Investigation on a thermoacoustically driven pulse tube cooler working at 80 K

The pulse tube cooler (PTC) driven by a thermoacoustic engine can completely eliminate mechanical moving parts, and then achieves a simpler and more reliable device. A Stirling thermoacoustic heat engine has been constructed and tested. The heat engine can generate a maximal pressure ratio of 1.19, which makes it possible to drive a PTC and get good performance. Frequency is one of the key operating parameters, not only for the heat engine but also for the PTC. In order to adapt to the relatively low design frequency of the PTC, the operating frequency of the thermoacoustic heat engine was regulated by varying the length of the resonance tube. Driven by the thermoacoustic engine, a single stage double-inlet PTC obtained the lowest refrigeration temperature of 80.9 K with an operating frequency of 45 Hz, which is regarded as a new record for the reported thermoacoustically driven refrigerators.     

300 Hz脉冲管制冷机特性研究

从实验和数值计算两个方面研究了1台工作频率为300 Hz的单级脉冲管制冷机的制冷特性.实验方面,验证了平均压力、入口压比、惯性管长度以及均流化元件对其制冷性能的影响,该制冷机在平均压力为3.96 MPa、入口压比为1.21时获得了79.6 K的最低制冷温度;数值计算方面,基于线性热声理论的模拟结果与实验结果进行了比较,以验证程序的有效性.     

Characterization of a 300 Hz thermoacoustically-driven pulse tube cooler

This article introduces our recent experimental advances on a 300 Hz pulse tube cooler driven by a thermoacoustic standing-wave engine. After some modifications on the engine, the integral system performance is improved, which leads to a better cooling performance of the high frequency pulse tube cooler compared with that in former reports. Cooling powers of the pulse tube cooler with different operating conditions have been measured in detail for the first time. So far, a lowest no-load temperature of 68 K and a maximum cooling power of 1.16 W at 80 K have been obtained with the mean pressure and the heating power being 4.1 MPa and 1 kW, respectively.     

Advances in a 300 Hz thermoacoustic cooler system working within liquid nitrogen temperature range

With the combined advantages of high reliability, compact size and low electromagnetic interference, a high frequency operating thermoacoustic cooler system, i.e. a pulse tube cooler driven by a thermoacoustic heat engine, is quite promising for space applications. This article introduced a high frequency standing-wave thermoacoustic heat engine-driven pulse tube cooler system working around 300 Hz with axial length being 1.2 m. To improve the thermal efficiency of such system, an optimization has been carried out, both analytically and experimentally, by observing the influence of the dimensions of the stack, the hot buffer length and the acoustic pressure amplifier tube length. So far, a no-load temperature of 68.3 K has been obtained with 4.0 MPa helium and 750 W heating power. With 500 W heating power, a no-load temperature of 76.9 K and 0.2 W cooling power at 80 K have been achieved. Compared with former reports, the performance has been improved.     

Influence of resonance tube length on performance of thermoacoustically driven pulse tube refrigerator

A resonance tube is an important component of a thermoacoustic engine, which has great influence on the performance of the thermoacoustically driven pulse tube refrigerator. A standing wave thermoacoustic engine is simulated with linear thermoacoustics. Computed results show that an appropriate accretion of the resonance tube length may lead to a decrease of the working frequency and an increase of the pressure amplitude, which will improve the match between the thermoacoustic engine and the pulse tube refrigerator. The theoretical prediction is verified by experiments. A refrigeration temperature as low as 88.6 K has been achieved with an optimized length of the resonance tube, helium as working gas, and 2200 W of heating power.     

热声驱动脉管制冷机的压力特性

自行研制了热声驱动脉管制冷机实验台,着重研究了热声驱动脉管制冷机的压力特性,明确了充气压力对超振温度、加热温度、制冷温度、压比及夺力振幅等的影响,实验表明,自行研制的热声压缩机在驱动脉管制冷机的情况下,仍可获１．０７以上的压比,基本可以满足驱动无阀型脉管制冷机的需要,在最近进行的实验中,以氮和氦作工质,分别获得了１９６Ｋ和１３８Ｋ的无负荷制冷温度,此外,本文还提出了进一步的改进方向。     

行波热声发动机加热器改进及其驱动脉管制冷机系统实验研究

对自行研制的行波型热声发动机中的核心部件加热器进行了改进.采用改进的热声发动机驱动单级小孔型脉管制冷机,以氦气为工质,在充气压力为2.2 MPa的条件下,获得了110 K的最低制冷温度.通过对实验结果的分析,着重阐明了热声发动机和脉管制冷机之间的频率匹配问题及其改进途径,为进一步深入研究指明了方向.     

行波热声发动机驱动的脉管制冷机研究

通过改变热声发动机谐振直路长度,研究系统在不同工作频率下的性能.研究发现,在一定条件下降低频率可以显著改善脉管制冷机的性能.在工作压力为2.7 MPa,加热功率为2 350W,工作频率为45 Hz时,双向进气型单级脉管制冷机获得了80.9 K的最低制冷温度,这是目前用热声制冷方法获得的最低制冷温度.     

