Pulse tube refrigerator with phase adjustment using equiangular spiral structure

Abstract

The present invention discloses a pulse tube refrigerator that uses an equiangular spiral structure for phase adjustment. The invention comprises a compressor, a precooler, a regenerator, a cold-end heat exchanger, a pulse tube, a hot-end heat exchanger, a tapered cavity, and a phase adjustment device. The phase adjustment device comprises a wall panel, a cover plate, a sealing plate, and an adjustable baffle. The wall panel is a long rectangular metal sheet coiled into an equiangular spiral shape. Two cover plates are fixed to the end faces of the space enclosed by the wall panel, forming an equiangular spiral cavity. The cavity opening is sealed by a sealing plate. Multiple adjustable baffles are arranged within the large end of the cavity to form a valve. One end of the regulating tube connects to the center starting position of the equiangular spiral cavity, and the other end connects to the tapered cavity. Gas enters the equiangular spiral cavity through the regulating tube, with the flow path gradually increasing. The small portion of the flow path serves as an inertia tube, while the large, closed portion serves as a gas reservoir. This overcomes the drawback of traditional pulse tube refrigerators requiring a separate inertia tube and gas reservoir, making it more suitable for acoustic power transmission and pulse tube refrigerator phase adjustment.

Description

Technical Field

[0001] The present invention belongs to the field of high-frequency pulse tube cryogenic refrigerators, and in particular relates to a pulse tube refrigerator that adopts an equiangular spiral structure for phase adjustment. Background Art

[0002] Future space technology requires new cryogenic refrigerators with high efficiency, low cost, and long life to extend the operational life of detectors and sensor systems. However, achieving high reliability and long-life operation of cryogenic refrigerators has been a research challenge. Cryogenic researchers have devoted significant effort to this end for decades. Existing mechanical refrigerators, such as Stirling and GM refrigerators, all have displacers that move in the low-temperature zone. The resulting wear, vibration, and contamination limit their long-term, maintenance-free operation. The greatest advantage of the Stirling pulse tube refrigerator is its simple structure and lack of moving parts at low temperatures, resulting in reliable operation, low vibration, and a long life. However, due to its fatal weakness: low thermodynamic efficiency, prototypes could only achieve a minimum cooling temperature of 124K, hindering its application since its invention. It was not until the introduction of a small orifice and gas reservoir at the hot end of the pulse tube that breakthrough progress was achieved, and the pulse tube refrigerator has gained worldwide attention. The inertia tube, as the phase adjustment element of the pulse tube refrigerator, adjusts the phase between the mass flow and pressure wave of the working fluid in the regenerator, thereby optimizing the performance and work-to-heat conversion efficiency of the pulse tube refrigerator. Conventional inertia tubes usually use metal tubes and gas reservoirs to connect for phase adjustment, but there are problems with insufficient phase adjustment capability or the inability to provide the phase adjustment angle required by the pulse tube refrigerator.

[0003] Stirling-type pulse tube refrigerators typically use an inertia tube and a gas reservoir as the phase adjustment mechanism, and circuit simulation is used to analyze the inertia tube. The inertia tube's phase adjustment capability is highly sensitive to the tube's geometric parameters. Analysis and experiments have shown that the inertia tube can adjust the phase over a wide range, enabling its use in high-power pulse tube refrigerators while also meeting the requirements for appropriate phase adjustment in smaller pulse tube refrigerators. The gas in the inertia tube undergoes alternating flow. Using circuit analogy, the gas flow resistance can be represented as a resistance characteristic, the working fluid's inertia as an inductive reactance, and the internal void volume as a capacitive reactance.

[0004] The inertia tube impedance can be expressed as: Re represents the Reynolds number of the working medium flowing in the tube, represents the mass flow rate, L represents the length of the inertia tube, ρ represents the density of the working gas, and D represents the inner diameter of the inertia tube.

