• Journal of Power Electronics
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• v.19 no.1
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• pp.265-277
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• 2019

The application of shunt active power filters (S-APFs) is considered to be the most popular approach for harmonic compensation due to its high simplicity, ease of installation and efficient control. Its functionality mainly depends upon the rapidness and precision of its internally built control algorithms. A S-APF is generally operated in the current controlled mode (CCM) with the detection of harmonic load current. Its operation may not be appropriate for the distributed power generation system (DPGS) due to the wide dispersion of nonlinear loads. Despite the fact that the voltage detection based resistive-APF (R-APF) appears to be more appropriate for use in the DPGS, the R-APF experiences poor performance in terms of mitigating harmonics and parameter tuning. Therefore, this paper introduces a direct harmonic voltage detection based control approach for the S-APF that does not need a remote harmonic load current since it only requires a local point of common coupling (PCC) voltage for the detection of harmonics. The complete design procedure of the proposed control approach is presented. In addition, experimental results are given in detail to validate the performance and superiority of the proposed method over the conventional R-APF control. Thus, the outcomes of this study approve the predominance of the discussed strategy.

• The Korean Journal of Nuclear Medicine Technology
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• v.13 no.1
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• pp.73-76
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• 2009

Purpose: Bone mineral densitometry test region advised by ISCD (International Society for Clinical Densitometry) is both site in case of femur, whereas our medical center measures left femur except for few extraordinary cases. It is said that right-handers had higher mean femur BMD in the left side than in the right side, but the factor influence the femur BMD is unknown. Thus, we investigate whether testing left femur only is a adequate clinical diagnosis. Materials and Methods: Subjects were 209 right-handers and 20 left-handers patient in Asan Medical Center from July to August, 30 to 70 years of age ($51{\pm}6.7$). Subjects fill out the questionnaire on hand preference and taking regular exercise. Total BMDs of bilateral femur were measured with GE Lunar Prodigy advance densitometer, and the statistical soft ware SPSS 12.0 for windows was used for statistical analysis. Results: In the total sample of the exercise group (n=127), the difference of both femur mean BMDs are $0.001{\pm}0.127\;g/cm^2$ and the non-exercise group's (n=102) both femur difference is $0.002{\pm}0.126\;g/cm^2$, there is no significant difference. And in exercise group, classified according to hand preference, each t-value is shown at right handers (n=114) are 0.65, left handers (n=13) are -0.39. Also, In non-exercise group, right handers (n=95) are -0.78, left handers (n=7) are -0.64. In the 95% confidence limit, there was no statistically significant difference (p>0.05). Conclusions: In recently researchs, there have been differences between both femurs according to hand preference. However, Our study have no significant difference both femurs BMDs. Therefore we suggest that BMD measurement of femur has no problem only one side, except for particular case like femur operation.

• Journal of Chest Surgery
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• v.31 no.4
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• pp.353-361
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• 1998

Hypothermia is widely acknowledged as fundamental component of myocardial protection during cardiac operations. Although it prolongs the period of ischemic arrest by reducing oxygen demands, hypothermia is associated with a number of major disadvantages, including its detrimental effects on enzymatic function, energy generation, and cellular integrity. The ideal way to rotect the heart is to electromechanically arrest it and perfus it with blood that is aerobic arrest. However alternative technique has been developed, based on the principles of electromechanical arrest and normothermic aerobic perfusion using continuous warm blood cardioplegia. To determine if continuous warm blood cardioplegia was beneficial in clinical practice during valvular surgery, we studied two groups of patients matched by numbers and clinical characteristics. Group included is 31 patients undergoing valvular surgery who received intermittent cold crystalloid cardioplegia. Group II included 30 patients undergoing valvular surgery who received continuous warm blood cardioplegia. Our results suggest that the heartbeat in 100% of patients treated with continuous warm blood cardioplegia converted to normal sinus rhythm spontaneously after the removal of the aortic cross-clamp, compared to only 31% of the cold cardioplegia group. After operation, pericardial closure rate was 90% area in the warm group, compared to 35% area in the cold group. 12 hours after the operation, the total amount of urine output in the warm group was greater than that in the cold group(2863${\pm}$127 ml versus 2257${\pm}$127 ml; p<0.05). After the operation, left diaphragmatic elevation developed in 55% of the cold group but in 0% of the warm group. CK-MB level in the warm group was significantly lower than cold group(2.28${\pm}$0.62 versus 9.96${\pm}$2.12; p<0.01) 1 hour after operation and CK-MB level in the warm group was significantly lower than cold group(1.80${\pm}$1.01 versus 6.00${\pm}$1.74; p<0.05) 12hours after operation. Continuous warm blood cardioplegia is at least as safe and effective as hypothermic technique in patients undergoing cardiac valvular surgery. Conceptually, this represents a new approach to the problem of maintaining myocardial preservation during cardiac operations.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.4
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• pp.294-303
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• 2005

