and 70LPM) in this study. To further investigate the bubble breakup phenomenon, computational simulation (ANSYSFLUENT) was used to determine the detailed flow properties in the VMBG. As a result, the bubble formation characteristics strongly dependent on the flow condition such as velocity, turbulent intensity and vorticity. As velocity increases in the throat section, there is a corresponding rise in turbulent intensity and vorticity in the divergent section, intensifying the bubble formation. Regarding geometric variations, a larger divergent angle (60º) leads to the formation of smaller and denser bubbles, with a velocity of 5.64m/s and turbulence of 0.411 while a smaller throat diameter (10mm) enhances bubble formation in the VMBG with a velocity of 5.08m/s and turbulence of 0.411. Additionally, a longer throat (30mm) promotes the creation of larger, elongated bubbles, with maximum turbulence of 0.262 while a shorter throat has maximum turbulence of 0.285 resulting in smaller, fragmented bubbles. To sum up, crucial parameters like geometrical configuration and flow conditions play a pivotal role in altering the flow characteristics and thus affecting the bubble formation, eventually leading to controlling the generated bubble size. This research could guide in designing VMBG according to the desired bubble size and application requirements.