Stirling-type pulse tube refrigerator (PTR) with cold compression: Cold compressor, colder expander

Park, J.,Ko, J.,Cha, J.,Jeong, S. Heywood Co ; Elsevier Science Ltd 2016 Cryogenics Vol.74 No.-

<P>This research paper focuses on the performance prediction and its validation via experimental investigation of a Stirling-type pulse tube refrigerator (PTR) equipped with a cold linear compressor. When the working gas is compressed at cryogenic temperature, the acoustic power (PV power) can be directly transmitted through the regenerator to the pulsating tube without experiencing unnecessary precooling process. The required PV power generated by the linear compressor, furthermore, can be significantly diminished due to the relatively small specific volume of the working gas at low temperature. The PTR can reach lower temperature efficiently with higher heat lift at the corresponding temperature than other typical single-stage Stirling-type PTRs. Utilizing a cryogenic reservoir as a warm end and regulating the entire operating temperature range of the PTR will enable a PTR to operate efficiently under space environment. In this research, the experimental validation as a proof of concept was carried out to demonstrate the capability of PTR operating between 80 K and 40 K. The linear compressor was submerged in a liquid nitrogen bath and the lowest temperature was measured as 38.5 K. The test results were analyzed to identify loss mechanisms with the simple numerical computation (linear model) which considers the dynamic characteristics of the cold linear compressor with thermo-hydraulic governing equations for each of sub components of the PTR. All the mass flows and pressure waves were assumed to be sinusoidal. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Experimental investigation on chill-down process of cryogenic flow line

Jin, L.,Park, C.,Cho, H.,Lee, C.,Jeong, S. Heywood Co ; Elsevier Science Ltd 2016 Cryogenics Vol.79 No.-

<P>This paper describes the cryogenic chill-down experiments that are conducted on a 12.7 mm outer diameter, 1.25 mm wall thickness and 7 m long stainless steel horizontal pipe with liquid nitrogen (LN2). The pipe is vacuum insulated during the experiment to minimize the heat leak from room temperature and to enable one to numerically simulate the process easily. The temperature and the pressure profiles of the chill-down line are obtained at the location which is 5.5 m in a distance from the pipe inlet. The mass flux range is approximately from 19 kg/m(2) s to 49 kg/m(2) s, which corresponds to the Reynolds numbers range from 1469 to 5240. The transient histories of temperature, pressure and mass flow rate during the line chill-down process are monitored, and the heat transfer coefficient and the heat flux are computed by an inverse problem solving method. The amplitude of the pressure oscillation and the oscillating period become larger and longer at higher pressure conditions. In the low mass flux conditions, the critical heat flux in horizontal pipes is not sensitive to mass flux, and is higher than that in vertical pipes. Kutateladze's correlation with the constant coefficient, B = 0.029, well matches the experimental data in the current work. In nucleate flow boiling regime, heat transfer coefficient, h, is proportional to (q')(n), and n is equal to 0.7. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Experimental investigation on no-vent fill process using tetrafluoromethane (CF₄)

Kim, Y.,Lee, C.,Park, J.,Seo, M.,Jeong, S. Heywood Co ; Elsevier Science Ltd 2016 Cryogenics Vol.74 No.-

<P>This paper investigates the transfer of liquid cryogens using a no-vent fill (NVF) process experimentally to identify the dominant NVF parameters. The experimental apparatus has been fabricated with extensive instrumentations to precisely study the effects of each NVF parameter. Liquid tetrafluoromethane (CF4) is selected as the working fluid due to its similar molecular structures and similar normal boiling point and triple point with liquid methane which has been considered as an attractive future cryogenic propellant. The experimental results show that the initial receiver tank wall temperature and the incoming liquid temperature are the primary factors that characterize the (non-equilibrium) thermodynamic state at the start of a NVF transfer. The supply pressure is also critical as it indicates the ability to condense vapor in the receiver tank. A non-dimensional map based on energy balance is proposed to find acceptable initial conditions of the filling volume at the desired final tank pressure. The non-dimensional map shows good agreement with the NVF data not only in this paper but also in the previous research. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Tandem-type pulse tube refrigerator without reservoir

Ki, T.,Jeong, S.,Ko, J.,Park, J. Heywood Co ; Elsevier Science Ltd 2015 Cryogenics Vol.72 No.1

In this paper, a tandem-type pulse tube refrigerator without a reservoir is discussed and investigated. For its practical application a tandem-type compressor is designed to generate two pulsating pressure waves with opposite phases, simultaneously. A tandem-type pulse tube refrigerator consists of a tandem-type compressor and two identical pulse tube refrigerators. The two identical pulse tube refrigerators share the same heat exchangers and one can be connected with the other by an inertance tube without a reservoir. In this proposed configuration, the mechanical vibration and temperature oscillations in the cold-end heat exchanger can be internally suppressed due to its intrinsic opposite-characteristic operation. To examine the quantitative evaluation of the tandem feature which does not require a reservoir in the pulse tube, an evolutionary approach has been attempted. A general structure of a pulse tube refrigerator is modified into tandem Stirling-type and GM-type machines and the transformed configuration has been simulated for tandem operation. The simulation results clearly demonstrate that a properly designed tandem-type pulse tube refrigerator without a reservoir can function favorably.

