Merrill Anderson Wilson

Reference electrode placement and seals in electrochemical oxygen generators

We report measurements and numerical calculations of the potential distribution within a thin solid electrolyte near active (current-bearing) electrodes. These studies demonstrate two principles: (1) In a flat-plate geometry, the electrolyte is approximately equipotential beyond a distance of about three electrolyte thicknesses from the edge of the active electrodes. (2) If one of the active electrodes on one side of the electrolyte extends beyond the other, it strongly biases the potential of the electrolyte far from the active region. We show that these effects make it challenging to measure electrode overpotential accurately on thin cells. However, we also show that these effects can be useful for protecting glass-ceramic seals in an oxygen generator stack against electrochemical degradation/delamination.

Electrochemical Oxygen Separation Using Solid Electrolyte Ion Transport Membranes

A novel process employing solid electrolyte-based ion-transport membranes enables the production of high-purity oxygen at elevated pressure from a feed stream of ambient pressure air. This technology exploits the theoretically infinite selectivity of oxygen ion migration through a dense ceramic electrolyte membrane under the influence of an externally applied electrical potential. The solid electrolyte is derived from cerium oxides with dopants added to enhance both ion transport and membrane processability. The oxidation and reduction reactions are promoted by the use of porous perovskite electrodes, which together with the electrolyte form an electrochemical cell. Stacks comprising multiple cells in a planar configuration have demonstrated excellent electrochemical performance and stability, mechanical integrity. and the capacity to produce high-purity oxygen over thousands of hours. An oxygen generator based on this technology must incorporate an integrated thermal management system air mover, power supply, and control systems.

Emissive Membrane Ion Thruster Concept

Experiments conducted on solid-state ionic membranes that convert atoms into ions that can in turn be extracted into energetic beamlets and thereby produce thrust are described. The capability of ionizing and transporting ions is shown to be both rapid (over 10 mA/cm 2 ) and efficient (of order 1 eV/ion). Although similar in appearance to cesium contact sources, solid-state ionic membrane devices are shown to operate successfully at lower temperatures (400 to 700 °C) thus making them much more efficient than cesium- based devices. The process of extracting the ions by field emission is shown to limit the extracted ion current density. The need to select an emissive surface material/propellant ion combination with a low work function is suggested. Based on successful demonstrations of ion extraction, the Emissive Membrane Ion Thruster is proposed and shown to offer the potential for substantial reductions in ion thruster system cost and complexity as well as improvements in scalability and reliability compared to existing ion thruster designs

Ion Emissive Membranes for Propulsion Applications

Experiments show electrostatic thrusters with components such as the discharge chamber or acceleration channel, solenoid or permanent magnets, hollow cathode, and keeper can be replaced by a simple, propellant‐selective, solid‐state, ion‐conducting membrane (Wilbur et al., 2007; Wilbur, Wilson, and Williams, 2005). In addition, analyzes show these membranes can be shaped, structured, and assembled into integrated thruster systems that will operate at much greater thrust densities and thruster efficiencies than those for state‐of‐the‐art, Hall and ion thrusters (Wilbur, Farnell, and Williams, 2005). The implications of these findings are revolutionary and promise an electrostatic propulsion system much less massive, more reliable, and less costly than ion and Hall thruster systems as they can be fabricated readily using traditional ceramic manufacturing techniques. The status of the Emissive Membrane Ion Thruster (EMIT) concept is described and recent measurements are used to estimate the performance of a ...

Fluid/Thermal Analysis of High Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This paper presents fluid flow and heat transfer study of a high temperature heat exchanger and chemical decomposer. The decomposer will be used as a part of the plant for hydrogen production. The decomposer is manufactured using fused ceramic layers that allow creation of channels with dimensions below one millimeter. The main purpose for this study is to increase thermal performance of the decomposer which can help to intensify sulfuric acid decomposition rate. Effects of using various channel geometries of the decomposer on the pressure drop are studied as well. A three-dimensional computational model is developed for the investigation of fluid flow and heat transfer in the decomposer. Several different geometries of the decomposer channels such as straight channels, ribbed ground channels, hexagonal channels, and diamond-shaped channels are examined. Based on results of the calculation, the recommendations for the improved design of the decomposer are obtained.Copyright

