The Thermotunnel Energy Converter (TTC) can convert thermal energy (at 800' - 1500'K) to electricity without moving parts and has the potential for greater efficiency than currently available thermionic and thermoelectric converters. The thermotunnel coi. verter operates by imposing a temperature gradient on closely spaced emitter and collector surfaces. The temperature gradient generates a thermal emf and a current due to the wave mechanical tunneling property of electrons. The Phase I feasibility evaluation has included a literature survey to determine the appropriate construction material for a TTC device, an extrapolation of existing transport property data, the formulation of a computer model to predict performance characteristics, a parametric study of operating variables, and definition of the experimental needs to reduce the concept to practice in Phase II. The Phase I analysis indicates that highly ordered pyrolytic graphite (HOPG) is a suitable material for the TTC device. The HOPG is composed of uniform layers of graphite arranged in an ordered lattice structure. Thermal conduction losses are reduced and electron transport is facilitated by the intercalation of HOPG with cesium. Extrapolation of existing transport data indicates that HOPG intercalated with potassium has figures-of-merit on the order of 10-1 'K-1. A computer model based on quantum mechanical considerations predicts maximum thermal-to-electrical efficiencies of about 30% for the TTC. The analysis shows that high current densities can be achieve(' with the TTC at operating temperatures of 800' -1500 K. The Phase I results indicate that the thermotunnel converter has sufficient technical merit to warrant further research. The Phase 11 effort will concentrate on fabricating a prototype device, measuring its output performance, and refining the analytical model to determine the practical potential of the technology.Anticapated Results Potential Commercial Applications as described by the awardee:Development of the thermotunnel converter could provide a major advance in static energy conversion technology used in space power systems (both radioisotope and reactor). In addition, the TTC could be used for increasing the efficiency of industrial fossil-fuel cogeneration systems.
