DRAINAGE BEHAVIOR OF AQUEOUS, POLYMERIC, AND OIL-BASED NITROGEN FOAMS: THEORETICAL AND EXPERIMENTAL INVESTIGATION

Foams can be formulated to have a wide range of densities and viscosities. This unique behavior makes foam suitable for underbalanced drilling where pressure exerted on formation is maintained below pore pressure and at the same time, favorable conditions for a good hole-cleaning can be established in the wellbore. Foams are also used as in fracturing, cementing, and, enhanced oil recovery applications. However, the disadvantage of foam is its inherent instability. The stability of aqueous foams in vertical conduits has been extensively investigated. However, in many industrial applications such as underbalanced drilling foam is used in inclined configurations. The stability of foams inclined conduits is not well understood. The effect of geometry is often ignored. In addition, polymer-based and non-aqueous foams with more complex flow and stability behavior are becoming more common. As a result, there is a strong need to investigate foams to better understand the effects of different operational factors (inclination, conduit geometry, base fluid type, and shearing) on their stability. Thus, the main goal of this study is to investigate each of these factors with respect to their impact on foam stability. To achieve this, foam stability experiments were conducted in concentric annulus and straight pipe sections. The pipe section is manufactured from a fully transparent PVC pipe, enabling visual inspection of foam structure and liquid drainage. The annulus is made of stainless steel casing and a rotating inner PTFE (polytetrafluoroethylene) rod. Three types of foams (aqueous, polymeric-based and oil-based foams) were used in the investigation. All tests were performed at 400 KPa and ambient temperature (22 ± 2oC). Foam quality was ranged from 40 - 80%, except for oil-based foam which was limited to 70% due to instability at high qualities. Foam rheology data was obtained from pipe viscometers before conducting stability tests. Two inclination angles (0o and 30o) were considered in this study. For tests conducted in the annulus, the rotation speed of the inner rod was varied (0, 4, and 7 rpm) to examine the impact of shearing on foam stability. Hydrostatic pressure data measured from the annular test section is converted into density profiles, which are used to determine the drained liquid volume as a function of time. In straight pipe sections, the volume of drained liquid was measured using a measuring tape. A digital camera with a microscope was used to capture images of foam in real-time to examine the process of foam decay (i.e. the degree of bubble coarsening and coalescence). Foam stability increased with quality. For a given quality, foam prepared with polymeric fluid was the most stable, while oil-based foam was the least. The wall effects can hinder bubble and drained liquid motion and consequently delay drainage. As a result, foam drained more slowly in the annulus than in pipe. Inclining the test sections resulted in much faster drainage, possibly due to the formation of a liquid layer between foam structure and container walls that flows down due to gravity, effectively avoiding the hydraulic flow resistance of foam structure. The effect of shearing on drainage was minimal for the level of shear rate applied. Channel-dominated model developed in this study is suitable for all foams considered (40-80%). Node-dominated model is not recommended for these wet foams as it tends to over predict liquid volume fractions at early time steps

Scaling laws and dynamics of bubble coalescence

The coalescence of bubbles and drops plays a central role in nature and industry. During coalescence, two bubbles or drops touch and merge into one as the neck connecting them grows from microscopic to macroscopic scales. The hydrodynamic singularity that arises when two bubbles or drops have just touched and the flows that ensue have been studied thoroughly when two drops coalesce in a dynamically passive outer fluid. In this paper, the coalescence of two identical and initially spherical bubbles, which are idealized as voids, that are surrounded by an incompressible Newtonian liquid is analyzed by numerical simulation. This problem has recently been studied (a) experimentally using high-speed imaging and (b) by asymptotic analysis in which the dynamics is analyzed by determining the growth of a hole in the thin liquid sheet separating the two bubbles. In the latter, advantage is taken of the fact that the flow in the thin sheet of non-constant thickness is governed by a set of one-dimensional, radial extensional flow equations. While these studies agree on the power law scaling of the variation of the minimum neck radius with time, they disagree with respect to the numerical value of the prefactors in the scaling laws. In order to reconcile these differences and also provide insights into the dynamics that are difficult to probe by either of the aforementioned approaches, simulations are used to access both earlier times than it has been possible in the experiments and also later times when asymptotic analysis is no longer applicable. Early times and extremely small length scales are attained in the new simulations through the use of a truncated domain approach. Furthermore, it is shown by direct numerical simulations in which the flow within the bubbles is also determined along with the flow exterior to them that idealizing the bubbles as passive voids has virtually no effect on the scaling laws relating minimum neck radius and time.This research was sponsored by the Petroleum Research Fund of the American Chemical Society, the Basic Energy Sciences Program of the United States Department of Energy, and the Engineering and Physical Sciences Research Council