[0005] The inductive reactance of the inertia tube can be expressed as:

[0006] The capacitance and resistance of the inertial tube are expressed as:

[0007] The capacitance and resistance of the gas reservoir are expressed as:

[0008] Therefore, the total impedance of the inertia tube can be expressed as:

[0009] The phase angle between the mass flow at the inlet of the inertia tube and the pressure wave is:

[0010] From formula (6), we can see that the phase modulation capability of the inertial tube is closely related to the impedance, capacitive reactance, and inductive reactance of the inertial tube. However, traditional inertial tubes use a single metal tube with a fixed length and diameter for phase modulation. Their phase modulation capability is low in flexibility and cannot be coordinated with phase modulation when parameters such as frequency and input power vary.

[0011] The invention patent with the patent number CN201710116594.6 discloses a pulse tube refrigerator, which includes a compression unit, a transmission pipe, a regenerator unit, a connecting pipe, a pulse tube unit, an inertia tube unit and a gas reservoir connected in sequence. The inertia tube unit includes at least two inertia tubes connected in parallel with each other; the parallel inertia tubes are used for phase adjustment, and the flow resistance is reduced by adding branches, thereby increasing the phase adjustment capability and improving the performance of the refrigerator; the parallel inertia tubes are used for phase adjustment, and the inertia tubes of each branch can be combined in various ways, thereby enhancing the flexibility of phase adjustment and expanding the range of phase adjustment. The inertia tube of this technology only uses two inertia tubes arranged in parallel to adjust the phase of the pulse tube refrigerator. Summary of the Invention

[0012] The purpose of the present invention is to address the problems existing in the prior art and provide a pulse tube refrigerator with flexible phase adjustment, low loss and high efficiency, which uses an equiangular spiral structure as a phase adjustment device.

[0013] The present invention comprises a compressor, a precooler, a regenerator, a cold end heat exchanger, a pulse tube, a hot end heat exchanger, a tapered cavity and a phase adjustment device which are connected in sequence.

[0014] The converging cavity is a frustum with a narrow top and wide bottom. Its upper end is connected to the inlet of the phase-shifting device, and its lower end is connected to the hot-end heat exchanger. After being compressed by the compressor, the high-temperature, high-pressure gas passes through the precooler and enters the regenerator. After further cooling in the regenerator, it absorbs heat from the cold-end heat exchanger and then enters the pulse tube. The temperature at the hot end of the pulse tube rises, and after passing through the hot-end heat exchanger, the gas undergoes heat exchange again before passing through the converging cavity and entering the phase-shifting device.

[0015] The phase adjustment device is a metal cavity consisting of a wall panel, a cover panel, a sealing plate, and an adjustable baffle. The wall panel is a long rectangular metal sheet coiled into an equiangular spiral shape. Upper and lower cover panels are fixed to the upper and lower end surfaces of the space enclosed by the wall panel, forming an equiangular spiral cavity. The cavity opening is sealed by a sealing plate. Two to four adjustable baffles are located within the large end of the cavity. These baffles are connected to the upper and lower cover panels via a rotating shaft. A knob is installed at one end of the shaft, forming a valve. By turning the knob, different adjustable baffles are rotated, and the rotated baffles divide the cavity, thereby changing the effective volume of the cavity. A through-hole is opened in one cover panel, corresponding to the center starting position of the equiangular spiral cavity. One end of the regulating tube connects to the tapering cavity, and the other end connects to the equiangular spiral cavity through the through-hole. The regulating tube is equipped with a regulating valve, which adjusts the gas volume and performs the phase adjustment function.

