• Title, Summary, Keyword: 성적계수

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Prediction on Maximum Performance of Cascade Refrigeration System Using R717 and R744 (R718-R744용 캐스케이드 냉동시스템의 최대 성능 예측)

  • Roh, Geun-Sang;Son, Chang-Hyo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.10
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    • pp.2565-2571
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    • 2009
  • In this paper, cycle performance analysis of cascade refrigeration system using $NH_3-CO_2$(R717-R744) is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree and condensing and evaporating temperature in the ammonia(R717) high temperature cycle and the carbon dioxide low temperature cycle. The COP of cascade refrigeration system increases with the increasing superheating degree, but decreases with the increasing subcooling degree. The COP of cascade refrigeration system increases with the increasing condensing temperature, but decreases with the increasing evaporating temperature. Therefore, superheating and subcoolng degree, evaporating and condensing temperature of cascade refrigeration system using $NH_3-CO_2$ have an effect on the COP of this system. A multilinear regression analysis was employed in terms of subcooling, superheating, evaporating, condensing, and cascade heat exchanger temperature difference in order to develop mathematical expressions for maximum COP and an optimum evaporating temperature.

Performance Analysis of R744(Carbon Dioxide) for Transcritical Refrigeration System (R744용 초임계 냉동사이클의 성능 분석)

  • Roh, Geun-Sang;Son, Chang-Hyo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.1
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    • pp.32-38
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    • 2009
  • In this paper, cycle performance analysis for cooling capacity, compression work and COP of R744($CO_2$) transcritical vapor compression refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : The cooling capacity of R744 increases with superheating degree, but decreases with the increasing evaporating temperature and outlet temperature of gas cooler. The compression work increases with superheating degree and cooling pressure of R744, but decreases with the increasing evaporating temperature. And, The COP increases with outlet temperature and evaporating temperature of R744 gas cooler, but decreases with the increasing superheating degree. Therefore, superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

Simulation of a Double Effect Double Stage Absorption Heat Pump for Usage of a Low Temperature Waste Heat (저온 폐열 활용을 위한 2중 효용 2단 흡수식 히트펌프 시뮬레이션)

  • Kim, Nae-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.11
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    • pp.7736-7744
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    • 2015
  • Considering the significant waste of industrial energy, effective use of low temperature waste heat is extremely important. In this study, a heat pump cycle with double effect and double stage was realized, which escalates the hot water temperature from $50^{\circ}C$ to $70^{\circ}C$ using $160^{\circ}C$ high temperature heat source and $17^{\circ}C$ low temperature heat source. The steam generated in the first generator condenses in the first condenser generating steam in the second generator. The steam condenses in the second condenser and is provided to the second evaporator. Part of the water out of the second evaporator is supplied to the first evaporator, which evaporates using low temperature waste heat. The evaporated steam enters the first absorber and the second evaporator. The steam out of the second evaporator is absorbed into the solution at the second absorber. The hot water temperature is raised in the second condenser and in the second absorber. Proper flow rates and UA values, which satisfied temperature lift $20^{\circ}C$ and COP 1.6, were deduced through trior and error. The COP increases as the temperature of the high temperature water increases, hot water temperature decreases and flow rate increases, waste water temperature and flow rate increases, solution circulation rate decreases. On the other hand, the temperature rise of the hot water increases as the temperature of the high temperature water increases, hot water temperature increases and flow rate decreases, waste water temperature and flow rate increases, solution circulation rate increases. In addition, the COP and hot water temperature rise increase as UAs of the heat exchangers increase.

Effect of Individuals' Perceptions of Sex-role and Open Marriage on Individuals' Intention of Extra-marital Sex : Focusing on Mediation Effect of the Acceptance of Extra-marital Relationship and Moderation Effect of Gender (성역할고정관념과 개방결혼에 대한 인식이 성적외도 실행의도에 미치는 영향: 혼외관계 수용성의 매개효과와 성별의 조절효과를 중심으로)

  • Shin, Sung-Ja
    • The Journal of the Korea Contents Association
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    • v.17 no.3
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    • pp.199-211
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    • 2017
  • The notable findings are as follow: First, men show higher level of perceiving open marriage, sex-role, acceptance of extra-marital relationship and intention of extra-marital sex than that of women. Second, the effects of men's perception of sex-role and open marriage, and the acceptance of extra-marital relationship have direct effects on their intention of extra-marital sex. The acceptance of extra-marital relationship shows the mediation effect on the path between that of open marriage and extra-marital sex among men. However, men's perception of sex-role does not affect the acceptance of extra-marital relationship. Lastly, women's perception of sex-role and open marriage, and the acceptance of extra-marital relationship directly influence the intention of extra-marital sex each, including the mediating effect of accepting extra-marital relationship between that of open marriage and extra-marital sex which are similar to the men's trend. Women's perception of sex-role show the direct effect on the acceptance of extra-marital relationship unlike man's trend. Therefore, the fact demonstrates that the effect of perceiving of sex-role on the intention of extra-marital sex is different according to gender. Some practical and political implications are discussed based on the study's findings.

CARIES DIAGNOSIS BY DIAGNODENT'S LASER FLUORESCENCE DETECTION IN VITRO (레이저형광측정을 통한 Diagnodent의 우식진단에 관한 생체외 연구)

  • Kim, Seong-Hyeong;Lee, Kwang-Hee;Kim, Dae-Eop;Park, Jong-Seok
    • JOURNAL OF THE KOREAN ACADEMY OF PEDTATRIC DENTISTRY
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    • v.27 no.1
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    • pp.24-31
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    • 2000
  • The purpose of study was to compare the laser fluorescence detection by Diagnodent(KaVo, Germany), visual inspection using dental explorers, and conventional dental radiography as diagnostic tests for dental caries. One hundred and three human premolars and molars which had no caries or fissure caries were tested by the three methods. Diagnodent scores increased as the scores of the other two tests increased(P<0.01) There were significant relationships between visual inspection scores and Diagnodent scores(Pearson 0.676, Spearman 0.694) and between radiography scores and Diagnodent scores(Pearson 0.623, Spearman 0.658) (P<0.01, all). Diagnodent test proved to have high sensitivity and low specificity and more studies are necessary to present the diagnostic criteria for progressive caries stages.

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A Study of Air-source Heat Pump Performance Analysis for Replacing Night Time Electric Heating Boiler (심야전기보일러 대체용 공기열 히트펌프 성능평가)

  • Jo, J.Y.;Jung, H;Lee, C.H.
    • Journal of the Korean Society of Mechanical Technology
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    • v.13 no.3
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    • pp.81-85
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    • 2011
  • The night time electric cost is cheaper due to electric supply and demand policy in Korea from 1985. Currently about 900,000 customers are using night time electric heating boilers and this causes shift of peak demand time to night in winter and increase of deficit spending. To solve this problem, replacing night time electric heating boiler by air-source heat pump using night time electricity has been proposed. An air-source heat pump can provide efficient heating equipment especially in a warm climate. For estimating the night time electric heat pump COP(Coefficient of Performance), Korean Standard KS C 9306:2010 and European Standard EN-14511:2004 is available. SCOP(Seasonal COP) using European weather bin data is also calculated. SCOP is not available yet but European Committee for Standardization will establish a standard in the near future. The evaluation result show that the replacing night time electric heating boiler by heat pump can be possible.