CN100427848C - A Thermoacoustic Driven Pulse Tube Refrigerator System - Google Patents

Abstract

The invention discloses a thermoacoustic driven pulse tube refrigerator system. It includes a pulse tube refrigerator and a traveling wave thermoacoustic engine. The pulse tube refrigerator has a refrigerator regenerator and a pulse tube connected in sequence. The traveling wave thermoacoustic engine has a traveling wave loop and a straight resonant path. The connected DC control components, main cooler, engine regenerator, heater, heat buffer pipe, sub cooler, feedback loop, and the sound power transmission pipe are connected between the room temperature end of the refrigerator regenerator and the engine traveling wave loop, It is characterized in that an inertial phase-adjusting tube is connected between the hot end of the pulse tube and the resonant straight path of the thermoacoustic engine. The invention changes the previous way that the end of the inertial tube is closed with a blind plate or an air reservoir, and directly connects the end of the inertial tube with the thermoacoustic engine. In addition to realizing the phase modulation function, the inertial tube also transmits part of the sound power transmitted from the hot end of the refrigerator pulse tube back to the engine, realizing the recovery of sound power, and improving the efficiency of the thermoacoustic driven pulse tube refrigerator system.

Description

A Thermoacoustic Driven Pulse Tube Refrigerator System

technical field

The invention relates to a thermoacoustic driven pulse tube refrigerator system, which is suitable for coupling between a thermoacoustic engine and a pulse tube refrigerator.

Background technique

The thermoacoustic effect is a phenomenon of mutual conversion between heat and sound, that is, the time-averaged thermodynamic effect in the sound field. A thermoacoustic heat engine is essentially a device that converts or transmits heat energy and sound energy through the thermoacoustic effect. The thermoacoustic heat engine can establish a reasonable phase relationship between the velocity and pressure of the oscillating fluid without external mechanical means. Therefore, no mechanical transmission components are required, which greatly simplifies the structure of the system. According to the direction of energy conversion, thermoacoustic effects can be divided into two categories: one is to use heat to generate sound, that is, heat-driven acoustic oscillation; the other is to use sound to generate heat, that is, sound-driven heat transfer. As long as certain conditions are met, the thermoacoustic effect can occur in the traveling wave sound field, the standing wave sound field and the combination of the two.

According to different sound field characteristics, thermoacoustic engines are mainly divided into three types: standing wave type, traveling wave type and standing wave traveling wave hybrid type. In the traveling wave sound field, the velocity wave and the pressure fluctuation have the same phase, but in the standing wave sound field, the two phases are 90° apart. Since the phase difference between the velocity and the pressure in the standing wave field is 90°, when the gas velocity at the plate stack is at the positive maximum, the gas moves in the plate stack channel to the limit of the hot end at high speed, skimming the positive half cycle motion Most of the displacement in (that is, skimming most of the temperature gradient), therefore, this process should be the most intense time period of heating. But this is also the time when the pressure changes the most. The gas is compressed rapidly during this period. The compression process and the heating process occur at the same time. From a thermodynamic point of view, it is not conducive to compression or heating. The hysteresis of heat transfer, this thermal hysteresis makes when the gas moves slowly to absorb heat, there is already a considerable temperature difference between the gas and the solid medium, resulting in a large irreversible loss. But we should also see that if there is no thermal hysteresis, the standing wave sound field cannot generate sound work theoretically, it generates sound work at the cost of reducing thermodynamic efficiency; similarly, when the gas undergoes the expansion process, it simultaneously experiences the The cooling process of high-speed movement to the low-temperature end, such a process is neither conducive to expansion nor heat release. From the above process analysis, it can be seen that in order to realize the conversion of heat and work in the standing wave field, it is necessary to use plate stacks with large spacing to form thermal hysteresis, so that part of the heating occurs after the compression process, and part of the cooling occurs after the expansion process. However, the irreversible thermodynamic process caused by the limited temperature difference heat transfer between gas and solid greatly reduces the efficiency of the whole device.

