Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2002-04-18
2003-12-09
Doerrler, William C. (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
Reexamination Certificate
active
06658862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to oscillating wave engines and refrigerators, and, more particularly, to thermoacoustic engines and refrigerators, including Stirling engines and refrigerators and their hybrids.
BACKGROUND OF THE INVENTION
According to thermodynamic principles, acoustic power in a gas—a nonzero time average product of oscillating pressure and oscillating volume flow rate—is as valuable as other forms of work such as electrical power, rotating shaft power, and hydraulic power. 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, e.g., 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.
Historically, Stirling's hot-air engine of the early 19th century was the first heat engine to use oscillating pressure and oscillating volume flow rate in a gas in a sealed system, although the time-averaged product thereof 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 thermoacoustically 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 efficiencies, greater reliabilities, and lower fabrication costs.
FIGS. 1
,
2
, and
3
show some prior art engine examples.
FIG. 1
shows a free-piston Stirling engine
10
integrated with a linear alternator
12
to form a heat-driven electric generator. High-temperature heat, such as from a flame or from nuclear fuel, is added to the engine at the hot heat exchanger
14
, ambient-temperature waste heat is removed from the engine at the ambient heat exchanger
16
, and oscillations of the gas
18
, piston
22
, and displacer
24
are thereby encouraged. The oscillations of piston
22
cause permanent magnet
26
to oscillate through wire coil
28
, thereby generating electrical power which is removed from the engine to be used elsewhere.
The conversion of heat to acoustic power occurs in regenerator
32
, which is a solid matrix smoothly spanning the temperature difference between hot heat exchanger
14
and ambient heat exchanger
16
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 solid matrix. Proper design of the dynamics of moving piston
22
and displacer
24
, their gas springs
34
/
36
, and gas
18
throughout the system causes the gas in the pores of regenerator
32
to move toward hot heat exchanger
14
while the pressure is high and toward ambient heat exchanger
16
while the pressure is low. The oscillating thermal expansion and contraction of the gas in regenerator
32
, 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 free-piston Stirling engine, and indeed all regenerator-based engines including all Stirling and traveling-wave engines, is that acoustic power flows into the ambient end of the regenerator, is amplified in the regenerator by a temperature gradient in the regenerator, and flows out of the hot end of the regenerator. Ideally, the heat exchangers at the ends of the regenerator are essentially transparent to this acoustic power flow. Ideally, the acoustic-power amplification factor in the regenerator is equal to the ratio of hot temperature to ambient temperature, both temperatures being measured in absolute units such as Kelvin.
In the free piston Stirling engine of
FIG. 1
, the acoustic power flowing out of the hot end of regenerator
32
is absorbed from the gas by the hot end of displacer
24
and immediately delivered to the gas at the opposite end of displacer
24
. There, some of the acoustic power flows into the ambient end of regenerator
32
to provide the original acoustic power for amplification, and the rest is delivered by gas
18
to piston
22
. Hence, circulating acoustic power flows through the regenerator from ambient to hot temperatures and is amplified therein.
FIG. 2
shows another regenerator-based engine: a thermoacoustic-Stirling hybrid engine delivering acoustic power to an unspecified load
42
(e.g., a linear alternator or any of the aforementioned refrigerators) to the right. High-temperature heat, such as from a flame, from nuclear fuel, or from ohmic heating, is added to the engine at hot heat exchanger
44
, most of the ambient-temperature waste heat is removed from the engine at main ambient heat exchanger
46
, and oscillations of the gas are thereby encouraged. The conversion of heat to acoustic power occurs in regenerator
48
, which is structurally and functionally identical to that described in
FIG. 1
for the free piston Stirling engine. Proper design of the acoustic network (including, principally, the feedback inertance
52
and compliance
54
) causes the gas in the pores of regenerator
48
to move toward hot heat exchanger
44
while the pressure is high and toward main ambient heat exchanger
46
while the pressure is low. The oscillating thermal expansion and contraction of the gas in regenerator
48
, 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.
As in the free piston Stirling engine, another way to view the operation of the thermoacoustic-Stirling hybrid engine is that acoustic power {dot over (E)}
C
flows into the ambient end of regenerator
48
, is amplified by the temperature gradient in regenerator
48
, and flows out of the hot end of regenerator
48
. In
FIG. 2
, the acoustic power {dot over (E)}
H
flowing out of the hot end of the regenerator splits into two portions {dot over (E)}
fb
and {dot over (E)}
res
at the resonator junction
40
, with the required amount {dot over (E)}
C
flowing into the ambient end of regenerator
48
to provide the original acoustic power for amplification, and the rest {dot over (E)}
res
being delivered to the right to the unspecified load
42
. Hence, again, circulating acoustic power flows through regenerator
42
from ambient to hot and is amplified therein.
FIG. 3
shows a standing-wave thermoacoustic engine delivering acoustic power to an unspecified load
62
to the right. The standing-wave thermoacoustic engine creates acoustic power from heat in a somewhat different way than do regenerator-based engines such as those shown in
FIGS. 1 and 2
. High-temperature heat, such as from a flame, from nuclear fuel, or from ohmic heating, is added to the standing-wave thermoacoustic engine at hot heat exchanger
64
, ambient-temperature waste heat is removed from the engine at the ambient heat exchanger
66
, and oscillations of the gas are thereby encouraged. The conversion of heat to acoustic power occurs in stack
68
, which is a solid matrix smoothly spanning the temperature difference between hot heat exchanger
64
and ambient heat exchanger
66
and containing pores through which the gas oscillates. The pores in stack
68
must be significantly larger than those in a regenerator operating under similar conditions, because excellent local
Backhaus Scott N.
Gardner David L.
Swift Gregory W.
Doerrler William C.
The Regents of the University of California
Wilson Ray G.
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