• Transactions of the KSME C: Technology and Education
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• v.2 no.1
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• pp.65-72
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• 2014

The purpose of this study is to design a heat insulator for reducing available energy loss in stratified thermal storage tank. Heat insulator is operated by buoyancy effect from density difference between hot and cold water without extra equipment. Analysis model using the Matlab Simulink was developed to estimate the internal temperature distribution in thermal storage tank and also used to select proper material and thickness of the heat insulator. Operational feasibility was confirmed through reduced scale experiment. As a result, heat insulator can effectively delay the formation of thermal boundary layer between hot and cold water. In reduced scale experiment, heat insulator can preserve additional 1540J of available energy. When applied to the real thermal storage tank, increase of 6% thermal storage efficiency can be expected.

• Journal of Korean Society on Water Environment
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• v.35 no.4
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• pp.362-369
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• 2019

In this study, biodegradation efficiency improvement of mixed sludge for the anaerobic digestion process in wastewater treatment plant was investigated. In order to release the organic material contained in the sludge cell and promote the hydrolysis step, mixed sludge of 7% TS (Total Solids) was physically shear-treated at a shear strength of 1,000 ~ 4,000 rpm and a maximum of 120 mins. As a result of the comparison between mixed sludge before and after the treatment, the concentration of $SCOD_{Cr}$(Soluble Chemical Oxygen Demand-chromium method) was increased through the conversion of granular organic matter into dissolved organic matter as shear strength and treatment time increases. The solubilization efficiency increased rapidly after 30 min of solubilization application time, and they were 11.23 %, 20.10 %, 22.52 % and 25.43% at 120 min for each shear strength conditions, respectively. Additionally, the BMP(Biochemical Methane Potential) test was conducted with the optimized samples to determine the increase of methane production by the shear pre-treatment. Consequently, methane production of each samples were 0.275, 0.310, 0.323 and $0.335m^3/kg\;VS_{add}$, which indicates that methane production was increased to a maximum of 21.28% compared to the control without the solubilization process ($0.262m^3/kg\;VS_{add}$). As a result, the physical shear-treatment is a promising process for sewage sludge pre-treatment to reduce the organic waste and increase the energy production.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.216-219
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• 2000

Pyrolysis products of woody biomass were consistedofvarious linear hydrocarbon, aromatics or condensed cyclic compounds. In order to obtain biomass pyrolysis products, more equipments and time were needed. But solvolysis of woody biomass with acetone easily obtained decomposition products and enhanced conversion rate(18.72%, max.) from woody biomass than pyrolysis of woody biomass. Beacause solvolysis with acetone improved conversion rate (26.64%, max.) of lignin. the whole conversion rate was improved. But above $300^{\circ}C$, lignin showed lower conversion rate, so the whole conversion rate decreased. Solvolysis products of woody biomass with acetone were same as pyrolysis products. Above $400^{\circ}C$, methoxy phenols were completely disappeared.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.3-8
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• 1986

The investigation of the effect of solvent structure on the first-order solvolysis of cis-$[Co(en)_2ClNO_2]^+$ion has been extended to water + co-solvent mixtures where the co-solvents are glycerol, ethylene glycol, isopropyl alcohol and t-butyl alcohol. Rates of solvolysis have been evaluated by spectrophotometric method at temperature 25∼30$^{\circ}$C. The polarity of solvent has influence on the variation of rate constant. The non-linear plot of the rate constant in log scale versus $\frac{D-1}{2D+1}$ implies that change in solvent structure with composition plays an important role in determining the variation of rate constant. The linearity of the plot of the rate constant in log scale versus the Grundwald-Winstein Y factor confirms that the solvolysis is an Id-type process with considerable extension of the metal chloride bond in the transition state. In the Kivinen equation the slope of the plot of log k versus $log(H_2O)$ suggests that the solvolysis is also an Id-type process. The application of free energy cycle shows that the effect of solvent structure is greater in the transition state than in the initial state.