[0016] Gas enters a cavity shaped like an equiangular spiral through a regulating tube, where the flow path gradually widens. The smaller portion of the flow path serves as the inertia tube, while the larger, closed portion serves as the gas reservoir. After passing through the equiangular spiral inertia tube, the gas converges directly at the cavity's largest cross-section. This overcomes the drawback of traditional pulse tube refrigerators, which require the inertia tube and gas reservoir to be separated, making it more suitable for acoustic power transmission and pulse tube phase modulation. Due to the naturally smooth transition between the tapering and widening of the equiangular spiral, the hydraulic diameter of the inertia tube varies at every location. By selecting different regulating baffles for closure and varying the volume of the gas reservoir, phase modulation capabilities with real-time adjustable phase angles are achieved.

[0017] The equiangular spiral satisfies the polar coordinate equation r = a·e kθ , r is the polar diameter, θ is the polar angle; the starting polar diameter is 1mm≤a≤3mm, the ending polar diameter is 50mm≤R≤150mm, and the expansion speed k=0.15~0.25. The sealing plate (8-3) is a rectangle with an aspect ratio of 1~1.2:1.

[0018] There are one or more phase adjustment devices, and multiple regulating tubes and regulating valves are correspondingly provided. One end of the multiple regulating tubes is directly connected to the tapering cavity, or is aggregated and connected to the tapering cavity, so as to realize the real-time change of the number of equiangular spiral structure inertia tubes and gas reservoirs connected in parallel to the pulse tube refrigerator.

[0019] Based on the acoustic power transmission characteristics of the equiangular spiral structure, the present invention changes the structure of the inertial tube from a traditional fixed-diameter metal tube to an equiangular spiral structure similar to a conch shell; and the large end of the equiangular spiral structure is sealed as an air reservoir, which solves the shortcoming that the inertial tube and the air reservoir need to be separated in the traditional pulse tube refrigerator. The equiangular spiral structure has smooth streamlines, which is easy to improve the acoustic power, reduces flow resistance, reduces air pressure drop, and improves the efficiency of the refrigerator. The transition from the gradually converging cavity to the gradually expanding cavity is natural and harmonious, which is very conducive to the amplification and attenuation of the acoustic power in the conch structure. The gas coming out of the pulse tube hot end heat exchanger first enters the small end inlet of the equiangular spiral structure. The pressure at the entrance of the gradually converging cavity is high, which is conducive to the gas flowing from the gradually converging cavity of the equiangular spiral structure to the gradually expanding cavity. The large-section end of the gradually expanding cavity is closed, forming a natural air reservoir structure.

[0020] The use of an equiangular spiral structure for the inertial tube and gas reservoir to regulate the phase of the pulse tube refrigerator offers high energy efficiency and places no special requirements on other pulse tube refrigerator components. This effectively addresses the issue of large phase differences between pressure waves and mass flow, improving the phase adjustment effect and the overall cooling capacity of the refrigerator. The flexible adjustment of the structural parameters of the equiangular spiral allows for significant scalability. Because the equiangular spiral structure is derived from the natural conch structure, the transition from the converging cavity to the expanding cavity is natural and harmonious, greatly facilitating the amplification and attenuation of acoustic power within the conch structure. This is significantly improved compared to conventional single inertial tubes of equal diameter and length matched to a gas reservoir with a suddenly increased cross-sectional area to regulate the phase of the pulse tube refrigerator. Due to the unique distribution and arrangement of the spiral structure, when the structure interacts with the airflow and is subjected to impact loads, the spiral changes the transmission method and location of the impact loads, effectively alleviating stress concentration, rationally distributing the energy generated during the impact, and improving the structure's impact resistance. This also achieves lightweight construction, reducing manufacturing and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 Schematic diagram of the phase modulation device;

[0023] Figure 3 It is a cross-sectional diagram of the wall plate, sealing plate and regulating partition in the phase adjustment device;

[0024] Figure 4 is a schematic diagram of the equiangular spiral of the wall panel;

[0025] Figure 5 Schematic diagram of the phase modulation effect of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, the pulse tube refrigerator using an equiangular spiral structure for phase adjustment includes a compressor 1, a precooler 2, a regenerator 3, a cold-end heat exchanger 4, a pulse tube 5, a hot-end heat exchanger 6, a tapered cavity 7, and a phase adjustment device 8 connected in sequence. The tapered cavity 7 is connected to the phase adjustment device 8 through an adjustment tube 9.

