Michael Schuller

In-Plane Thermal Conductivity in Thin Carbon Fiber Composites

The objective of this study was to determine whether fiber type, fiber angle, and filler material affected the in-plane thermal conductivity of thin (7-15 mils thickness) carbon fiber composites. Two sets of samples were tested: low thermal conductivity samples made with polyacrylonitrile-based fibers (k = 6.8 W/m .K) in Fiberglast epoxy resin, and high thermal conductivity samples fabricated with coal-pitch-based fibers (k = 620 W/m . K) in cyanate ester resin. Samples were fabricated from 0/90 woven cloths and warped to obtain a range of fiber-pattern angles from 25/ - 25 to 65/ - 65. The filler effect on thermal conductivity was evaluated on additional samples prepared with 10% volume fraction of graphite powder in the matrix. Thermal conductivity of the low thermal conductivity samples was in the range of 15-20 W/m . K and showed up to a 15 % improvement when the angle of the fibers was varied. High thermal conductivity samples showed thermal conductivities between 60 and 150 W/m . K, with an improvement up to 60% when the angle of the fibers relative to the heat flux direction was changed from 0/90 to 25/-25. The samples with graphite powder did not show any enhancement in thermal performance. As potential alternatives, unidirectional tape and eGrafs Spreadershield® foils were also tested, showing good thermal performance.

Vacuum testing of high efficiency multi-base tube AMTEC cells: February 1997–October 1997

The next generation of PX-series AMTEC cell (PX-3, PX-4, and PX-5 series) has been studied. Experimental data showed that improvements made to the cell design have continually increased electric power output and conversion efficiency. Work included analysis of efficiency, investigation of the effects of negative temperature margin, evaluation of performance degradation and performance comparisons between cells. To date, the best PX-series cells tested at AFRL/VSDV provided an electric power output of 5.05 watts (PX-4C) and a conversion efficiency of 15% (PX-3A). Steady and continuous improvement in design and test results imply that design goals of 6 watts and 22% efficiency per cell will be surpassed.

Molten Salt-Carbon Nanotube Thermal Energy Storage for Concentrating Solar Power Systems Final Report

We demonstrated that adding nanoparticles to a molten salt would increase its utility as a thermal energy storage medium for a concentrating solar power system. Specifically, we demonstrated that we could increase the specific heat of nitrate and carbonate salts containing 1% or less of alumina nanoparticles. We fabricated the composite materials using both evaporative and air drying methods. We tested several thermophysical properties of the composite materials, including the specific heat, thermal conductivity, latent heat, and melting point. We also assessed the stability of the composite material with repeated thermal cycling and the effects of adding the nanoparticles on the corrosion of stainless steel by the composite salt. Our results indicate that stable, repeatable 25-50% improvements in specific heat are possible for these materials. We found that using these composite salts as the thermal energy storage material for a concentrating solar thermal power system can reduce the levelized cost of electricity by 10-20%. We conclude that these materials are worth further development and inclusion in future concentrating solar power systems.

Advanced electrodes for AMTEC

Texas A&M University has begun an investigation of materials and fabrication methods which will improve AMTEC electrode performance. The study currently involves gathering data on materials which meet the basic requirements of operating in an AMTEC cell, and sorting out candidates possessing characteristics conducive to efficient AMTEC operation. An initial assessment has shown Iridium as a promising metal electrode candidate. Sodium-containing double-oxides, with melting temperatures above AMTEC operating temperatures, including NaNbO3 and Na2Ti3O7, have been identified as possible electrode dopants, to enhance the sodium conductivity of an electrode. Photo-deposition and Evaporative-deposition will be investigated further as electrode fabrication techniques.

