Robert M. Wham

Mass Transport from Single Droplets in Imposed Electric Fields

Electric field effects on mass transfer involving droplets in a 2-ethyl-hexanol medium are studied. Single water droplets are observed under the influence of both steady and pulsed electric fields. Droplet oscillations result in the latter case, enhancing the continuous phase mass transfer coefficient. These data are compared with results from both nonoscillating mass transfer and theoretical models. 8 refs., 8 figs.

Wall effects on flow past fluid spheres at finite Reynolds number : wake structure and drag correlations

Abstract Following the pioneering works of Leal and coworkers, a detailed report is made on the dynamics of recirculating wakes that form at finite Reynolds number Re due to vorticity accumulation at the rear of a fluid sphere that is either suspended in a tube by an upflowing fluid ( the fluidized drop problem ) or falling in a tube ( the falling drop problem ). The axisymmetric, steady flow of a Newtonian fluid past the fluid sphere is determined by finite element analysis using a consistent penalty formulation. By way of example, the flow past a fluid sphere that is falling in a tube for which the ratio of the tube radius to the drop radius 1 λ = 5 undergoes remarkable transitions when the ratio of the viscosity of the drop to that of the ambient fluid, κ, varies over a narrow range. When κ ≤ 2.75, no wake forms behind the sphere as Re increases. When 3 ≤ κ Re = Re c (1) , grows, and eventually disappears as Re rises above a certain amount Re c (2) . Remarkably, when κ = 3, these critical Reynolds numbers are as low as Re c (1) = 51 ± 1 and Re c (2) = 77 ± 1. When κ ≥ 10, it is shown by using as many as 46,000 velocity degrees of freedom that the detached eddy attaches to the drop when Re exceeds a critical value, Re ≥ Re c ∗ , which was heretofore unknown. Whereas only a single, large-primary-eddy is present inside the drop when Re c ∗ , a second but much smaller-secondary-eddy also forms inside the drop upon attachment. Two new correlations are developed that account for the effects of a tube wall and finite fluid inertia on drag for fluidized and falling droplets. Moreover, in contrast to related correlations of others for fluid spheres that are placed in an infinite expanse of ambient fluid, the new correlations are valid over the entire range of Reynolds numbers considered.

Effect of slurry heating rate on short-contact-time coal liquefaction

Abstract The effects of changes in heating rate of a coal/solvent slurry on conversions to pyridine-soluble material have been examined. Dramatic increases in conversions were observed when the coal/solvent mixture was maintained at a temperature of 589 K for 10 min before heating to reaction conditions of 700 K for 5 min. In particular, conversion increased from 32.0 to 76.7 wt % and the ratio of oils to preasphaltenes increased by a factor of four. The temperature range for the greatest effect is observed to be 550–595 K while 450 K shows no change in conversion. The mechanism is thought to be chemisorption of the solvent or solvent occlusion which would increase the concentration of hydrogen donor in the coal matrix thus affecting the reaction environment. Additional studies to further define the details of the programmed heating rate as well as explore the mechanism are needed.

Electric Field-Enhanced Coalescence of Liquid Drops

Abstract A fundamental understanding of drop coalescence and growth is of importance to separations and materials processing. Under external driving forces, drops dispersed in an immiscible fluid collide and coalesce with each other due to their relative motion. As a result of drop coalescence, the average drop size in the dispersion increases over time, improving the separation process. Collision and coalescence of spherical, conducting drops bearing no net charge in dilute, homogeneous dispersions are considered theoretically under conditions where drop motion results from gravity settling and electric field-induced attraction. A trajectory analysis is used to follow the relative motion of two drops and predict pairwise collision rates. A population dynamics equation is then solved to predict the time evolution of the size distribution and the average size of drops. The results show that the rate of drop collision and growth can be increased significantly by applying an electric field, in accord with fu...

A Simple Kinetic Model for the Alpha Radiolysis of Water Sorbed on NpO2

Abstract Alpha radiolysis experiments have been performed on NpO2 that contains sorbed moisture. A high dose rate to the sample was achieved by spiking it with ~7000 ppm 244Cm during preparation. Pressure monitoring of sample containers showed that a low, steady-state pressure plateau is reached. This plateau indicates a situation in which the forward reaction (i.e., radiolysis of water) is equal to the back reaction (i.e., the reformation of H2O). In this technical note, a simple kinetic model that can be used for predicting steady-state pressures under practical conditions is described.