The gap size of the regenerator packing in the traveling wave thermoacoustic engine is much smaller than the thermal penetration depth of the gas, which realizes the ideal thermal contact between the solid and the gas, and the heating and cooling are approximately reversible isothermal processes. At the same time, velocity and pressure are in phase in the traveling wave sound field. At the regenerator of a traveling wave thermoacoustic engine, when the gas is compressed rapidly, the gas travels at a small velocity across the small temperature increment on the regenerator, so it can be compressed efficiently, while during heating, The gas has the largest positive velocity and crosses the largest temperature growth range, while the pressure changes very little at this time, so it can achieve an efficient endothermic expansion process, which is undoubtedly very important for the conversion of heat energy to sound work from a thermodynamic point of view. Favorable; similarly, when the gas enters the pressure reduction stage, the gas movement speed is small, and it passes through the small temperature range of the thermoacoustic regenerator, so it is beneficial to the pressure reduction. When the gas pressure drops to a certain level, the speed becomes larger and the temperature The change is rapid, the gas releases heat to the regenerator, and the gas undergoes expansion and then releases heat. From the above analysis, it can be seen that the thermoacoustic conversion process in the traveling wave sound field proceeds naturally without the participation of irreversible processes, and the small hydraulic radius of the regenerator can ensure the isothermal heat transfer between the gas and the regenerator. Therefore, the traveling wave thermoacoustic The engine theoretically performs a reversible thermoacoustic conversion process, which can obtain higher thermodynamic efficiency than a standing wave thermoacoustic engine. Generally speaking, there is no thermoacoustic engine with a pure traveling wave sound field, and the traveling wave thermoacoustic engines currently under development are all traveling wave standing wave hybrid thermoacoustic engines. Therefore, the thermoacoustic engine whose thermoacoustic core components are in the loop structure is usually called a traveling wave thermoacoustic engine.

A pulse tube refrigerator is generally composed of a regenerator, a pulse tube, a heat exchanger at the cold and hot ends, a deflector, and a phase adjustment mechanism. According to the air supply method, it can be divided into Stirling type and G-M type. The former adopts a valveless connection between the compressor and the refrigerator, and the latter has a high-low pressure switching valve between the compressor and the refrigerator. According to the arrangement of regenerator and pulse tube, pulse tube refrigerator can be divided into linear type, U type and coaxial type. In addition, in order to obtain a lower refrigeration temperature, multi-stage refrigerators have also appeared. At present, thermoacoustic-driven pulse tube refrigerators mostly use single-stage pulse-tube refrigerators, and researchers have begun to use thermoacoustic-driven multi-stage pulse-tube refrigerators. Since the cooling capacity of a pulse tube refrigerator is directly related to the magnitude of the sound work passing through the pulse tube, and the magnitude of the sound work depends on the intensity and phase of the pressure fluctuation and velocity fluctuation, the phase modulation mechanism is very important for the pulse tube refrigerator.

The development of pulse tube refrigerators is almost the history of the improvement and development of phase modulation methods. In 1963, Gifford and Longsworth of the United States invented the pulse tube refrigerator by using the cooling effect generated by the periodic pressure oscillation of the gas on a thin-walled empty tube closed at one end, called the basic pulse tube refrigerator. The single-stage refrigerator obtained at that time The minimum refrigeration temperature is 124K. In 1966, Gifford and Longsworth proposed the surface heat pump principle to explain the refrigeration principle of the pulse tube refrigerator. The theory points out that the cyclic compression and expansion of any gas microgroup in the pulse tube will produce a large temperature gradient, and the heat will be gradually transferred from the cold end to the hot end due to the thermal contact between the air mass and the wall surface of the pulse tube, resulting in a cooling effect.

In 1984, Mikulin and others in the former Soviet Union made a major innovation on the hot end of the basic pulse tube refrigerator, introducing a gas store and small holes to form a small hole gas store type pulse tube refrigerator. The gas enters the pulse tube from the load heat exchanger, and enters the gas storage through the small hole and the hot end heat exchanger after being pushed. During the deflation process, not only the gas remaining in the pulse tube returns to the low-pressure gas source through the load heat exchanger and regenerator, but also part of the gas in the gas storage returns to the pulse tube for expansion. This is not only good for taking away the heat of compression during the compression (inflation) process, but also increases the amount of working fluid in the pulse tube, greatly improving the cooling capacity of the pulse tube refrigerator. Mikulin uses air as the working medium, and the minimum refrigeration temperature reaches 105K. It is regarded as a milestone in the history of pulse tube refrigerator development. In 1986, American scholar Radebaugh et al. made a further improvement to Milkulin’s scheme, moving the small hole from between the pulse tube and the hot end heat exchanger to between the gas storage and the hot end heat exchanger, and replacing the small hole with a needle valve. Helium is used as the working fluid, and the minimum no-load refrigeration temperature is 60K. This is a Stirling-type (reversible) pulse-tube refrigeration cycle. In order to explain the principle of the small hole pulse tube refrigerator, Radebaugh et al. based on the analysis of the enthalpy flow theory, came to the important conclusion that the phase difference between the mass flow and the pressure wave in the pulse tube is the key factor affecting the cooling capacity. Based on phase theory, a series of novel phase shifters are proposed to improve the performance of pulse tube refrigerators.