[0028] The converging chamber 7 is a frustum with a smaller top and larger bottom. Its upper end is connected to the inlet of the phase adjustment device 8, and its lower end is connected to the hot-end heat exchanger 6. After being compressed by the compressor 1, the high-temperature, high-pressure gas passes through the precooler 2 and enters the regenerator 3. After being further cooled by the regenerator 3, it absorbs heat from the cold-end heat exchanger 4 and then enters the pulse tube 5. The temperature at the hot end of the pulse tube rises. After passing through the hot-end heat exchanger 6, the gas undergoes heat exchange again before passing through the converging chamber 7 and entering the phase adjustment device 8.

[0029] like Figure 2 and 3 As shown, the phase adjustment device 8 is a metal cavity, comprising a wall plate 8-1, a cover plate 8-2, a sealing plate 8-3, and an adjustable baffle 8-4. The wall plate 8-1 is a rectangular metal strip formed into an equiangular spiral shape. The upper and lower cover plates are fixed to the upper and lower end surfaces of the space enclosed by the wall plate, forming an equiangular spiral cavity. The opening of the cavity is sealed by the sealing plate 8-3. Multiple (two in this embodiment) adjustable baffles 8-4 are positioned within the large end of the cavity. These baffles 8-4 are connected to the upper and lower cover plates via a rotating shaft. A knob is provided at one end of the shaft, forming a valve. Rotating the knob rotates different adjustable baffles 8-4 to change the effective volume of the cavity. One of the cover plates has a through hole corresponding to the center starting position of the equiangular spiral cavity. A regulating tube 9 connects to the tapering cavity 7 at one end and to the equiangular spiral cavity at the other end through a through hole. The regulating tube 9 is equipped with a regulating valve, which adjusts the gas volume and performs the phase adjustment function.

[0030] Gas enters the equiangular helical cavity through a regulating tube, where the flow path gradually widens. The smaller portion of the flow path serves as the inertia tube, while the larger, closed portion serves as the gas reservoir. After passing through the equiangular helical inertia tube, the gas converges directly at the cavity's largest cross-section. This overcomes the drawback of traditional pulse tube refrigerators requiring separate inertia tubes and gas reservoirs, making it more suitable for acoustic power transmission and pulse tube phase modulation. Due to the naturally smooth transition between the tapering and widening of the equiangular helical curve, the hydraulic diameter varies at every position throughout the inertia tube, achieving comprehensive, gradual, and continuous phase modulation capabilities.

[0031] like Figure 4 As shown, the equiangular spiral satisfies the polar coordinate equation r = a·e kθ, r is the polar diameter, θ is the polar angle; the starting polar diameter is 1mm≤a≤3mm, the ending polar diameter is 50mm≤R≤150mm, and the expansion speed k=0.15-0.25. The sealing plate (8-3) is a rectangle with an aspect ratio of 1-1.2:1. In this embodiment, the starting polar diameter is 1.2mm, the ending polar diameter is 60mm, and the expansion speed is 0.2.

[0032] There are one or more phase adjustment devices 8, and multiple regulating tubes 9 and regulating valves are correspondingly provided for the multiple phase adjustment devices 8. One end of the multiple regulating tubes is directly connected to the tapering cavity 7, or is connected to the tapering cavity 7 after being aggregated, so as to realize the real-time change of the number of equiangular spiral structure inertia tubes and gas reservoirs connected in parallel to the pulse tube refrigerator.