Thermal characteristics of conduction cooled 600kJ HTS SMES system

Kim, S.,Sim, K.,Kim, H.J.,Bae, J.H.,Lee, E.Y.,Seong, K.C.,Jeong, S. Heywood Co ; Elsevier Science Ltd 2009 Cryogenics Vol.49 No.6

A 600kJ HTS SMES is developed and tested in Korea. The HTS SMES consists of 22 double pancake coils wound on each aluminum alloy bobbin. It is cooled by two GM cryocoolers down to around 6K and current is charged through HTS current leads up to 275A. Beside the heat penetration from room temperature structures, heat generation in the HTS coil is inevitable because of the joint resistances and the intrinsic property of the HTS tape such as index loss. Moreover, during the charging and discharging operation, AC loss of the HTS conductor and eddy current loss in the coil bobbin and metallic structures are generated. Therefore, the heat generation should be effectively removed by the cryocooler to ensure the stable operation of the coil. In the HTS SMES, aluminum alloy conduction plates outside the each coil are used as thermal paths to the cryocoolers. This paper describes the thermal characteristics of the HTS SMES for the charging and discharge operation.

Effect of composition on critical current density of Bi2212/Ag round wires

Kim, S.C.,Ha, D.W.,Oh, S.S.,Sohn, H.S. Heywood Co ; Elsevier Science Ltd 2009 Cryogenics Vol.49 No.6

We have fabricated Bi2212/Ag round wires using three kinds of precursor to study the effect of a narrow variation of composition. Slightly different compositions - Bi<SUB>2.17</SUB>Sr<SUB>1.94</SUB>Ca<SUB>0.89</SUB>Cu<SUB>2.0</SUB>O<SUB>x</SUB>(N13), Bi<SUB>2.15</SUB>Sr<SUB>1.94</SUB>Ca<SUB>0.89</SUB>Cu<SUB>2.0</SUB>O<SUB>x</SUB>(N14), and Bi<SUB>2.17</SUB>Sr<SUB>1.98</SUB>Ca<SUB>0.89</SUB>Cu<SUB>2.0</SUB>O<SUB>x</SUB>(N15) - were used and Sr/Ca ratio of them were 2.18, 2.18, and 2.22, respectively. The Ag ratios of the wires were 2.7-2.8 and average filament diameter was 19-21μm. DTA analysis of the wire showed the peritectic temperature of three wires was very similar value of the range of 880-881<SUP>o</SUP>C. The best engineering critical current density (J<SUB>e</SUB>) of three wires at 4.2K and 0T was 414-448A/mm<SUP>2</SUP> at the maximum process temperature range of 884-892<SUP>o</SUP>C. The n-value of N14 showed 13.6, whereas other two wires showed lower n-value, estimating the existence of micro-cracks. Although Bi2212/Ag round wires fabricated by three kinds of composition showed similar J<SUB>e</SUB> value, n-value was quite different. It is likely that the fabrication process such as the drawing as well as the composition of precursor will affect on J<SUB>e</SUB> of Bi2212/Ag round wire.

Cryogenic system for COMET experiment at J-PARC

Ki, T.,Yoshida, M.,Yang, Y.,Ogitsu, T.,Iio, M.,Makida, Y.,Okamura, T.,Mihara, S.,Nakamoto, T.,Sugano, M.,Sasaki, K.i. Heywood Co ; Elsevier Science Ltd 2016 Cryogenics Vol.77 No.-

Superconducting conductors and cryogenic refrigeration are key factors in the accelerator science because they enable the production of magnets needed to control and detect the particles under study. In Japan, a system for COMET (Coherent Muon to Electron Transition), which will produce muon beam lines, is under the construction at J-PARC (Japan Proton Accelerator Research Complex). The system consists of three superconducting magnets; the first is a pion-capture solenoid, the second is a muon-transport solenoid, and the third is a detector solenoid. It is necessary to cool down the magnets efficiently using two-phase helium and maintain them securely at 4.5K. For stable cryogenic refrigeration of the magnets, a suitable cooling method, structures, and the irradiation effect on materials should be investigated. In this paper, we focus on the development of an overall cryogenic system for cooling the capture and transport solenoids. A conduction-cooling method is considered for cooling the capture and transport solenoids because of the advantages such as the reduction of total heat load, fewer components, and simplified structure. To supply cryogenic fluids (4.5K liquid helium and 58K gas helium) and currents to the conduction-cooled magnets subjected to high irradiation, cryogenic components (cooling paths in the magnets, transfer tubes, and a current lead box) are developed. Based on the environment of high irradiation, the conditions (temperature and pressure) of helium in cooling paths are estimated, as well as the temperature of the capture magnet. We develop a dynamic model for quench simulation and estimate the maximum pressure in the cooling pipe when the capture magnet quenches. We conclude with a discussion of the next steps and estimated challenges for the cryogenic system.

Electrical parameter evaluation of a 1MW HTS motor via analysis and experiments

Baik, S.K.,Kwon, Y.K.,Kim, H.M.,Kim, S.H.,Lee, J.D.,Kim, Y.C.,Park, H.J.,Kwon, W.S.,Park, G.S. Heywood Co ; Elsevier Science Ltd 2009 Cryogenics Vol.49 No.6

A 1MW class HTS (high-temperature superconducting) synchronous motor has been developed. Design concerns of the developed motor are focused on smaller machine size and higher efficiency than conventional motors or generators with the same rating simultaneously reducing expensive Bi-2223 HTS wire which is used for superconducting field coil carrying the operating current around 30K (-243<SUP>o</SUP>C). Influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power during motor and generator operation. The developed motor was also analyzed by three-dimensional electromagnetic FEM (finite element method) to get magnetic field distribution, inductance, electromagnetic stress and so forth. This motor is aimed to be utilized for industrial application such as large motors operating in large plants. The HTS field coil of the developed motor is cooled by way of Neon thermosiphon mechanism and the stator (armature) coil is cooled by water through hollow copper conductor. This paper also describes evaluation of some electrical parameters from performance test results which were obtained at steady state in generator and motor mode of our HTS machine.