• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.8
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• pp.571-579
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• 2011

Heat pump systems for commercial building with variable refrigerant flow(VRF) are expanding a market due to high energy efficiency, lower maintenance cost and easy installation comparing with the conventional heat pump with the constant refrigerant flow. In general, heat pump systems degrade the energy efficiency in the extremely low temperature regions. In this study, VRF heat pump system with refrigerant heating is experimentally investigated to overcome the low heating performance in the extremely low temperature regions. VRF heat pump system with refrigerant heating is found out the sufficient heating performance in the -25 degree temperature condition comparing with the conventional heat pump system and is obtained more than 2,500 kPa high pressure in the evaporator at low temperature.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.2
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• pp.172-180
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• 2013

In this paper, we propose an energy-efficient camera operating scheme to save energy which can be used for mass surveillance cameras. This technique determines how many cameras should be turned on in the consideration of the velocity vector of monitoring targets, which is acquired by DSRC object tracking, the model of the specification of installed cameras, and the road model of installed sites. Also, we address other techniques used to save energy for the surveillance system as well. Throughout performance evaluation, we demonstrate the excellence of our proposed scheme compared with previous approaches.

• Journal of KIISE
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• v.42 no.5
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• pp.671-680
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• 2015

Numerous clustering schemes have been proposed to increase energy efficiency in wireless sensor networks. Clustering schemes consist of a hierarchical structure in the sensor network to aggregate and transmit data. However, existing clustering schemes are not suitable for use in wireless multimedia sensor networks because they consume a large quantity of energy and have extremely short lifetime. To address this problem, we propose the Energy-Aware Cooperative Communication (EACC) method which is a novel cooperative clustering method that systematically adapts to various types of multimedia data including images and video. An evaluation of its performance shows that the proposed method is up to 2.5 times more energy-efficient than the existing clustering schemes.

• Particle and aerosol research
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• v.17 no.2
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• pp.29-36
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• 2021

In this study, the clean air delivery rate (CADR) of ceiling air circulator (CAA) was determined under indoor environmental simulation conditions. An air filter was used to provide air cleaning ability to the CAA. The CADR of filter adapted CAA was evaluated and compared with the value of commercial air purifier. The installation of mesh-shaped filter on the CAA showed particle reduction effect on the particles over 0.4 ㎛ in diameter, but the CADR was up to 0.25 m³/min. When the filter having 99.9% in collection efficiency was installed on the CAA, its CADR was 1.52 m³/min, while the CADR of commercial air purifier was 3.19 m³/min.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.125.1-125.1
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• 2010

A high efficiency polymer electrolyte membrane (PEM) fuel cell stack was developed for pressurized pure hydrogen and oxygen supplying conditions. The design objective for the cell stack was to maximize the electric efficiency and to minimize exhaust-gas emissions from it simultaneously. To achieve this objective, the cell stack was designed to use pure hydrogen and oxygen as fuel and oxidant, respectively, and to be operated under high gas inlet pressures and in a stage-wise dead-end operation mode. Major components constituting the cell stack, such as membrane electrode assembly, bipolar-plate, and gasket, have been developed to meet a target durability even in severe operating conditions: high gas inlet pressures and usage of pure oxygen. A high-power fuel cell stack was assembled using these components to verify the performance. The cell stack showed a good performance in terms of the efficiency and maximum power output.

• Corrosion Science and Technology
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• v.21 no.3
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• pp.171-183
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• 2022

The performance and inhibitory action of the aqueous extract of Cyperus Conglomeratus's leaves against corrosion of XC70 steel in a 1M HCl acid medium are studied by the determination of the weight loss, the potentiodynamic polarization curves analysis, and electrochemical impedance measurements (electrochemical techniques). The corrosion inhibitory efficiency of XC70 steel increases with the increasing concentration of the green inhibitor, however, the corrosion rate of the steel decreases. Weight loss measurements show that the maximum percentage corrosion inhibition efficiency is approximately 61.86%, while the analysis of the mixed character polarization curves shows that the inhibitor could achieve an inhibition efficiency of 86.96%. The electrochemical impedance study confirmed that the value of the charge transfer resistance (R_ct) increases and the value of the double layer capacity (C_dl) decreases with increasing concentration of the aqueous extract of Cyperus Conglomeratus's leaves, thus increasing the inhibition efficiency. The study showed that this aqueous extract acts by adsorption on the metal surface; this adsorption follows the Langmuir isotherm. This research work showed that Cyperus Conglomeratus leaves extract acts as an effective and eco-friendly inhibitor on mild steel in an acid medium.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.18 no.4
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• pp.12-21
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• 2022

