Browsing by Author "Zhou, Shuyi"

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    Experimental and numerical study on microbubble coalescence dynamics
    (2017-12) Zhou, Shuyi; Zhu, Likun; Yu, Whitney (Huidan); Agarwal, Mangilal
    This thesis work aims to make a better knowledge on the insights of physics on microbubble coalescence process, using experimental and numerical approaches. The neck growth and bubble surface wave propagation at the early stage of coalescence, merging preference, as well as a reaction-channel modified microfluidic gas generator are presented in the thesis. Coalescence of unequal-sized microbubbles captive on solid substrate was observed from cross-section view using synchrotron high speed imaging technique and a mi- crofluidic gas generation device. The bridging neck growth and surface wave propaga- tion at the early stage of coalescence were investigated by experimental and numerical methods. The results show that theoretical half power law of neck growth rate is still valid when viscous effect is neglected. However, the inertial-capillary time scale is based on the radius of smaller parent microbubble. The surface wave propagation rate is proportional to the inertial-capillary time scale, which is based on the radius of larger parent microbubble of a coalescence pair. Meanwhile, the relationship of preference distance and size inequality microbub- bles were studied using the same micrfluidic gas generator and observation facilities. The size inequality of parent microbubbles would affect the preference distance of merged bubble in between. The merged bubble gets less closer to the larger parent bubble with an exponent of 1.82 as a reference, which largely affected by shear stress begotten on the solid interface. To express this phenomenon distinguished with free merging bubble pair, we propose the wall shear stress hinders the process of that parent bubbles move towards to each other during coalescence Our hypothesis was confirmed by identical coalescence simulation via ANSYS Fluent. To address the multiple measurement, utilization of Java based photography pro- cessing software ImageJ was applied as a key point to the thesis work. To acquire more microbubble coalescence cases on experiment for study, we enhanced the perfor- mance of microfluidic gas generator with reaction channel optimization. An optimized design on increasing the number of parallel reaction channel from single to triple, was applied to obtain a higher gas generation rate. Also the gas vent shape was modified from triangle to rectangle to provide more information on reaction channel optimiza- tion. The gas generation rate and H2O2 conversion rate were provided to further discuss.
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    Study on coalescence dynamics of unequal-sized microbubbles captive on solid substrate
    (Elsevier, 2018-11) Zhou, Shuyi; Cao, Yuanzhi; Chen, Rou; Sun, Tao; Fezzaa, Kamel; Yu, Huidan; Zhu, Likun; Mechanical Engineering, School of Engineering and Technology
    The dynamics of bubble coalescence are of importance for a number of industrial processes, in which the size inequality of the parent bubbles plays a significant role in mass transport, topological change and overall motion. In this study, coalescence of unequal-sized microbubbles captive on a solid substrate was observed from cross-section view using synchrotron high-speed imaging technique and a microfluidic gas generation device. The bridging neck growth and surface wave propagation at the early stage of coalescence were investigated by experimental and numerical methods. The results show that theoretical half-power-law of neck growth rate is still valid when viscous effect is neglected. However, the inertial-capillary time scale is associated with the initial radius of the smaller parent microbubble. The surface wave propagation rate on the larger parent microbubble is proportional to the inertial-capillary time scale.
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    Understanding Microbubble Coalescence Using High-Speed Imaging and Lattice Boltzmann Method Simulation
    (Office of the Vice Chancellor for Research, 2016-04-08) Zhou, Shuyi; Cao, Yuanzhi; Chen, Rou; Chen, Chuanyi; Yu, Huidan (Whitney); Zhu, Likun; Sun, Tao
    Microbubble coalescence is one of the important research areas of bubble dynamics. The purpose of this research is to seek deeper understanding and relative mathematical relation on microbubble coalescence. To fulfill that, we conducted both experiments and simulations. For the part of experiment, we fabricated a microfluidic gas generator with better performance leading corresponding fluidic chemical reaction. After that we utilized ultrafast synchrotron X-ray imaging facility at the Advanced Photon Source of Argonne National Laboratory to capture the gas generating and microbubble merging phenomena using high speed imaging. These experiments show how the microbubbles with the same ratio contact and merge in the reaction channel and different concentration of reactants. As for the part of simulation, we lead the simulation basing on lattice Boltzmann method to simulate microbubble coalescence in water with unequal diameter ratio. Focuses are on the effects of size inequality of parent bubbles on the coalescence geometry and time. The “coalescence preference” of coalesced bubble closer to the larger parent bubble is well captured. A power-law relation between the preferential relative distance and size inequality is consistent to the recent experimental observations. Meanwhile, the coalescence time also exhibits power-law scaling, indicating that unequal bubbles coalesce faster than equal bubbles.