In recent years, the lattice Boltzmann method (LBM) has emerged as a powerful tool that has replaced conventional macroscopic techniques like Computational Fluid Dynamics (CFD) in many applications. The LBM starts from meso- and microscopic Boltzmann's kinetic equation to determine macroscopic fluid dynamics. The origins of LBM can be drawn back to lattice gas cellular automata (LGCA); however it lacks Galilean invariance and creates statistical noise in the system. LBM on the other hand does away from these drawbacks of LGCA, and is easy to implement in complex geometries and can be used to study microscopic flow behavior in complex fluids/fluid mixtures. In this work, the LBM is used as a tool to study isothermal bubble dynamics of single and multiple bubbles in heavier fluids. Some benchmark problems have been solved to prove the effectiveness of LBM over conventional solvers and results have been compared to analytical/existing solutions. Flow behavior at different flow parameters have been recorded and presented. Bubble shape regimes have been classified based on the important two-phase flow parameters, namely the Eotvos number, Morton number, Reynolds number and the Weber number. Single bubble simulations have been conducted in fairly large domains to capture terminal velocities, which have been compared to existing theoretical solutions, obtained using the potential flow theory. The terminal velocities so obtained have also been used for the estimation of drag and drag coefficient for a range of Eotvos and Reynolds numbers, and the drag coefficient so computed has been compared with those predicted by existing correlations and analytical expressions. Bubble dynamics and collision and coalescence for multiple bubbles rising under the influence of gravity in fully periodic domains have been simulated using LBM, and the flow behavior around such bubbles prior to and after coalescence have been studied and the results presented. The study of multiple bubble dynamics reveals the influence of the wake on the shape and collision of downstream bubbles, and yields valuable insights into the physics of intermediate stages when multiple bubbles collide and form an elongated/stretched bubble. The flow and bubble coalescence behavior predicted in this study compares very well with experimentally captured bubble dynamics and with data present in literature. Possible extensions of the present study have been highlighted for future research.

Labeling of consumer products is not only required by regulatory bodies for product identification, but it also serves as a symbol of product quality and prestige. Bubbles under the label are unsightly and impact customer satisfaction. Pressure Sensitive Adhesive (PSA) labels currently make up more than eighty percent of all labels in the market today, yet little research could be found addressing causes of bubbling in an industrial setting. A root cause analysis for bubble development included four aspects: label application, environmental conditions of shipping and storage, defects in glass bottle geometry, and oil contamination. The most significant findings from each area were as follows: Label Application. Force and contact time were confirmed to be significant factors in reducing label bubbling. The equipment settings directly related to these factors should be controlled and monitored. Environmental Conditions. None of the environmental conditions caused growth or appearance of additional bubbles as was the hypothesis. All 4 test conditions had a significant Paired T-test but in the reduction of bubble size. Glass Defects. A random sample of bottles showed very poor capability of the bottle dimensions. However, low capability to produce within specification limits does not necessarily lead to bubbling. A direct comparison test was done to compare diameters and variation from bubbled bottles to non-bubbled. No measurements that could reasonably be related to bubbles caused by glass defectiveness were statistically different. Oil Contamination. Initial data analysis showed that certain oil types had a higher chance of causing bubbling. However, after a controlled experiment was performed, the results were inconclusive that oil contamination pre or post-labeling could cause bubbling in isolation. The experiment did confirm the importance of sufficient pressure in the label application process.

Page 104 was not included in the thesis. / <p> The work presented in this thesis relates to one of the most important problems in the design of high-density, high-speed bubble memory systems. A new approach for the analysis, design and optimization of bubble circuits is developed. This formulation is suited to computer-aided methods of solution.</p> <p> A micromagnetic approach to the modeling of permalloy bubble circuits is examined. Basic to the approach is the discretization of the circuit into very small regions to simulate the ferromagnetic essence of the permalloy. This method of analysis is very useful in studying submicron bubble circuits. However, the numerical difficulties as well as the excessive computer time required for such analysis led to careful consideration of possible approximations. A continuum model for analyzing field access bubble circuits has, thus, been developed and used to characterize arbitrary shaped permalloy structures. Various propagation circuits, including gap tolerant circuits, and bubble replicators are analyzed and the results compared to experimentally available data.</p> <p> A model for studying bubble size and position fluctuations is introduced. The model assumes that the bubble domain is circular. However, with slight modifications it can accept general elliptical shapes. For various propagation circuits, the model results are in excellent agreement with experimental measurements in the literature.</p> <p> An algorithm for bubble circuit optimization is developed and discussed in detail. The problem is formulated as a constrained minimax objective which is suited to nonlinear programming methods of solution. Typical examples of T-I propagation circuits are furnished to illustrate the approach.</p> / Thesis / Doctor of Philosophy (PhD)

