STATIC ENERGY CONVERSION STUDIES TECHNICAL DOCUMENTARY REPORT NO. ASD-TDR-63-372

摘要

The general concept of the solid-state Nernst-effect generator is considered; the efficiency is calculated in terms of the materials figure of merit ZNT, defined analogously to the figure of merit for thermo-electric materials. The ideal Nernst material would be a semimetal with zero Hall coefficient. The value of ZNT is calculated theoretically for such a material and found to be limited by the phonon thermal conductivities, provided that the product of the magnetic field and carrier mobility (in lab units) is greater than 10°; otherwise, the finite field is the limiting factor. The optimum geometry of a Nernst generator is considered from the point of view of conserving magnetic field volume as well as obtaining the highest possible output power at convenient voltages. The electrical transport parameters for pyrolytic graphite and BiSbSn alloys were measured in magnetic fields up to 35 kilogauss; the thermal conductivity was measured at zero field. Pyrolytic graphite, in spite of its large thermal conductivity, had the highest ZNT:0.045 at 35 kilogauss and 670°K; it is estimated that ZNT will increase to 0.13 at 100 kilogauss. The specific weight of a pyrolytic graphite aerospace generator utilizing the magnetic field of a superconducting solenoid cooled by solid H2 is estimated to be as low as 95 lb/kw(e) (exclusive of the weight of the heat source, however) for a hot-side operating temperature of 1200°K.