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<p>Flow Accelerated Corrosion (<em>FAC</em>) is defined as a flow enhanced mass transfer phenomenon that results in pipe wall thinning of the piping system and results in abrupt failure in some cases. <em>FAC</em> is controlled by the transport of corrosion species from the wall to the bulk fluid and is determined by the local distribution of the mass transfer coefficient. The overall objective of this research is to investigate the mass transfer in pipe bends arranged in single and dual S- shape configurations under single and annular two phase flow conditions. A novel wall dissolving mass transfer technique was developed to measure the local mass transfer distribution under a Schmidt number (<em>Sc</em>) of 1280, which mimics the level of carbon steel in water in industrial applications. Flow field measurements using Particle Image Velocimetry (<em>PIV</em>) and flow visualizations using laser induced fluorescence were performed to understand the causal relation between the mass transfer and the flow dynamics.</p> <p>The mass transfer in single 90^o bends under single phase flow was measured for a range of <em>Re</em> from 40,000 to 130,000. Three regions of elevated mass transfer rates were determined in the single bend, (i) near the inlet to the bend inner wall, (ii) midway on the bend inner wall sides and (iii) near the outlet of the bend outer wall. The maximum mass transfer enhancement relative to the upstream pipe was found to occur near the outlet of the single bend outer wall and spans over the first part of the downstream pipe with a magnitude of approximately 1.8. The surface roughness of the test sections were determined at the end of each experiment and found to be in the fully rough wall region. The mass transfer coefficient at the high mass transfer locations was found to scale as <em>Re</em>^0.92. The maximum enhancement was found to be independent of <em>Re</em> for the range of <em>Re</em> studied here.</p> <p>For the dual S- shape bends, tests were performed for different separation distances <em>L/D</em> of 0, 1 and 5. The <em>L/D</em>=0 case were tested for a range of <em>Re</em> from 40,000 to 130,000. The maximum mass transfer enhancement relative to the upstream pipe was found to occur when there was no separation distance between the bends. This maximum occurred at the transition from the first bend outer wall to the second bend inner wall with a magnitude of approximately 3.2. The mass transfer enhancement was found to decrease when the separation distance between the two bends was increased. A second region of high mass transfer enhancement was found to occur midway on the second bend inner wall in the form of two symmetric regions shifted from the centerline with a magnitude of 2.8.</p> <p>The effect of air and water superficial velocities for annular flow in the range of <em>J_v</em>= 22- 29.5 m/s, and <em>J_L</em>= 0.17- 0.41 m/s on the mass trasnfer in single and dual S- shape bends was determined. The maximum mass transfer was found to occur midway on the centerline of the bend outer wall for the single bend case. This location corresponded to the entrained liquid droplet impingment and anticipated high velocity region due to liquid film thining. A second high mass transfer region was observed on the latter part of the bend outer wall. The effect of the air superficial velocity on the mass transfer enhancement was more significant than the effect of the water superficial velocity.</p> <p>The maximum mass transfer enhancement in the S- shape bend geometry under annular two phase flow was found to always occur on the first bend outer wall at a similar location to the single bend case. The mass transfer in the second bend was lowest for the zero separation distance between the bends, and increased with an increase in the separation distance. The maximum mass transfer in the second bend occurred near the outlet of the second bend outer wall with a magnitude of approximately 60% of that in the first bend when the separation distance was zero. The maximum mass transfer in the second bend was found to increase with an increase in separation distance to reach approximately 85% of that in the first bend for <em>L/D</em>=40. The location of the maximum region was observed to shift in the upstream direction as the separation distance was increased to approach the location of the single bend maximum near <em>L/D</em>=40.</p> <p>Flow field measurements showed matching of the areas with high mean flow velocity on the inlet portion of the single bend inner wall. The high velocity stream was observed to shift toward the outer wall near the bend outlet. Similar features were observed in the first bend of the S- shape configuration. The flow velocity increased significantly near the transition from the first bend outer wall to the second bend inner wall of the dual S-shape bend. High turbulent kinetic energy was measured near the outlet of the single bend outer wall and inner wall. Similar kinetic energy distribution was observed on the first bend of the S- shape. The turbulent kinetic energy downstream of the first bend increased to approximately twice that in the first bend and was observed to travel from the outlet of the first bend inner wall to the second bend inner wall. For two phase annular flow, the phase redistribution visualization showed liquid separation from the core flow and deposition on the bend wall. Three locations of deposition were observed (a) on the first bend outer wall near <em>ϕ</em>₁ of 50^o, (b) between the 50^o and the outlet of the first bend (c) on the latter part of the second bend outer wall.</p> / Doctor of Philosophy (PhD)

