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The diagnosis and management of intraorbital foreign bodies are challenging for surgeons. Foreign bodies made of wood and those located close to the optic nerve are especially difficult to manage. Herein, we report our experience with the diagnosis and management of intraorbital wooden foreign bodies utilizing magnetic resonance imaging (MRI). A 50-year-old man presented to the emergency room with a laceration on his left upper eyelid. No foreign bodies were visible through the laceration, and computed tomography findings showed only evidence of cellulitis with abscess formation. Despite drainage and antibiotics, the cellulitis worsened; subsequently, we found multiple wooden foreign bodies on MRI. Surgical removal was performed, excluding those in the intraconal space to avoid optic nerve damage. The patient recovered well and has not experienced any ophthalmic complications at 1 year of follow-up.

This research paper discusses the free-piston Stirling cryocooler (FPSC) in conjunction with a dual-opposed linear compressor. The system was tested under various operational conditions. The developed compressor can produce mass flow with an efficiency exceeding 60%; a loss analysis was conducted with care. The dynamic and thermal aspects of the experimental results are extensively verified via the numerical model. The model describes the physical characteristics of the Stirling cryocooler when a damping effect is applied to the displacer. The damping effect incorporated in the model is expressed through a function of the expansion work at the cold-end. It was also confirmed that the damped motion of the displacer is more suitable than undamped motions for describing real situations. The relevant dynamic characteristics of the piston and the displacer are also explained through the introduction of a phasor diagram. The developed model explains the physics of the Stirling cryocooler well, while accurately explaining the quantity of losses (i.e. heat conduction, imperfection of regenerator and shuttle heat transfer) that are distributed at its cold-end. The thermal load is regulated at various cold-end temperatures of 110 K, 120 K, 150 K and 190 K, and the system is capable of exerting maximum Carnot efficiencies of 25%, 27%, 28% and 29%, respectively.

Supplemental Digital Content is available in the text, A variety of reconstructive options including skin grafts, loco-regional flaps, and free flaps exist for the coverage of facial defects. Each technique has advantages and disadvantages. In this study, we present our experience with relaxed skin tension line (RSTL)-oriented, keystone-designed perforator island flap (KDPIF) reconstructions, in consideration of the facial aesthetic unit concept for coverage of small to moderate facial defects. Between May 2016 and February 2018, 17 patients (11 men and 6 women), with an average age of 63.53 years (range: 37–83 years) underwent KDPIF reconstructions to cover facial defects. We performed the KDPIF reconstructions in consideration of the RSTLs and facial aesthetic unit concept. We retrospectively reviewed the defect causes, locations, and sizes, and flap sizes, types, and survivals, as well as the complications. Cosmetic outcomes were evaluated using the Harris 4-stage scale from 3 independent plastic surgeons’ point of view, and postoperative satisfactory surveys from all patients. All defects were successfully covered with KDPIF. The defect sizes varied from 1.5 × 1.5 cm2 to 3 × 3.5 cm2. The flap sizes varied from 1.5 × 3 cm2 to 3 × 5.5 cm2. All flaps fully survived and there were no postoperative complications. The average subjective patient satisfaction score was 8.29 (range: 7–10) and the objective cosmetic outcomes were favorable (fair, good, or excellent). Considering its simplicity and safety, the KDPIF is a good reconstruction option with few complications and high reproducibility. The RSTL-oriented KDPIF reconstruction is a good reconstructive option for covering small to moderate facial defects with superior aesthetic outcomes.

