Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter] Page: 5 of 33
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2. Background of Directed Reflectivity Condenser (DRC) Concept
The basic concept behind the DRC approach is to use the properties of 'corner cube' reflectors to return
thermal radiation from a hot source directly back to it. It is desirable for many applications to minimize
thermal radiation transfer from hot surfaces to cooler regions. In general circumstances, such radiation
leaves the hot surface, proceeds to cooler surfaces, often by a series of reflections and absorptions. Often
the radiation is partially or mostly reflected from the first surfaces it encounters and then is progressively
absorbed at the subsequent surfaces it encounters during multiple reflections. This principle is the basis for
the design of standard "black body" radiation standards which use the opening of a highly polished,
reflecting, narrow angle cone as the standard. In order to minimize transfer from a hot surface, it is desirable
for the first surface the radiation encounters to preferentially reflect that radiation directly back to the hot
source. So-called "corner cube" or "retro" reflectors have precisely this property and at optical frequencies
they are used for high efficiency reflectors in applications from highway signs to retro-reflectors for laser
ranging of the moon's surface. In the DRC approach investigated here, we apply retro-reflectors to internal
surfaces of AMTEC converters upon which the thermal radiation from the AMTEC hot zone falls in order
to send the maximum amount of thermal energy back to the source, without scattering or reflecting it to other
absorbing surfaces. Even highly specular reflection of thermal
radiation from any other surface configuration is unlikely to
return the radiation to the source. whose radiation loss it is
desired to reduce.
A corner cube or retro-reflector consists of the intersection,
at right angles, of 3 planar reflecting surfaces. The geometry
of such a corner is such that incoming rays are reflected back in
the direction from which they come. The returning ray will be
translated laterally by an amount determined by the distance
from the cube apex at which it first hits the corner. In the
corner cube array shown in Figure 1, a light ray impinging on
any point within the opening of any one of these corners
undergoes 3 reflections from intersecting planar surfaces and is
returned as a ray parallel to the incoming ray. It is generally
desirable to minimize the lateral translation of the rays and this
can be done by reducing the pitch (distance between the apices)
of the surface. Figure 2 shows a schematic drawing of a planar
array of corner cube reflectors of the sort used in the initial
3. Summary of the Results of Phase I Work
The overall Phase 1 program objective has been to determine
whether it is feasible to use a Directed Reflectivity Condenser
(DRC) in an AMTEC system to provide enhanced electric
power density, efficiency and reliability for space power
applications. If these enhancements can be confirmed, it
should be possible to establish the potential utility of the DRC
concept for enhancement of the efficiency of AMTEC
cells/systems suitable for a wide variety of practical space and
terrestrial applications. Specific task objectives were to
Figure 1 Light Ray Path at Retroreflector.
Figure 2 Array of Corner Cube Reflectors.
LIGHT REFLECTION PATH
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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/m1/5/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.