The grades of steel used for automotive bodies are interstitial free steel grades and titanium stabilized ultra-low carbon steel grades. During the manufacturing of these grades, the addition of titanium in liquid steel is achieved in the steel refining units and may cause processing problems. Titanium reacts with the dissolved aluminum and oxygen to form complex solid aluminum titanate type micro-particles (inclusions). During the flow of titanium alloyed steel grades containing solid inclusions (such as aluminum titanate and alumina type inclusions), the clog accompanied by steel skull can be formed at the submerged entry nozzle between the tundish and the mold. To reduce the effects of aluminum titanate type inclusions, they can be either modified or removed. The current study focused on the removal of Al2O3, TiO2, and Al2TiO5 inclusions by dissolving them in slag in the temperature range of 1430 – 1600 °C using a high-temperature confocal scanning laser microscope. In this technique, a single particle (inclusion) is placed on the surface of a solid slag, and the inclusion-slag system is heated to steelmaking temperatures. The dynamic changes in inclusion size are measured to determine dissolution kinetics and mechanism. This work has developed a complex oxide particle synthesis technique and provides the first-ever kinetic data for removal of aluminum titanate inclusions into steelmaking slags. It is found that Al2O3 inclusions have a slower dissolution rate than that of Al2TiO5 inclusions followed by TiO2 inclusions. The rate-controlling steps are investigated using a shrinking core model. It is shown that the rate-controlling step for dissolution of both Al2O3 and Al2TiO5 inclusion types is the mass transfer of alumina. Evidence in support of this finding is the particle-slag interface characterization by line scan analysis and calculated diffusivity values being inversely proportional to the viscosity of slag. The dissolution path of aluminum titanate is proposed in the following steps. First, aluminum titanate dissociates into alumina, titanium oxide and oxygen while slag penetrates through the particle. In the next step, the alumina and titanium oxide dissolves in slag, and the oxygen leaves the system. The existence of gas bubbles enhances the overall rate of Al2TiO5 dissolution. The current work establishes a detailed understanding of the dissolution of Al-Ti-O type inclusions in steelmaking slags. This knowledge will inform steelmakers on which inclusions of different chemistry can be removed preferably and develop strategies on better slag design to produce superior quality steel with reduced operational downtime. / Thesis / Doctor of Philosophy (PhD)

A numerical model based on fundamental engineering principles was developed and validated to establish a relationship between process parameters and the final properties of woodbased composite boards. The model simulates the mat formation, then compresses the reconstituted mat to its final thickness in a virtual press. The number of interacting variables during the hot-compression process is prohibitively large to assess a wide variety of data by experimental means. Therefore, the main advantage of the model based approach that the effect of the hot-compression parameters on the final properties of wood-based composite boards can be monitored without extensive experimentation. The mat formation part of the model is based on the Monte Carlo simulation technique to reproduce the spatial structure of the mat. The dimensions and the density of each flake are considered as random variables in the model, which follow certain probability density distributions. The parameters of these distributions are derived from data collected on industrial flakes by using an image analysis technique. The model can simulate the structure of a threelayer oriented strandboard (OSB) mat as well as the structure of random fiber networks. A grid is superimposed on the simulated mat and the number of flakes, the thickness, and the density of the mat at each grid point are computed. Additionally, the model predicts the change in several void volume fractions within the mat and the contact area between the flakes during consolidation. The void volume fractions are directly related to the physical properties of the mat, such as thermal conductivity, diffusivity, and permeability, and the contact area is an indicator of the effectively bonded area within the mat. The heat and mass transfer part of the model predicts the change of air content, moisture content, and temperature at designated mesh points in the cross section of the mat during the hotcompression. The water content is subdivided into vapor and bound water components. The free water component is not considered in the model due to the low (typically 6-7 %) initial moisture content of the flakes. The gas phase (air and vapor) moves by bulk flow and diffusion, while the bound water only moves by diffusion across the mat. The heat flow occurs by