An integral crank driven Stirling cryocooler is solidly based on concepts of direct IR detector mounting on the cryocooler’s cold finger, and the integral construction of the cryocooler and Dewar envelope. Performance factors of the cryocooler depend on operating conditions of the cryocooler such as a cyclic mean pressure of the working fluid, a rotational speed of driving mechanism, a thermal environment, a targeted operation temperature and etc.. At given charging condition of helium gas, the cyclic mean pressure of helium gas in the cryocooler changes with temperatures of the cold end and the environment. In this study, effects of the cyclic mean pressure of helium gas on performances of the Stirling cryocooler were investigated by numerical analyses using the Sage software. The simulation model takes into account thermodynamic losses due to an inefficiency of regenerator, a pressure drop, a shuttle heat transfer and solid conductions. Simulations are performed for the performance variation according to the cyclic mean pressure induced by the temperature of the cold end and the environment. This paper presents P-V works in the compression and expansion space, cooling capacity, contribution of losses in the expansion space.

The superconducting NMR magnets have used cryogen such as liquid helium for their cooling. The conduction cooling method using cryocoolers, however, makes the cryogenic cooling system for NMR magnets more compact and user-friendly than the cryogen cooling method. This paper describes the thermal and structural analysis of a cryogenic conduction cooling system for a 400 MHz HTS NMR magnet, focusing on the magnet assembly. The highly thermo-conductive cooling plates between HTS double pancake coils are used to transfer the heat generated in coils, namely Joule heating at lap splice joints, to thermal link blocks and finally the cryocooler. The conduction cooling structure of the HTS magnet assembly preliminarily designed is verified by thermal and structural analysis. The orthotropic thermal properties of the HTS coil, thermal contact resistance and radiation heat load are considered in the thermal analysis. The thermal analysis confirms the uniform temperature distribution for the present thermal design of the NMR magnet within 0.2 K. The mechanical stress and the displacement by the electromagnetic force and the thermal contraction are checked to verify structural stability. The structural analysis indicates that the mechanical stress on each component of the magnet is less than its material yield strength and the displacement is acceptable in comparison with the magnet dimension.

>> This paper describes the continuing effort to analysis and design on dynamic and electrical behaviorof gamma-type free piston Stirling engine/generator with dual–opposed linear generator for domestic micro-CHP (Combined Heat and Power) system. The double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric sinusoidal displacementand are connected with moving magnet type linear generators for power generation. To operate Stirling engine/ generator, combustion heat of natural gas is supplied to hot-end and heat is rejected from cold-end by coolingwater. The temperature difference across the displacer induces the oscillating motion, and it can be explained withmass-spring vibration system. The purpose of this paper is to describe the design process of linear generator for the double acting free-piston Stirling engine. Key words : Double acting free piston Stirling engine/alternator(양방향 자유 피스톤 스털링엔진 /발전기), Lineargenerator(선형발전기), Piston(피스톤), Displacer(변위기), Operating frequency(작동주파수)

Most of the Stirling cryocoolers used for infrared detector cooling in domestic is imported. Because the cooler has a high price, short life and poor durability, demand for the coolers continues steadily. However, the cooler is highly related to defense and space technology, technology transfer or co-development with the countries having experties in cooler design is very limited. The pulse tube cooler to be developed in this study is such that the mechanical piston in low temperature actuating part is replaced by the gas piston and linear compressor is adopted, which results in low vibration, long life and better durability. It is expected that development of the pulse tube cooler will not only improve our technology to the level of advanced countries, but also enhance the skills in designing and manufacturing of the infrared detector.

Rationale: Surgical treatment of hidradenitis suppurativa (HS) is challenging. Wide excision of affected lesions followed by skin graft or flap coverage has been recommended to achieve remission and prevent recurrence. Herein, we present our experience of bilateral inferomedial gluteal defects coverage using symmetrical keystone flaps (KFs) designed parallel to relaxed skin-tension lines (RSTLs). Patient concerns: An 18-year-old man was admitted for chronic inflammatory lesions in both inferomedial gluteal areas. Diagnoses: Physical examination revealed multiple sinuses with broad surrounding scars in both inferomedial gluteal areas, which led to a diagnosis of HS. Interventions: We performed wide excision on all affected lesions. The size of the final defects was 6 × 10 cm on the right side, and 5 × 9 cm on the left side. We covered the defects with KFs 9 × 15 cm (right) and 8 × 12 cm (left), which were based on the hotspots of the interior gluteal artery and internal pudendal artery perforators, and parallel to RSTLs. Outcomes: The flaps were inset without tension on each side, and the donor sites were closed primarily. All flaps fully survived and there were no postoperative complications. The patient was satisfied with the final outcome after 6 months of follow-up. Lessons: Successful reconstruction of bilateral inferomedial gluteal defects was achieved after resection of HS using symmetrical KFs designed parallel to RSTLs. The KF technique considering RSTLs could be a good reconstructive option for gluteal HS.