Stratospheric constituent measurements using UV solar occultation technique

The photochemistry of the stratospheric ozone layer was studied as the result of predictions that trace amounts of pollutants can significantly affect the layer. One of the key species in the determination of the effects of these pollutants is the OH radical. A balloon flight was made to determine whether data on atmospheric OH could be obtained from lower resolution solar spectra obtained from high altitude during sunset

Bubble Interactions at Multi-Fluid Interfaces

Numerous industrial applications and environmental phenomena are centered around bubble interactions at multi-fluid interfaces. These applications range from metallurgical processing to direct contact evaporation and solid shell formation. Environmental phenomena, such as bubble collisions with the sea surface microlayer and the collision of liquid encapsulated bubbles, were also considered as motivators for this work. Although the associated flow dynamics are complex, they play a vital role in governing the related application outcome, be it in terms of mass or heat transfer efficiency, bubble shell production rate, chemical reaction rate, etc. For this reason, a fundamental understanding of the fluid dynamics involved in the bubble interactions are required to aid in optimal system design. In this work, rigorous experimental work was supplemented by in-depth theoretical analysis to unravel the physics behind these bubble interactions. The focus of the present work is to develop an improved understanding of bubble interactions at liquid-liquid and compound interfaces. Extensive testing has been carried out to identify and classify flow regimes associated with single bubble and bubble stream passage through a liquid-liquid interface. Dimensionless numbers were identified and employed to map these regimes and identify transition criteria. The extension of one identified regime, bubble shell formation, to the field of direct contact evaporation was considered through the development of a numerical model to predict bubble growth in an immiscible liquid droplet. Additional dimensional analysis was carried out for the characterization of bubble collisions at solid and free surfaces. Previously developed numerical models were employed to form the relationship between the appropriate dimensionless groups capable of characterizing such collisions. This relationship was then used to describe a practical method for predicting the radial film size formed during the collision. Finally, three numerical models were developed to predict the bubble motion and the spatiotemporal evolution of the film(s) formed during the collision of a bubble with a liquid-liquid, solid-liquid-liquid, and gas-liquid-liquid interface. These models were validated through additional experiments carried out for this work as well as from data found in literature

The dynamics of static bubbles: the drainage and rupture of quiescent bubbles can enrich, aerosolize, and stress suspended microorganisms

Bubbles are ubiquitous influencing a multitude of biological processes in natural and industrial environments; this influence is especially relevant during and after bubble rupture. Indeed, the influence of a bubble can extend well beyond its lifetime via the droplets produced when it ruptures. These droplets are known to effectively transport nearby particulates including bacteria and viruses into the surroundings, which in addition to affecting human health can influence global climate by acting as cloud condensation nuclei. Further, the bubble's rupture is a violent event that has been linked to decreased cell viability in bioreactors. However, in all these applications many of the studies have taken an empirical approach, making the results difficult to generalize. Here we combine theory and experiment to investigate the static and dynamic interactions between bubbles and the surrounding microorganisms at a free interface. Our first study focuses on the equilibrium shape a bubble forms after reaching the surface of a liquid. Existing literature is limited to a bubble resting on a flat interface; for example, the surface of a pool or calm lake. However, there are instances where this assumption no longer applies -- a bubble bursting on a raindrop, for example. By relaxing this assumption, we show how a curved boundary alters the final shape of the bubble. Our next study focuses on the enrichment of particulates in the cap of a bursting bubble. As a bubble rises to a free surface, particulates in the bulk liquid are frequently transported to the surface by attaching to the bubble's interface. When the bubble ruptures, a fraction of these particulates are often ejected into the surroundings in film droplets with particulate concentrations higher than the liquid from which originate. However, the precise mechanisms responsible for this enrichment are unclear. By simultaneously recording the drainage and rupture events with high-speed and standard photography, we directly measure the concentrations in a thin bubble film. Based on our results, we develop a physical model and provide evidence that the enrichment is due to a combination of scavenging and film drainage. Our next study focuses on the conditions necessary for a jet droplet to be produced. Past research shows that droplet production is halted when either gravitational or viscous effects are significant. Through systematic experimentation we uncover an intermediate region where both effects are significant, leading to an early end of droplet production. By numerically decoupling the gravitational effects into before and after rupture, we find that the equilibrium shape is responsible for the existence of this intermediate region. Our last study focuses on quantifying the localized stresses produced during spontaneous bubble bursting. Directly simulating each bubble and its effect on the suspended cells in a bioreactor is currently infeasible. Here we illustrate how the results of past works, which disagree by several orders of magnitude for similarly sized bubbles, are primarily a result of the chosen numerical mesh, not the underlying physics. By implementing a particle tracking method, we eliminate this mesh dependence and quantify the extent or volume effected by a single bubble bursting event. Based on our results, we develop a generalizable framework that could be integrated into existing models as a parameterization, removing the need to simulate both phases.2019-07-09T00:00:00