conduction and convection. The spatial derivatives of the resulting coupled partial differential equations are discretized by finite differences. The resulting ordinary differential equation in time is solved by a differential-algebraic system solver (DDASSL). The internal environment within the mat can be predicted among different initial and boundary conditions by this part of the hot-compression model. In the next phase of the research, the viscoelastic (time, temperature, and moisture dependent) response of the flakes was modeled using the time-temperature-moisture superposition principle of polymers. A master curve was created from data available in the literature, which describes the changing relaxation modulus of the flakes as a function of moisture and temperature at different locations in the mat. Then the flake mat was compressed in a virtual press. The stress-strain response is highly nonlinear due to the cellular structure of the mat. Hooke's Law was modified with a nonlinear strain function to account for the behavior of the flake mat in transverse compression. This part of the model gives insight into the vertical density profile formation through the thickness of the mat. Laboratory boards were produced to validate the model. A split-plot experimental design, with three different initial mat moisture contents (5, 8.5, 12 %), three final densities (609, 641, 673 kg êm3 or 38, 40, 42 lb ê ft3), two press platen temperatures (150, 200 °C), and three different press closing times (40, 60, 80 s) was applied to investigate the effect of production parameters on the internal mat conditions and the formation of the vertical density profile. The temperature and gas pressure at six locations in the mat, and the resultant density profiles of the laboratory boards, were measured. Adequate agreement was found between the model predicted and the experimentally measured temperature, pressure, and vertical density profiles. The complete model uses pressing parameters (press platen temperature, press schedule) and mat properties (flake dimensions and orientation, density distribution, initial moisture content and temperature) to predict the resulting internal conditions and vertical density profile formation within the compressed board. The density profile is related to all the relevant mechanical properties (bending strength, modulus of elasticity, internal bond strength) of the final board. The model can assist in the optimization of the parameters for hot-pressing woodbased composites and improve the performance of the final panel. / Ph. D.

One of the most significant challenges faced when modeling mass transfer from contaminant source zones is uncertainty regarding parameter estimates. These rate parameters are of particular importance because they control the connectivity between a simulated contaminant source zone and the aqueous phase. Where direct observation has fallen short, this study attempts to interpret field data using an inverse modeling technique for the purpose of constraining mass transfer processes which are poorly understood at the field scale. Inverse modeling was applied to evaluate parameters in rate-limited models for mass transfer. Two processes were analyzed: (i) desorption of hydrophobic contaminants and (ii) multicomponent Non-Aqueous Phase Liquid (NAPL) dissolution. Desorption was investigated using data obtained from elution experiments conducted with weathered sediment contaminated with 2,4,6 trinitrotoluene (TNT) (Sellm and Iskandar, 1994). Transport modeling was performed with four alternative source models, but predictive error was minimized by two first-order models which represented sorption/desorption using a Freundlich isotherm. The results suggest that first-order/Freundlich models can reproduce dynamic desorption attributed to high-and-low relative energy sorption sites. However, additional experimentation with the inversion method suggests that mass constraints are required in order to appropriately determine mass transfer coefficients and sorption parameters. The final portion of this research focused on rate-limited mass transfer from multicomponent NAPLs to the aqueous phase. Previous work has been limited to bench and intermediate scale findings which have been shown to inadequately translate to field conditions. Two studies were conducted in which numerical modeling was used to reproduce dissolution from multicomponent NAPL sources. In the first study, a model was generated to reproduce dissolution of chloroform (TCM), trichloroethylene (TCE) and tetrachloroethylene (PCE) observed during an emplaced-source field experiment conducted within a flow cell (Broholm et al., 1999). In the second study, a methodology was developed for analyzing benzene, toluene, ethylbenzene and xylene (BTEX) data during a field-scale mass transfer test conducted within a vertically-smeared source zone (Kavanaugh, 2010). The findings suggest that the inversion technique, when provided appropriate characterization of site and source parameters and when given appropriate dataset resolution, represents a viable method for parameter determination. Furthermore, the findings of this research suggest that inversion-based modeling provides an innovative predictive method for determining mass transfer parameters for multicomponent mixtures at the field scale. / Ph. D.