This research paper describes the design methodology of the free-piston Stirling engine (FPSE) and its demonstration. The FPSE is equipped with a dual-opposed linear alternator. The design and experiment are mainly focused on understanding how the FPSE dynamically behaves. Based on the data obtained from experiments, the operational issues regarding the output and dynamic characteristics are discussed in detail. The FPSE can accept approximately 4.2 kW at the engine head with a temperature of 525 °C. As a heat source, city-supplied natural gas is used. The linear alternator stably produces 961 We-electricity at a resonance frequency of 60 Hz. The deduced efficiency of the linear alternator is 70–75% of the thermodynamic work generated by the engine. The integrated system, FPSE, has an overall efficiency of 23.0% when comparing the heat supplied to the electrical output. The FPSE was also proven with a direct connection to the grid, so it can generate and sell electricity back to the grid. The equipped resonant capacitor enables this by compensating for the power factor. The experiment results show that the design methodology is able to adequately explain the behavior of the FPSE.

Cryogenic cooling system for HTS electric power devices requirea reliable and efficient highs -capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit -type heat exchanger is adopted for cold and warm -end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and l inear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no -load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

It is one of important design issues in the high-temperature superconducting fault current limiter (HTS-FCL) to estimate how much liquid nitrogen vaporizes during its quench process. This paper describes the small scale experiment about the vaporization of subcooled liquid nitrogen by instantaneous heat generation corresponding to the quench in HTS-FCL. In the experiment, the heat is given liquid nitrogen by Joule heating of the stainless steel strip for the short time of about 100 ms. The time variations of temperature and pressure in the liquid nitrogen test chamber are measured for different subcooling conditions of liquid nitrogen and various heat flux conditions. In addition, the amount of vaporization of liquid nitrogen is calculated from experimental results according to the subcooling of liquid nitrogen. The experimental results show that the vaporization of liquid nitrogen strongly depends on heat flux and subcooling conditions. The amount of vaporization linearly decreases with the increase in the subcooling of liquid nitrogen. The calculation results about the amount of vaporization suggest that the subcooling of more than 20 K is necessary to suppress bubble generation for the heat flux condition of 46 W/cm 2 or more.

Stirling type pulse tube cryocoolers are very attractive for cooling of diverse application because it has it has several inherent advantages such as no moving part in the cold end, low manufacturing cost and long operation life. A moving magnet type linear motor of dual piston configuration is designed, and this compressor could be operated with the electric power of 100 W at the operating frequency of 50 Hz. A pulse tube cold finger with a double segmented inertance tube was designed for the desired cooling capacity. The coiled inertance tube was assembled inside the reservoir. In experiment, the pulse tube cryocooler is capable of providing the cooling capacity of 2.0 W at 80 K with power consumption of 99.1 W. Random and sinusoidal vibration tests have been conducted to evaluate their performance characteristics and structural integrity.

Abstract : In this paper, we carried out the basic design of 36 MTD natural gas BOG re-liquefaction system to recover the generated natural gas during performance test of LNG pump and natural gas compressor. The re-liquefaction process of natural gas is designed to have 1500 kg/h of liquefaction rate with reverse Brayton refrigeration cycle. With the designed process, the variat ion of liquefaction rate is calculated for various inlet conditions of feed gas. From results, the liquefaction rate is more sensitive for inlet temperature than gas composition. The specifications of equipments such as gas blower, natural gas compressor, cryogenic heat exchanger and nitrogen compander are determined on the basis of the designed process. The requirement of power consumption and cooling water are also determined through the basic design.

