• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.11
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• pp.2083-2090
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• 2008

In this paper, we propose a method for control of temperature and the direction of wind in an air-cooler using thermal images and fuzzy inference rules in order to achieve energy saving. In a simulation for controlling temperature, a thermal image is transformed to a color distribution image of $300{\times}400$ size to analyze the thermal image. A color distribution image is composed of R, G and B values haying temperature values of Red, Magenta, Yellow, Green, Cyan and Blue. Each color has a temperature value from $24.0^{\circ}C$ to $27.0^{\circ}C$ and a color distribution image is classified into height hierarchies from level 1 to level 10. The classified hierarchies have their peculiar color distributions and temperature values are assigned to each level by temperature values of the peculiar colors. The process for controlling overall balance of temperature and the direction of wind in an indoor space is as follows. Fuzzy membership functions are designed by the direction of wind, duration time, and temperature and height values of a color distribution image to calculate the strength of wind. After then, the strength of wind is calculated by membership values of membership functions.

• Korean Journal of Remote Sensing
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• v.37 no.5_3
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• pp.1405-1423
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• 2021

Precipitation is one of the main factors that affect water and energy cycles, and its estimation plays a very important role in securing water resources and timely responding to water disasters. Satellite-based quantitative precipitation estimation (QPE) has the advantage of covering large areas at high spatiotemporal resolution. In this study, machine learning-based rainfall intensity models were developed using Himawari-8 Advanced Himawari Imager (AHI) water vapor channel (6.7 ㎛), infrared channel (10.8 ㎛), and weather radar Column Max (CMAX) composite data based on random forest (RF). The target variables were weather radar reflectivity (dBZ) and rainfall intensity (mm/hr) converted by the Z-R relationship. The results showed that the model which learned CMAX reflectivity produced the Critical Success Index (CSI) of 0.34 and the Mean-Absolute-Error (MAE) of 4.82 mm/hr. When compared to the GeoKompsat-2 and Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN)-Cloud Classification System (CCS) rainfall intensity products, the accuracies improved by 21.73% and 10.81% for CSI, and 31.33% and 23.49% for MAE, respectively. The spatial distribution of the estimated rainfall intensity was much more similar to the radar data than the existing products.

• KIPS Transactions on Computer and Communication Systems
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• v.10 no.7
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• pp.199-204
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• 2021

Digital substation refers to a substation that digitizes functions and communication methods of power facilities such as monitoring, measuring, control, protection, and operation based on IEC 61850, an international standard for the purpose of intelligent power grids. Based on the intelligent operating system, efficient monitoring and control of power facilities is possible, and automatic recovery function and remote control are possible in the event of an accident, enabling rapid power failure recovery. With the development of digital technology and the expansion of the introduction of eco-friendly renewable energy and electric vehicles, the spread of direct current distribution systems is expected to expand. MVDC is a system that utilizes direct current lines with voltage levels and transmission capacities between HVDCs applied to conventional transmission systems and LVDCs from consumers. Converting existing lines in substations, where most power equipment is alternating current centric, to direct current lines will reduce transmission losses and ensure greater current capacity. The process bus of a digital substation is a communication network consisting of communication equipment such as Ethernet switches that connect installed devices between bay level and process level. For MVDC linkage to existing digital substations, the process level was divided into two buses: AC and DC, and a system that can be comprehensively managed in conjunction with diagnostic IEDs as well as surveillance and control was proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.29-34
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• 2019

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its large energy band gap and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, electric conductivity of porous n-type SiC semiconductors fabricated from ${\beta}-SiC$ powder at $2000^{\circ}C$ in $N_2$ atmosphere was comparable to or even larger than the reported values of SiC single crystals in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$, while thermal conductivity was kept as low as 1/10 to 1/30 of that for a dense SiC ceramics. In this work, for the purpose of decreasing sintering temperature, it was attempted to fabricate porous reaction-sintered bodies at low temperatures ($1400-1600^{\circ}C$) by thermal decomposition of polycarbosilane (PCS) impregnated in n-type ${\beta}-SiC$ powder. The repetition of the impregnation and sintering process ($N_2$ atmosphere, $1600^{\circ}C$, 3h) resulted in only a slight increase in the relative density but in a great improvement in the Seebeck coefficient and electrical conductivity. However the power factor which reflects the thermoelectric conversion efficiency of the present work is 1 to 2 orders of magnitude lower than that of the porous SiC semiconductors fabricated by conventional sintering at high temperature, it can be stated that thermoelectric properties of SiC semiconductors fabricated by the present reaction-sintering process could be further improved by precise control of microstructure and carrier density.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.642-648
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• 2019

