• Tribology and Lubricants
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• v.36 no.3
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• pp.139-146
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• 2020

Global warming has led to an increase in demand of eco-friendly vehicles, such as electric cars, for reducing greenhouse gas emissions, and especially, regulating carbon dioxide generation. In addition, electric vehicles are equipped with an electric drive-type hermetic scroll compressor and a refrigerant, which exhibit current and future trends of using environmentally friendly refrigerants, including R-1234yf. In this study, polyol ester-based refrigeration oils are prepared via condensation esterification of polyol and fatty acids. The oils can be combined with R-1234yf refrigerant for applications in air conditioning and cooling systems of electric vehicles. The structure of synthetic polyol esters is confirmed via ¹H-NMR and FT-IR spectrum analysis, and the composition of the polyol ester is analyzed via gas chromatogram analysis. Furthermore, kinematic viscosity, viscosity index, total acid value, pour point, and color are analyzed as fundamental physical properties of the synthetic polyol esters. The compatibility and chemical stability of the synthetic polyol ester combined with the R-1234yf refrigerant are obtained via high temperature and high pressure oil-resistant refrigerant tests. The changes in the oil color and catalyst activity are observed before and after the experiment to determine whether it is suitable as a refrigerator oil.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.12
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• pp.820-824
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• 2008

Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, the electret filter is made by electrospinning process using Polystyrene which is dissolved by 5 : 5 of Tetrahydrofuran (THF) and Dimethylformamide (DMF). Also the electrical properties and the filtration performances of electrospun filter media are Quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. The surface charge potential and the surface charge density of electrospun PS filters are increased with increasing applied voltage and saturated at 30 kV of applied voltage. Also collection efficiency of electro spun filters is increased with increasing surface charge potential and surface charge density. But the surface charge potential is decreased by natural decay and it causes deterioration of particle collection efficiency.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.403-410
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• 2007

In this study, natural refrigerants and their mixtures that can supplement and replace R12 and R134a in automobile air-conditioners are studied. R134a is currently used as the refrigerant in new motor vehicle air conditioners, replacing the ozone depleting refrigerant R12. Although R134a has no ozone depletion potential, it has a relatively large global warming potential, approximately 1300 times that of $CO_2$ over a 100 year time horizon. For this reason, performance of natural refrigerants and their mixtures containing R152a, RE170 (Dimethylether, DME) and R600a (Isobutane) are measured under 2 different temperature conditions. They were tested in a refrigerating bench tester with an open type compressor. The test bench provided about 4 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. Test results show that the coefficient of performance (COP) of these refrigerants is up to 21.55% higher than that of R12 in all temperature conditions. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for automobile air-conditioners.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.8
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• pp.325-330
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• 2016

This study was conducted to develop a heating system for a fuel cell-driven electric vehicle. The system consists of a compressor, an expansion device and three heat exchangers. A conventional air source heat exchanger is used as primary heat exchanger of the system, and an additional water source heat exchanger is used as a pre-heater to supply heat to the upstream air of the primary heat exchanger. On the other hand, the third heat exchanger consists of a water-to-refrigerant heat exchanger. The heat source of the pre-heater and the water-refrigerant heat exchanger is the waste heat from the fuel cell's stack. In the experiment, the indoor and the outdoor air temperature were fixed, and the compressor speed, EEV opening and waste heat temperature were varied. The results indicate that the $COP_h$ of the proposed system is 3.01 when the system is operating at a 1,200 rpm compressor speed, 50% EEV opening, and $50^{\circ}C$ waste heat source temperature in air pre-heater operation. However, when the system uses a water-refrigerant heat exchanger, the $COP_h$ increases to up to 9.42 at the same compressor speed and waste heat source temperature with 75% EEV openings.

• Journal of Food Hygiene and Safety
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• v.23 no.2
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• pp.157-162
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• 2008

Enterobacter sakazakii was initially referred to as yellow-pigmented Enterobacter cloacae and reclassified in 1980. E. sakazakii infection cause life-threatening meningitis, septicemia, and necrotizing enterocolitis in infants. Powdered infant formula (PIF) and baby foods may be the important vehicle of E. sakazakii infection. It has been reported that E. sakazakii was isolated from PIF and sunsik ingredients produced in Korea. Some infants have been fed sunsik as a weaning diet. Therefore, it is necessary that this organism should be inactivated on preparing PIF and sunsik at homes and in hospitals. The cocktail of three Korean E. sakazakii strains (human, sunsik and soil isolates) were used to investigate the inactivation of this organism with hot water at 50, 60, 65, 70 and $80^{\circ}C$ and microwave heating for 60, 75, 90, 105 and 120 sec. Reconstituted PIF and sunsikwere inoculated with cocktailed vegetative cells of E. sakazakii at 6 log CFU/mL. Thermal inactivation of vegetative cells of E. sakazakii were achieved by reconstituted PIF and sunsik with hot water at $60^{\circ}C$ or greater and with microwave heating at 2,450 MHz for 75 sec or longer. Considering that biofilm formation of E. sakazakii was adapted to survive the dry environment that is PIF and sunsik and thermal resistance increased, it is suggested that inactivation of E. sakazakii was used by hot water at $70^{\circ}C$ or greater and microwave heating for 90 sec or longer. Reconstituted PIF and sunsik were inoculated with cocktailed vegetative cells of E. sakazakii at 2 to 3 log CFU/mL to investigate the growth curve of this organism and stored at 5, 10, 15, 20, 25, 30 and $35^{\circ}C$. Viable counts slightly changed at 5, $10^{\circ}C$ during 48 h but grew at $15^{\circ}C$ or greater. Considering that E. sakazakii is able to grow in infant formula milk at refrigerator temperature, reconstituted PIF and sunsik that are not immediately consumed should be discarded or stored at refrigeration temperatures within 24 h.