This paper describes experimental study on GM-type pulse tube refrigerator (PTR). In a PTR, the pulse tube is only filled with working gas and there exists secondary flow due to a large temperature difference between cold-end and warm-end. The stability of secondary flow is affected by orientation of cold-head and thus, the cooling performance is deteriorated by gas mixing due to secondary flow. In this study, a single stage GM-type pulse tube refrigerator is fabricated and tested. The cooing performance of the fabricated PTR is measured as varying cold-head orientation angle and the results are used as reference data. Then, we divided interior space of pulse tube into three segments, and fixed the various size of screen mesh at interface of each segment to suppress the performance degradation due to secondary flow. For various configuration of pulse tube, no-load test and heat load test are carried out with the fixed experimental condition of charging pressure, operating frequency and orifice valve turns. From experimental results, the fine screen mesh shows the effective suppression of performance degradation for the large orientation angle, but the use of screen mesh cause the loss of cooling capacity rather than the case of no insertion into pulse tube. It should be compromised whether the use of screen mesh in consideration of the installation limitation of a GM-type pulse tube refrigerator.

Usually, the AC loss from the superconducting element of an SFCL due to the load current is very small because it is composed of the combination of bifilar windings with very small reactance. Although the AC loss is small enough, we should be albe to predict for the design and control of the cryogenic system. In fact, an SFCL for the transmission voltage class may not generate ignorable AC loss because of the inevitable space between the HTS wires for the high voltage insulation and cryogenic efficiency. To measure the AC loss dependency on the space between the 2G HTS wires with the width of 4.4 mm, we prepared an experimental setup which could adjust the distance between the wires. We used two 500-mm length HTS wires in parallel and applied the current in the opposite direction for each wire to simulate a part of a current limiting module for a high voltage SFCL. We also put two couples of voltage taps at the ends of each wire and a cancel coil in the voltage measurement circuit to compensate the reactive component from the voltage taps. In this condition, we varied the distance between the wires to investigate the change of the transport current loss. A similar experimental study with HTS wire with the width of 12 mm is now in progress.

This paper describes experimental study on the orientation dependence of GM-type pulse tube refrigerator with helium and neon as working gas. A pulse tube refrigerator generates refrigeration work with gas expansion by gas displacer in the pulse tube. The pulse tube is only filled with working gas and there exists secondary flow due to large temperature difference between cold-end and warm-end. The stability of secondary flow is affected by orientation of cold-head and thus cooling performance is deteriorated by gas mixing due to secondary flow. In this study, a single stage GM-type pulse tube with orifice valve as a phase control device is fabricated and tested. The fabricated pulse tube refrigerator is tested with two different working gases of helium and neon. First, optimal valve opening and operating frequency are determined with experimental results of no-load test. And then, the variation of no-load temperature as orientation angle of cold-head is measured for two different working gases. Effect of orientation dependence of cold-head as working gas is discussed with experimental results.

KEPCO Research Institute has been researching a Superconducting Fault Current Limiter (SFCL) which is considered one of solutions of fault current problems with Korea Institute of Machinery & Materials (KIMM) and Hanyang University since 2011. In this paper, we fabricated a current limiting module and conducted electrical short circuit tests for checking the validity of the transmission level SFCL design. Based on the short circuit characteristics of the second generation High Temperature Superconductor (HTS), we analyzed the short circuit characteristics of 3 parallel connected superconducting wires. The structure of the HTS wire is as follows: the stainless steel stabilizer of is laminated on the superconductor layer and under the substrate, both of which are electrically jointed with solder. We fabricated the current limiting module which has 40 series and 6 parallel connections and studied the short circuit characteristics of the module under various voltage levels.

