• Title/Summary/Keyword: Saturation coefficient

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A study on the characteristics of evaporation heat transfer of carbon dioxide flowing upward in a vertical smooth tube (이산화탄소의 수직원관 내 상향유동 증발열전달 특성에 관한 연구)

  • Kim, Yong-Jin;Cho, Jin-Min;Kim, Min-Soo
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2217-2221
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    • 2007
  • Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical tube have been investigated by experiment. Before the test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. A smooth tube with outer diameter of 5 mm and length of 1.44 m was selected as a test tube. The test was conducted at mass fluxes of 212 to 530 kg/$m^2s$, saturation temperature of -5 to 20$^{\circ}C$, and heat fluxes of 20 to 45 kW/$m^2$. As the vapor quality and mass fluxes increase, the heat transfer coefficients of carbon dioxide are decreased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase.

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Evaporation pressure drop of $CO_2$ in a horizontal tube (수평관내 이산화탄소의 증발 압력강하)

  • Lee Dong-Geon;Son Chang-Hyo;Oh Hoo-Kyu
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.5
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    • pp.552-559
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    • 2005
  • The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation pressure drop of $CO_2$ are highly dependent on the vapor qualify, heat flux and saturation temperature. The evaporation pressure drop of $CO_2$ is very lower than that of R-22. In comparison with test results and existing correlations. the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

The Experimental Study on the Heat Transfer of HFC134a for Condensation Tubes with Various Enhanced Surfaces (응축전열관 외부형상 변화에 따른 HFC134a의 열전달 실험)

  • Park Chan-Hyoung;Lee Young-Su;Jeong Jin-Hee;Kang Yong-Tae
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.8
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    • pp.613-619
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    • 2006
  • The objectives of this paper are to study the characteristics of heat transfer for enhanced tubes (19.05 mm) used in the condenser with high saturation temperatures and to provide a guideline for optimum design of a condenser using HFC134a. Three different enhanced tubes are tested at a high saturation temperature of $59.8^{\circ}C$ (16 bar); a low-fin and three turbo-C tubes.. The refrigerant, HFC134a is condensed on the outside of the tube while the cooling water flows inside the tube. The film Reynolds number varies from 130 to 330. The wall subcooling temperature ranges from $2.7^{\circ}C$ to $9.7^{\circ}C$. This study provides experimental heat transfer coefficients for condensation on the enhanced tubes. It is found that the turbo-C(2) tube provides the highest heat transfer coefficient.

Evaporation Heat Transfer and Pressure Drop in Micro-Fin Tubes Before and After Tube-Expansion (마이크로핀관의 확관 전후 열전달 및 압력강하 변화 특성에 관한 연구)

  • Hwang, Yun-Uk;Kim, Min-Su
    • 연구논문집
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    • s.34
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    • pp.29-38
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    • 2004
  • The objective of this study is to investigate the pressure drop and heat transfer characteristics of the micro-fin tubes before and after the tube-expansion process. Test tubes are single-grooved micro-fin tubes made of copper with an outer diameter of 9.52 mm before the tube-expansion. The direct heating method is applied in order to make the refrigerant evaporated in the micro-fin tubes. The test ranges of the heat flux, mass flux, and the saturation pressure are 5 to 15kW/$m^2$, 100 to 200 kg/$m^2s$ and 540 to 790 kPa, respectively. The effects of the mass flux, heat flux, and the saturation pressure of the refrigerant on the pressure drop and the heat transfer are presented for the refrigerant R22. In the test conditions of this study, the heat transfer coefficient for the micro-fin tube after the tube-expansion is about 16.5% smaller than that before the tube-expansion because the fin height of micro-fin is reduced and the fin shape becomes flatter. The micro-fin tube after the tube-expansion has about 7.7% greater average pressure drop than that before the tube-expansion process.

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Kinetic Studies of Lactic Acid Fermentation(Part 4) -Kinetic Stuies on Continuous Cultivation- (유산균발효에 관한 동력학적연구(제4보) -연속배양에 있어서의 동력학적연구-)

  • LEE Keun-Tai;YANG Hyeun-Suk
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.15 no.3
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    • pp.179-184
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    • 1982
  • The behavior of continuous flow culture of Lartobacillus bulgricus was investigated by application of Monod's kinetic model. The parameters obtained from Monod's chemostat theory successfully predicted the behavior of the chemostat. Then, it was found that Monod's kinetics were applicable to the growth rate dependence on glucose concentration. Under steady-state condition, the maximum growth rate, saturation constant, and wash out were found to be 0.62/hr, 7.69 g/1, 0.51/hr of continuous culture. And the optimum condition for the highest cell production was 0.41/hr in dilution rate, and at that point the cell production rate was 0.178g/1 hr.

