Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter] Page: 21 of 33
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results of this analysis are shown in Figure 17. For this case the wall thickness was set at 0.015", a suitable
thickness for a smooth wall and the hot end temperature was set at 900 C.. As in the other separate radial
converter cases shown in this work, the performance with the DRW wall is slightly below that with a smooth
wall. Because the DRW surface requires, of virtually all incoming radiation, a 3-surface reflection, the
'effective' emissivity of the DRW wall surface, independent of its directionality, is e = 1 - (1 - Eo)3. The
intrinsic emissivity, E0, of the example presented, at E =0.10 thus would, for a DRW surface, correspond to
Ea = 0.035. If the scale of the corner DRW surfaces is sufficiently small, it may be feasible for the surface
to preferentially hold a liquid sodium film as has been shown to occur for the so called "Creare micro-
machined condenser."' The Creare surface is machined in such a way as to trap sodium through capillary
action. A liquid sodium film can have an intrinsic emissivity as low as 0.02 in the infrared region important
for the peak radiation transfer effect so the 0.035 value is plausibly within reach. On the simplest conclusion
based on these predicted values and for a 0.015" wall thickness, a DRW with an intrinsic E = 0.035 would
have an efficiency value 2% higher than for a smooth wall with the same effective emissivity. A thinner
wall and/or a shorter converter length would tend to increase this advantage further.
While a significantly lower emissivity might alter this conclusion, the sample DRC surfaces that we were
able to have made, would have emissivities approximately equivalent to those assumed for this plot.
Effect of Cell Wall Thickness to Radial Cell Performance
ec=0.01, Ewa1=0.1, Thot=900C, Cell Length 2.5"
W 17 . .$r 17
3 16 7 -- FPC Cewith WalThickness 0.015"
.- - - ... DRC Colwith WaflThickness 0.015'
15 / - --- FPC Cell with Wall Thickness 0.020"
--- --- DRC Cellwith Wail Thickness 0.020" 18
--- FPC Cet with Wall Thickness 0.015'
14 -- --- -"" ORC Cel with Wal Thickness 0.015"
J, ---"- FPC Cewith Wail Thickness 0.020"
13 --0-- DRC Cell with Wall Thickness 0.020"
2.0 2.5 3.0 3.5 4.0 4.5
Figure 17 Radial Converter Efficiency and Power as Affected by Changes in Converter Wall Thickness.
l 'Condenser Design for AMTEC Power Conversion', Christopher J. Crowley, Proceedings of the 26th
Intersociety Energy Conversion Engineering Conference, Vol. 4, p 456 (1991).
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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/m1/21/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.