The biogeochemical processes responsible for production and emission of ammonia from stored liquid dairy manure are governed by environmental factors (e.g. manure temperature, moisture) and manure characteristics (e.g. total ammoniacal nitrogen concentration, pH). These environmental factors and manure characteristics vary spatially as a result of spatially heterogeneous physical, chemical, and biological properties of manure. Existing process-based models used for estimating ammonia emission consider stored manure as a homogeneous system and do not consider these spatial variations leading to inaccurate estimations. In this study, a one-dimensional compartmental biogeochemical model was developed to (i) estimate spatial variation of temperature and substrate concentration (ii) estimate spatial variations and rates of biogeochemical processes, and (iii) estimate production and emission of ammonia from stored scraped liquid dairy manure. A one-dimension compartmentalized modeling approach was used whereby manure storage is partitioned into several sections in vertical domain assuming that the conditions are spatially uniform within the horizontal domain. Spatial variation of temperature and substrate concentration were estimated using established principles of heat and mass transfer. Pertinent biogeochemical processes were assigned to each compartment to estimate the production and emission of ammonia. Model performance was conducted using experimental data obtained from National Air Emissions Monitoring Study conducted by the United States Environmental Protection Agency. A sensitivity analysis was performed and air temperature, manure pH, wind speed, and manure total ammoniacal nitrogen concentration were identified as the most sensitive model inputs. The model was used to estimate ammonia emission from a liquid dairy manure storage of a dairy farm located in Rockingham and Franklin counties in Virginia. Ammonia emission was estimated under different management and weather scenarios: two different manure storage periods from November to April and May to October using historical weather data of the two counties. Results suggest greater ammonia emissions and manure nitrogen loss for the manure storage period in warm season from May to October compared to the storage period in cold season from November to April. / Ph. D. / Dairy manure is a byproduct of dairy farming that can be used as a fertilizer to provide essential plant nutrients such as nitrogen, phosphorus, and potassium. However, manure can only be applied to crop lands in a certain time of the year during growing seasons. Further, discharge of dairy manure into natural environment is prevented by the environmental regulations. Therefore, manure storage structures are used to store liquid dairy manure until time permits for land application or use for other purposes. During the storage, liquid dairy manure goes through biological, chemical, and physical processes and release manure gases that are linked to deteriorate human and animal health and contribute to environmental pollution. Ammonia is one of the manure gases released to atmosphere from stored liquid dairy manure. Furthermore, release of ammonia from stored manure reduce nitrogen content and reduce fertilizer value of stored manure. Implementing control measures to mitigate ammonia emission is necessary to prevent ammonia emission and reduce nitrogen loss from stored manure. Deciding and applying of appropriate control measures require knowledge of the rate at which ammonia emission occurs and when ammonia emission occurs. Use of process-based models is one of the less expensive and reliable method for estimating ammonia emission from stored liquid dairy manure. Process-based model is a mathematical model that simulates processes related to ammonia production and emission from stored manure. Even though, there are several process-based models available for estimating ammonia emission from stored liquid dairy manure, these models do not fully represent the actual processes and conditions relevant to production and emission of ammonia. For instance, spatial variation of temperature and total ammoniacal nitrogen concentration within stored manure is not considered in existing process-based models. Therefore, in this study a new compartmental process-based model was developed for estimating these spatial variations and production and emission of ammonia from stored liquid dairy manure. The model uses weather data and manure management information as inputs for estimating ammonia emission and nitrogen loss. The performance evaluation of the compartmental process-based model revealed that air temperature, manure pH, wind speed, manure total ammoniacal nitrogen concentration are important model inputs for estimating ammonia emission from stored liquid dairy manure. The model was used to estimate ammonia emission from a dairy farm located in Rockingham and Franklin counties in Virginia. Results suggest greater ammonia emissions and manure nitrogen loss for the manure storage period in warm season from May to October compared to the storage period in cold season from November to April.

