Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter] Page: 16 of 33
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Phase I - Conclusions
The DRC concept appears to work. The two experimental test cells built and run give results consistent with
the full thermal analyses we have carried out. The analysis predicts a significant reduction in the parasitic
thermal losses in AMTEC cells, and it would presumably also work in other applications for which radiation-
based thermal transfer is important. For the cylindrical geometries examined, the maximum reduction in
thermal transfer is expected to be limited to approximately 20%. The Phase 1 program funding and time
limits did not permit investigation of the more complex geometries involved in the Series 3 AMTEC cell
designs. While a 20% reduction in parasitic losses DRC Performance
appears to be the limiting value, a reduction of-12
% is predicted for a first cut analysis of current cell 0.12 ----
In a cell designed to operate at 30% efficiency, the 0 . . -0-0-8
reduction of 12% inparasitic thermal losses leads to . . . ._ .
an improvement in cell efficiency to about 31% if a
one considers only the overall thermal loss effect. E 0.04 - --
Under design constraints which arise at these -- --
efficiency levels, modifications which can add 1% to E
efficiency, merit consideration, particularly when a o.0 -- - -
number of modifications can act independently with
each adding several percent to the efficiency. (0.02)0 4 8 12 16 20 24 28
A second effect, however, may be more significant. . DRC Number
In operation of vapor-vapor AMTEC cells, a Figure 11 Relationship Between Improved Efficiency and
limitation in power output for a given heat input DRC Number.
surface temperature arises due to temperature
gradients along the BASE tubes. As the tubes are heated from the 'bottom' (as seen for example in Fig. 1),
and heat is withdrawn along their length by the sodium working fluid and radiated from their upper ends, the
upper end of the tubes is colder than the bottom end which is closest to the hot surface. The lowered
temperature reduces the output toward the tube end and lowers overall performance. The DRC offers the
potential to reduce the thermal radiation loss from the 'top' ends of the tubes, to level the temperature
distribution and thereby increase the power output. Increased power output has a larger effect on efficiency
than a comparable decrease in the parasitic losses. This effect may contribute to the high performance
observed for the PX-DRC cell. A similar effect on the BASE tube temperature profile can be achieved by
interposing radiation shields between the hot zone and the condenser, but such shielding invariably produces
a restriction in the sodium flow path, increases the vapor pressure at the cathode and reduces the power
output in that way. Use of a DRC, which accomplishes the radiation-based thermal transfer reduction
without benefit of constricting shields may offer a very significant advantage.
4. Phase H Work
For intermediate systempower levels of order 100's of watts, converter design configurations are heavily
influenced by the need for efficient combustor performance. The radial or donut converter configuration
offers a central cavity for combustion and a modular capability in that converters can be stacked, preserving
the central combustion space while increasing the system power level in defined increments. A schematic
diagram of the radial converter design is shown in Figure 12 and a photograph is shown in Figure 13. This
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Hunt, Thomas K. Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter], report, September 10, 2001; United States. (https://digital.library.unt.edu/ark:/67531/metadc717643/m1/16/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.