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Yoo, Changkyoo 경희대학교 2006 環境硏究 論文集 Vol.15 No.-
Due to increasing environmental constraints and the necessity of reliable wastewater treatment, efficient modeling and monitoring methods are becoming more and more important. Reliable modeling and monitoring techniques of biological wastewater treatment plant (WWPT) are necessary to maintain the system performance as close as possible to optimal conditions. The ultimate objective of this research is to suggest the integrated framework of modeling, process monitoring, control and optimization for a sustainable biological wastewater treatment operation like activated sludge process (ASP) and sequencing batch reactor (SBR). Under the proposed approach, process information obtained from statistical monitoring techniques is utilized to monitor the biological treatment process, to monitor a microbial population dynamics, to design the supervisory control, and finally to optimize the operating condition. Finally, a study to provide an integrated framework is attempted. It has been applied to a pilot-scale SBR and showed the power and advantages of the proposed method.
Yoo, ChangKyoo,Kim, Min Han Elsevier 2009 Journal of environmental management Vol.90 No.8
<P><B>Abstract</B></P><P>This paper presents industrial experience of process identification, monitoring, and control in a full-scale wastewater treatment plant. The objectives of this study were (1) to apply and compare different process-identification methods of proportional-integral-derivative (PID) autotuning for stable dissolved oxygen (DO) control, (2) to implement a process monitoring method that estimates the respiration rate simultaneously during the process-identification step, and (3) to propose a simple set-point decision algorithm for determining the appropriate set point of the DO controller for optimal operation of the aeration basin. The proposed method was evaluated in the industrial wastewater treatment facility of an iron- and steel-making plant. Among the process-identification methods, the control signal of the controller's set-point change was best for identifying low-frequency information and enhancing the robustness to low-frequency disturbances. Combined automatic control and set-point decision method reduced the total electricity consumption by 5% and the electricity cost by 15% compared to the fixed gain PID controller, when considering only the surface aerators. Moreover, as a result of improved control performance, the fluctuation of effluent quality decreased and overall effluent water quality was better.</P>
Magneto-exciton in a GaN/Ga<sub>1−<i>x</i></sub>Al<sub><i>x</i></sub>N quantum dot
Revathi, M.,Yoo, ChangKyoo,John Peter, A. Elsevier 2010 Physica E, Low-dimensional systems & nanostructure Vol.43 No.1
<P><B>Abstract</B></P><P>Magneto-exciton bound donor is investigated theoretically in a GaN/Ga<SUB>1−<I>x</I></SUB>Al<SUB><I>x</I></SUB>N quantum dot within the framework of single band effective mass approximation and compared with the experimental results. Binding energies on excitons bound hydrogenic donors and the diamagnetic susceptibility are obtained as a function of dot radius and magnetic field. The valence-band anisotropy is included in our theoretical model using different hole masses in different spatial directions. Zeeman effect is calculated through the energy dependent effective mass. The dependence of donor bound exciton diamagnetic shift is found. The interband optical transition of GaN/Ga<SUB>1−<I>x</I></SUB>Al<SUB><I>x</I></SUB>N dot is computed with various structural parameters in the influence of magnetic field. Our results show that (i) quantum size, the magnetic field and the interband optical transitions have a considerable influence on neutral donor exciton states, (ii) the diamagnetic susceptibility increases with the magnetic field and is not pronounced for smaller dot radii and (iii) the found diamagnetic shift is agreed with the other experimental investigator [Yoichi Yamada et al., 2000 [26]].</P>
Rashidi, Jouan,Yoo, ChangKyoo Elsevier 2018 Energy conversion and management Vol.162 No.-
<P><B>Abstract</B></P> <P>A new power and cooling cogeneration cycle is proposed that combines the Kalina power cycle and the ejector absorption refrigeration cycle with an ammonia-water mixture as the working fluid. The proposed system, Kalina power-cooling with an ejector cycle (KPCE), originates from the Kalina power and cooling cycle (KPCC) and introduces an ejector before the evaporator. Thermodynamic analyses from the viewpoints of energy efficiency, as well as comparisons between KPCC and KPCE under the same initial conditions, were conducted for the cycles’ refrigeration output and thermal efficiency. Energy analysis results showed that the KPCE provides a performance improvement without greatly increasing system complexity. At the same power production level, the refrigeration output and thermal efficiency of KPCE is 13.5% higher and 17% more than KPCC, respectively. Energy losses due to inefficient heat recovery design of the system are identified by cross heat pinch analysis. All three preheaters of the system showed an inefficient design of heat recovery. After redesigning, power, and power-cooling efficiencies showed 7% and 4.3% increases, respectively. The effect of four important input parameters including three pressure levels and ammonia mass fraction on the KPCE performance are investigated to optimize the system. The optimized KPCE performance improved by 17.9% and 13.6% for power and power-cooling efficiency while the total annual cost of the system could decrease by 6.8%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Proposed a novel power-cooling cogeneration system based on ejector absorption and Kalina cycles. </LI> <LI> Model-based comparisons according to energy, economic, thermodynamic analyses. </LI> <LI> Optima heat recovery design with heat pinch analysis. </LI> <LI> The optimized KPCE improved power and power-cooling efficiency by 17.9% and 13.6%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>