In 1990, on the basis of theoretical analysis, Zhu Shaowei and Wu Peiyi proposed a new type of pulse tube refrigerator, called a two-way inlet pulse tube refrigerator. It is based on the small hole type, and a gas distributor is used to connect the hot end of the pulse tube and the hot end of the regenerator. This scheme has obtained the lowest cooling temperature of 42K. The analysis pointed out that in the small hole type pulse tube refrigerator, a part of the gas oscillates back and forth in the pulse tube, neither enters the gas storage through the small hole, nor enters the regenerator from the cold end heat exchanger, consumes work but does not produce Refrigeration effect, called reactive gas. Two-way air intake is to set the second air inlet, and the part of the gas that does not participate in refrigeration is directly introduced into the hot end of the pulse tube from the outlet of the compressor without passing through the regenerator, thereby increasing the cooling capacity of the regenerator per unit mass of gas. Now, pulse tube refrigerators all over the world are widely adopting this scheme no matter in single-stage or multi-stage structure, which is regarded as another milestone in the development history of pulse tube refrigeration.

In 1988, Matsubara of Nihon University proposed a dual-piston pulse tube refrigerator. Because this structure can recover the expansion work, reduce the irreversible loss caused by small holes, and improve the performance of the refrigerator. Its disadvantage is that an expansion piston is added, which reduces the reliability of the pulse tube refrigerator. In 1993, Matsubara and others developed a four-valve pulse tube refrigerator, which removed the small holes and the gas reservoir. The phase modulation effect of this structure is not realized by the small hole gas reservoir but by another pair of switching valves connecting the hot end of the pulse tube and the intake and exhaust pipes of the compressor.

In 1992, Zhou Yuan and others from the Cryogenic Center of the Chinese Academy of Sciences proposed a new arrangement called a multi-channel bypass pulse tube refrigerator. A small hole is connected between the middle part of the pulse tube and the middle part of the regenerator, allowing a part of the gas in the regenerator to enter the middle temperature point of the pulse tube to generate a cooling effect.

In 1994, when Kanao et al. in Japan were studying small-hole high-frequency pulse tube refrigerators, they found that replacing the small-hole valve with a capillary tube of appropriate size could improve the performance of the pulse tube refrigerator. From then on, the researchers started the inertial tube phase modulation theory. Research. In 1996, Godshalk et al. clearly pointed out that the long-necked tube uses the inertial effect of the high-frequency oscillating air flow to control the phase relationship between the pressure wave and the velocity wave in the study of using a thermoacoustic engine to drive a pulse tube refrigerator. The inertial tube is an ideal phase modulation method suitable for the Stirling-type pulse tube refrigerator. It not only has a strong phase modulation ability, but also enhances the pressure ratio in the pulse tube without producing a DC effect. However, for micro-pulse tube refrigerators whose compressor discharge volume is less than 2cm ³ , the ideal phase cannot be obtained only by using inertial tubes.

In addition, there are various phase adjustment methods such as internal phase adjustment type, thermal expansion type, increasing gas storage pressure method, and double valve and double small hole type, all of which improve the performance of pulse tube refrigerators to varying degrees.

In summary, the phase relationship between the pressure wave and the velocity wave in a pulse tube refrigerator is a key factor affecting its performance. Regenerator losses are one of the major losses in a pulse tube refrigerator. From the perspective of thermoacoustics, the purpose of phase modulation is to achieve the traveling wave phase at the regenerator of the pulse tube, that is, the pressure wave and the velocity wave are in the same phase. At present, whether it is a Stirling type or a G-M type pulse tube refrigerator, the cooling efficiency in the 80K temperature range has reached or even exceeded the level of the Stirling refrigerator and the G-M refrigerator.

The pulse tube refrigerator driven by a thermoacoustic engine is a high-frequency Stirling type pulse tube refrigerator. At present, the phase adjustment method of small hole gas storage and two-way air intake is mostly used. The two-way air intake can reduce the refrigeration temperature to a certain extent and improve the performance of the pulse tube refrigerator. However, the existence of two-way air intake leads to a loop in the pulse tube refrigerator, which is easy to cause a time-averaged unidirectional mass flow, so that the axial temperature distribution of the pulse tube and the regenerator deviates from linearity. This unidirectional mass flow places an additional heat load on the pulse tube refrigerator, resulting in a reduction in cooling capacity. Therefore, many researchers have begun to turn their attention to inertial tube phase modulation. In theory, inertial tubes have stronger phase modulation capabilities, so that the pulse tube refrigerator can reach the traveling wave phase at the regenerator. At present, when the inertial tube is used for phase adjustment, one end of the inertial tube is connected to the hot end of the pulse tube, and the other end can be closed with a blind plate or connected to a gas reservoir. Since the diameter of the inertial tube is generally small, if the end is closed with a blind plate or connected to the gas bank, the acoustic work transmitted from the hot end of the pulse tube will be completely consumed, which will reduce the performance coefficient of the entire thermoacoustic driven pulse tube refrigeration system.