This paper describes experimental investigation on neon refrigeration system using commercial helium compressor. In this paper, neon refrigeration cycle is calculated with assumption of ideal heat exchanger. From analysis, 32.6 K of the lowest temperature and 0.945 of quality after expansion are predicted. Cryogenic heat exchangers for pre cooler and main heat exchanger are designed and fabricated with configuration of tube-in-tube heat exchanger. In experiments, cooling performance test are performed as variation of charging pressure and orifice hole diameter. From experimental results, the lowest temperature of 44.0 K was measured with 500 orifice and 1500 kPa of charging pressure.

This paper describes experimental study on GM-type pulse tube refrigerator with neon as a working fluid instead of helium. Neon gas has similar compression characteristics with helium gas because it is a monoatoimc gas. In experiments, a cooling performance test was performed with same compressor and pulse tube refrigerator for neon and helium as working gas. From experimental results, a PTR with neon show the improved cooling performance than a PTR with helium. Cooling performance and operating characteristics of a PTR were discussed and compared for two different working gas.

HTS (high temperature superconducting) motor that utilizes superconductor as the field winding has advantage of compactness, light weight and high efficiency, but it has an inherent disadvantage that the rotor must be cooled down at cryogenic temperature. Conventionally, HTS rotor was cooled by circulation of cryogenic fluid such as helium or neon, and the cooling system was installed outside of the motor to prevent it from being rotated. In this paper, however, the prototype of the HTS motor with an on-board cryocooler, is fabricated and tested. The experimental system is composed of the stator with conventional copper winding, the rotor with superconductor, and the rotating cryocooler as a novel concept of cooling system. The rotor is fabricated as the race-track coil with 2G, YBCO tape and situated in the 110 mm diameter cryostat. It is designed to minimize heat invasion from room temperature environment and be compatible with the coaxial structure of the cryocooler. The cryocooler is in physically and thermally contact with the HTS rotor while being rotated together. Two kinds of refrigerator, a Stirling refrigerator and an inline-type PTR (Pulse Tube Refrigerator) are used individually as the on-board cryocooler. The whole system is carefully integrated and fabricated for rotating stability. Several temperature sensors and voltage taps are installed to monitor the conditions of the HTS rotor and the cryocooler while their signals are acquired by the bluetooth data acquisition system during the operation. The HTS motor is successfully operated with 120 rpm of rotating speed. In the rotating test, 70 A current is supplied to the superconducting rotor. Further developmental design issues for on-board cryocooling system are addressed and discussed in this paper.

Superconducting magnetic energy storage (SMES) has attracted a great deal of interest from the viewpoint of energy saving. The magnet of conduction-cooled high temperature superconducting (HTS) SMES is cooled down by a cryocooler. One of the most important problems to be assured the protection of magnet and cryocooler is breakdown at cryogenic temperature. In this study, we investigated insulation materials such as Kapton, Aluminum Nitride(AIN), Alumina(), glass fiber reinforced plastics(GFRP) and vacuum in cryogenic temperature. Also, we analyzed statistically the Weibull distribution of breakdown voltage.

Stirling type pulse tube cryocoolers are very attractive for cooling of diverse application because it has it has several inherent advantages such as no moving part in the cold end, low manufacturing cost and long operation life. To develop the Stirling-type pulse tube cryocooler, we need to design a linear compressor to drive the pulse tube cryocooler. A moving magnet type linear motor of dual piston configuration is designed and fabricated, and this compressor could be operated with the electric power of 100 W and the frequency up to 60 Hz. A single stage coaxial type pulse tube cold finger aiming at over 1.5 W at 80K is built and tested with the linear compressor. Experimental investigations have been conducted to evaluate their performance characteristics with respect to several parameters such as the phase shifter, the charging pressure and the operating frequency of the linear compressor.

