Greg A. Whyatt

Compact fuel processors for fuel cell powered automobiles based on microchannel technology

One possible route to the development of compact fuel processing technology is through the application of microchannel technology. Also called micro chemical and thermal systems (micro-cats), microchannel technology is hardware that incorporates engineered microchannels that provide more rapid heat and mass transport, and therefore faster processing rates, than can be realised within systems employing conventional fluid passages. Hardware size is reduced without reducing the processing capacity of the system. Researchers at the US Department of Energys (DOEs) Pacific Northwest National Laboratory (PNNL) are currently developing microchannel heat-exchangers, reactors and separators as components for compact hydrogen generators for fuel cells. This effort, funded by the DOEs Office of Transportation Technology, is now demonstrating high performance in compact units. Over the past year, the project team has concentrated most of its effort on the demonstration of an overall microchannel steam reforming system, including four microchannel steam reformers and more than 24 microchannel heat-exchangers, which as a system are intended to provide both high energy efficiencies and high power densities. Work is also under way on other microchannel components that may ultimately find value within an automotive fuel processing system or within distributed power systems.

Cost Study for Manufacturing of Solid Oxide Fuel Cell Power Systems

Executive Summary Solid oxide fuel cell (SOFC) power systems can be designed to produce electricity from fossil fuels at extremely high net efficiencies, approaching 70%. However, in order to penetrate commercial markets to an extent that significantly impacts world fuel consumption, their cost will need to be competitive with alternative generating systems, such as gas turbines. This report discusses a cost model developed at PNNL to estimate the manufacturing cost of SOFC power systems sized for ground-based distributed generation. The power system design was developed at PNNL in a study on the feasibility of using SOFC power systems on more electric aircraft to replace the main engine-mounted electrical generators [Whyatt and Chick, 2012]. We chose to study that design because the projected efficiency was high (70%) and the generating capacity was suitable for ground-based distributed generation (270 kW). The electricity costs for a mass manufactured solid oxide fuel cell could be competitive with centralized power production plants with costs estimated to be in the

Diffusion and Leaching of Selected Radionuclides (Iodine-129, Technetium-99, and Uranium) Through Category 3 Waste Encasement Concrete and Soil Fill Material

0.07-0.08/kWh range based on a cost model using a standard approach to manufacturing solid oxide fuel cells. A process flow sheet was developed to understand the steps required to manufacture the units, as well as to estimate the materials, equipment, and labor required to make them. Equipment was sized to meet a production volume of 10,000 units per year. Appropriate material and equipment prices were collected. A sputtering approach was also examined using the model to project the decreases in costs associated with the process. The process not only reduces material costs but increases the power density of the fuel cell by 50%. The increased power density reduces the number of repeat units required to make up the 270 kW fuel cell stack. Stack costs decreased by 33%. However, due the BOP and the remainder of costs associated in power system manufacturing and installation, the cost of electricity was only reduced by

Demonstration of Energy Efficient Steam Reforming in Microchannels for Automotive Fuel Processing

0.002/kWh. In addition, to the 10,000 units per year production scale model was adjusted to reflect the costs of production at 50, 250, 1000 and 4000 units of production per year. Material prices were adjusted to reflect purchase levels. Machinery and labor were adjusted to reflect the production scale.

Anomalous water expulsion from carbon-based rods at high humidity

An assessment of long-term performance of Category 3 waste-enclosing cement grouts requires data about the leachability/diffusion of radionuclide species (iodine-129, technetium-99, and uranium) when the waste forms come in contact with groundwater. Leachability data were collected by conducting dynamic (ANS-16.1) and static leach tests on radionuclide-containing cement specimens. The diffusivity of radionuclides in soil and concrete media was collected by conducting soil-soil and concrete-soil half-cell experiments.