The rotating wall vessel (RWV) bioreactor is a well-established cell culture device for the simulation of microgravity for suspension cells and the generation of spheroids and organoids. The key to the success of these systems is the generation of a delicately maintained fluid dynamics system which induces a solid body rotation capable of suspending cells and other particles in a gentle, low-shear environment. Despite the unique capabilities of these systems, the inherently delicate nature of their fluid dynamics makes the RWV prone to multiple failure modes. One of the most frequently occurring, difficult to avoid, and deleterious modes of failure is the formation of bubbles. The appearance of even a small bubble in an RWV disrupts the crucial laminar flow shells present in the RWV, inducing a high-shear environment incapable of maintaining microgravity or producing true spheroids. The difficulty of eliminating bubbles from the RWV substantially increases the learning curve and subsequent barrier-to-entry for the use of this technology. The objective of this study is to create a novel RWV design capable of eliminating the bubble formation failure mode and to demonstrate the design’s efficacy. The tested hypothesis is: “The addition of a channel capable of segregating bubbles from the fluid body of the RWV will protect its crucial fluid dynamics system while enabling the growth of consistently sized and properly formed cell spheroids, improving ease of use of the RWV and decreasing experimental failure.” / Bioengineering

Micro-particles are ubiquitous in microsystems. The effective manipulation of micro-particles is often crucial for achieving the desired functionality of microsystems and requires a fundamental understanding of the particle dynamics. In this dissertation, the dynamics of two types of micro-particles, Janus catalytic micromotors (JCMs) and magnetic clusters, in complex environment are studied using numerical simulations. The self-diffusiophoresis of JCMs in a confined environment is studied first. Overall, the translocation of a JCM through a short pore is slowed down by pore walls, although the slowdown is far weaker than the transport of particles through similar pores driven by other mechanisms. A JCM entering a pore with its axis not aligned with the pore axis can execute a self-alignment process and similar phenomenon is found for JCMs already inside the pore. Both hydrodynamic effect and 'chemical effect', i.e., the modification of the concentration of chemical species around JCMs by walls and other JCMs, play a key role in the observed dynamics of JCMs in confined and crowded environment. The dynamics of bubbles and JCMs in liquid films covering solid substrates are studied next. A simple criterion for the formation of bubbles on isolated JCMs is developed and validated. The anomalous bubble growth law (r~t^0.7) is rationalized by considering the relative motion of growing bubbles and their surrounding JCMs. The experimentally observed ultra-fast collapse of bubbles is attributed to the coalescence of the bubble with the liquid film-air interface. It is shown that the collective motion of JCMs toward a bubble growing on a solid substrate is caused by the evaporation-induced Marangoni flow near the bubble. The actuation of magnetic clusters using non-uniform alternating magnetic fields is studied next. It is discovered that the clusters' clockwise, out-of-plane rotation is a synergistic effect of the magnetophoresis force, the externally imposed magnetic torque and the hydrodynamic interactions between the cluster and the substrate. Such a rotation enables the cluster to move as a surface walker and leads to unique dynamics, e.g., the cluster moves away from the magnetic source and its trajectory exhibits a periodic fluctuation with a frequency twice of the field frequency. / Ph. D.

Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces Through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing. / Doctor of Philosophy / Electric charges are often found in naturally or artificially formed droplets, such as raindrops, waterfall, and inkjet printer. Neutral droplets impact on flat surfaces will usually trap a bubble inside because of the viscosity of air. The air bubble entrapped can be ignored if the droplet is water because the air bubble will eventually pinch-off. However, if the droplet is metal or some other viscous liquid, the air bubble will stay inside the liquid. This entrapped air bubble is undesired under some circumstances. For example, the existence of air bubble during metal 3D printing can influence the physical property. I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the maximum charges a droplet can carry for representative impact conditions, the electric stress will dominate the deformation of droplet. A conical liquid tip forms at the droplet bottom, avoiding the entrapment of air bubble. The critical charge level is experimentally proved to be only dependent on the gas viscosity and impact velocity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.

No description available.