Steam assisted gravity drainage(SAGD) is a process that drills well in the underground oil sands layer, injects hightemperature steam, lowers the viscosity of buried bitumen, and recovers it to the ground. Recently, direct contact steam generator(DCSG) is being developed to maximize steam efficiency for SAGD process. The DCSG requires high technology to achieve pressurized combustion and steam generation in accordance with underground pressurized conditions. Therefore, it is necessary to develop a combustion technology that can control the heat load and exhaust gas composition. In this study, process analysis of high-pressurized DCSG was conducted to apply oxygen enrichment technology in which nitrogen of the air was partially removed for increasing steam production and reducing fuel consumption. As the process analysis conditions, methane as the fuel and normal air or oxygen enriched air as the oxidizing agent were applied to high-pressurized DCSG process model. A simple combustion reaction program was used to calculate the property variations for combustion temperature, steam ratio and residual heat in exhaust gas. As a major results, the steam production efficiency of DCSG using the pure oxygen was about 6% higher than that of the normal air due to the reducing nitrogen in the air. The results of this study will be used as operating data to test the demonstration device.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.4
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• pp.287-297
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• 2014

For several decades, many countries operating nuclear power plants have been studying the various disposal alternatives to dispose of the spent nuclear fuel or high-level radioactive waste safely. In this paper, as a direct disposal of spent nuclear fuels for deep geological disposal concept, the rod consolidation from spent fuel assembly for the disposal efficiency was considered and analyzed. To do this, a concept of spent fuel rod consolidation was described and the related concepts of disposal canister and disposal system were reviewed. With these concepts, several thermal analyses were carried out to determine whether the most important requirement of the temperature limit for a buffer material was satisfiedin designing an engineered barrier of a deep geological disposal system. Based on the results of thermal analyses, the deposition hole distance, disposal tunnel spacing and heat release area of a disposal canister were reviewed. And the unit disposal areas for each case were calculated and the disposal efficiencies were evaluated. This evaluation showed that the rod consolidation of spent nuclear fuel had no advantages in terms of disposal efficiency. In addition, the cooling time of spent nuclear fuels from nuclear power plant were reviewed. It showed that the disposal efficiency for the consolidated spent fuel rods could be improved in the case that cooling time was 70 years or more. But, the integrity of fuels and other conditions due to the longer term storage before disposal should be analyzed.

• The Journal of the Acoustical Society of Korea
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• v.30 no.5
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• pp.281-294
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• 2011

Physics-based sound synthesis usually requires high computational costs and this results in a restriction of its use in real-time applications. This motivates us to implement the sound synthesis algorithm of plucked-string instruments using multi-core processor architectures and determine the optimal processing element (PE) configuration for the target instruments. To determine the optimal PE configuration, we evaluate the impacts of a sample-per-processing element (SPE) ratio that is defined as the amount of sample data directly mapped to each PE on system performance and both area and energy efficiencies using architectural and workload simulations. For the acoustic guitar, the highest area and energy efficiencies are achieved at a SPE ratio of 5,513 and 2,756, respectively, for the synthesis of musical sounds sampled at 44.1 kHz. In the case of the classical guitar, the maximum area and energy efficiencies are achieved at a SPE ratio of 22,050 and 5,513, respectively. In addition, the synthetic sounds were very similar to original sounds in their spectra. Furthermore, we conducted MUSHRA subjective listening test with ten subjects including nine graduate students and one professor from the University of Ulsan, and the evaluation of the synthetic sounds was excellent.

• Membrane Journal
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• v.29 no.6
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• pp.339-347
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• 2019

Forward osmosis (FO) is operated at a lower pressure than reverse osmosis (RO), which has great advantages in terms of fouling control, maintenance, membrane cleaning, and potential energy reduction. In particular, since the membrane fouling layer of the forward osmosis process has a relatively loose and dispersed property, it is possible to control the membrane fouling by physical cleaning, unlike the reverse osmosis process. However, existing studies do not apply the proper cleaning flow rate for forward osmosis physical cleaning, and thus there is a limit that the optimal operation can not be performed. Therefore, this study aims to evaluate the justification of proper flow rate that can show high efficiency cleaning with economical energy amount. The membrane fouling experiments of the forward osmosis process were maintained at a circulating flow rate of 8.54 cm/s and the recovery rates were compared with the three cleaning flow rates. As a result of this experiment, it was confirmed that the 2 × speed cleaning showed the same efficiency as the water permeability recovery rate of the 3 × speed cleaning, and it was confirmed that the 2 × speed cleaning was an appropriate flow rate with high cleaning efficiency and economical SEC.