• Food Science and Preservation
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• v.9 no.3
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• pp.332-337
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• 2002

This study was undertaken in order to compare reflux extraction(RE) and microwave-assisted extraction(MAE) in extraction efficiency and establish optimum microwave extraction conditions in obtaining Ligularia fischeri extracts. A considerable reduction in extraction time was accomplished by MAE. When 70% methanol 50% methanol 70% ethanol, or 50% ethanol was used, MAE extract contained equal levels of soluble solid and total polyphenol as obtained by RE. The optimum microwave-assisted extraction conditions for Ligularia fischeri were achieved by 120∼150 watts of microwave energy and 4∼8 minutes of extraction time. No significant changes were found in antioxidant activity with DPPH scavenging method over the variation of microwave energy or extraction time. The use of diluted methanol or ethanol improved soluble solid content(30%), total polyphenol content(2.7%) and antioxidant activity(68%).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.213-221
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• 2012

In this paper, a dynamic power management system is proposed to reduce energy consumption for multiple clients in cloud computing environments. The proposed system monitors both keyboard and mouse input from the user, available memory, and CPU usage in the virtual machine. If the system detects no keyboard and mouse input for a certain amount of time and both available memory and CPU usage reach predefined threshold value, the manager in the virtual machine orders the client to shutdown the client machine, which results in significant power save. The developed system is applied to the real university computer lab and the performance of the system is evaluated.

• Journal of the Korea Society of Computer and Information
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• v.16 no.2
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• pp.217-224
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• 2011

Existing wire based physical security system solutions show limitations in time and space. In order to solve these deficiencies, a remote physical security system has been implemented using smart phone based on mobile cloud computing technique. The security functions of mobile cloud computing technique include mobile device user authentication, confidentiality of communication, integrity of information, availability of system, and target system access control, authority management and secure hand off etc. Proposed system has been constructed as remote building management system using smart phone, and also has been efficient to reduce energy cost (5~30%), result of system average access and response time 7.082 second. This systems are evaluated to have high efficiency compared to performance.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.6
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• pp.94-102
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• 2001

The thermodynamic second law analysis, which means available energy or exergy analysis, for the indicated performance of Otto cycle engine has been carried out. Each operating process of the engine is simplified and modeled into the thermodynamic cycle. The calculation of the lost work and exergy through each process has been done with the thermodynamic relations and experimental data. The experimental data were measured from the test of single cylinder Otto cycle engine which operated at 2500 rpm, WOT(Wide Open Throttle) and MBT(Minimum advanced spark timing for Best Torque) condition with different fuels: gasoline, methanol and mixture of butane-methanol called M90. Experimental data such as cylinder pressure, air and fuel flow rate, exhaust gas temperature, inlet gas temperature and etc. were used for the analysis. The proposed model and procedure of the analysis are verified through the comparison of the work done in the study with experimental results. The calculated results show that the greatest lost work is generated during combustion process. And the lost work during expansion, exhaust, compression and induction process follows in order.

• Food Science and Preservation
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• v.11 no.1
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• pp.88-93
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• 2004

This study was conducted in order to compare reflux extraction(RE) and microwave-assisted extraction(MAE) in extraction efficiency and establish optimum microwave extraction conditions in obtaining Aster scaber Thunb extracts. Extraction time was reduced considerably in MAE. When 70％ methanol, 50％ methanol, 70％ ethanol, or 50％ ethanol was used, no difference was found in the amount of soluble solid and total phenol between MAE and RE. The optimum microwave-assisted extraction conditions for Aster scaber Thunb were achieved by 120-150 watts of microwave energy and 4∼8 minutes of extraction time. No significant changes were found in antioxidant activity using DPPH scavenging method over the variation of microwave power or extraction time. The use of diluted methanol or ethanol improved soluble solid content(30.8％), total polyphenol content(2.9％) and antioxidant activity(69％ ).

• Journal of IKEEE
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• v.16 no.3
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• pp.224-234
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• 2012

This paper describes an energy harvesting circuit using solar and vibration energy with MPPT(Maximum Power Point Tracking) control for micro sensor nodes. The designed circuit employs MPPT control to harvest maximum power available from a PZT vibration element and an integrated solar cell. The harvested energies are simultaneously combined and stored in a storage capacitor, and then managed and transferred into sensor node by PMU(Power Management Unit). MPPT controls are implemented using the linear relationship between the open-circuit voltage of an energy transducer and its MPP(Maximum Power Point) voltage. The proposed circuit is designed in a CMOS 0.18um technology and its functionality has been verified through extensive simulations. The designed energy harvesting circuit and integrated solar cell occupy $2.85mm^2$ and $8mm^2$ respectively.