Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2002-06-06
2003-05-13
Doerrler, William C. (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C060S520000
Reexamination Certificate
active
06560970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to regenerator-based oscillating-gas engines and refrigerators, and, more particularly, to thermoacoustic engines and refrigerators, including Stirling engines and refrigerators and pulse-tube refrigerators, and hybrids thereof.
BACKGROUND OF THE INVENTION
According to thermodynamic principles, acoustic power in a gas (a nonzero time average product of oscillating pressure and oscillating volumetric flow rate) is as valuable as other forms of work, such as electrical power, rotating shaft power, hydraulic power, and the like. For example, acoustic power can be used to produce refrigeration, such as in orifice pulse-tube refrigerators; it can be used to produce electricity, via linear alternators; and it can be used to generate rotating shaft power with a Wells turbine. Furthermore, acoustic power can be created from heat in a variety of heat engines such as Stirling engines and thermoacoustic engines. See, for example
Thermoacoustics: a unifying perspective for some engines and refrigerators
, G. W. Swift, to be published by the Acoustical Society of America in 2002; available in pre-publication format at http://www.lanl.gov/projects/thermoacoustics/Book/index.html.
Historically, Stirling's hot-air engine of the early 19th century was the first regenerator-based heat engine to use oscillating pressure and oscillating volumetric flow rate in a gas in a sealed system, although the time-averaged product of oscillating pressure and oscillating volumetric flow rate was not called acoustic power. Since then, a variety of related engines and refrigerators have been developed, including Stirling refrigerators, Ericsson engines, orifice pulse-tube refrigerators, standing-wave thermoacoustic engines and refrigerators, free-piston Stirling engines and refrigerators, and thermoacoustic-Stirling hybrid engines and refrigerators. Combinations thereof, such as the Vuilleumier refrigerator and the thermoacousically driven orifice pulse-tube refrigerator, have provided heat-driven refrigeration.
Much of the evolution of this entire family of acoustic-power thermodynamic technologies has been driven by the search for higher efficiency, greater reliability, and lower fabrication cost.
FIG. 1
shows one example of such a prior art regenerator-based engine: a thermoacoustic-Stirling hybrid engine, described in “Traveling Wave Device With Mass Flux Suppression,” G. W. Swift, U.S. Pat. No. 6,032,464, Mar. 7, 2000; “A thermoacoustic-Stirling heat engine,” S. Backhaus et al., Nature 399, 335-338 (1999); “A thermoacoustic-Stirling heat engine: Detailed study,” S. Backhaus et al., J. Acoust. Soc. Am. 107, 3148-3166 (2000). The engine delivers acoustic power
10
to an unspecified load (e.g., a linear alternator or any of the aforementioned refrigerators) to its right. High-temperature heat, such as from a flame or from nuclear fuel, is added to the engine at hot heat exchanger
12
, most of the ambient-temperature waste heat is removed from the engine at ambient heat exchanger
14
, and oscillations of the gas are thereby caused.
As in all of the regenerator-based engines listed above, the conversion of heat to acoustic power occurs in regenerator
16
, which is a solid matrix smoothly spanning the temperature difference between hot heat exchanger
12
and ambient heat exchanger
14
, and containing small pores through which the gas oscillates. The pores must be small enough that the gas in them is in excellent local thermal contact with the heat capacity of the solid matrix. Proper design of toroidal acoustic network
18
(including, principally, inertance
22
and compliance
24
) causes the gas in the pores of regenerator
16
to move toward hot heat exchanger
12
while the pressure is high and toward ambient heat exchanger
14
while the pressure is low. The oscillating thermal expansion and contraction of the gas in regenerator
16
, attending its oscillating motion along the temperature gradient in the pores, is therefore temporally phased with respect to the oscillating pressure so that the thermal expansion occurs while the pressure is high and the thermal contraction occurs while the pressure is low.
Those skilled in the art understand that another way to view the operation of the thermoacoustic-Stirling hybrid engine, and indeed all regenerator-based engines including all Stirling and traveling-wave engines, is that acoustic power {dot over (E)}
0
flows into the ambient end (i.e., the end adjacent to ambient heat exchanger
14
) of regenerator
16
, is amplified in regenerator
16
by the temperature gradient in regenerator
16
, and flows out of the hot end (i.e., the end adjacent to hot heat exchanger
12
) of regenerator
16
. Ideally, the acoustic-power amplification factor in regenerator
16
is equal to the ratio of hot temperature to ambient temperature, both temperatures being measured in absolute units such as Kelvin. In
FIG. 1
, the acoustic power {dot over (E)}
H
flowing out of the hot end of regenerator
16
through thermal buffer tube
72
splits into two portions {dot over (E)}
load
and {dot over (E)}
fb
at the resonator junction, with the required amount {dot over (E)}
0
flowing into the ambient end of regenerator
16
to provide the original acoustic power for amplification, and the rest {dot over (E)}
load
being delivered to the load. Hence, circulating acoustic power flows through regenerator
16
from ambient to hot and is amplified therein.
Two heat exchangers
12
,
14
, one adjacent to each end of regenerator
16
, are vital for the operation of such an engine. Both of these heat exchangers typically put the oscillating internal gas in intimate thermal contact with a steadily flowing external fluid such as water, air, or combustion products. Here, hot heat exchanger
12
must supply heat to the internal, thermodynamic working gas from an external heat source such as combustion products flowing from a burner. Similarly, ambient heat exchanger
14
must remove heat from the internal gas, rejecting that heat to an external heat sink such as a flowing stream of ambient-temperature water or air.
In common practice in heat exchanger design, both the internal gas and the external fluid are subdivided into many parallel portions that are interwoven, most often in cross flow. In a cross flow shell and tube heat exchanger, the internal gas often oscillates axially through a large number of parallel tubes, while the external fluid flows around the outside of the tubes perpendicular to the tube axes. In a finned tube heat exchanger, the external fluid may flow axially through a number of parallel tubes, while the internal gas oscillates around the finned outsides of the tubes perpendicular to the tube axes.
A similar description can be provided for a prior art thermoacoustic-Stirling hybrid refrigerator described in “Traveling Wave Device With Mass Flux Suppression,” G. W. Swift, et al., U.S. Pat. No. 6,032,464, Mar. 7, 2000; “Acoustic recovery of lost power in pulse-tube refrigerators,” G. W. Swift et al., J. Acoust. Soc. Am. 105, 711-724 (1999), shown in FIG.
2
. Similar to the thermoacoustic-Stirling hybrid engine shown in
FIG. 1
, essential features of the refrigerator are that acoustic power {dot over (E)}
0
must flow through regenerator
32
from ambient heat exchanger
42
to cold heat exchanger,
38
, acoustic power is thereby attenuated, and the pores of regenerator
32
must be small enough to provide excellent thermal contact between the gas and the solid matrix. Proper design of toroidal acoustic network
34
(including, principally, inertance
36
and compliance
38
) causes the gas in the pores of regenerator
32
to move toward cold heat exchanger
38
while the pressure is high and toward ambient heat exchanger
42
while the pressure is low. Acoustic power {dot over (E)}
C
moves through thermal buffer tube
82
to combine with the input power {dot over (E)}
drive
to return through toroidal acoustic network
34
. The oscillating entropy of the gas in regenerator
32
, attending its oscil
Doerrler William C.
The Regents of the University of California
Wilson Ray G.
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