• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.432-438
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• 2003

This paper describes a modified Roebuck compression device as a potential compression device of a rotating cryogenic refrigeration system in superconducting machine such as generator or motor. The conventional cryogen transfer method from stationary refrigeration system to rotating system can be eliminated by an on-board cryogenic refrigeration system that utilizes well-designed multi-stage modified Roebuck compression device. This paper shows basic thermodynamic analysis of modified Roebuck compression device and its application for compressing neon at 77 K with substantial pressure ratio when the rotor diameter is 0.8 m with rotating speed of 3600 rpm. The device does not require any moving part in rotating frame, but two separate thermal reservoirs to convert thermal energy into mechanical compression work. The high temperature thermal reservoir is atmospheric environment at 300 K and the low temperature thermal reservoir is assumed as a liquid nitrogen bath at 77 K. The concept of the compression device in this paper demonstrates its usefulness of generating high-pressure neon at 77 K for rotating J-T neon refrigeration cycle of superconducting rotor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.928-936
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• 1999

An experimental study was performed to investigate characteristics of an inverter driven water-to-water refrigeration system with a variation of compressor frequencies and expansion devices. The frequency of a compressor varied from 30Hz to 75Hz, and performance of the systems applying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve(EEV) were measured. The load conditions were altered by varying the temperature of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test conditions were deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimum control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in an inverter refrigeration system due to active control of flow area with a change of compressor frequency and load conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1101-1106
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• 2004

Magnetic refrigeration is based on the magnetocaloric effect (MCE)-the ability of some materials to heat up when magnetized and cool down when demagnetized. A rotary magnetic refrigeration device using gadolinium (Gd) ribbon and permanent magnets was constructed for experimental study. Gd ribbon attached around a rotating wheel is cyclically magnetized and demagnetized by permanent magnets and exchanges heat with liquid in the surrounding container. Temperature of the liquid in each divided section of the container was measured and the experimental results obtained in this study were discussed.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.7 no.4
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• pp.257-267
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• 1978

Hermetically sealed refrigeration comperessor use for household refrigerotor, room air conditioner, require effective performance, stable condifion. From now, I'm going to tell you about characteristics of motors, starters and protecting device for compressors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.366-381
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• 1995

A performance analysis of refrigeration system using the HFC-134a and scroll compressor is performed numerically. The refrigeration system mainly consists of various standard components such as heat exchanger, compressor, and expansion device. The model for heat exchanger performance is based on a tube-by-tube method which is analyzed separately by considering the cross-flow heat transfer with the outdoor air flow and pressure drop. Compressor is used the scroll-type compressor which has many merits such as high efficiency, low noise and vibration, and small in size. Short-tube is included as an expansion device. Vapour and liquid line are also considered for the performance analysis of refrigeration system. Using the modeling of various components of refrigeration system, a performance comparison of CFC-12 and HFC-134a is performed numerically for the various outdoor air temperature and various values of short-tube diameter. As the results of this study, the refrigeration system performance decreases as the outdoor air temperature increases. And the optimum short-tube diameter based on COP is 1.37mm for this system.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.3
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• pp.100-106
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• 2009

As an effort to prevent environmental problems caused by ozone depletion and global warming, alternative refrigerants are being developed, and one of the candidates is carbon dioxide. To overcome slightly low efficiency of $CO_2$ refrigeration system, air-conditioning cycle using an ejector was suggested. Ejector compensates throttling loss in an expansion device by reducing compression work. In this study, the ejector refrigeration cycle using $CO_2$ as a refrigerant is investigated to understand the effect of the mixing section diameter and refrigerant charge amount on the performance. If mixing section diameter is too large or too small, either cases show low performance. The optimum refrigerant charge amount which gives the best performance is found for standard operating conditions. The air-conditioning cycle was analyzed for several operating conditions.

• Journal of ILASS-Korea
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• v.5 no.3
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• pp.1-8
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• 2000

Spray as a liquid atomization technique has wide applications of combustion, painting, chemical, medical and agricultural purpose, and so on. Capillary tubes and expansion valves, as an expansion device of vapor compression type refrigerators, has been used from the early time. But there are some problems in practice, the former can't control refrigerant flowrate exactly and the later most of imported are expensive relatively and has some difficulties to install. Choosing an injector as a new concept of expansion device of refrigerator in this study to improve such troubles of the coming expansion device, the refrigerant spray behavior and refrigeration characteristics are evaluated experimentally. It is verified that the injector with a good function of refrigerant atomization plays a desirable role of refrigerant expansion in the actual refrigeration cycle.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.40-45
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• 2011

The purpose of research is to understand the characteristics of refrigeration system having a liquid-vapor phase separator after expansion device and precooling heat exchanger. After expansion process of typical refrigerant of freezer, R134a, the cold vapor of the expanded refrigerant mixture is separated in the liquid-vapor separator and introduced in the precooling heat exchanger to enable the liquid refrigerant to be subcooled. The analysis results showed that the increasing rate of refrigeration capacity and COP can be 8.6% and 1.4%, each. The cause of these performance improvements is due to the difference of the slope of saturated vapor and saturated liquid lines in Mollier diagram of refrigerant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.5
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• pp.418-425
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• 2006

An AHX (Accumulator Heat exchanger) consists of a commercial accumulator and an inner heat exchanger located inside of the accumulator. The AHX is used in multi air-conditioners to assure that liquid-phase refrigerant enters into the expansion device. This purpose is achieved by heat transfer between the refrigerant leaving the evaporator and the refrigerant leaving the condenser. In this study, the effects of AHX on the performance of a refrigeration system using R-22 were measured and the test results were analyzed. The operating characteristics of the refrigeration system with the AHX are considerably different from those without the AHX. Therefore, it is required to determine optimum refrigerant charge and optimum operating conditions when the AHX is used in the refrigeration system having a constant flow-area expansion device such as capillary tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.10
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• pp.925-931
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• 2000

Refrigerating ability of vapor compression refrigerator is decided by the harmonic work of it's components such as compressor, condenser, evaporator, expansion device, and so on. In this study, choosing refrigerant injectors as a new one of expansion device, temperature change of the cold room, ice freezing ability, and power consumption on flowrate of injector and refrigerant charging condition are evaluated experimentally. As the results of this study, it is verified that the spray injection type refrigeration system has some merits according to the flowrate and spray pattern of injector and charging quantum of refrigerant. And there are some design factors such as spray pattern and shape of spray chamber to utilize and fabricate this refrigerant injection type refrigerator.