[0033] The following is a comparison of the phase adjustment performance of the two inertia tubes in parallel system of patent number CN201710116594.6 and the phase adjustment performance of the equiangular spiral structure phase adjustment device in the embodiment. The inertia tube of patent number CN201710116594.6 only uses two inertia tubes arranged in parallel to adjust the phase of the pulse tube refrigerator. This embodiment uses the inertia tube of the equiangular spiral structure and the gas reservoir structure. Figure 5 It can be seen (the dotted line in the figure is the adjustment capability curve of the inertia tube of CN201710116594.6, and the solid line is the adjustment capability curve of the inertia tube of this embodiment) that due to the natural smooth transition characteristics of the tapering and gradually opening equiangular spiral, the hydraulic diameter of the entire inertia tube is different at various positions, thereby obtaining the comprehensive gradual continuous phase adjustment capability as shown in the figure.

[0034] The phase adjustment capability of the phase adjustment device using the equiangular spiral structure of the present invention is always greater than that of CN201710116594.6. Therefore, the inertia tube and gas reservoir structure using the equiangular spiral structure can significantly improve the phase adjustment performance of the inertia tube.

[0035] The above description is only an example of a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pulse tube refrigerator using an equiangular spiral structure for phase adjustment, comprising a compressor (1), a precooler (2), a regenerator (3), a cold end heat exchanger (4), a pulse tube (5), a hot end heat exchanger (6), a tapered cavity (7), and a phase adjustment device (8) connected in sequence, characterized in that: The tapered cavity (7) is in the shape of a truncated cone with a small top and a large bottom. The upper end of the tapered cavity (7) is connected to the inlet of the phase adjustment device (8), and the lower end is connected to the hot end heat exchanger (6). The high-temperature and high-pressure gas compressed by the compressor (1) enters the regenerator (3) through the precooler (2). After being further cooled by the regenerator (3), it absorbs heat from the cold end heat exchanger (4) and then enters the pulse tube (5). The temperature of the hot end of the pulse tube rises. After passing through the hot end heat exchanger (6), the gas exchanges heat again, then passes through the tapered cavity (7), and then enters the phase adjustment device (8). The phase adjustment device (8) is a cavity made of metal, comprising a wall plate (8-1), a cover plate (8-2), a sealing plate (8-3) and an adjusting partition (8-4); the wall plate (8-1) is a long rectangular metal plate coiled into an equiangular spiral shape, and the upper and lower cover plates (8-2) are fixed to the upper and lower end surfaces of the space enclosed by the wall plate (8-1) to form an equiangular spiral cavity, and the opening of the cavity is closed by the sealing plate (8-3); 2 to 4 adjusting partitions (8-4) are arranged in the large end part of the cavity, and the adjusting partitions (8-4) are connected to the upper and lower cover plates through a rotating shaft, and a knob is provided at one end of the rotating shaft to form a valve; a through hole is opened on one cover plate, and the through hole corresponds to the central starting position of the equiangular spiral cavity; one end of the adjusting pipe (9) is connected to the gradually shrinking cavity (7), and the other end is connected to the equiangular spiral cavity through the through hole; the adjusting pipe (9) is provided with a regulating valve, and the gas volume is adjusted by the regulating valve; The gas enters the cavity of equiangular spiral shape through the regulating tube (9), and the flow channel gradually increases from small to large, wherein the small part of the flow channel serves as an inertia tube, and the part with a large end closed serves as a gas reservoir; The equiangular spiral satisfies the polar coordinate equation r=a·e kθ , r is the polar diameter, θ is the polar angle; the starting polar diameter is 1mm≤a≤3mm, the ending polar diameter is 50mm≤R≤150mm, and the expansion speed is k=0.15~0.25; There are one or more phase-adjusting devices; multiple regulating pipes and regulating valves are correspondingly provided for the multiple phase-adjusting devices, and one end of the multiple regulating pipes is directly connected to the tapering cavity, or is connected to the tapering cavity after being aggregated.

2. The pulse tube refrigerator using an equiangular spiral structure for phase adjustment according to claim 1, wherein: The sealing plate is a rectangle with a length-to-width ratio of 1 to 1.2:1.

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