A submerged-media biological aerated filter (BAF) has been studied to 1) evaluate oxygen transfer kinetics under conditions without biological growth and 2) determine the influence of biological growth on the rate of oxygen transfer. Collectively, the study evaluates the rates of supply and consumption of oxygen in BAFs. The mass-transfer characteristics of a submerged-media BAF were initially determined over a wide range of gas and liquid flow rates without the presence of bacteria. The mass-transfer coefficients (KLa(T)) were measured using a nitrogen gas stripping method and were found to increase as both gas and liquid superficial velocities increase, with values ranging from approximately 40 to 380 h??. The effect of parameters including the gas and liquid velocities, dirty water to clean water ratio, and temperature dependence was successfully correlated within +/- 20% of the experimental KLa value. The effects of the media size and gas holdup fractions were also investigated. Stagnant gas holdup did not significantly influence the rate of oxygen transfer. Dynamic gas holdup and the difference between total and stagnant gas holdup were found to increase with an increase in gas velocity. Neither liquid velocity nor liquid temperature was determined to have a significant impact on gas holdup. A tertiary nitrification BAF pilot unit was then operated for 5 months downstream of a secondary treatment unit at a domestic wastewater treatment facility. The study investigated the oxygen transfer capabilities of the nitrifying unit with high oxygen demand requirements through a series of aeration process tests and explored the presence of oxygen transfer enhancements by further analyzing the actual transfer mechanism limitations. It was determined that (assuming OTE equals 20 percent) aerating the BAF pilot unit based on the stoichiometric aeration demand resulted in overaeration of the unit, especially at lower pollutant loading rates. Endogenous respiration contributed to only 2 to 7 percent of the total oxygen demand with regions of biomass activity changing with varying loading conditions. An enhanced oxygen transfer factor was determined in the biologically active pilot. Although it cannot be definitively concluded that the observed oxygen transfer factor is either due to biological activity or not simply an artifact of measurement/analysis techniques, the enhancement factor can be mathematically accounted for by either an increase in the KLa factor or the associated driving force using a proposed enhanced bubble theory. / Master of Science

I takt med att behovet av att minska utsläppen av växthusgasen ökar, ökar även intresset för negativa utsläpp. En lovande teknik för att uppnå negativa utsläpp är koldioxidlagring från biomassa, även kallad BECCS (Bio-Energy Carbon Capture and Storage). Trots teknologins mognad är de stora energibehoven vid lösningsmedelsregenerering ett hinder för storskalig implementering. I den här studien utforskas den relativt okända kinetiken för lösningsmedelsregenerering av kaliumkarbonat i ett steg för att optimera processen. Dessutom undersöks möjligheten att använda vanadin(V)oxid som katalysator för att förbättra desorptionshastigheten. Experimentella analyser utfördes i en sats-reaktor och gick ut på att undersöka förändringen av lösningsmedlets loading över tid genom regelbundna titreringar. Utöver detta undersöks den påverkan som temperatur och omrörning har på desorptionshastigheten. Experimenten utförs vid atmosfärstryck och temperaturer från 80°C till 100°C. Resultaten visade på god repeterbarhet trots svårigheter med temperaturöverskridningar. Desorptionshastigheten var lägre vid 80°C och 90°C än vid 100°C, men de logaritmiska hastighetskonstanterna följde inte en linjär relation mot temperaturinverserna vilket antyder att reaktionen är begränsad av massöverföring. Vidare påverkade inte användandet av en katalysator desorptionskinetiken märkbart, vilket än en gång antyder ett massöverföringsberoende. Slutligen visades ingen märkbar skillnad i desorptionshastighet trots olika omrörningshastigheter. Detta beror troligen på den redan höga massöverföringen som sker vid kokpunkten. Sammanfattningsvis bidrar denna studie med insikter för att förbättra effektiviteten hos regenereringen av lösningsmedel vid BECCS, vilket är avgörande för att motverka utsläppen och möta utmaningarna med klimatförändringarna.