• Membrane and Water Treatment
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• 제3권1호
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• pp.63-76
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• 2012

Mother liquid discharged from a salt-manufacturing plant was electrodialyzed at 25 and $40^{\circ}C$ in a continuous process integrated with $SO_4{^{2-}}$ ion low-permeable anion-exchange membranes to remove $Na_2SO_4$ and recover NaCl in the mother liquid. Performance of electrodialysis was evaluated by measuring ion concentration in a concentrated solution, permselectivity coefficient of $SO_4{^{2-}}$ ions against $Cl^-$ ions, current efficiency, cell voltage, energy consumption to obtain one ton of NaCl and membrane pair characteristics. The permselectivity coefficient of $SO_4{^{2-}}$ ions against $Cl^-$ ions was low enough particularly at $40^{\circ}C$ and $SO_4{^{2-}}$ transport across anion-exchange membranes was prevented successfully. Applying the overall mass transport equation, $Cl^-$ ion and $SO_4{^{2-}}$ ion transport across anion-exchange membranes is evaluated. $SO_4{^{2-}}$ ion transport number is decreased due to the decrease of electro-migration of $SO_4{^{2-}}$ ions across the anion-exchange membranes. $SO_4{^{2-}}$ ion concentration in desalting cells becomes higher than that in concentration cells and $SO_4{^{2-}}$ ion diffusion is accelerated across the anion-exchange membranes from desalting cells toward concentrating cells.

• 동력기계공학회지
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• 제9권1호
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• pp.82-88
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• 2005

This paper presents numerical study on dynamic characteristics of evaporator to control evaporator superheat and compressor capacity with optimum condition in refrigeration system. It is very important to reduce energy consumption and to keep room temperature within a very restricted range with minimum oscillation in some special applications of the refrigeration system. Heat exchange is mainly happened in the evaporator. So, making mathematical model of evaporator and analyzing evaporator characteristics are necessary in order to control the superheat and the capacity of the system. A mathematical model based on the one dimensional partial differential equations representing mass and energy conservation and a tube-wall energy is described. A set of ordinary differential equation is formulated by integrating separately over the two regions(two-phase and vapor) generally presented in a heat exchanger.

• 대한지역사회영양학회지
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• 제21권1호
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• pp.25-36
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• 2016

Objectives: The purpose of this study was to investigate effects of nutrition education providing school lunch by personalized daily needed food exchange units using Food Exchange System for adolescent athletes. Methods: The subjects were 60 sports high school students (educated group, 30 vs. noneducated group 30). Nutrition education was provided for 4 weeks (40 min/lesson/week). In addition, personalized school lunch was served for 4 weeks, nutrition education period. The personalized lunch were provided Food Exchange Units according to personalized daily needed energy. The lessons were '5 Major nutrients, functions and foods', 'My daily needed energy and food exchange units by Food Exchange System', 'My meal plan by food exchange units according to my daily needed energy' and 'Smart choice of healthy snacks and eating outs'. After nutrition education, we examined the differences in anthropometric characteristics, nutrition knowledge, dietary attitude and dietary intake between the educated and the non-educated group. Results: We observed improvements in lean body mass in the educated group. With regard to nutrition knowledge, there were improvements in 'Functions of vitamins', 'Functions of minerals', 'Foods of fat', 'Foods of vitamin', and 'Foods of mineral' in the educated group. In relation to dietary attitude, there were improvements in 'Taking a meal with family and friend', 'Taking a meal at ease', 'Taking a meal with kimchi and vegetables', 'Taking a meal with three kinds of side dishes', 'Priority of choosing snacks' and 'Type of snacks' in the educated group. With regard to dietary intakes according to Dietary Reference Intakes for Koreans, there were improvements in intakes levels of fiber, vitamin A, vitamin C, folate, calcium, iron and zinc. The index of nutrition quality, as indicated by nutrition adequacy ratio also improved in the educated group. Conclusions: These results showed that a nutrition education program providing education lessons and personalized school lunch by food exchange units according to daily needed energy showed positive changes in nutrition knowledge, dietary attitude and dietary intake of adolescent athletes. Nutrition education program providing personalized school lunch by Food Exchange Units may improve dietary behaviors and dietary intakes of adolescents.

• 대한지역사회영양학회지
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• 제22권4호
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• pp.307-322
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• 2017

Objectives: This study examined the effects of nutrition education focused on personalized daily energy requirement and food units using Food Exchange System on anthropometric, biochemical characteristics, nutrition knowledge, dietary attitude and nutrient intakes for overweight and obese in a public health center. Methods: The subjects were 60 overweight/obese women based on BMI (educated 30 vs. non-educated 30, 50~64 years). Educated group was provided individual and/or group lessons (40 min/lesson/week, 5 week), 'Introduction: obese & health', '6 nutrients and 6 food groups', 'My obesity & daily needed energy', 'Meal planning for personalized daily energy and food units using Food Exchange Systems', and 'Smart food choices'. After education, we examined the differences in anthropometric/biochemical characteristics, nutrition knowledge, dietary attitude and nutrient intakes between educated group and non-educated group. Results: After nutrition education, in the educated group, there were improvements on anthropometric/biochemical characteristics, nutrition knowledge, dietary attitude and nutrient intakes in the educated group compared to the non-educated group. We observed a decrease in the mean weight, total cholesterol (TC) and the incidence of overweight/obesity and hypercholesterolemia and an increase in the mean lean body mass. The scores of nutrition knowledge, 'Function of carbohydrate, protein, vitamin, mineral' and 'Food Sources of fat, vitamin, mineral' were increased. The scores of dietary attitudes, 'Taking a joyful meal, a leisurely meal, a balanced meal, a meal with sufficient vegetables, a meal with diversity, a meal with spicy foods, a meal with overeating' were increased. The intakes of energy, carbohydrate, fat, protein, vitamin A, thiamin, Zn and cholesterol were decreased. The scores of INQ, protein, vitamin A, vitamin C, thiamin, riboflavin, vitamin B6, folate, Ca, P, Fe, Zn were increased. Conclusions: The nutrition education focused on personalized daily energy requirement and food exchange unit using Food Exchange System for overweight and obese may improve food behavior, dietary intakes and symptoms of overweight and obese, even in a community health center.