A Stirling type pulse tube refrigerator with an active phase control has been experimentally investigated. A phase shifter, which controls the phase angle between the mass flow and the pressure inside a pulse tube, plays a key roll in the performance of pulse tube refrigerators. In this study, an electrically driven and mechanically damped linear compressor, which is directly connected at the warm end of the pulse tube using a connecting tube, is used as the active phase controller (APC). Therefore, this active phase control pulse tube refrigerator (APCPTR) has no reservoir. Amplified electric signals of a function generator are supplied to both the main linear compressor, which is used as the pressure wave generator (PWG), and the APC. The type of these two linear compressors is a dual-opposed piston. The advantage of this phase sifter is easy to control the electric input power and the phase angle between the PWG and the APC. In order to clarify the characteristics of the APCPTR, the cold end temperature and the gas pressure have been measured.

Cool-down characteristics of a miniature J–T refrigerator with a pressurized vessel, which has different initial pressures of nitrogen gas, were investigated by experiment. The supply and exhaust pressures, the temperatures on the surface of the cryostat, and the mass flow rate were measured simultaneously to analyze the cool-down characteristics of the J–T refrigerator with a pressurized vessel or reservoir. The results show the effect of the supply pressure on the cold end temperature of the J–T refrigerator. The influence of the supply pressure and the temperature on the mass flow rate during the cool-down stage is discussed in details.

To develop a stable and compact small-sized superconducting magnetic energy storage (SMES) coil, which provides electric power with high quality to sensitive electric loads, we fabricated a SMES coil and tested it. Because such a large-sized superconducting coil quenches far away from its critical current, the recovery current is frequently used as a stability criterion in the coil fabrication. Therefore, we first investigated the recovery current characteristics of the large current conductor, which was used in our SMES coil fabrication. The test results indicate that the recovery currents measured in the conductor are nearly identical to those based on the single wire. This implies that the recovery current is affected by the conductor's cooling condition rather than its size and current capacity. In the SMES coil test the first quench occurred at 1250 A, which is equivalent to the stored energy of about 2 MJ. It corresponds to the quench current density of about 130 A/mm/sup 2/. This value is much higher in comparison with that reported in the other work. In addition, the first quench current of the coil agrees well with the measured recovery current of the conductor having similar cooling condition with it. This means that to determine the recovery current of a conductor is, first of all, important in the design and fabrication of a large-sized superconducting coil.

A superconducting solenoid with large inner diameter has much lower current capacity than expected from short wire sample tests, and a solenoid of multi-strand cable has worse results. It is known that this degradation is observed when the inner diameter of the solenoid is bigger than a certain value (30 cm usually). However the reason is not clarified yet and some people called this just the "size effect." To obtain some clues to understand the size effect and to develop big solenoids with higher operating current, we prepared and tested two sample solenoids made of Rutherford type cables with and without soldering. Quench currents and AC losses of the two solenoid coils are measured and compared. The test results show that the soldering on the Rutherford cable improves the current capacity, but makes the AC loss much higher.

This paper presents design, manufacturing process and test results in the optimum operating condition for the free piston free displacer (FPFD) type Stirling cryocooler designed and manufactured by Korea Institute of Machinery and Materials. FPFD Stirling cryocooler is currently under development for cooling infrared detector. The compressor in the Stirling cryocooler uses opposed linear motors to drive opposed pistons. The performance of FPFD Stirling cryocooler is evaluated as a function of charging pressure and operating frequency. In general, as the charging pressure is increased, optimum-operating frequency of the compressor is increased but resonant frequency of the displacer is almost constant. The prototype has achieved no load temperature of 49 K and cooling power of 0.5 W at 72 K.

The purpose of this study is to analyze the characteristics of the linear compressor for Stirling cryocooler. To ensure high performance and long life of the free piston, free displacer Stirling cryocooler, the operating parameters of the linear compressor should be optimized. The experimental results show the operating frequency of the linear compressor has significant effect to the input power characteristics, and the compressor with higher charging pressure of working fluid has high pressure ratio. For the high performance of the linear compressor, compressor has uniform magnetic force with different stroke, and the optimal operating frequency with respect to the charging pressure.