A cryogen-free Vuilleumier type pulse tube cryocooler operating below 10 K

Vuilleumier (VM) type pulse tube cryocooler (PTC) utilizes the thermal compressor to drive the low temperature stage PTC. This paper presents the latest experimental results of a cryogen-free VM type PTC that operates in the temperature range below 10 K. Stirling type pre-coolers instead of liquid nitrogen provide the cooling power for the thermal compressor. Compared with previous configuration, the thermal compressor was improved with a higher output pressure ratio, and lead and HoCu₂ spheres were packed within the regenerator for the low temperature stage PTC for a better match with targeted cold end temperature. A lowest no-load temperature of 7.58 K was obtained with a pressure ratio of 1.23, a working frequency of 3 Hz and an average pressure of 1.63 MPa. The experimental results show good consistency in terms of lowest temperature with the simulation under the same working condition.     

Regenerator performance improvement of a single-stage pulse tube cooler reached 11.1 K

In order to improve the cooling performance of pulse tube cooler (PTC) at 20-40 K, hybrid regenerators are often employed. In this paper a three-layer regenerator, which consists of woven wire screen, lead sphere and Er₃Ni is optimized to enhance the cooling performance and explore the lowest attainable refrigeration temperature for a single-stage PTC. The efforts focus on the temperature range of 80-300 K, where woven wire screens are used. Theoretical and experimental studies are carried out to study the metal material and the mesh size effect of woven wire screens on the performance of the single-stage G-M type PTC. A lowest no-load refrigeration temperature of 11.1 K was obtained with an input power of 6 kW. The PTC can supply 17.8 W at 20 K and 39.4 W at 30 K, respectively.     

A single-stage pulse tube cooler reached 12.6 K

A single-stage G-M type pulse tube cooler (PTC) was designed and tested to explore the lowest attainable refrigeration temperature and to further improve the cooling performance in the temperature range of 15-40 K. The magnetic material Er₃Ni was used as part of the regenerative material besides the phosphor-bronze and the lead so as to improve the efficiency of the regenerator. With an input power of 6 kW, a lowest no-load refrigeration temperature of 12.6 K was obtained, which is a new record for the single-stage PTC. The cooling capacity at 15-40 K was also significantly improved, which may extend the application of the single-stage PTC for the cooling of superconductors and cryopumps.     

A 300 Hz two-stage pulse tube cryocooler that attains 58 K

We present a two-stage pulse tube cryocooler working at 300 Hz driven by a thermoacoustic engine. Compared to the previous experimental results, the combined inertance tube with different diameters that is used in the second stage is found to play the key role in phase shifting and to lead to superior cooling. Two different wall thickness tubes are tested in the experiments. After the optimization, the second-stage cold end achieves a no-load temperature of 57.9 K with an average pressure of 3.8 MPa, and a cooling capacity of 0.5 W at 81.88 K.     

Numerical investigation on a 300 Hz pulse tube cryocooler driven by a three-stage traveling-wave thermoacoustic heat engine

A 300 Hz pulse tube cryocooler (PTC) driven by a three-stage traveling-wave thermoacoustic heat engine (TSTHE) has been proposed and studied in this paper. In the configuration, three identical thermoacoustic heat engine units are evenly incorporated in a closed traveling-wave loop, in which three pulse tube cryocoolers are connected to the branch of each thermoacoustic heat engine. Compared with the conventional thermoacoustic heat engine which involves a traveling-wave loop and a long resonator, it has advantages of compact size and potentially high thermal efficiency. A TSTHE–PTC system was designed, optimized and studied in detail based on the thermoacoustic theory. Firstly, numerical simulation was conducted to design the system thus the optimum structure parameters of the system were obtained. With the operating condition of 4 MPa mean pressure and high working frequency, a cooling power of 7.75 W at 77 K and an overall relative Carnot efficiency of 11.78% were achieved. In order to better understand the energy conversion characteristics of the system, distributions of key parameters such as acoustic work, phase difference, dynamic pressure, volume flow rate and exergy loss were presented and discussed. Then, the coupling mechanism of the system was investigated. In addition, influence of coupling position on the system performance was further studied.     

A high frequency cascade thermoacoustic engine

A miniature cascade thermoacoustic engine, which consisted of one standing-wave stage and one traveling-wave stage in series, was built and tested, which length was about 1.2 m, operating at 470 Hz using helium as working gas. The cascade modeling, the simulation and the primary experimental results are described in this paper. Four different configurations of the miniature cascade thermoacoustic engines had been designed and compared. According to the analysis, the diameter ratio of stages was designed to extend the traveling-wave region, which optimized value was about 1.69. The peak-to-peak value of the acoustic pressure was predicted to arrive to 3 bar at the 3 MPa mean pressure of helium when 300 W heating power was the input. The features of the engine were predicted delivering 68 W acoustic power with a thermal efficiency of up to 22.74% (the ratio of acoustic power to heater power). Due to careful designing, the engine self-excited the oscillation smoothly from the first experiment. An onset temperature gradient of about 4.5 K/mm was achieved, and the peak-to-peak acoustic pressure was 48 KPa at the 2 MPa mean pressure when 200 W heating power was the input. The design computation and experimental results showed a rather good agreement between the measured and calculated pressure phasor and temperatures distributions in the cascade thermoaoustic engine.     

