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Investigation on a Thermoacoustically Driven Pulse Tube Cooler Working at 80 K

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Investigation on a Thermoacoustically Driven Pulse Tube Cooler Working at 80 K http://www.paper.edu.cn Cryogenics 45 (2005) 380–385 www.elsevier.com/locate/cryogenics Investigation on a thermoacoustically driven pulse tube cooler working at 80 K L.M. Qiu *, D.M. Sun, W.L. Yan, P. Chen, Z.H. Gan, X.J. Zhang, G.B. Chen Institute of Refrigeration and Cryogenic Engineering, Zhejiang University, Hangzhou 310027, China Received 12 August 2004; received in revised form 25 December 2004; accepted 20 January 2005 Abstract 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 reso- nance 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. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Thermoacoustics (C); Pulse tube cooler (E); Frequency match (D) 1. Introduction Using a coaxial single-stage pulse tube cooler driven by a standing-wave thermoacoustic engine, one of the A thermoacoustically driven refrigeration system em- present authors, Chen obtained a refrigeration tempera- ploys a thermoacoustic engine converting thermal en- ture of 115 K in 2003 [2] and 88.6 K in 2004 [3]. All ergy into acoustic power, which can be in turn used to those above thermoacoustically driven refrigeration sys- drive a pulse tube cooler or other kinds of thermoacou- tems had employed standing-wave thermoacoustic en- stic refrigerator. With a simpler structure, such refriger- gines, in which the inherent irreversibility resulted in ation systems can operate by using environment-friendly low efficiency. It is suggested that a thermoacoustic en- working gases and make use of industrial waste heat as gine with higher efficiency should be employed to further well as solar energy. It is highly promising in many decrease the refrigeration temperature. The Stirling ther- applications, especially in natural gas liquefaction moacoustic engine experiences Stirling cycle in its regen- located in remote areas or coastal areas. erator, which has potentially higher efficiency [4] and Research in thermoacoustic field has been booming makes it possible to get a lower refrigeration tempera- in recent years. Swift and Radebaugh succeeded in con- ture by driving a PTC. For this purpose, Ueda et al. structing an orifice pulse tube cooler driven by a stand- tested a thermoacoustically driven refrigeration system ing-wave thermoacoustic engine and obtained a with a loop and a resonance tube. By simultaneous mea- refrigeration temperature around 91 K in 1990 [1]. surements of pressure p and velocity U, they put the sec- ond regenerator at a precise location in the loop and * Corresponding author. Tel./fax: +86 571 879 52793. refrigeration temperature as low as À25 °C was obtained E-mail address: [email protected] (L.M. Qiu). without involving any moving parts [5]. Yazaki et al. 0011-2275/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cryogenics.2005.01.006 中国科技论文在线 http://www.paper.edu.cn L.M. Qiu et al. / Cryogenics 45 (2005) 380–385 381 directly embedded a second regenerator into the loop of the temperature of the outside wall of the heater, Tout. a traveling-wave thermoacoustic engine [6]. The high- To reflect the real temperature of thermal energy re- light of their setup is that traveling-wave thermoacoustic source and to give reference to practical applications, engine and cooler are directly coupled in a simple loop. temperature referred in this paper is Tin. Heating With helium–argon mixture as working gas, refrigera- power is adjusted by changing the charging voltage tion temperature reached 246 K with such simple to the heaters and is displayed by a digital dynamo- configuration. meter. In experiment, the working gas is helium of In 1999, Backhaus and Swift upgraded a thermal effi- high purity. ciency up to 30% by introducing a resonance tube into a Pressure data are acquired and analyzed by a real- looped tube [7]. But report on a PTC driven by such an time system. As shown in Fig. 1, pressure sensors la- engine has not been found so far. We designed and fab- beled as P1, P2 and P3 are located along the resonance ricated such a Stirling thermoacoustic engine to drive a tubes, in order to observe the pressure oscillation and single stage double inlet PTC [8]. Experimental results the acoustic power entering the resonance tubes. P4, show that the engine has the merits of large pressure