For several decades researches and developments on superconducting magnetic energy storage (SMES) system have been done for efficient electric power management. Korea Electrotechnology Research Institute (KERI) have developed a 1-MJ 300-kVA SMES System for improving power quality in sensitive electric loads. It consists of an IGBT (Insulated Gate Bipolar Transistor) based power conversion module, NbTi mixed matrix conductor superconducting magnet and a cryostat with HTS current leads. The authors developed the code for design of a SMES magnet, which could find the parameters of the SMES magnet having minimum amount of superconductors for the same stored energy, and designed the 1-MJ SMES magnet by using it. And they have designed and fabricated cryostat with kA class HTS current leads for a 1-MJ SMES System. This paper describes the design, fabrication and experimental results for a 1-MJ SMES System.

The authors have developed a small-sized superconducting magnetic energy storage (SMES) magnet with the nominal storage capacity of 1 MJ, which provides electric power with high quality to sensitive electric loads. In large magnets such as the SMES magnets the stability, which is determined by several factors, e.g., conductor's cooling condition and operating current, magnet's winding structure, is a crucial problem. For the stable and compact SMES magnet development, two kA class conductors with different copper ratios were selected as candidate conductors. The effect of the cooling condition, the copper ratio, and the conductor's size upon the recovery currents was investigated experimentally. The test results indicate that the recovery current characteristics of the strands vary considerably according to their insulation method. In the fully insulated strands with a low copper ratio, the recovery current densities range from 10 to 20% of their engineering critical current densities. The recovery current density of the 30-conductor with a cooling channel is about a factor of 1.8 higher than that without a cooling channel.

For the development of a small-sized superconducting magnetic energy storage (SMES) system we designed, fabricated and tested a model coil consisting of five coils with different features, e.g., winding tensions, bore diameters and materials, cooling channels. The results show that even in the highly prestressed small coil, about 70% of the coil's critical current is degraded. The quench currents of the coils with narrow cooling channels are two times as high as that of the coil without spacers. The test results also indicate that the usual training effect depends on the winding tensions of the coils but the quench characteristic does not change according to materials of the bobbin.

A nuclear magnetic resonance (NMR) magnet composed of a high-temperature superconductor (HTS) is expected to contribute to a smaller size and a higher magnetic field (>1 GHz) of the NMR magnet due to its high critical current density under high magnetic field and better mechanical properties. The high operating temperature of HTS NMR magnets also makes conduction cooling by a cryocooler available. The conduction cooling system combined with a cryocooler is compact and user-friendly but has critical issues about the design of conduction cooling passages and the mechanical vibration. The small-scale HTS magnet with the conduction cooling system is fabricated and tested to check the issues and establish the design basis as a preliminary step for the development of a 400-MHz HTS NMR magnet. Thermal analysis for heat loads and thermal resistances at main joints is performed from the temperature distribution of the cooling system. The vibration levels at the crycooler and the vacuum chamber are discussed in comparison to the vibration criterion of NMR magnets. In addition, the design approach to the conduction cooling system for the HTS NMR magnet is discussed.

In this study, we developed neon refrigeration system using commercial helium compressor which was originally designed for GM cryocooler. We performed this research as precedent study before developing neon refrigeration system for small-scale hydrogen liquefaction system. The developed system is based on precooled Linde-Hampson system with liquid nitrogen as precoolant. Design parameters of heat exchangers are determined from thermodynamic cycle analysis with operating pressure of 2 MPa and 0.4 MPa. Heat exchangers have concentric-tube heat exchanger configuration and orifice is used as Joule- Thomson expansion device. In experiments, pressure, temperature, mass flow rate and compressor input power are measured as charging pressure. With experimental results, the characteristics of heat exchanger, Joule-Thomson expansion and refrigeration effect are discussed. The developed neon refrigeration system shows the lowest temperature of 43.9 K.