Reestablishing the Supply of Plutonium-238

The US Department of Energy has presented a plan to use existing reactors at Oak Ridge National Laboratory (ORNL) and Idaho National Laboratory (INL) and processing facilities at ORNL, modified as needed, to produce Pu. The basic capabilities that need to be put into place to produce new Pu are (1) neptunium storage and transport, (2) target fabrication, (3) target irradiation, and (4) chemical processing of irradiated targets to recover Pu. Neptunium currently in storage at INL will be shipped to ORNL during CY 2015. The target design has progressed to a prototypic target design that is expected to be used for production. Initial chemical processing experiments have shown successful recovery of neptunium and plutonium, but overall product purity has not been as high as desired.

Constant Rate Production: DOE Approach to Meeting NASA Needs for Radioisotope Power Systems for Nuclear-Enabled Launches

The use of radioisotope power systems (RPSs) for nuclear-enabled National Aeronautics and Space Administration (NASA) missions is made possible through a long-standing arrangement between the Department of Energy (DOE) and NASA. The requirements for the power system come from NASA, but DOE performs the procurement, fueling, testing, and delivery. A challenge has been interplay between the schedule for RPS availability from DOE versus the schedule for competitively selected missions. By mutual agreement, the actual operations to procure an RPS and prepare it for fueling have always been delayed until the final selection of a mission. The timeline for a New Frontiers–class mission leaves approximately 5 to 6 years from the time of final mission selection to the actual launch date. The number of RPSs used for a New Frontiers–class mission can be one to three units. If one or two units are needed, the timeline from the decision point to the launch date is a challenge, but it is achievable. The activities taking place include manufacturing the power system, producing the fuel, and performing the assembly/testing and delivery operations. If the mission selected requires three RPSs, the logistics of accomplishing all activities during the 5–6 years is problematic. The challenge involves obtaining the necessary resources for plutonium production, heat source production, and assembly/testing operations. Typically, the time between RPS-enabled missions requires staffing reduction down to 65%–75% of peak staffing levels to reduce costs. Coupling the ~2 year duration needed for hiring, training, and obtaining the appropriate security clearances for the required staff with the requirement for the RPS to arrive at Kennedy Space Center 6 months before the launch erodes much of the 5–6 years available to comfortably support the use of three RPSs. To provide better support for NASA RPS missions, a different approach for the production of heat sources was devised—constant rate production. This involves a higher level of base capability at DOE national laboratories to provide a stabilized workforce. This will enable 10–15 heat sources to be produced annually and placed into a stable intermediate form to enable storage for up to several years leading to quick production of general purpose heat source modules when a mission is selected. The upfront production of 238Pu is maintained so material is constantly in the pipeline. Production of key specialized components is also maintained using this model.

Plutonium-238 supply project — Additional processing enabling power for future NASA missions

For more than five decades, Radioisotope Power Systems (RPSs) have enabled space missions to operate in locations where the Suns intensity is either too dim, obscured, or otherwise inadequate for solar power or other conventional power-generation technologies. The natural decay of the radioisotope plutonium-238 (238Pu) provides the heat source used by an RPS to generate electricity (as well as heat to keep key subsystems warm) for National Aeronautics and Space Administration (NASA) missions such as Voyagers 1 and 2, the Cassini mission to Saturn, the New Horizons flyby of Pluto, and the Mars Curiosity rover. The United States has not produced new 238Pu since the late 1980s. RPS-powered missions have continued since then using existing 238Pu inventory managed by the U.S. Department of Energy (DOE), including material purchased from Russia. NASA and DOE have determined that a new domestic supply is needed to ensure the continued availability of RPSs for future NASA missions. Using funding provided by NASA since 2011, DOE is currently executing a project to reestablish a 238Pu supply capability using its existing facilities and reactors. The project, known as the Plutonium-238 Supply Project (PSP) is led by the DOE Oak Ridge National Laboratory (ORNL). This paper will provide an overview of the PSP approach, its progress to date, and the potential benefits to NASA of missions that could be enabled by the new production of 238Pu.