Breakup of a liquid rivulet falling over an inclined plate: Identification of a critical Weber number

A compact, energy-efficient microchannel steam reforming system has been demonstrated. The overall volume of the reactor is 4.9 liters while that of the supporting network of heat exchangers is 1.7 liters1. The reactor contains alternating reaction and combustion gas channels, arranged in crossflow, to provide heat to the reaction. Use of a microchannel configuration in the steam reforming reactor produces rapid heat and mass transport which enables fast kinetics for the highly endothermic reaction. The microchannel architecture also enables very compact and highly effective heat exchangers to be constructed. A network of microchannel heat exchangers allows recovery of heat in the reformate product and combustion exhaust streams for use in vaporizing water and fuel, preheating reactants to reactor temperature and preheating combustion air. As a result of the heat exchange network, the system exhaust temperatures are typically ∼50°C for the combustion gas and ∼130°C for the reformate product while the reactor is operated at 750°C. While reforming isooctane at a rate sufficient to supply a 13.7 kWe fuel cell, the system achieved 98.6% conversion with an estimated overall system efficiency after integration with WGS and PEM fuel cell of 44% (electrical output / LHV fuel). The efficiency estimate assumes integration with a WGS reactor (90% conversion CO to CO2 with 100% selectivity) and a PEM fuel cell (64% power conversion effectiveness with 85% H2 utilization for an overall 54% efficiency) and does not include parasitic losses for compression of combustion air.

Diffusion of Iodine and Rhenium in Category 3 Waste Encasement Concrete and Soil Fill Material

Three water adsorption-desorption mechanisms are common in inorganic materials: chemisorption, which can lead to the modification of the first coordination sphere; simple adsorption, which is reversible; and condensation, which is irreversible. Regardless of the sorption mechanism, all known materials exhibit an isotherm in which the quantity of water adsorbed increases with an increase in relative humidity. Here, we show that carbon-based rods can adsorb water at low humidity and spontaneously expel about half of the adsorbed water when the relative humidity exceeds a 50-80% threshold. The water expulsion is reversible, and is attributed to the interfacial forces between the confined rod surfaces. At wide rod spacings, a monolayer of water can form on the surface of the carbon-based rods, which subsequently leads to condensation in the confined space between adjacent rods. As the relative humidity increases, adjacent rods (confining surfaces) in the bundles are drawn closer together via capillary forces. At high relative humidity, and once the size of the confining surfaces has decreased to a critical length, a surface-induced evaporation phenomenon known as solvent cavitation occurs and water that had condensed inside the confined area is released as a vapour.

Microchannel reactors with temperature control

We have numerically investigated the breakup of a rivulet falling over a smooth inclined plate using the volume of fluid method. Rivulet breakup is a complex phenomenon dictated by many factors, such as physical properties (viscosity and surface tension), contact angle, inertia, and plate inclination. An extensive simulation was conducted wherein these factors were systematically investigated. Regimes for a stable rivulet and an unstable rivulet that leads to breakup are examined in terms of a critical value of the Weber number (Wecr) that delineates these regimes. A higher Wecr implies that a higher flow rate is required to maintain a stable rivulet. The impact of liquid properties is characterized by the Kapitza number (Ka). Variation of Wecr with Ka shows two trends depending on the Ka value of the liquid. Liquids with lower Ka values, corresponding to high viscosities and/or low surface tensions, show linear variation and smaller value of the critical Weber number. In other words, the lower the liquid...

Electrical Generation for More-Electric Aircraft using Solid Oxide Fuel Cells

Assessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e. sorption or precipitation). This understanding will enable accurate prediction of radionuclide fate when the waste forms come in contact with groundwater. A set of diffusion experiments using carbonated and non-carbonated concrete-soil half cells was conducted under unsaturated conditions (4% and 7% by wt moisture content). Spiked concrete half-cell specimens were prepared with and without colloidal metallic iron addition and were carbonated using supercritical carbon dioxide. Spikes of I and Re were added to achieve measurable diffusion profile in the soil part of the half-cell. In addition, properties of concrete materials likely to influence radionuclide migration such as carbonation were evaluated in an effort to correlate these properties with the release of iodine and rhenium.