• 천문학회보
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• 제36권1호
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• pp.56.1-56.1
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• 2011

To understand the effect of the initial rotation for tidally bounded clusters with mass spectrum, we performed N-body simulations for the clusters with different degrees of initial rotation and compared to Fokker-Planck results. We confirmed that the cluster evolution is accelerated by the initial rotation as well as the mass spectrum. For the slowly rotating models, the time evolution of mass, energy and angular momentum show good agreements between N-body and Fokker-Planck calculations. On the other hand, for the rapidly rotating models, there are significant differences between two approaches at the beginning of the evolution. By investigating cluster shapes, we concluded that these differences are mainly due to secular instability that takes place for very rapidly rotating clusters. The shape of cluster for N-body simulations becomes tri-axial or even prolate, while the 2-dimensional Fokker-Planck simulation can treat only oblate type axisymmetric systems. We also founded that there is the angular momentum exchange from high mass to low mass.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.542-545
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• 2008

Experiments have been performed to investigate effects of pulsating cathode flow on a 10-cell proton exchange membrane fuel cell (PEMFC) stack. For all the experiments, the flow rate, temperature and relative humidity of hydrogen at the anode inlet are fixed. The effects of the pulsating frequency, amplitude and flow rate at the cathode inlet on performance of 10-cell PEMFC are examined. The polarization and power curves show that the power output and limiting current is substantially increased when the pulsating component is added to cathode flow channel. The maximum power output increases by up to 38% and enhancement of the overall performance is more pronounced at lower flow rate region.

• 한국수소및신에너지학회논문집
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• 제23권1호
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• pp.19-25
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• 2012

The efficiency and life time of the Proton Exchange Membrane fuel cell (PEMFC) system is critically affected by incoming gas with humidity which should be maintained properly at normal operating conditions. Typically, incoming gas of automotive fuel cell is humidified by external humidifier but the characteristics of device is rarely reported. In this study, characteristics of water transfer in the membrane humidifiers have been experimentally investigated for flow rates of gas and for different flow arrangement under steady state condition. At first, capability of mass transfer through the membrane is examined at constant temperature. Then, the temperature distribution effect on the capability of mass transfer is tested over various inlet conditions. In summary, this research presents the mass transfer capability of hydrophilic membrane over various operating conditions.

• Agricultural and Biosystems Engineering
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• 제1권2호
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• pp.73-80
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• 2000

Aerodynamics in a naturally ventilated multi-span greenhouse with plants was analyzed numerically by the computational fluid dynamics (CFD) simulation. To investigate the potential application of CFD techniques to greenhouse design and analysis, the numerical results of the CFD model were compared with the results of a steady-state mass and energy balance numerical model. Assuming the results of the mass and energy balance model as the standard, reasonably good agreement was obtained between the natural ventilation rates computed by the CFD numerical model and the mass and energy balance model. The steady-state CFD model during a sunny day showed negative errors as high as 15% in the morning and comparable positive errors in the afternoon. Such errors assumed to be due to heat storage in the floor, benches, and greenhouse structure. For a west wind of 2.5 m s$^{-1}$ , the internal nonporous shading screens that opened to the east were predicted to have a 15.6% better air exchange rate than opened to the west. It was generally predicted that the presence of nonporous internal shading screens significantly reduced natural ventilation if the horizontal opening of the screen for each span was smaller that the effective roof vent opening.

• Membrane and Water Treatment
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• 제1권1호
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• pp.13-37
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• 2010

The performance of an electrodialyzer for concentrating seawater is predicted by means of a computer simulation, which includes the following five steps; Step 1 mass transport; Step 2 current density distribution; Step 3 cell voltage; Step 4 NaCl concentration in a concentrated solution and energy consumption; Step 5 limiting current density. The program is developed on the basis of the following assumption; (1) Solution leakage and electric current leakage in an electrodialyzer are negligible. (2) Direct current electric resistance of a membrane includes the electric resistance of a boundary layer formed on the desalting surface of the membrane due to concentration polarization. (3) Frequency distribution of solution velocity ratio in desalting cells is equated by the normal distribution. (4) Current density i at x distant from the inlets of desalting cells is approximated by the quadratic equation. (5) Voltage difference between the electrodes at the entrance of desalting cells is equal to the value at the exits. (6) Limiting current density of an electrodialyzer is defined as average current density applied to an electrodialyzer when current density reaches the limit of an ion exchange membrane at the outlet of a desalting cell in which linear velocity and electrolyte concentration are the least. (7) Concentrated solutions are extracted from concentrating cells to the outside of the process. The validity of the computer simulation model is demonstrated by comparing the computed results with the performance of electrodialyzers operating in salt-manufacturing plants. The model makes it possible to discuss optimum specifications and operating conditions of a practical-scale electrodialyzer.

• 대한기계학회논문집
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• 제10권1호
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• pp.150-156
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• 1986

본 논문에서는 열전달을 포함한 사이클 해석의 좀 더 실제적인 경우로서, 주어진 연소가스로부터 랜킨사이클을 사용하여 동력을 추출할 때 최대의 출력을 추출하기 위한 사이클의 운전조건을 고찰하고, 대표적인 랜킨 사이클에 대하여 여러가지 운전조건에 따른 출력등을 계산하여, 그 결과를 고찰하였다.