• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.1
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• pp.48-58
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• 2001

For the past few decades the vapor compression cycle with a solution circuit (VCCSC) has been known to provide high efficiency and variable capacity. In this study performance of a VCCSC cycle is examined through computer simulation. In the simulation heat exchangers were modelled by specifying UA or effectiveness values while the compressor performance was specified by an isentropic efficiency. Aqua/ammonia solution was chosen as the working fluid which can be used in the high temperature range. The results show that there exists an optimum operation condition which is dependent upon the temperatures of the external heat transfer fluids(HTFs). Besides the HTF\`s temperature, the maximum system pressure and the size of the solution heat exchanger are shown to have an influence on the optimum operation condition. Finally, as compared to a simple vapor compression heat pump with HFC134a, the COP of the VCCSC is shown to be 2∼22% higher.

• KSBB Journal
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• v.23 no.2
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• pp.169-176
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• 2008

The concentration of fresh gel from Aloe vera L. by using ulfrafiltration (UF) process was investigated and analyzed. The two membranes (organic and ceramic) with different molecular weight cut-off (MWCO) and modules (flat sheet and tubular) was used. Under optimum operation conditions, ceramic (zirconium dioxide) tubular membrane with MWCO of 50 kDa resulted in higher flux, less fouling, more turbid, higher total solid, higher polysaccharide and less aloin content. Optimum operation conditions were transmembrane pressure of 1.0 bar, feed velocity of 240 L/hr and temperature of $23^{\circ}C$. Volume concentration factor of aloe gel was 3.13 at permeate flux of $51.1\;L/m^2{\cdot}hr$ after processing time of 1.66 hr. Aloin in fresh aloe gel by UF process was effectively removed as permeate and bioactive polysaccharide content was 2.1 times higher than that of fresh aloe gel. These results allowed a very good level of concentration degree and polysaccharide content. Thus, ultrafiltration process of this study was suitable for the concentration of fresh aloe gel though the aloe concentrate showed both the viscosity decrease and partially separation of liquid layer during storage at $4^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2508-2515
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• 1996

Determination of an optimal feed rate is valuable in the sense of the precision and efficient machining. In this regard, a new surface roughness model for the face milling operation that considered the radial and axal runouts of the inserts in the cutter body was developed. The validity of the model was proved through the cutting experiments, and the model is able to predict the real machined surface roughness exactly with the information of the insert runouts and the cutting conditions. From the estimated surface roughness value, the maximum feed rate that obtains a maximum naterial removal rate under the given surface roughness constraint can be selected by using a bisection method. Therefore, this mehod for optimizing the feed rate can be well applied to the using a bisection method. Therefore, this method for optimizing the feed rate can be well applied to the using selsction of the cutting condition during the NC data generation in CAM.

• KSBB Journal
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• v.13 no.4
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• pp.411-417
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• 1998

The possibility of application of membrane type immobilized adsorbent to the fed-batch or perfusion culture system with anchorage-independent cells as well as batch system was investigated. The improvement in cell density and cell viability due to the combination of immobilized adsorbent with each culture system was evaluated for the investigation, and the optimum culture system employing immobilized adsorbent system was suggested based on the results. It was observed that the system with immobilized adsorbent showed better cell growth and cell viability than that without immobilized adsorbent in every operation system of batch, fed-batch, and perfusion. In case of batch system, 200% improvement of maximum cell density was observed in the system where ammonium chloride was added on purpose. And 50% improvement of maximum cell density was observed in the fed-batch system where ammonium ion accumulates significantly, while small increase in maximum cell density was observed in the perfusion system where dilution of waste byproducts exists. Especially, the fed-batch system showed the most significant improvement on cell growth because both compensation of nutrient and removal of ammonium ion occurred simultaneously in the system. Therefore a combined system of immobilized adsorbent and fed-batch operation could be suggested as an optimum system with in situ removal of ammonium ion.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.2
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• pp.235-244
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• 2006

A PCF(Pore Controllable Fiber Filter) process was applied as a pretreatment of water treatment for reduction of turbidity. The experimental results obtained from the PCF showed that the removal efficiency of turbidity without coagulation was around over 70 percent. However, the removal efficiency of turbidity by the coagulation-PCF process was high as much as over 95%. Thus, the coagulation pretreatment was required for the better operation of the PCF. The SEM (Scanning Electron Microscope) images of fiber before and after filtration showed that the filtration mechanism of PCF filter is both controlling attachment mechanism and Sieving mechanism through fiber pore. For the coagulation-PCF process, optimum dosage of coagulant was needed for the economical operation, and for this, determining the optimum dosage by using a filter column test. Also only 16mg/L of alum was used to obtain high algae removal efficiency over 90%. Therefore, it can be concluded that coagulation-PCF process is very effective pretreatment process for algae removal.