Contents of the invention

The object of the present invention is to provide a thermoacoustic driven pulse tube refrigerator system.

It includes a pulse tube refrigerator and a traveling wave thermoacoustic engine. The pulse tube refrigerator has a refrigerator regenerator and a pulse tube connected in sequence. The traveling wave thermoacoustic engine has a thermoacoustic engine traveling wave loop and a resonant straight path. The thermoacoustic The engine traveling wave loop has DC control components, main cooler, engine regenerator, heater, thermal buffer pipe, secondary cooler, feedback loop connected in sequence, the room temperature side of the refrigerator regenerator and the thermoacoustic engine traveling wave An acoustic power transmission tube is connected between the loops, and the feature is that an inertial tube is connected at the tee between the traveling wave loop of the thermoacoustic engine and the straight resonant path.

The invention changes the previous way that the end of the inertial tube is closed with a blind plate or an air reservoir, and directly connects the end of the inertial tube with the thermoacoustic engine. Therefore, in addition to realizing the phase modulation function, the inertial tube can also transfer a part of the sound power transmitted from the hot end of the pulse tube refrigerator back to the thermoacoustic engine, realizing the recovery of sound power, and improving the thermal energy to a certain extent. Acoustically driven pulse tube refrigerator system efficiency.

Description of drawings

The accompanying drawing is a schematic diagram of a thermoacoustic driven pulse tube refrigerator system.

Detailed ways

The thermoacoustic driven pulse tube refrigerator system shown in the accompanying drawing is composed of a traveling wave thermoacoustic engine, a pulse tube refrigerator and other accessories. A pulse tube refrigerator has a refrigerator regenerator 1 and a pulse tube 2 connected in sequence, and a traveling wave thermoacoustic engine has a traveling wave loop and a resonant straight path 10, wherein the traveling wave loop has a DC control component 3 and a main cooling circuit connected in sequence. 4, engine regenerator 5, heater 6, heat buffer pipe 7, sub-cooler 8, feedback loop 9. The hot end of the regenerator of the pulse tube refrigerator is connected to the thermoacoustic engine through a pipeline 11 with an inner diameter of about 8 mm, which is used to transmit sound power from the thermoacoustic engine into the pulse tube refrigerator. A slender tube with an inner diameter of about 1 to 4 mm and a length of 2 to 5 m is connected to the hot end of the pulse tube refrigerator, and its end is directly connected to the engine pipeline. This slender tube is the inertia tube 12 . The inertia tube 12 can be a stainless steel tube, a copper tube, or even a plastic hose. In the schematic diagram of the connection method shown in the accompanying drawing, the end of the inertial tube is connected to the tee between the thermoacoustic engine loop and the straight resonant path. When the engine and the pulse tube refrigerator start to work, the sound power is input from the regenerator of the pulse tube refrigerator, and heat transfer occurs in the regenerating heat, thereby generating a cooling effect at the cold head of the pulse tube refrigerator. At this time, the inertia tube has two functions. One is that its diameter and length determine the phase of the pressure fluctuation and velocity fluctuation in the pulse tube refrigerator, ensuring that the regenerator of the pulse tube refrigerator is in the traveling wave phase; The sound work transmitted from the hot end of the pulse tube is fed back to the thermoacoustic engine, which improves the efficiency of the thermoacoustic driven pulse tube refrigerator system.

Claims (1)

1. A thermoacoustic driven pulse tube refrigerator system, which comprises a pulse tube refrigerator and a traveling wave thermoacoustic engine, and the pulse tube refrigerator has a refrigerator regenerator (1) and a pulse tube (2) connected in sequence, and the row The wave thermoacoustic engine has a thermoacoustic engine traveling wave loop and a resonant straight path (10), wherein the thermoacoustic engine traveling wave loop has a DC control component (3), a main cooler (4), and an engine regenerator ( 5), heater (6), thermal buffer tube (7), sub-cooler (8), feedback loop (9), there is sound power transmission between the room temperature end of the regenerator of the refrigerator and the traveling wave loop of the thermoacoustic engine The pipe (11) is characterized in that: an inertial pipe (12) is connected at the tee between the thermoacoustic engine traveling wave loop and the resonant straight path, and the other end of the inertial pipe is connected to the hot end of the pulse tube.

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