Stephen M. Masutani

Hydrate formation on the surface of a CO2 droplet in high-pressure, low-temperature water

A comprehensive kinetic model of hydrate formation on the surface of a CO2 droplet in high-pressure, low-temperature water is developed. The model predicts that the hydrate layer formed is very thin and that the formation time is less than two seconds. These predictions are consistent with experimental observations. The mechanism of CO2 hydrate formation also is discussed.

The influence of droplet size and biodegradation on the transport of subsurface oil droplets during the Deepwater Horizon spill: a model sensitivity study

Abetter understanding of oil droplet formation, degradation, and dispersal in deepwaters is needed to enhance prediction of the fate and transport of subsurface oil spills. This research evaluates the influence of initial droplet size and rates of biodegradation on the subsurface transport of oil droplets, specifically those from theDeepwaterHorizon oil spill. A three-dimensional coupledmodel was employedwith components that included analyticalmultiphase plume, hydrodynamic and Lagrangianmodels. Oil droplet biodegradationwas simulated based onfirst order decay rates of alkanes. The initial diameter of droplets (10–300 μm) spanned a range of sizes expected fromdispersant-treated oil. Results indicate thatmodel predictions are sensitive to biodegradation processes, with depth distributions deepening by hundreds ofmeters, horizontal distributions decreasing by hundreds to thousands of kilometers, andmass decreasing by 92–99%when biodegradation is applied compared to simulationswithout biodegradation. In addition, there are twoto four-fold changes in the area of the seafloor contacted by oil droplets among scenarios with different biodegradation rates. The spatial distributions of hydrocarbons predicted by themodel with biodegradation are similar to those observed in the sediment andwater column, although themodel predicts hydrocarbons to the northeast and east of thewell where no observations weremade. This study indicates that improvement in knowledge of droplet sizes and biodegradation processes is important for accurate prediction of subsurface oil spills.

Stress Concentration Factors for Oblique Holes in Pressurized Thick-Walled Cylinders

Elastic stress concentration factors (SCFs) for internally pressurized thick cylindrical vessels with oblique circular crossholes are reported. Results of finite-element analyses for two wall ratios (k equal to 2.25 and 4.5) and a range of crosshole ratios (d from 0.1 to 0.5) show that SCFs sharply increase with the inclination a of the crosshole axis. These findings are consistent with earlier empirical design guidelines based on experimental investigations.

Preliminary assessment of the potential coupling between atmospheric temperature and CO2 concentration via ocean water overturning

A box model of the atmosphere and ocean mixed-layer, overlying an advective-diffusive deep ocean, is used to investigate the coupled effect of a changing rate of ocean water overturning on atmospheric temperature and carbon concentration. Under the assumption that overturning slows down with increasing temperatures, a long-term detrimental feedback is possible via enhanced greenhouse forcing, whereas the beneficial feedback (cooling trend) previously discussed by other authors seems to prevail in the short term (e.g., one to three centuries).

Diversity of Archaea Communities within Contaminated Sand Samples from Johnston Atoll

ABSTRACT A molecular 16S rRNA gene (SSU rDNA) analysis was performed for the determination of Archaea communities in polycyclic aromatic hydrocarbon (PAH)- and polychlorinated biphenyl (PCB)-contaminated sand samples obtained from Johnston Atoll. The objective of this study was to investigate Archaea community structure and phylogenetic diversity in a PAH- and PCB-contaminated marine environment that may potentially be intrinsically bioremediating these compounds. The clones obtained from this analysis were equally represented between the Crenarchaeota and Euryarchaeota phyla. This isolated marine environment is predominantly reef habitat, suggesting that the xenobiotic compounds introduced over time influenced the community structure of autochthonous Archaea. Phylogenetic diversity within these samples suggests that the resident Archaea populations were only distantly related to cultivated taxa and cloned sequences found in the public domain from both marine and terrestrial origins.

Influence of Ocean CO2 Sequestration on Bacterial Elemental Cycling

Publisher Summary Emissions of atmospheric CO 2 from combustion of fossil fuels and alterations in land use have contributed to increases in global surface air temperatures over the past century. Carbon dioxide in the atmosphere is a major greenhouse gas. Increasing atmospheric concentrations are believed to be responsible for a gradual warming of the Earth. International research teams are working on a variety of strategies to sequester CO 2 , and one of those efforts involves the deep ocean. An international collaboration to conduct a field experiment on CO 2 ocean sequestration was initiated in December 1997. The goal of this project is to evaluate the feasibility of transporting and containing anthropogenic CO 2 in the deep ocean. This chapter focuses on studies being conducted as part of the field experiment assessing the influence of decreased pH from CO 2 dissolution on bacterial production in the ocean. A preliminary analysis of the variation in bacterial production under different values of pH and temperature, conducted in July 1999, indicated that there was no measurable effect on the microbial population in the first 24 hrs of the experiment. However, there was a rapid decline in bacterial production with decreases in pH over a 96 hour incubation period. In addition, the impact of reduced pH was more pronounced when the bacteria were grown at warmer temperatures—that is, with a more rapid production rate.

Droplet Number Spectra in the Jet Atomization Regime

A previous model [1] to determine the number spectra of droplets generated by the injection of a fluid into another fluid is extended to cases of instantaneous disruption (near-zero jet breakup time). Under this scenario, droplets immediately form at the injection nozzle from unstable antisymmetric jet-surface waves. Resulting droplet characteristics only depend on the initial jet-surface disturbance. Full atomization is attained as the jet fluid is consumed by a series of successive droplet formation events that peel away the jet surface. The model is applied when the initial jet-surface disturbance is represented as broad-band white noise: each peel is characterized by a selected wave amplitude and high-cutoff wavenumber. Very good agreement was observed between model results and experimental droplet number spectra [2] obtained in the atomization regime.Copyright

International Field Experiment Nozzle and Large Tank Studies

Publisher Summary Two primary objectives of the International Field Experiment on CO2 Ocean Sequestration were to obtain data for comparison with model predictions of induced perturbations to sea water chemistry and to investigate the dynamics of buoyant plumes of dissolving liquid CO2 droplets rising in the density stratified deep ocean under the influence of currents. Design of the experiment and subsequent interpretation of the results required prior quantitative understanding of the dependence of liquid CO2 droplet size on injection parameters. The importance of CO2 hydrate formation with regard to droplet dissolution, droplet hydrodynamics, agglomeration, and system blockage and fouling also needed to be evaluated. Between 1998 and 2002, experiments were conducted by the project team in various pressure chamber facilities for this purpose. Because accurate, real-time, in situ measurement of CO2 droplet size would be difficult to implement during the field experiment, laboratory calibrations of the multi-orifice injection nozzles to be deployed were also performed. This chapter summarizes the primary results of these preparatory studies. The experiments were conducted in a number of facilities in the United States and Japan. The general configuration employed in the tests was a water tank into which liquid CO2 or an analog fluid, such as silicone fluid, was injected. Field experiment injection system components and diagnostics were also deployed in these tanks for testing.