• Proceedings of the KSME Conference
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• 2000.04b
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• pp.90-95
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• 2000

Condensation heat transfer experiments for R-22 and R-407C refrigerants mixed with mineral oil and POE oil respectively were performed in straight and U-bend sections of a microfin tube. Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to $400 kg/m^2s$ and an inlet quality from 0.5 to 0.9. The enhancement factors for R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. They decreased rapidly as the mass flux decreased and inlet quality increased. The heat transfer coefficients in the U-bend were the maximum at the $90^{\circ}$ position. The heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficients at the first straight section.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.442-447
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• 2010

FPSO (Floating Production Strorage and Offloading) method for LNG industry is efficient and facile compared to onshore NG (Natural Gas) treatment facility. Five simple natural gas liquefaction cycles for FPSO are presented and simulated in this paper. SMR (Single Mixed Refrigerant) cycle, SNE (Single Nitrogen Expander) cycle, DNE (Double Nitrogen Expander) cycle, PNE (Precooled Nitrogen Expander) cycle, and PDNE (Precooled Double Nitrogen Expander) cycle are compared. Simple analysis results in this paper show that precooling process and adding an expander in the liquefaction cycle is an effective way to increase liquefaction efficiency.

• Progress in Superconductivity and Cryogenics
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• v.10 no.4
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• pp.38-42
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• 2008

Miniature J-T cryocooler using nitrogen or argon has been widely adopted in cooling infrared sensor for space/military application and cryosurgery. Argon or nitrogen, however, has relatively low specific cooling power compared to nitrous oxide, but the ultimate operating temperature is much lower than nitrous oxide. On the other hand, nitrous oxide has large specific cooling power, but the operating temperature is limited to its boiling point (>183K). To compromise the different characteristics of these gases, the performance of miniature J-T cryocooler using argon and nitrous oxide mixture is investigated in this paper. Three different compositions of mixture (25/75, 50/50, and 75/25 molar fraction) are blended and tested. The results are compared with the experiments of pure argon and pure nitrous oxide. The experimental results show some encouraging potentiality of mixed refrigerant J-T cryocooler. The critical clogging problem, however, was observed with argon and nitrous oxide mixture, and the lowest achievable temperature with this mixture was limited to the freezing point of nitrous oxide. The paper discusses detailed clogging process of the mixture and suggests an alternative.

• Journal of Power System Engineering
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• v.19 no.6
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• pp.82-88
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• 2015

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.37-44
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• 2005

An experimental study was conducted to analyze performance of a heating system with variation of control logic of the system. The system uses a solar as heat source and composed with heat pump that uses R-22 as working fluid. The difference between the developed system and the commercially available heating system is working fluid. The solar assisted heating system which was widely distributed in the market uses water as a working fluid. It could be freezing in case of the temperature drops down under freezing point. The anti-freezing fluids such as methyl-alcohol or ethylene-glycol are mixed with the water to protect the freezing phenomena. However, the system developed in this study uses a refrigerant as a working fluid. It makes the system to run under zero degree temperature conditions. Another difference of the developed system compare with commercial available one is auxiliary heating method. The developed system has removed an auxiliary electric heater that has been used in conventional solar assisted heating system. Instead of the auxiliary electric heater, an air source heat exchanger which generally used as an evaporator of a heat pump was adapted as a backup heating device of the developed system. As results, an efficiency of the developed system is higher than a solar assisted heat pump with auxiliary electric heater. The merit of the developed system is on the performance increment when the system operates at a lower solar energy climate conditions. In case of the developed system operates at a normal condition, COP of the solar collector driven heat pump is higher than the air source heat exchanger driven heat pump's.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3253-3259
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• 2009

In this study, a computer simulation has been performed for the refrigeration cycle using mixed refrigerants in order to decrease the process stream temperature to $-20^{\circ}C$. Refrigerant supply temperature was assumed to be $-30^{\circ}C$ considering the temperature difference as $10^{\circ}C$ with process stream. Peng-Robinson equation of state model was selected for the computer simulation. A new alpha function proposed by Twu et al was used for an accurate prediction of pure component vapor pressure experimental data. One fluid mixing rules were used for the estimation of mixture vapor-liquid equilibria calculations. A commercial process simulator, PRO/II with PROVISION was utilized for the simulation of the overall refrigeration process. In order to minimize the compressor power consumption, we have optimized the two-stage compression system by varying the first stage compressor outlet pressure. Finally, we could obtain the minimum total power 755.7kW at the first stage compressor outlet pressure, 6 bar.