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Periodicity Dependence of Magnetic Anisotropy and Magnetization of FeCo Heterostructure

  • Kim, Miyoung
    • Journal of Magnetics
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    • v.21 no.1
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    • pp.6-11
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    • 2016
  • The magnetic anisotropy energy (MAE) and the saturation magnetization $B_s$ of (110) $Fe_nCo_n$ heterostructures with n = 1, 2, and 3 are investigated in first-principles within the density functional theory by using the precise full-potential linearized augmented plane wave (FLAPW) method. We compare the results employing two different exchange correlation potentials, that is, the local density approximation (LDA) and the generalized gradient approximation (GGA), and include the spin-orbit coupling interaction of the valence states in the second variational way. The MAE is found to be enhanced significantly compared to those of bulk Fe and Co and the magnetic easy axis is in-plane in agreement with experiment. Also the MAE exhibits the in-plane angle dependence with a two-fold anisotropy showing that the $[1{\overline{I}}0]$ direction is the most favored spin direction. We found that as the periodicity increases, (i) the saturation magnetization $B_s$ decreases due to the reduced magnetic moment of Fe far from the interface, (ii) the strength of in-plane preference of spin direction increases yielding enhancement of MAE, and (iii) the volume anisotropy coefficient decreases because the volume increase outdo the MAE enhancement.

An experimental study on heat transfer characteristics in a vertical micro-fin tube during evaporation process of carbon dioxide flowing upward (이산화탄소의 마이크로 핀관 내 상향유동 증발열전달 특성에 관한 연구)

  • Kim, Yong-Jin;Cho, Jin-Min;Kim, Min-Soo
    • Proceedings of the SAREK Conference
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    • 2007.11a
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    • pp.247-251
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    • 2007
  • Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical micro-fin tube have been investigated by experiment. Before a test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. The micro-fin tube with outer diameter of 5 mm and length of 1.44 m was selected as the test section. The test was conducted at mass fluxes of 318 to $530\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat fluxes of 15 to $30\;kW/m^2$. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are increased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase, and there was not much of influence of mass flux on the heat transfer coefficients.

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An Experimental Study on the Characteristics of Evaporative Heat Transfer of Carbon Dioxide (이산화탄소의 증발열전달 특성에 관한 실험적 연구)

  • 조은석;윤석호;김민수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.1
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    • pp.38-45
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    • 2002
  • Evaporative heat transfer characteristics of carbon dioxide have been investi- gated by experiment. The experiments have been carried out for a seamless stainless steel tube of the outer diameter of 9.55 mm, the inner diameter of 7.75 mm and the length of 5.0 m. Direct heating method was used for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. Experiments were conducted with$CO_2$of purity 99.99% at saturation temperatures of 0.0 to 10.5$^{\circ}C$, heat fluxes of 12 to 27kW/$m^2$s and mass fluxes of 212 to 530 kg/$m^2$s. The heat transfer coefficients of $CO_2$are decreased as the vapor quality increases and these phenomena are explained by dimensionless Weber and Bond numbers. The heat transfer coefficients of$CO_2$increase when the heat and mass fluxes increase, and the saturation temperature effects are minor in the test range of this study. The present experimental data are compared with six renowned correlations with root-mean-squared deviations ranging from 23.0 to 94.9% respectively.

Quantification of Diesel in Soils using the Partitioning Tracer Method with Two-dimensional Soil Box (분배성 추적자 기법을 이용한 디젤 오염 토양의 정량적 오염도 평가에 관한 2차원 토조 실험 연구)

  • Rhee, Sung-Su;Lee, Gwang-Hun;Park, Jun-Boum
    • Journal of Soil and Groundwater Environment
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    • v.15 no.1
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    • pp.66-72
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    • 2010
  • The partitioning tracer method is to estimate the residual saturation of nonaqueous phase liquid (NAPL) in soils by analyzing tracer's retardation induced by the reversible partitioning of tracer with NAPL. This study is to estimate the residual diesel saturation in soils using the partitioning tracer method. Two-dimensional soil box was used to represent the 2-dimensional flows of groundwater and tracer solution in the saturated aquifer, and the soil box was filled with soil and then saturated with water. The residual diesel saturation was induced in saturated soil, and the partitioning tracer method was applied. The results from batch-partitioning experiment indicated that the diesel-water partitioning was linear with respect to tracer's concentration, and the partition coefficient of tracer between diesel and water was measured by their linearities. The groundwater flow in the saturated aquifer was simulated in the 2-dimensional soil box, and the residual diesel contamination was visually identified. The results from the partitioning tracer method with or without diesel in soils confirmed that 4-methyl-2-pentanol, 2-ethyl-1-butanol and 1-hexanol, can be used as a detecting method for diesel contamination. By the accuracies of estimations for diesel contamination using the partitioning tracer method, 2-ethyl-1- butanol showed the highest accuracy with 83%.

Heat Transfer Characteristics in the Evaporator of a Soft Ice Cream Maker (소프트 아이스크림 제조기 증발기의 전열 특성)

  • Byun, Ho-Won;Lee, Jin-Wook;Kim, Nae-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.4
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    • pp.1466-1473
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    • 2012
  • Soft icecream is made by scraping an ice formed on the inside of the cylindrical evaporator, where R-404A is evaporating in the annulus. The heat transfer characteristics of the refrigerant evaporation and those during icecream formation were experimentally investigated. Results show that the refrigerant-side heat transfer coefficients are highly dependent on the location in the evaporator due to the complex annulus configuration. The heat transfer coefficient at the inlet is generally lower than those of other locations. The average heat transfer coefficient increases as heat flux increases or saturation temperature decreases. A correlation is developed to predict the refrigerant-side heat transfer coefficient. The icecream-side heat transfer coefficient oscillates continuously due to the periodic removal of ice formed on the surface. The average heat transfer coefficient during icecream formation is approximately 280 W/$m^2K$, and that during single-phase cooling increased from 150 W/$m^2K$ to 250 W/$m^2K$.