Miniature Joule-Thomson refrigerators have been widely used for rapid cooling of infrared detectors, probes of cryosurgery, thermal cameras, missile homing head and guidance system, due to their special features of simple configuration, compact structure and rapid cool-down characteristics. Typical performance factors of the Joule-Thomson refrigerator are cool-down time, temperature of the cold end, running time and gas consumption. Those depend on operating conditions such as the pressure of the gas, thermal environment and etc.. In this study, experimental study of a miniature Joule- Thomson refrigerator with the gas pressure up to 12 MPa were performed to investigate the effects of the thermal environment (-40 ~ 50 °C). In experiments, to obtain the information of cool-down time, gas consumption and etc., the temperature of the cold end, mass flow rate and pressure of the argon gas are simultaneously measured. The Joule-Thomson refrigerator in cold thermal environment has rapid cool-down characteristics and small gas consumption. In the cold environmental condition, the Joule-Thomson refrigerator has high mass flow rate during cool-down process and in steady state.

This paper presents a proportional pressure reducing valve for clutch control system and for tilting pad angle control of the hydraulic pump system. The proportional pressure reducing valve of this study has a spool with a reducing pressure control pin and a proportional solenoid actuator instead of an on-off solenoid actuator. The solenoid actuator consists of a bobbin with coils, a plunger and a core with a control cone. The control cone is a very important equipment for the attraction force adjustment and controls the flux saturation and the flux leakage. So the attraction force is constant in the range of the control cone. In this study, a new proportional reducing valve with a pressure control pin was proposed and the validity of the new mechanism with a pressure control pin was discussed. The dynamic characteristics of the object proportional pressure reducing valve were studied by numerical analysis using the mathematical model. Also, the static and the dynamic characteristics of the new pressure reducing valve were tested by testing system which is based on test standard.

Cooling capacity and cool‐down time of a Joule‐Thomson (J‐T) refrigerator depends on mass flow rates of refrigerants and their enthalpy changes. It is obvious that the mass flow rate through the J‐T refrigerator depends on supply pressure; it increases as the supply pressure increases. Furthermore the mass flow rate increases as the temperature of the cold end decreases when the supply pressure does not change during the cool‐down process. In this study, the cool‐down characteristics of a miniature J‐T refrigerator (fixed orifice / demand flow type) with different pressures of nitrogen and argon gas, were investigated by experiment. To analyze the cool‐down characteristics of the refrigerator, the supply and exhaust pressure, the temperatures on the surface of the cryostat, and the mass flow rate were measured simultaneously. The results show the effect of the supply pressure on the performance of the refrigerator. The influence of the supply pressure and the temperature on the mass flow rate during the cool‐down stage is discussed in detail.

Miniature Joule Thomson refrigerators have been widely used for the cooling of infrared detectors, cryosurgery, thermal cameras, missile homing heads, and guidance systems because they have a simple, compact structure and rapid cooldown characteristics.

Publisher Summary This chapter investigates the influences of the radial clearance on the performance of Stirling refrigerator by numerical simulation. The Stirling refrigerator has the clearance in the compressor and cold finger. Its cooling capacity comes from the relation of the pressure in the expansion space and motion of displacer. In the radial clearance of the cold finger, the parasitic dynamic losses from the leakage flow and shuttle heat losses are inevitably occurred. Therefore, to get the maximum performance of the refrigerator, the radial clearance should be optimized. The SAGE is used to investigate the effects of the operating frequency, the stroke of the displacer and the radial clearance between the seal rings and the expander on the cooling performance. The calculation results show that the enthalpy flow through the refrigerator is a dominant heat loss. The leakage flow through the clearance has the effects on the cooling capacity through the gross refrigeration, the enthalpy flow, and the shuttle heat loss. The enthalpy flow through the clearance depends on the operating frequency and the radial clearance of the cold end, whereas the shuttle loss depends on the stroke of the displacer.