Innovative Schematic Concept Analysis for a Space Suit Portable Life Support Subsystem

Conceptual designs for a space suit Personal Life Support Subsystem (PLSS) were developed and assessed to determine if upgrading the system using new, emerging, or projected technologies to fulfill basic functions would result in mass, volume, or performance improvements. Technologies were identified to satisfy each of the functions of the PLSS in three environments (zero-g, Lunar, and Martian) and in three time frames (2006, 2010, and 2020). The viability of candidate technologies was evaluated using evaluation criteria such as safety, technology readiness, and reliability. System concepts (schematics) were developed for combinations of time frame and environment by assigning specific technologies to each of four key functions of the PLSS -oxygen supply, waste removal, thermal control, and power. The PLSS concepts were evaluated using the ExtraVehicular Activity System Sizing Analysis Tool, software created by NASA to analyze integrated system mass, volume, power and thermal loads. The assessment resulted in the Texas Engineering Experiment Station recommending to NASA an evolution path from the existing PLSS to a long duration, low mass PLSS suitable for Martian missions.

Development, evaluation, and design applications of an AMTEC converter model

Issues associated with the development of an alkali metal thermal‐to‐electric conversion (AMTEC) converter model that serves as an effective design tool were investigated. The requirements and performance prediction equations for the model were evaluated, and a modeling methodology was established. It was determined by defining the requirements and equations for the model and establishing a methodology that Thermal Desktop, a recently improved finite‐difference software package, could be used to develop a model that serves as an effective design tool. Implementing the methodology within Thermal Desktop provides stability, high resolution, modular construction, easy‐to‐use interfaces, and modeling flexibility.

Improved sodium pool temperature control in a sodium exposure test cell

In this paper we discuss a design change to the sodium exposure test cell (SETC) developed by JPL for evaluating alkali metal thermal to electric conversion (AMTEC) electrodes. This change, the addition of an antechamber to contain the sodium pool, was made to improve the control of the sodium pool temperature in the test, in order to improve the consistency and repeatibility of the electrode performance measurements. Experimental results and post test analysis showed that the change was very successful in controlling the location and temperature of the sodium pool. Using heater tape capable of higher temperature operation, we were able to duplicate electrochemical impedance spectroscopy results from earlier SETCs. These results indicate that when earlier SETC sodium pool temperatures were measured at 210-240/spl deg/C, the effective sodium pool temperature was actually 385-400/spl deg/C. The change in the overall length of the experimental apparatus also moved the specimens into a region in the oven with a flatter temperature profile, reducing the temperature gradient between the samples from 50-60/spl deg/C to 10-20/spl deg/C.

Performance measurements of advanced AMTEC electrodes

These results are from sodium exposure test cell experiments with advanced AMTEC electrodes performed at Texas AM the minority of the results are for ceramic electrodes. Initial results for iridium and titanate electrodes have been good, but degrade with time.

Trough type concentrating solar power plant cost assessment with component scaling

A detailed numerical and empirical systems analysis tool was developed which incorporated component scaling cost equations. It was benchmarked against the known data from the Andasol-1 plant in Spain, and then used to evaluate the effect of changes in the size of the solar field, the thermal energy storage system, and the power block on the levelized cost of electricity (LCOE) for the plant. The simulation result indicates that when the power plant capacity increases from 50 MW to 400 MW, the LCOE decreases by 32%. Also, the model’s results indicate that an oversized field and thermal energy storage tanks help to lower the LCOE.© 2012 ASME

AMTEC material studies

Texas A&M University, in conjunction with Advanced Modular Power Systems, is performing a series of material studies on key components of an alkali metal thermal to electric conversion (AMTEC) cell for the NASA outer planets power system program. These studies involve SEM, x-ray mapping, EDS, and WDS analysis of AMTEC components from unexposed (as built) samples, from sodium exposure tests, and from operating cells, specifically PX-4C and PX-5B run at the Air Force Research Lab’s Phillips Research Site. Findings are still prelimary, but indicate that recrystallization regions seen in the oven samples are an artifact of excess sodium and oxygen levels in those tests, more potassium is present than expected, and that diffusion bonding between the current collector and electrode takes place.