Use of biochar as a slag foaming agent in EAF steelmaking

Abstract. The transition to fossil-neutral steel production involves finding a substitute for fossil-based carbonaceous materials used in the EAF process. Foaming of slag is an important part of EAF steelmaking, where usually fossil-based carbonaceous material is injected into the melt to cause the foaming of the slag. The aim of this thesis is to study the suitability of biochar as a foaming agent. In the theory part of the thesis the EAF process and the slag foaming phenomenon are reviewed at a general level. The properties of the slag and their effect on the foaming phenomenon are reviewed, and the composition limits of the slag favorable for the foaming are evaluated. In addition, biochar, its production and properties are briefly presented. The theory part also includes a literature review of previously made studies related to the use of biochar as a slag foaming agent. In the experimental part of the thesis some laboratory-scale slag foaming experiments were performed. The slag used in the experiments was from an actual EAF process. The observation of the foaming during the experiments was performed by imaging the experiments with a CCD camera using a laser light source. By analyzing the obtained video image, the foaming behavior could be evaluated. After the experiments the cooled slag and the crucibles were analyzed with microscopical methods. Based on the results, the biochar used in the experiments acted as a foaming agent in a similar way to the coke dust. During the injection the iron oxide in the slag was reduced, creating CO bubbles that caused the foaming phenomenon and an increase in the volume of the slag.Biohiilen käyttö kuonan kuohutuksessa valokaariuunissa. Tiivistelmä. Siirryttäessä fossiilineutraaliin terästuotantoon täytyy valokaariuuniprosessissa käytettäville fossiilisille hiilimateriaaleille löytää korvaaja. Kuonan kuohutus on valokaariuuniprosessin tärkeä vaihe, jossa käytetään tavallisesti fossiilista, injektoitavaa hiilimateriaalia kuohun aikaansaamiseksi. Tämän diplomityön tavoitteena on selvittää biohiilen soveltuvuutta kuohutusagentiksi. Työn teoriaosassa on esitetty yleisesti valokaariuuniprosessi sekä kuonan kuohuminen ilmiönä. Kuonan ominaisuuksia ja niiden vaikutusta kuohumiseen käydään läpi, ja kuohumisilmiön kannalta suotuisia kuonan koostumusrajoja pyritään arvioimaan. Lisäksi biohiili, sen valmistus ja ominaisuudet esitellään lyhyesti. Teoriaosaan on sisällytetty myös kirjallisuusselvitys aiemmin suoritetusta tutkimuksesta biohiilen käyttöön kuohutusagenttina liittyen. Työn kokeellisessa osiossa suoritettiin laboratoriotason kuonankuohutuskokeita. Kuonana kokeissa käytettiin todellisesta valokaariuuniprosessista saatua kuonaa. Kuohumisen havainnointi kokeiden aikana suoritettiin kuvaamalla CCD-kameralla laservalonlähdettä apuna käyttäen. Saatua videokuvaa analysoimalla kuohumiskäyttäytymistä voitiin arvioida. Kokeiden jälkeen jäähtynyttä kuonaa ja upokkaita analysoitiin mikroskooppisilla menetelmillä. Tulosten perusteella kokeissa käytetty biohiili toimi kuohutusagenttina hyvin samankaltaisesti kuin koksipöly. Injektoinnin aikana kuonan sisältämä rautaoksidi pelkistyi muodostaen kuohumisreaktion aiheuttavia CO-kuplia, ja kuonan tilavuus kasvoi