• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.73-79
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• 2011

A portion of oil for lubrication of compressor flows together with refrigerant in the refrigeration system. If the oil discharge from a compressor is increased in the refrigeration system, not only pressure drop is increased in other components, such as evaporator and gas cooler, but also heat transfer coefficient in the heat exchangers is decreased. Oil discharge rate from a compressor may strongly depend on operating conditions of a compressor. In this study, one stage single rotary compressor is employed for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Oil circulation ratio(OCR) can be estimated by measured mixture density. The results obtained indicate that the oil circulation ratio(OCR) is increased as the suction temperature or compressor operating frequency is increased. Oil circulation ratio(OCR) correlation of the compressor is also suggested.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.893-898
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• 2009

The quantity of discharged oil from a compressor is one of the most important issues for proper operation of refrigeration system. If the oil is increased in the system not only pressure drop is increased in other components, such as evaporator and gas cooler but also heat transfer coefficient in the heat exchangers is decreased. In addition, the lack of oil in the compressor may cause a critical of the system failure. In this study, one stage single rotary compressor is used for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Characteristics of oil circulation ratio have been investigated for $CO_2$ rotary compressor in the range of operation frequency 45 Hz to 63 Hz and the suction temperature range of $0^{\circ}C$ to $15^{\circ}C$. The results obtained indicate that the oil circulation ratio is increased as the suction temperature or compressor operating frequency is increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.255-262
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• 2014

To investigate the effect of oil on evaporation heat transfer of plate heat exchanger, evaporation heat transfer experiment was carried out using experimental apparatus for micro gear pumped R134a-oil circulation. By varying oil circulation rate of POE oil from 0 to 5%, evaporation heat transfer performance of plate heat exchanger was investigated. As OCR(Oil Circulation Ratio) increases, the evaporation heat transfer coefficient of R134a decreases and pressure drop increases. When the evaporating temperature is $30^{\circ}C$ and the refrigerant mass flow rate is 80 g/s, evaporation heat transfer rate decreases by 10 % and pressure drop increases by 10% at 2% of OCR condition.

• Tribology and Lubricants
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• v.13 no.2
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• pp.74-81
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• 1997

The purpose of this study is to develop a cold rolling oil with lubricity and mill cleanness property under the rolling conditions of high reduction ratio and high rolling speed. Six kinds of oil samples were blended. Evaluation of lubricity and anti-seizuro property of the samples were carried out with a laboratory scale rolling mill, where the contact conditions between work roll and strip are very close to actual cold rolling mill. Laboratory evaluation for dispersion, contamination, anti-oil stain property and residual carbon, etc. were carried out with several testers such as longterm circulation tester, Coulter counter and Conradson tester. A new high speed cold rolling oil with good lubricity and mill cleanness property was developed compared with the previously developed rolling oil.

• Economic and Environmental Geology
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• v.49 no.1
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• pp.63-75
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• 2016

The ratio of fractured reservoir is very high in oil & gas fields around the world. The demand of drilling technology for fractured reservoir is expected to increase continuously if oil and gas prices are economical. The purpose of the review study is to help operator or driller in selecting of proper drilling technology for preventing a lost circulation in the fractured formation. In order to achieve this goal, fractured reservoir(formation) they are classified into partial lost circulation formation and total lost circulation formation. In case of partial lost circulation formation, the drilling problem can be solved by using LCM(lost circulation material) mud additive and squeezing cement. For shallow depth, total lost circulation formation can be drilled safely and economically with casing drilling method. Also, for deeper depth, problems of total lost circulation in formation can be solved by applying mud cap, which is one of the drilling methods. This was confirmed through field application such as Italy's Medusa-1 field and Qatar's North field.

• Transactions of Materials Processing
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• v.16 no.1 s.91
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• pp.20-24
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• 2007

Polypropylene substrate with hair-like nano features(aspect $ratio{\sim}10$) on the surface is fabricated by injection molding process. Pure aluminum plate is anodized to have nano pore array on the surface and used as a stamper for molding nano features, The size and the thickness of the stamper is $30mm{\times}30mm$ and 1mm. The fabricated pore is about 120nm in diameter and 1.5 um deep. For molding of a substrate with nano-hair type of surface features, the stamper is heated up over $150^{\circ}C$ before the filling stage and cooled down below $70^{\circ}C$ after filling to release the molded part. For heating the stamper, stamper itself is used as a heating element by applying electrical power directly to each end of the stamper. The stamper becomes cooled down without circulation of coolant such as water or oil. With this new stamper heating method, nano hairs with aspect ratio of about 10 was successfully injection molded. We also found the heating & cooling process of the stamper is good for releasing of molded nano-hairs.

• Journal of the Korea Convergence Society
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• v.13 no.1
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• pp.375-386
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• 2022

Work involving standing or walking for a long time can cause swelling, pain, and fatigue in the lower extremities due to the effect of gravity on the circulation of the body. This study aimed to confirm the effects of aromatherapy essential oils, as a complementary and alternative therapy, on lower extremity edema, pain, and fatigue when applied as a foot bath or spray. The study was conducted after daytime work over two consecutive days on nurses who volunteered at the E University Hospital in D Metropolitan city between 15 August 2018 and 11 October 2018. This randomized controlled study. The foot bath group received a foot bath in 9 L of water containing 0.5 ml of essential oil blended with grapefruit and peppermint in a 1:1 ratio. The spray group received the same solution in 3% dilution in the form of a spray. Edema was assessed by measuring calf and ankle circumference, while pain and fatigue were evaluated using a numerical rating scale. Data were analyzed by ANOVA and repeated-measures ANOVA. The calf circumference in the foot bath and spray groups significantly reduced compared to that in the control group (F = 14.053, p <.001) after the interventions. Lower extremity pain (F = 42.497, p < .001) and fatigue (F = 20.641, p < .001) also significantly reduced in the foot bath and spray groups compared to those in the control group after the interventions. Foot bath is recommended to relieve swelling and pain in the lower extremities, and aroma spray is highly recommended considering the ease of application.