THERMOACOUSTIC POWER SYSTEMS FOR SPACE APPLICATIONS Page: 2 of 8
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technology. The next two sections describe the design and construction of a 100-W class
TASHE and its initial tests using an acoustical resonator as a replacement for a linear alternator.
APPARATUS
The layout of the TASHE is shown in Figure 1. Essentially, it is composed of a looped flow path
filled with high-pressure helium gas. The loop contains the regenerator, heat exchangers, and
other ductwork necessary to force the gas in the regenerator to execute the Stirling cycle
(Backhaus, 2000). The mass of the first laboratory TASHE up to the resonator/alternator
interface is approximately 900 grams. The total mass was measured after several pieces of
instrumentation were installed, but before a final closure weld was made. At this 100-W scale,
the TASHE contributes less than 10% of the mass in the 10 W/kg space power system desired by
NASA (Mondt, 2001). Additional mass savings are expected in a flight design. If designed for a
flight system instead of laboratory convenience, much of the instrumentation and bolting flanges
would be removed. Also, much of the extraneous metal in the TASHE could be removed, and
aluminum could be substituted for several of the stainless steel components.
In Figure 1, the oscillating flow through the lower face of the secondary ambient heat exchanger
impinges on a piston of a linear alternator. Our initial tests use an acoustical resonator that
mimics the linear alternator (not shown). The reactive impedance of the resonator behaves like
the mass of the piston, and the dissipation in the resonator and an adjustable acoustic load
(Backhaus, 2000) duplicates the electrical load across the linear alternator's electrical terminals.
The oscillating flow path in the top of the loop is a small gap between two Inconel 625 parallel
plates forming the hot heat exchanger. High-temperature heat enters the system by solid
conduction through the top plate (maximum operating metal temperature of 650 C). There are
many small-diameter pins that are machined into the bottom plate and welded into holes through
the top plate. These do not serve to increase the heat transfer area. They are supports to keep the
thin top plate from bowing outward under the action of the internal pressure. In the test, the
high-temperature heat is generated by 4 electrically-powered heaters embedded in a nickel block
(not shown) cemented to the top surface of the hot heat exchanger.
Since the TASHE has no moving parts, its geometry can be very flexible. The design shown in
Figure 1 is chosen so that the hot end of the TASHE is flat and exposed on one end. This
configuration allows for a simple thermal and mechanical interface to the GPHS. In principle,
solid conduction from the GPHS to the hot heat exchanger could be used to couple the heat into
the TASHE. An interface of this type should not require any additional metal to transport the
heat to the TASHE or to support the GPHS. This provides an additional mass savings when the
converter is integrated with the rest of the power system. With no moving parts in the hot end of
the TASHE, creep of the hot end material induced by the high temperatures and high internal
pressure will not cause any performance issues due to the loss of a critical tolerance.
Proceeding down the right leg of the loop is the regenerator, which is composed of a stack of
stainless-steel screen housed in an Inconel 625 cylinder. Below the regenerator is the main
ambient heat exchanger. It is an aluminum cylinder with 48 long holes drilled through. In these
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Backhaus, S.; Toward, E. & Petach, M. THERMOACOUSTIC POWER SYSTEMS FOR SPACE APPLICATIONS, article, October 2001; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc715418/m1/2/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.