P5, P6 and P7 are located at the three-way tube, iner- amplitude and good mono-frequency characteristic with tance tube, jet pump and main cooling heat exchanger, helium as working gas. As the design frequency of the respectively, in order to observe the distribution of PTC is about 15 Hz, we regulate the operating frequency acoustic field in the torus. Pressure data acquisition sys- of the thermoacoustic heat engine by varying the length tem comprises of pressure sensors, a data acquisition of resonance straight tube. Based on better frequency clip, a PII computer and a self-developed program match between the engine and the single stage double- based on Labview 6.1 by National Instruments (NI) inlet PTC, a minimum refrigeration temperature of Inc. The pressure sensors are of linear silicon piezo- 80.9 K is then obtained with working frequency of electric type (KPY 46R) and supplied by Infineon Tech- 45 Hz. nologies, Germany. The data acquisition clip is NI PC-1200, 12 bits in precision and 100 ks/s in sampling frequency. 2. Experimental apparatus A single stage double-inlet pulse tube cooler is adopted in this experiment. Table 1 gives the structure In this paper, the thermoacoustically driven PTC sys- parameters and material of its regenerator. The design tem consists of a traveling-wave thermoacoustic engine, frequency of the PTC is about 15 Hz. Driven by a a single-stage double-inlet PTC, vacuum system, as mechanical oil-free compressor, the PTC reached shown in Fig. 1, and measurement system. The structure 60 K with pressure ratio of 1.35. In addition, the joint of each part of the thermoacoustic heat engine was pre- tube between the engine and the cooler has the length viously introduced in Ref. [8]. and inner diameter of 0.6 m and 0.004 m, respectively. Two calibrated NiCr–NiSi thermocouples (with The joint tube is put in a water coat to cool the gas ±5 K accuracy) are arranged in the heater and their entering the PTC. A calibrated Rh–Fe resistance ther- locations are shown in Fig. 1. Deep in the heater, mometer (with 0.1 K accuracy) is applied to measure one shows the temperature of the cartridge heaters, the refrigeration temperature at the cold end of the Tin; while the other located on the outside wall shows PTC. to 2 7 A P6 P7 8 1 A 2 3 to 4 PTC to vacuum pump 4 Tout Tin 5 P5 A-A P4 P3 P2 P1 Fig. 1. Schematic of the thermoacoustically driven pulse tube cooler system. 1: Main cooling heat-exchanger, 2: regenerator, 3: heater, 4: thermal buffer tube (TBT), 5: secondary cooling heat-exchanger, 6: feedback tubes, 7: compliance, 8: jet pump, 9: resonance tubes. 中国科技论文在线 http://www.paper.edu.cn 382 L.M. Qiu et al. / Cryogenics 45 (2005) 380–385 Table 1 Structure parameters of the pulse tube cooler and regenerative material Pulse tube (mm) Regenerator (mm) Regenerative material Volume of reservoir (cm3) B10.1 · 0.35 · 119 B14.5 · 0.35 · 116 250 Mesh stainless-steel screen 400 3. Experimental results 0.05 3.1. Performance of thermoacoustic engine Working Gas: He 0.04 Heating Power: 2050 W Working Pressure: 0.92 MPa We first carried out non-load experiments on the P1 P2 thermoacoustic engine with 4 m long resonance tubes. 0.03 P3 P5 Fig. 2 shows the relationship between pressure ampli- tude and heating power at different locations as shown 0.02 in Fig. 1. In experiment, the maximal heating tempera- Relative level ture and working pressure are 600 °C and 2.08 MPa. Pressure amplitude is the direct driving force to the 0.01 PTC. It is apparent that the amplitude of pressure oscil- lation increases from P2 to P7 gradually and reaches the 0.00 maximum above the main cooler, which indicates a 50 60 70 80 90 100 110 120 130 140 150 160 standing-wave distribution along the engine. The largest Frequency (Hz) pressure amplitude occurs at P7 is 0.18 MPa (the corre- Fig. 3. Frequency analysis of pressure wave. sponding pressure ratio is 1.19), and the corresponding heating power and temperature (Tin) are 4360 W and 600 °C, respectively. thermoacoustic refrigerators to achieve stable refrigera- Fig. 3 shows frequency spectra of pressure waves tion temperature. when the pressure oscillation gets the most intensive, with the filling pressure of 0.9 MPa. The heating power 3.2. Influence of total resonance tube length is 2050 W and the heating temperature is 600 °C. The fundamental frequency is about 72 Hz and harmonic According to boundary conditions of acoustic field components are around 145 Hz.
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