• Journal of Biosystems Engineering
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• v.4 no.2
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• pp.65-83
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• 1979

Low-temperature drying systems have been extensively used for drying cereal grain such as shelled corn and wheat. Since the 1973 energy crisis, many researches have been conducted to apply solar energy as supplemental heat to natural air drying systems. However, little research on rough rice drying has been done in this area, especially very little in Korea. In designing a solar drying system, quality loss, airflow requirements, temperature rise of drying air, fan power and energy requirements should be throughly studied. The factors affecting solar drying systems are airflow rate, initial moisture content, the amount of heat added to drying air, fan operation method and the weather conditions. The major objectives of this study were to analyze the effects of the performance factors and determine design parameters such as airflow requirements, optimum bed depth, optimum temperature rise of drying air, fan operation method and collector size. Three hourly observations based on the 4-year weather data in Chuncheon area were used to simulate rough rice drying. The results can be summarized as follows: 1. The results of the statistical analysis indicated that the experimental and predicted values of the temperature rise of the air passing through the collector agreed well. 2. Equilibrium moisture content was affected a little by airflow rate, but affected mainly by the amount of heat added, to drying air. Equilibrium moisture content ranged from 12.2 to 13.2 percent wet basis for the continuous fan operation, from 10.4 to 11.7 percent wet basis for the intermittent fan operation respectively, in range of 1. 6 to 5. 9 degrees Centigrade average temperature rise of drying air. 3. Average moisture content when top layer was dried to 15 percent wet basis ranged from 13.1 to 13.9 percent wet basis for the continuous fan operation, from 11.9 to 13.4 percent wet basis for the intermittent fan operation respectively, in the range of 1.6 to 5.9 degrees Centigrade average temperature rise of drying air and 18 to 24 percent wet basis initial moisture content. The results indicated that grain was overdried with the intermittent fan operation in any range of temperature rise of drying air. Therefore, the continuous fan operation is usually more effective than the intermittent fan operation considering the overdrying. 4. For the continuous fan operation, the average temperature rise of drying air may be limited to 2.2 to 3. 3 degrees Centigrade considering safe storage moisture level of 13.5 to 14 perceut wet basis. 5. Required drying time decrease ranged from 40 to 50 percent each time the airflow rate was doubled and from 3.9 to 4.3 percent approximately for each one degrees Centigrade in average temperature rise of drying air regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on required drying time. 6. Required drying time increase ranged from 18 to 30 percent approximately for each 2 percent increase in initial moisture content regardless of the fan operation methods, in the range of 18 to 24 percent moisture. 7. The intermittent fan operation showed about 36 to 42 percent decrease in required drying time as compared with the continuous fan operation. 8. Drymatter loss decrease ranged from 34 to 46 percent each time the airflow rate was doubled and from 2 to 3 percent approximately for each one degrees Centigrade in average temperature rise of drying air, regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on drymatter loss. 9. Drymatter loss increase ranged from 50 to 78 percent approximately for each 2 percent increase in initial moisture content, in the range of 18 to 24 percent moisture. 10. The intermittent fan operation: showed about 40 to 50 percent increase in drymatter loss as compared with the continuous fan operation and the increasing rate was higher at high level of initial moisture and average temperature rise. 11. Year-to-year weather conditions had a little effect on required drying time and drymatter loss. 12. The equations for estimating time required to dry top layer to 16 and 1536 wet basis and drymatter loss were derived as functions of the performance factors. by the least square method. 13. Minimum airflow rates based on 0.5 percent drymatter loss were estimated. Minimum airflow rates for the intermittent fan operation were approximately 1.5 to 1.8 times as much as compared with the continuous fan operation, but a few differences among year-to-year. 14. Required fan horsepower and energy for the intermittent fan operation were 3. 7 and 1. 5 times respectively as much as compared with the continuous fan operation. 15. The continuous fan operation may be more effective than the intermittent fan operation considering overdrying, fan horsepower requirements, and energy use. 16. A method for estimating the required collection area of flat-plate solar collector using average temperature rise and airflow rate was presented.

• Journal of Biosystems Engineering
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• v.4 no.2
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• pp.64-64
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• 1979