Design Considerations for High Temperature, Ceramic Heat Exchangers

The recent developments in the energy industry have kindled renewed interest in producing energy (alternative fuels and electricity) more efficiently. This has motivated the development of higher temperature cycles and their associated equipment. In this paper we will discuss several design configurations coupled with the inherent properties of preferred ceramic materials to assess the viability and design reliability of ceramic heat exchangers for next generation high temperature heat exchangers. These analyses have been extended to conceptually compare the traditional shell and tube heat exchanger with shell and plate heat exchangers. These analyses include hydrodynamic, heat transfer, mechanical stress and reliability models. It was found that ceramic micro-channel heat exchanger designs proved to have the greatest reliability due to their inherent mechanical properties, minimal thermo-mechanical stresses while improving the performance efficiency in a compact footprint.Copyright

Compact, Ceramic Heat Exchangers and Microchannel Devices: Joining and Integration

Many energy conversion systems use thermal processes to convert chemical energy to mechanical or electrical energy. In these situations, microchannel components can be used to make heat exchangers and microreactors to make processes more energy efficient. Ceramic heat exchangers permit operation at higher temperatures than with other materials. Additionally, compact heat exchangers are highly efficient and cost-effective. This talk will describe principles of design, methods of fabrication, and joining methods for ceramic, compact heat exchangers for integration of such heat exchangers into practical applications. Particular emphasis will be placed on methods for joining silicon carbide to itself and the results of a novel bonding method that can be performed art relatively low temperatures in air. The mechanical behavior, at room temperature and elevated temperature, of this bonding method will be compared to that of diffusion bonded joints.

Viability of Ceramic High Temperature Heat Exchangers in NGNP Applications

The recent developments in the energy industry have kindled renewed interest in producing energy more efficiently. This has motivated the development of higher temperature cycles and their associated equipment. In this paper we will discuss several design configurations coupled with the inherent properties of preferred ceramic materials to assess the viability and design reliability of ceramic heat exchangers for next generation high temperature heat exchangers. These analyses have been extended to conceptually compare the traditional shell and tube heat exchanger with shell and plate heat exchangers. These analyses include hydrodynamic, heat transfer, mechanical stress and reliability models applicable to an Intermediate Heat Exchanger (IHX) and Process Coupling Heat Exchangers. It was found that ceramic micro-channel heat exchanger designs proved to have the greatest reliability due to their inherent mechanical properties, minimal thermo-mechanical stresses while improving the performance efficiency in a compact footprint.Copyright

Optimization of Micro-Channel Features in a Ceramic Heat Exchanger

It has been proposed that compact ceramic heat exchangers can be used for high temperature, corrosive applications. This paper discusses the development and optimization of a microchannel heat exchanger for the decomposition of sulfuric acid as part of the hydrogen producing sulfur iodine thermo-chemical cycle. The optimization process combines thermal-hydraulic and structural modeling (UNLV) with empirical performance and validation testing (Ceramatec, Inc.). Within the designs investigated, the micro-channel features were varied to adjust the cross-sectional profiles and the “tortuosity” of the serpentine flow paths to increase the thermal performance while maintaining low pressure drops and thermo-mechanical stresses within system. The results of these coupled optimization efforts and the associated overall performance improvement will be reported.Copyright

Dynamic Flow of Micro-Channels in a Ceramic Heat Exchanger

This poster presents a comparison of flow between four possible designs for ceramic high temperature heat exchanger that is used as a sulfuric acid decomposer which may be used for hydrogen production within the sulfur iodine thermo-chemical cycle. The decomposer is manufactured using fused ceramic layers that allow creation of tailored micro-channels with dimensions below one millimeter. The baseline design uses parallel straight channels with rectangular cross sections. This design will be compared with other proposed designs where varying cross sections and serpentine flow paths can improve the heat transfer with minimal effects on the pressure drop. Measurements have been taken using a dynamic pressure mat that has been calibrated to allow for precise measurements of the flow data. Results of this research are used as a basis for investigation optimal design of the decomposer that can provide maximum thermal performance while maintaining low pressure drops and thermo-mechanical stresses within system.