• Progress in Superconductivity and Cryogenics
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• v.12 no.4
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• pp.41-45
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• 2010

Miniature Joule-Thomson refrigerators have been widely used for rapid cooling of infrared detectors, optoelectronic device, and integrated circuits of micro electronics. The typical J-T refrigerator consists of the recuperative heat exchanger with the double helical tube and fin configuration, J-T nozzle, a mandrel, Dewar and a compressed gas storage bottle. In this study, to predict the thermodynamic behaviors of the refrigerator with a compressed gas storage bottle during the cool-down time, numerical study of transient characteristics for a J-T refrigerator was developed. A simplified transient one.dimensional model of the momentum and energy equations was simultaneously solved to consider the thermal interactions of the each component of the refrigerator. To account for effects of the thermal mass of the solid, the heat capacities of the tube, fins, mandrel and Dewar are considered. The results show the charged gas pressure of the gas storage bottle has significant effects on the performance of the J-T refrigerator. At the elevated gas pressure of the gas storage bottle, the large capacity of the compressed gas storage does not need to get the fast cool-down performance of the J-T refrigerator in the cool-down stage.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.71-76
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• 2002

To achieve good cryogenic circumstances by Gifford-McMahon cryocooler, we have to constitute optimal conditions with various factors for G-M cryocooler. In this study, cool-down characteristics were presented with some factors using brass matrix mesh (1st stage) and Pb ball (2nd stage) as regenerator materials for the heat exchangers. The effects of the variations of Helium gas pressure and cycle frequency on the cooling capacity of G-M cryocooler are investigated experimentally. The presented results could be summarized as follows : 1) As the steady state pressure increases, 'no load temperature' decreases but cooling capacity increases. 2) It is confirmed that the characteristics of the specific heat of the regenerator materials agree well with the cool-down characteristics of 10 K cryocooler.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.6 s.261
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• pp.531-538
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• 2007

In this study, an air conditioning system using carbon dioxide as a refrigerant was developed for automotive cabin cooling. Experiments have been carried out to examine the steady state and dynamic characteristics of this system. The system consists of a compressor, a gas cooler, an evaporator, an expansion device, an internal heat exchanger and an accumulator. The compressor is a variable displacement type, driven by the electric motor, and the gas cooler and the evaporator are aluminum extruded heat exchangers of micro channel type. The $CO_2-refrigerant$ charge, the compressor speed, the air inlet temperature of the gas cooler, the air inlet temperature and the air flow rate of the evaporator and the cooling load are varied and the performance of the system is experimentally investigated. As the compressor speed increased, cooling capacity increased, but the coefficient of performance was deteriorated. As the cabin air temperature or the air flow rate to the cabin was set high, both the cooling capacity and the COP increased. In the cool down experiment with 1.0 or 2.0 kW of heat load, the dynamic characteristics of the air-conditioning system were investigated. For a given capacity of compressor, cool down speed was monitored, and the temperature change was acceptable fur low heat load condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.600-609
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• 1998

The experimental investigation of thermal response characteristics by the air flow through the porous media has been carried out. The packed spheres of steel or glass were considered as the porous media in the present study. Temperature distributions of the fluid in the porous media as well as pressure drops through the porous media were measured. The transient temperature variations in the porous media are compared favorably with the analytical results in the high Reynolds number ranges. However, in the low Reynolds number ranges, the experimental data deviate from the analytical results, due to the dominant heat conduction penetration to the upstream direction, which is not considered in the analytical model. The cool-down response of porous media is found to be dependent upon the specific dimensionless time considering the material property and air velocity. The heat discharge process is recommended to be operated until a certain time, considering the cost efficiency.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.320-323
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• 2003

This paper presents the results of a series of performance tests for the Stilting cryocooler. A free piston and free displacer(FPFD) Stilting cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM. Our coolers are specifically designed to work in the thermal imaging device and to meet requirements such as cooling capacity, COP and high reliability. In this work, Stilting cryocooler is designed, manufactured and fabricated, and performance characteristics for the cooling capacity / applied input power and cool down time are investigated. This cooler delivers approximately 0.9W cooling at 80K for 30W ~ 40W of input power. And, It takes approximately 2 minutes to cool down to 80K at the ambient temperature of 23$^{\circ}C$.