The purpose of this research was to apply a discrete-bubble model to predict the performance of several hypolimnetic oxygenators. The model is used to predict the oxygen transfer rate in a hypolimnetic oxygenator based on the initial bubble size formed at the diffuser. The discrete-bubble model is based on fundamental principles, and therefore could also be applied to other mass transfer applications involving the injection of bubbles into a fluid. The discrete-bubble model has been applied to a linear bubble-plume diffuser, a full-lift hypolimnetic aerator and the Speece Cone with promising results. The first step in this research was to investigate the principals of bubble formation at a submerged orifice, bubble rise velocity and bubble mass transfer. The discrete-bubble model is then presented. The model traces a single bubble rising through a fluid, accounting for changes in bubble size due to mass transfer, temperature and hydrostatic pressure. The bubble rise velocity and mass transfer coefficients are given by empirical correlations that depend on the bubble size. Bubble size is therefore recalculated at every increment and the values for the bubble rise velocity and mass transfer coefficients are continually updated. The discrete-bubble model is verified by comparison to experimental data collected in large-scale oxygen transfer tests. Finally, the discrete-bubble model is applied to the three most common hypolimnetic oxygenation systems: the Speece Cone, the bubble-plume diffuser, and the full-lift hypolimnetic oxygenation systems. The latter being presented by Vickie Burris in her thesis, <i>Hypolimnetic Aerators: Predicting Oxygen Transfer and Water Flow Rate</i>. / Master of Science

Water utilities can experience problems from bubble formation during conventional treatment, including impaired particle settling, filter air binding, and measurement as false turbidity in filter effluent. Coagulation processes can cause supersaturation and bubble formation by converting bicarbonate alkalinity to carbon dioxide by acidification. A model was developed to predict the extent of bubble formation during coagulation which proved accurate, using an apparatus designed to physically measure the actual volume of bubble formation. Alum acted similar to hydrochloric acid for initializing bubble formation, and higher initial alkalinity, lower final solution pH, and increased mixing rate tended to increase bubble formation. Lastly, the protocol outlined in Standard Methods for predicting the degree of supersaturation was examined, and when compared to this work, the Standard Methods approach produces an error up to 16% for conditions found in water treatment. Air entrainment and ozonation are the key causes of dissolved gas supersaturation and eventual bubble formation in water treatment plants. Total dissolved gas probes (TDGP) are now available to directly measure supersaturation and have many advantages compared to conventional techniques. Bubble formation during coagulation-flocculation hindered particle sedimentation, producing settled turbidities double that of solutions without dissolved gases. In a filtration study, run time to one half of initial flow was decreased by 54% when the source water was increased from 0.1 to 0.2 atm supersaturation. Indeed, even at 0.05 atm supersaturation, run length was only 21 hours in solutions without added particulate matter. A case study confirmed that bubble formation can interfere with coagulation and filtration processes at conventional treatment plants. / Master of Science

Hypolimnetic oxygenation systems, such as linear bubble-plume diffusers, are used to improve raw water quality. Linear bubble-plume diffusers were installed in Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR). Diffusers induce mixing that aids distribution of oxygen throughout the hypolimnion. The induced mixing also creates an undesirable effect by increasing hypolimnetic oxygen demand (HOD). Nevertheless, oxygenation systems are commonly used and long-term oxygenation is hypothesized to actually decrease HOD. Increased oxygen concentrations in combination with the induced mixing affect the location of the oxic/anoxic boundary relative to the sediment water interface. If the oxic/anoxic boundary is pushed beneath the sediment/water interface, the concentrations of soluble iron and manganese in the bulk water are reduced. This work was performed to further validate a recently published bubble-plume model that predicts oxygen addition rates and the elevation in the reservoir where the majority of the oxygen is added. Also, the first field observations of a theoretically expected secondary plume are presented. Model predicted addition rates were compared to observed accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Observations in both reservoirs showed evidence of horizontal spreading that correlated well with plume-model predictions and of vertical spreading below diffuser elevations, showing oxygen penetration into the sediment. Experimental observations of a theoretically expected secondary plume structure also correlated well with model predictions. Plume-induced mixing was shown to be a function of applied gas flow rates, and was observed to increase HOD. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that the increase in oxygen concentration is not the cause of the increased HOD. Long-term oxygenation resulted in an overall decrease in background HOD as well as a decrease in induced HOD during diffuser operation. Elevated oxygen concentrations and mixing, which occur naturally during destratification and artificially during oxygenation, were observed to coincide with low dissolved metal concentrations in CCR. Movement of the oxic/anoxic boundary out of the sediment, which is also common during stratified periods, appears to facilitate transport of reduced Mn to the overlying waters. Hypolimnetic oxygenation increased oxygen concentrations throughout the hypolimnion, including down to the SWI, and induced mixing, although not to the extent observed during destratification. Subsequently, elevated Mn concentrations were observed to be restricted to the benthic waters located immediately over the sediments, while bulk (hypolimnion) water Mn concentrations remained low. The good agreement between the model and the experimental data show that the model can be used as a predictive tool when designing and operating bubble-plume diffusers. Linear bubble-plume diffusers provide sufficient horizontal and vertical spreading to enable oxygen to reach the sediments. Hypolimnetic oxygenation, despite the increased HOD, is a viable method to manage the negative consequences of hypolimnetic anoxia in water-supply reservoirs. / Ph. D.