Low-temperature drying systems have been extensively used for drying cereal grain such as shelled corn and wheat. Since the 1973 energy crisis, many researches have been conducted to apply solar energy as supplemental heat to natural air drying systems. However, little research on rough rice drying has been done in this area, especially very little in Korea. In designing a solar drying system, quality loss, airflow requirements, temperature rise of drying air, fan power and energy requirements should be throughly studied. The factors affecting solar drying systems are airflow rate, initial moisture content, the amount of heat added to drying air, fan operation method and the weather conditions. The major objectives of this study were to analyze the effects of the performance factors and determine design parameters such as airflow requirements, optimum bed depth, optimum temperature rise of drying air, fan operation method and collector size. Three hourly observations based on the 4-year weather data in Chuncheon area were used to simulate rough rice drying. The results can be summarized as follows: 1. The results of the statistical analysis indicated that the experimental and predicted values of the temperature rise of the air passing through the collector agreed well.2. Equilibrium moisture content was affected a little by airflow rate, but affected mainly by the amount of heat added, to drying air. Equilibrium moisture content ranged from 12.2 to 13.2 percent wet basis for the continuous fan operation, from 10.4 to 11.7 percent wet basis for the intermittent fan operation respectively, in range of 1. 6 to 5. 9 degrees Centigrade average temperature rise of drying air.3. Average moisture content when top layer was dried to 15 percent wet basis ranged from 13.1 to 13.9 percent wet basis for the continuous fan operation, from 11.9 to 13.4 percent wet basis for the intermittent fan operation respectively, in the range of 1.6 to 5.9 degrees Centigrade average temperature rise of drying air and 18 to 24 percent wet basis initial moisture content. The results indicated that grain was overdried with the intermittent fan operation in any range of temperature rise of drying air. Therefore, the continuous fan operation is usually more effective than the intermittent fan operation considering the overdrying.4. For the continuous fan operation, the average temperature rise of drying air may be limited to 2.2 to 3. 3 degrees Centigrade considering safe storage moisture level of 13.5 to 14 perceut wet basis.5. Required drying time decrease ranged from 40 to 50 percent each time the airflow rate was doubled and from 3.9 to 4.3 percent approximately for each one degrees Centigrade in average temperature rise of drying air regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on required drying time.6. Required drying time increase ranged from 18 to 30 percent approximately for each 2 percent increase in initial moisture content regardless of the fan operation methods, in the range of 18 to 24 percent moisture.7. The intermittent fan operation showed about 36 to 42 percent decrease in required drying time as compared with the continuous fan operation.8. Drymatter loss decrease ranged from 34 to 46 percent each time the airflow rate was doubled and from 2 to 3 percent approximately for each one degrees Centigrade in average temperature rise of drying air, regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on drymatter loss. 9. Drymatter loss increase ranged from 50 to 78 percent approximately for each 2 percent increase in initial moisture content, in the range of 18 to 24 percent moisture. 10. The intermittent fan operation: showed about 40 to 50 percent increase in drymatter loss as compared with the continuous fan operation and the increasing rate was higher at high level of initial moisture and average temperature rise.11. Year-to-year weather conditions had a little effect on required drying time and drymatter loss.12. The equations for estimating time required to dry top layer to 16 and 1536 wet basis and drymatter loss were derived as functions of the performance factors. by the least square method.13. Minimum airflow rates based on 0.5 percent drymatter loss were estimated.Minimum airflow rates for the intermittent fan operation were approximately 1.5 to 1.8 times as much as compared with the continuous fan operation, but a few differences among year-to-year.14. Required fan horsepower and energy for the intermittent fan operation were3. 7 and 1. 5 times respectively as much as compared with the continuous fan operation.15. The continuous fan operation may be more effective than the intermittent fan operation considering overdrying, fan horsepower requirements, and energy use.16. A method for estimating the required collection area of flat-plate solar collector using average temperature rise and airflow rate was presented.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.322-322
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• 2016

Phase change memory (PCM) has attracted much attention as one of the most promising candidates for next-generation nonvolatile memory. In that regard, the purposes of the study are to propose reference of effective pulse parameter to control phase switching operation and to invest the effect of nitrogen doped in PCM materials for improved cycling stability and economic energy consumption. Switching operation of PCM is affected by electric pulse parameter and as shown in figure.1 are composed to RT(rising time), ST(setting time), FT(falling time) and the effect of these parameter was precisely investigated. Transmission electron microscope (TEM) was used to confirm fine structure and retention cycle test was conducted to confirm reliability. Finally improvement reliability and economic power consumption in quantitatively are obtainable by optimum pulse parameter and nitrogen doping in GST material. these study is related to the engineering background of other semiconductor industries and it have confirmed to possibility further applications.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.12
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• pp.1498-1506
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• 1999

In this paper, a hybridization of Evolutionary Strategy (ES) and a Two-Phase Neural Network(TPNN) is applied to the optimal environmental and economic operation. As the evolutionary computation, ES is to search for the global optimum based on natural selection and genetics but it shows a defect of reducing the convergence rate in the latter part of search, and often does not search the exact solution. Also, neural network theory as a local search technique can be used to search a more exact solution. But it also has the defect that a solution frequently sticks to the local region. So, new algorithm is presented as hybrid methods by combining merits of two methods. The hybrid algorithm has been tested on Emission Constrained Economic Dispatch (ECED) problem and Weighted Emission Economic Dispatch (WEED) problem for optimal environmental and economic operation. The result indicated that the hybrid approach can outperform the other computational efficiency and accuracy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.12
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• pp.873-880
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• 2010

The present study developed a computer simulation program to determine the optimum strategy and capacity of a micro combined heat and power(CHP) system. This simulation program considered a part-load electrical/thermal efficiency and transient response characteristics of CHP unit. The result obtained from the simulation was compared with the actual operation of 30 kW gas engine driven micro CHP system. It was found that the simulation could reproduce the daily operation behavior, such as operating hours and mean load factor, closely to the actual behavior of the system and could predict the amount of electrical/thermal output and fuel consumption with the error of less than 12%.