This paper presents a fast back-type transfer device for snack food processing that uses the inertia of transferred material. A conventional conveying system is a drive system that uses a belt conveyor and mechanical crank, which generate noise and vibration and cause environmental pollution. Vibration and noise are reduced in the proposed fast back feeding device by using a counterweight. The crank drive unit was replaced with a linear servomotor, and an equilibrium device was designed to balance the force due to acceleration. This makes it is possible to adjust the forward and backward speed and acceleration through PLC control. A vibration damper device offsets the vibration force of the periodic shock form. The main cause of the vibration was identified through vibration analysis, and reduction measures were established. We verified the effectiveness of the vibration by making a prototype and performing about 10 vibration tests. Because no mechanical transducer is needed, energy loss, noise, and vibration do not occur, and the operating speed is not limited.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.111-117
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• 2019

This study proposed the fabrication and deposition of high purity crystalline $core-TiO_2/shell-Al_2O_3$ nanoparticles. Morphological properties of $core-TiO_2$ and coated $shell-Al_2O_3$ were confirmed by transmission electron microscope (TEM) and transmission electron microscope - energy dispersive spectroscopy (TEM-EDS). The electrical properties of the prepared $core-TiO_2/shell-Al_2O_3$ nanoparticles were evaluated by applying them to a working electrode of a Dye-Sensitized Solar Cell (DSSC). The particle size, growth rate and the main crystal structure of $core-TiO_2$ were analyzed through dynamic light scattering system (DLS), scanning electron microscope (SEM) and X-ray diffraction (XRD). The $core-TiO_2$, which has a particle size of 17.1 nm, a thin film thickness of $20.1{\mu}m$ and a main crystal structure of anatase, shows higher electrical efficiency than the conventional paste-based dye-sensitized solar cell (DSSC). In addition, the energy conversion efficiency (6.28%) of the dye-sensitized solar cell (DSSC) using the $core-TiO_2/shell-Al_2O_3$ nanoparticles selectively controlled to the working electrode is 26.1% higher than the energy conversion efficiency (4.99%) of the dye-sensitized solar cell (DSSC) using the conventional paste method.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.819-825
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• 2018

Porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were prepared by applying both template method and Kirkendall diffusion effect to electrospinning process. During heat-treatment processes, the solid Fe nano-metals formed by initial heat-treatment in the carbon matrix were converted into the hollow structured ${\alpha}-Fe_2O_3$ nanospheres. In particular, PS nanobeads added in the spinning solution were decomposed and formed numerous channels in the composite, which served as a good pathway for Kirkendall diffusion gas. The resulting porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were applied as an anode material for lithium-ion batteries. The discharge capacities of the nanofibers for the 30th cycle at a high current density of $1.0A\;g^{-1}$ was $776mA\;h\;g^{-1}$. The good lithium ion storage property was attributed to the synergetic effects of the hollow ${\alpha}-Fe_2O_3$ nanospheres and the interstitial nanovoids between the nanospheres. The synthetic method proposed in this study could be applied to the preparation of porous nanofibers comprising hollow nanospheres with various composition for various applications, including energy storage.

• Membrane Journal
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• v.30 no.6
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• pp.395-408
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• 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have gained much attention as eco-friendly energy conversion devices without emission of environmental pollutant. Polymer electrolyte membrane (PEM) that can transfer proton from anode to cathode and also prevent fuel cross-over has been regarded as a key component of PEMFCs. Although perfluorinated polymer membranes such as Nafion® were already commercialized in PEMFCs, their high cost and toxic byproduct generated by degradation have still limited the wide spread of PEMFCs. To overcome these issues, development of hydrocarbon based PEMs have been studied. Incorporation of cross-linked structure into the hydrocarbon based PEM system has been reported to fabricate the PEMs showing both high proton conductivity and outstanding physicochemical stability. This study focused on the various cross-linking strategies to the preparation of cross-linked PEMs based on hydrocarbon polymers with ion conducting groups for application in PEMFCs.

• Clean Technology
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• v.27 no.2
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• pp.132-138
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• 2021

Research is being conducted on graphene to provide graphene having both excellent physical as well as electrical properties in addition to unique physical properties. In this study, Hummer's method, which is a representative method for chemical exfoliation, was applied in order to investigate the possibility of the mass production of high-quality graphene oxide. Three types of graphite (graphite, crystalline graphite, and expanded graphite) were used in the preparation of graphene oxide with variations in the amount of potassium permanganate added, reaction temperature, and reaction time. Then a Fourier transform infrared spectroscopy (FT-IR), a Raman spectrometer, and a transmission electron microscope (TEM) were used to measure the quality of the prepared graphene oxide. Of the three types of graphite used in this experiment, crystalline graphite showed the highest quality. The prepared graphene oxide was then purified with an organic solvent, and an analysis conducted using energy dispersive X-ray spectroscopy (EDS). From the results of the residual values, we were able to confirm that both acid wastewater and wastewater were best purified using cyclohexane. The method for manufacturing graphene oxide as well as the method of purification using organic solvents that are presented in this study are expected to have less of an environmental impact, making them environmentally friendly. This makes them suitable for use in various industrial fields such as the film industry and for heat dissipation and as coating agents.

• Journal of Powder Materials
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• v.28 no.2
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• pp.143-149
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• 2021

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x(ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.