Source: {"pile_set_name": "USPTO Backgrounds"}

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.
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 xe2x80x9ctoroidalxe2x80x9d 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, xe2x80x9cTraveling Wave Device with Mass Flux Suppression, issued Mar. 7, 2000, to Swift et al. and U.S. Pat. No. 6,314,740, xe2x80x9cThermoacoustic System,xe2x80x9d 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 xe2x80x9ccascadexe2x80x9d 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 xe2x80x9cCascaded Thermoacoustic Devices,xe2x80x9d 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 xe2x80x9cA review of pulse tube refrigeration,xe2x80x9d 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; examples include a stream of indoor air to be cooled and dehumidified, or a stream of methane to be cooled and cryogenically liquefied. Hence, the typical heat exchanger in these engines and refrigerators must transfer heat between a steadily flowing xe2x80x9cprocess fluidxe2x80x9d stream and an oscillating xe2x80x9cworking gasxe2x80x9d stream that is the thermodynamic working substance of the oscillating-wave engine or refrigerator. The working gas is often pressurized helium gas. At small power levels, simple geometries such as stacks of copper screens suffice as heat exchangers, but at higher powers the thermal conductivity of solids is insufficient to carry the required heats, so that geometrically complicated heat exchangers must usually be used to bring the process fluid and working gas into intimate thermal contact.
M. Mitchell, xe2x80x9cPulse tube refrigerator,xe2x80x9d U.S. Pat. No. 5,966,942, Oct. 19, 1999, teaches a design to avoid a geometrically complicated heat exchanger for the ambient heat exchanger 76 (FIG. 4A) at the ambient end of the pulse tube 84 of an orifice pulse tube refrigerator. As illustrated in FIG. 4B, which is adapted from FIGS. 1 and 11 in the ""942 patent, ambient heat exchanger 76 and orifice 86 can be replaced by a dissipative heat-transfer loop 88 containing one or more (two are shown in FIG. 4B) fluidic diodes 92, 94 that convert some of the oscillatory power in the oscillating wave into circulating flow of the working gas around loop 88. The dissipation in fluidic