Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2002-08-13
2003-10-28
Doerrler, William C. (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C060S520000
Reexamination Certificate
active
06637211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to oscillating wave engines and refrigerators, and, more particularly, to Stirling engines, Stirling refrigerators, orifice pulse tube refrigerators, thermoacoustic engines, thermoacoustic refrigerators, and hybrids and combinations thereof.
BACKGROUND OF THE INVENTION
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 working 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 in which simplicity, reliability, and low fabrication costs have been achieved by the elimination of moving parts, especially elimination of moving parts at temperatures other than ambient temperature.
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 hot heat exchanger
14
, ambient-temperature waste heat is removed from the engine at ambient heat exchanger
16
, and oscillations of working 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 working gas
18
oscillates. The pores must be small enough that working gas
18
in the pores is in is 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 working gas
18
throughout the system causes the working 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 working 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.
The absence of crankshafts and connecting rods contributes to the simplicity, reliability, and low fabrication costs of the free-piston Stirling engine.
FIG. 2
shows a “toroidal” 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. See, e.g., U.S. Pat. No. 6,032,464, “Traveling Wave Device with Mass Flux Suppression, issued Mar. 7, 2000, to Swift et al. and U.S. Pat. No. 6,314,740, “Thermoacoustic System,” issued Nov. 13, 2001, to deBlok et al. 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 working gas are thereby encouraged. Mass flux suppressor
50
acts to minimize time-averaged mass flux of the working gas and attendant heat loss. The oscillations deliver acoustic power to load
42
.
FIG. 3
shows a “cascade” thermoacoustic-Stirling hybrid engine comprising a standing-wave thermoacoustic engine and a Stirling engine in series, without any piston therebetween, as described in U.S. patent application Ser. No. 10/125,268 “Cascaded Thermoacoustic Devices,” G. W. Swift et al., filed Apr. 18, 2002. High-temperature heat is added at the two hot heat exchangers
52
,
54
; ambient-temperature waste heat is removed at the three ambient heat exchangers
56
,
58
,
62
; and oscillations of the working gas are thereby encouraged. The oscillations deliver acoustic power to a load
64
, such as a linear alternator or a pulse tube refrigerator, below the bottom of FIG.
3
. The conversion of heat to acoustic power occurs in regenerator
66
according to the same processes as described in the context of
FIG. 1
above. Stack
68
has larger pore sizes than regenerator
66
, and conversion of heat to acoustic power in stack
68
occurs by a similar process, but with some different details regarding time phasing, as described in the '268 patent application.
The simplicity, reliability, and low fabrication cost of the toroidal thermoacoustic-Stirling hybrid engine and of the cascade thermoacoustic-Stirling hybrid engine, compared to earlier Stirling engines, comes from the elimination of pistons previously needed.
FIG. 4A
shows a piston-driven orifice pulse tube refrigerator, as described for example by R. Radebaugh in “A review of pulse tube refrigeration,” Adv. Cryogenic Eng., volume 35, pages 1191-1205 (1990). The motion of piston
70
causes oscillations in the working gas throughout the refrigerator. Low-temperature heat is removed from a load by the refrigerator at cold heat exchanger
72
, and ambient-temperature waste heat is rejected from the refrigerator at the two ambient-temperature heat exchangers
74
,
76
, the larger of which is commonly called the aftercooler, i.e., heat exchanger
74
. Heat pumping up the temperature gradient occurs in regenerator
78
because the working gas in the pores of regenerator
78
is caused to move toward cold heat exchanger
72
while the pressure is high and toward aftercooler
74
while the pressure is low. This necessary time phasing between oscillating pressure and oscillating motion is created by acoustic impedance network
82
above pulse tube
84
, which sets the relative amplitudes and time phasing of the pressure and velocity at its entrance. Earlier Stirling refrigerators achieved the correct time phasing by means of a cold piston (whose motion was coordinated with that of the drive piston) instead of by means of the acoustic impedance network. However, the technical challenge of sealing around such a piston at cryogenic temperatures was severe. Hence, the simplicity, reliability, and low fabrication cost of the orifice pulse tube refrigerator compared to earlier Stirling refrigerators comes from the elimination of the cold piston.
Although much progress has recently been made in the elimination of moving parts from these oscillating-wave engines and refrigerators, the simplification of the heat exchangers offers a second opportunity for dramatic improvement in simplicity, reliability, and low fabrication cost, particularly in engines and refrigerators of high power. All engines and refrigerators must reject waste heat to ambient temperature, and the ambient temperature is often present as a flowing fluid stream, such as a fan-driven air stream or a flowing water stream. Engines must also accept heat from a source at a higher temperature, which may be in the form of a flowing stream of combustion products from a burner. Refrigerators must withdraw heat from a load at lower temperature, which is sometimes in the form of a flowing stream; exampl
Backhaus Scott N.
Swift Gregory W.
Doerrler William C.
Wilson Ray G.
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