Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter] Page: 12 of 33
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and the cap was removable. Two condenser surfaces were built, one was a simple, flat copper plate and the
other was a copper corner cube surface simulating a DRC. The surfaces of both were polished to improve
their reflectivity. Copper was chosen as the surface material to provide a reasonable simulation of the
infrared reflectivity of a wall wetted by a liquid sodium surface film. The mock up cell was put together and
evacuated to eliminate any effects of convective transfer and to prevent oxidation of the copper at the high
operating/test temperatures. The O-ring provided a removable vacuum seal and allowed for easy changeover
from flat plate to DRC 'condenser' surfaces. The hot zone of this cell was a produced by a cartridge heater
installed in a stainless steel heater well. To eliminate uncertainty in operating conditions between the flat
plate and the copper cube surface, the temperatures of the cold (condenser) end and the cell wall were also
controlled using Thermcraft electrical heaters and electronic temperature controllers.
To study the effect of the DRC, the 'condenser' temperature and the input power to the hot end were held
constant and the hot end temperature was monitored while the condenser type was changed. For a given heat
input, the hot end temperature in the mock cell with the DRC at the condenser end is expected to be higher
because the DRC redirects the radiation headed toward the cold end back to the source, the hot end in this
case. The advantage in terms of the difference in power required, with and without the DRC, to the keep hot
end at the same temperature was then investigated. The condenser temperature for a constant power source
with and without the DRC was also measured. For
the same hot end temperature, the condenser
temperature is expected to be lower with the DRC
inside the mock up cell than with the FPC.
Type-K thermocouples were used to monitor the
temperatures and for ease of power measurement, a
regulated DC power supply was used to drive the
heater input to the hot end. The results of the testing
are presented in the following. Table 7 shows the
type of cold end surface, cold end temperature, hot
end temperature, the power input to the hot end, the
difference in the temperatures between the flat and
DRC case and the reduction in power input in the
DRC case when the temperature difference between
the two cases is reduced to zero. Results are
presented for two different cold end temperatures and
3 different power inputs. In each of the five cases
listed in Table 7, the hot end temperature for the
DRC case was higher by 5 - 10 degrees and the -
difference increased with increases in power input.
The reduction in power required to bring the hot end
temperature for the DRC case back to the,,
temperature value observed for the flat plate was
about 5 - 7 %. Table 8 shows the change in cold end
temperature with the input power held constant. In
these two cases, FPC and DRC, the hot end
temperature is almost the same, but the condenser
temperature for the DRC is 5 - 6 degrees lower. Figure 7 Photograph of DRC 'Dummy' Test Cell,
Showing both FPC and DRC-End Caps.
There is a relatively simple method for
determining the relative contributions of parasitic heat losses that are contributed by thermal conduction and
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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/m1/12/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.