DESIGN OF AMTEC TEST ASSEMBLY WITH OSC-RECOMMENDED THERMAL INSULATION, AND COMPARISON OF TEST RESULTS WITH ANALYTICAL PERFORMANCE PREDICTIONS

摘要

The analytical results presented in the preceding three papers require confirmatory tests. OSC had previously recommended detailed designs for electrically heated multicell test assemblies with prototypic side insulation, to be tested in vacuum. Such test assemblies permit direct efficiency measurements with heat losses prototypic of a real generator, without the use of guard heaters and questionable correction factors. Two such test assemblies were built by AMPS, Inc., one with four OSC-recommended cells described in a previous publication, and one with eight cells that simulated one half of a symmetrical 16-cell generator. Coupled thermal, electrical, and fluid flow analyses to determine the parametric performance of both assemblies were carried out by OSC. The four-cell assembly has been tested with a fixed heat input and a wide range of output voltages by AFPL. Comparison of analytical and experimental results described in the present paper revealed that the test data points tracked the analytical predictions well, which lends confidence in the validity of the analyses employed in OX's system studies described in the preceding paper. Only the data points at the highest voltages deviated somewhat from the analytical predictions. Those deviations may be partially due to still unquantified leakage currents. In addition, OSC's detailed analyses indicate that at the high voltages the tested cells had negative temperature margins in which the temperature of the evaporator exceeds that of the BASE tube. As explained, this can result in sodium condensation in the BASE tubes, leading to internal shorts in the multitube cell, which may account for the observed deviation between the analytical and experimental results at the high-voltage end of the test range.