• Analytical Science and Technology
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• v.30 no.5
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• pp.240-251
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• 2017

1,1,1,2-Tetrafluoroethane (HFC-134a), which is used as refrigerant in air conditioners, has been recently regulated as a greenhouse gas and is recommended for reuse by refining. It is very important to quantitatively analyze trace impurities present in the refrigerant to evaluate the criteria for reuse. In this study, trace impurities including C, H, Cl, and F, which are difficult to quantify because there are no reference materials, were quantitatively analyzed by a gas chromatograph-atomic emission detector (GC/AED); for this analysis, this was preceded by a qualitative analysis with a GC-mass selective detector (GC/MSD). In addition, the AED response was investigated using a hydrocarbon mixed reference material, which was proportional to the number of atoms in the component. Fifteen refrigerant components were detected as trace impurities in HFC-134a by qualitative analysis of trace impurities including C, H, Cl, and F in the samples. Based on the results of the qualitative analysis, quantitative analysis of trace impurities using AED showed that the highest mole fractions were for the $CHClF_2$ component ($45438.38{\mu}mol/mol$) in one sample and for the $C_2H_2ClF_3$ component ($1311.47{\mu}mol/mol$) in another sample. From this study, it has been shown that it is possible for this analytical method to be applied to the qualitative and quantitative analysis of trace compounds in refrigerants, which are difficult to quantify because of the absence of reference materials.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.230-236
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• 2001

We developed a built-in sensor bearing to measure the rotor motion of a rolling piston type compressor for the air conditioner. Because of needs for the high efficiency and long life span of compressor, and the usage of alternative refrigerants, the operating condition of the compressor becomes more severe. The accurate measurement of the rotor motion of the compressor can contribute greatly to the design and analysis of the hydrodynamic bearing. However, it is difficult to measure accurately the shaft behavior of small compressor because of the small space for the sensor mount, high temperature and pressure of compressor, oil mixed with refrigerant, and electromagnetic noise of the motor. To overcome these difficulties, we develop the cylindrical capacitive sensor that is built in the hydrodynamic bearing and calibrate the built-in sensor bearing indirectly through measuring the oil relative permittivity. We measured the rotor motion as well as suction and discharge pressures in various conditions. The several experimental results show that the developed built-in sensor bearing can measure the rotor motion not only in steady state but also in transient state.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.1
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• pp.82-91
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• 1997

R-410a and R-407c witch have the best potential among the substances being considered as R-22 alternatives were tested as "drop in" refrigerants against a set R-22 baseline tests for comparison. The performance evaluations were carried out in a psychrometric calorimeter test facility using the residential split-type air conditioner under the ARI rating conditions. Other than the use of different lubricant and a hand-operated expansion valve, one of the commercial systems was selected for the experiment. Performance characteristics were measured; compressor power, capacity, VCR, mass flow rate and COP. The tests showed that R-407c can be directly applied to the existing refrigeration system because of its similar vapor pressure and other thermopysical properties with those of R-22. However, it required change to the volume flow rate of compressor in order to achieve the similar performance with R-22 because of its relatively small VCR and capacity. Meanwhile, R-410a has too high a vapor pressure to be applied to the existing system and this feature results in relatively low COP of the system compared to that of R-22. But this could be improved by changing compressor design considering R-410a's relatively high VCR and capacity compared to those of R-22.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.200-208
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• 2021

Compare to the gaseous hydrogen, liquid hydrogen has various advantages: easy to transport, high energy density, and low risk of explosion. However, the hydrogen liquefaction process is highly energy intensive because it requires lots of energy for refrigeration. On the other hand, the cold energy of the liquefied natural gas (LNG) is wasted during the regasification. It means there are opportunities to improve the energy efficiency of the hydrogen liquefaction process by recovering wasted LNG cold energy. In addition, hydrogen production by natural gas reforming is one of the most economical ways, thus LNG can be used as a raw material for hydrogen production. In this study, a novel hydrogen production and liquefaction process is proposed by using LNG as a raw material as well as a cold source. To develop this process, the hydrogen liquefaction process using hydrocarbon mixed refrigerant and the helium-neon refrigerant is selected as a base case design. The proposed design is developed by applying LNG as a cold source for the hydrogen precooling. The performance of the proposed process is analyzed in terms of energy consumption and exergy efficiency, and it is compared with the base case design. As the result, the proposed design shows 17.9% of energy reduction and 11.2% of exergy efficiency improvement compare to the base case design.