Comparison of two different ways of using inertance tube in a pulse tube cooler

It is well known that the pressure wave should lead the volume flow rate at the ambient end of the pulse tube for a high-efficiency operation of a pulse tube cooler. Inertance tube can provide such a phase relationship without DC flow problem. However, inertance tube is always connected with a reservoir in previous literatures. Through theoretical calculation here, inertance tube without a reservoir can also provide a rather large phase-leading effect. Thus phasor diagram is used to analyze the relationship between phase-leading requirement and the pulse tube geometry. Roughly speaking, a larger void volume of pulse tube would require a larger phase-leading effect. Comparison experiments are also done on a thermoacoustically-driven pulse tube cooler. With i.d.2 mm tube as inertance tube, the tube without reservoir yields close results in terms of lowest temperature to that of the tube with reservoir and both give much better performance than that of an orifice with reservoir. Finally, the advantages of using inertance tube without reservoir are given.     

An energy-focused thermoacoustic-Stirling heat engine reaching a high pressure ratio above 1.40

A new tapered resonator was introduced in the thermoacoustic-Stirling heat engine (TASHE) to explore its potential of achieving higher pressure ratio. With average pressure of 1.5 MPa and heating power of 3 kW, a high pressure ratio above 1.40 was obtained, which is very beneficial to be a powerful driving source of pulse tube cryocoolers or thermoacoustic refrigerators. Moreover, a relatively low onset temperature of 73 °C was also observed that showed the feasibility of its application in the field of using low quality heat sources.     

Effect of different working gases on the performance of a small thermoacoustic Stirling engine

The performance of a small thermoacoustic Stirling heat engine (TASHE) was investigated with three kinds of working gases experimentally and numerically. The examined performances focused on the operating frequency, onset temperature, pressure amplitude and some temperature characteristics after onset. The working frequency with nitrogen, argon and helium as the working gas was 45 Hz, 42 Hz and 130 Hz, respectively. The engine worked with helium in a much wider range of mean pressure than with nitrogen and argon. There was an optimal mean pressure for the minimum onset temperature for each working media. Using nitrogen and argon as working gas rather than helium, another optimal mean pressure for the highest pressure ratio was obtained in the experiment. The loop dimension was indispensable in determining the frequency and the highest pressure ratio was observed in the resonator cavity.     

A single-stage GM-type pulse tube cryocooler operating at 10.6 K

In order to explore the lowest attainable refrigeration temperature and improve cooling performance at temperatures around 20 K for a single-stage G-M type pulse tube cryocooler (PTC), numerical and experimental studies were performed. The National Institute of Standards and Technology (NIST) numerical model known as REGEN was applied to the simulation of a G-M type PTC for the first time. Based on the calculation results, a single-stage G-M type PTC was designed, fabricated and tested. The performance improvement of the regenerator in the temperature range of 10-80 K was investigated. The calculations predicted a lowest temperature of 10 K. A lowest temperature of 10.6 K was achieved experimentally with an input power of 7.5 kW, which is the lowest temperature ever achieved by a single-stage PTC. Further more, the cryocooler can provide a cooling power of 20 W at 20.6 K and 39.5 W at 30 K, respectively.     

High-power Stirling-type pulse tube cooler working below 30 K

High-power Stirling-type pulse tube coolers (PTCs) are promising candidates for cooling HTS devices and gas liquefaction or separation applications. Nevertheless, till now most high-power Stirling-type PTCs are not able to reach a refrigeration temperature below 35 K. Here, a high-power two-stage Stirling-type PTC was designed, manufactured and experimentally investigated. In order to realize a convenient coupling with a thermal load, U-shape configuration is adopted in both stages, which makes it more challenging to distribute the gas flow and reduce dead volume in the cold end heat exchanger. By optimizing operating conditions, flow straightener, and double-inlet opening, the cooler has reached no-load refrigeration temperatures of 29.6 K and 27.1 K at 55 Hz and 40 Hz, respectively. Furthermore, the cooler is able to provide cooling powers of 50 W at 45.6 K and 100 W at 59.3 K when input pV powers are 4.77 kW and 4.59 kW, respectively.     

High frequency two-stage pulse tube cryocooler with base temperature below 20 K

High frequency (30-50 Hz) multi-stage pulse tube coolers that are capable of reaching temperatures close to 20 K or even lower are a subject of recent research and development activities. This paper reports on the design and test of a two-stage pulse tube cooler which is driven by a linear compressor with nominal input power of 200 W at an operating frequency of 30-45 Hz. A parallel configuration of the two pulse tubes is used with the warm ends of the pulse tubes located at ambient temperature. For both stages, the regenerator matrix consists of a stack of stainless steel screen. At an operating frequency of 35 Hz and with the first stage at 73 K a lowest stationary temperature of 19.6 K has been achieved at the second stage. The effects of input power, frequency, average pressure, and cold head orientation on the cooling performance are also reported. An even lower no-load temperature can be expected from the use of lead or other regenerator materials of high heat capacity in the second stage.