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.57-61
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• 2015

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1089-1096
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• 2001

The cool-down performance after soaking is very important in an automotive air-conditioning system and is considered as the key design variable. Therefore, understanding of the overall transient characteristics of the system is essential to the preliminary design as well as steady-state characteristics. The objective of this study is to develop a computer simulation model and estimate theoretical1y the transient performance of an automotive air-conditioning system. To accomplish this, a mathematical modelling of each component, such as compressor, condenser, expansion valve, and evaporator, is presented first of all. For a detailed calculation, condenser and evaporator are divided into many subsections. Each sub-section is an elemental volume for modelling. In models of expansion valve and compressor, dynamic behaviors are not considered in an attempt to simplify the ana1ysis, but the quasi-static ones are just considered, such as the relation between mass flow rate and pressure drop in expansion device, polytropic process in compressor, etc. The developed simulation model is validated with a comparison to laboratory test data of an automotive air-conditioning system. The overall time-tracing properties of each component agreed fairly well wish those of test data in this case.

• Journal of the Korean Institute of Gas
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• v.5 no.2 s.14
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• pp.52-61
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• 2001

Cryogenic LNG(Liquefied Natural Gas) which is stored in the cylindrical storage tanks of $100,000m^3$ has very complex flow phenomena and the changes of thermal properties with exterior conditions and operation modes. These complex thermofluid behaviors are affected by the storage, exterior conditions of LNG, design specifications and heat transfer characteristics of tanks. Also, those have influence on the stable storage and supply of LNG in the storage tanks. Thus this study peformed the analysis on the 2-D heat transfer of the tank with exterior conditions, on the Cool Down Process in order to cool down the LNG Storage Tank at the initial normal state, and on the Filling Process considered for incoming and rising of LNG. The analysis on the Mixing LNG Storage was studied too. At last, the visualized program on the complex thermofluidodynamic analysis was developed on the basis of the above analyses. The development of this program becomes to be used to the basic design of the commercial tanks as well as to assure technical skill of the analysis on the thermal stability of the stored LNG in the LNG Storage Tank.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1329-1334
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• 2004

The most compact and convenient pulse tube cryocooler for practical applications is the coaxial type. It can replace Stirling cryocooler without any change to the Dewar or the connection to the cooled devices. The experimental results of the coaxial inertance tube pulse tube cryocooler for cooling superconductor RF filter are presented in this paper. To find optimal conditions of inertance tube pulse tube cryocooler, no load temperature according to the variations of inertance tube volume, reservoir volume are measured, and the cool down characteristics at the particular conditions are presented. In case of the coaxial type inertance tube pulse tube refrigerator, cool down time is the lowest in the inertance tube diameter of 1.3 mm and inertance tube length of 1900 mm and lowest temperature is 112K. This results are not satisfactory for practical applications. So, We propose vacuum insulation between regenerator and pulse tube in the Stirling type coaxial pulse tube cryocooler. Stirling type coaxial pulse tube cryocooler with the vacuum insulation between regenerator and pulse tube was designed and manufactured by KIMM(Korea Institute of Machinery and Materials). The optimal conditions will be tested for Stirling type coaxial pulse tube cryocooler with the vacuum insulation between regenerator and pulse tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.4
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• pp.457-463
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• 1999

The Joule-Thomson cryocooler with $H_2$gas has been developed. Cool-down characteristics and the cooling performance of a JT cryocooler have been investigated in detail. The JT cryocooler consists of JT expansion valve, heat exchanger, expansion chamber, compressed $H_2$gas storage tank, $LN_2$precooler, heater and a cryostat. The precooling process using both $GN_2$and $LN_2$was peformed to cool down the inside components of cryocooler under the maximum inversion temperature of $H_2$. The $H_2$expansion experiments have been peformed for 2-5MPa of H$_2$pressure to evaluate steady state temperatures of the cryocooler. It is found that the steady state temperatures are decreased as the H$_2$pressures are increased. The effects of cooling temperatures on the performance have been evaluated for various $H_2$and $N_2$pressures. It is seen that the cooling loads are increased, as the cooling temperature and operating pressure are increased.