This paper describes the analysis results of a series f Round-Robin test that was performed to intercompare inspection and diagnosis techniques for characterization of pressure tube f a pressurized heavy water reactor under the Coordinated Research Project(CRP) of IAEA's nuclear Power Programme. For this test, six nations, Korea, Canada, India, Argentina, Rumania, and China that currently have pressurized heavy water reactors under operation involved, and the "KOR-1" pressure tube sample prepared by Korea was used. Two kinds of NDE technique, ultrasonic and eddy current test, were applied for these tests. The "KOR-1" pressure tube sample contains total 12 artificial flaws such as crack-like EDM notches, wear that is similar to the real flaws and can be produced on the pressure tubes during plant operation. Test results showed that seven laboratories from six nations detected all twelve flaws in "KOR-1" specimen by using ultrasonic and eddy current test methods, and ultrasonic test method was more accurate than eddy current test method in flaw detectin and sizing. ID flaws in pressure tube sample were more easily detected and accurately sized than OD flaws.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.248-254
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• 2016

Efficacious wastewater treatment is essential for increasing sewage sludge volume and implementing strict environmental regulations. The operation cost of sludge treatment amounts up to 50% of the total costs for wastewater treatment plants, therefore, an economical sludge destruction method is crucially needed. Amid several destruction methods, wet air oxidation (WAO) can efficiently treat wastewater containing organic pollutants. It can be used not only for sludge destruction but also for useful by-product production. Volatile fatty acids (VFAs), one of many byproducts, is considered to be an important precursor of biofuel and chemical materials. Its high reaction condition has instituted the study of gravity pressure reactor (GPR) for an economical process of WAO to reduce operation cost. Simulation of subcritical condition was conducted using Aspen Plus with predictive Soave-Redlich-Kwong (PSRK) equation of state. Conjointly, simulation analysis for GPR depth, oxidizer type, sludge flow rate and oxidizer injection position was carried out. At GPR depth of 1000m and flow rate of 2 ton/h, the conversion and yield of VFAs were 92.02% and 0.17g/g, respectively.

• Journal of Hydrogen and New Energy
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• v.22 no.3
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• pp.305-312
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• 2011

The use of a separator to control stack temperature in a molten carbonate fuel cell was studied by numerical simulation using a computational fluid dynamics code. The stack model assumed steady-state and constant-load operation of a co-flow stack with an external reformer at atmospheric pressure. Representing a conventional cell type, separators with two flow paths, one each for the anode and cathode gas, were simulated under conditions in which the cathode gas was composed of either air and carbon dioxide (case I) or oxygen and carbon dioxide (case II). The results showed that the average cell potential in case II was higher than that in case I due to the higher partial pressures of oxygen and carbon dioxide in the cathode gas. This result indicates that the amount of heat released during the electrochemical reactions was less for case II than for case I under the same load. However, simulated results showed that the maximum stack temperature in case I was lower than that in case II due to a reduction in the total flow rate of the cathode gas. To control the stack temperature and retain a high cell potential, we proposed the use of a separator with three flow paths (case III); two flow paths for the electrodes and a path in the center of the separator for the flow of nitrogen for cooling. The simulated results for case III showed that the average cell potential was similar to that in case II, indicating that the amount of heat released in the stack was similar to that in case II, and that the maximum stack temperature was the lowest of the three cases due to the nitrogen gas flow in the center of the separator. In summary, the simulated results showed that the use of a separator with three flow paths enabled temperature control in a co-flow stack with an external reformer at atmospheric pressure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.171-179
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• 1997

During the day time in summer, peak of air conditing load, and electric power management system lies under overloaded condition. The reason is the enlarged peak load value of electric power caused by increased air-cooling load in summer. To prevent load concentration during day time and overloaded condition of power management system, some energy storage methods are suggested. One of these methods is ice storage system. Water has some good properties as P.C.M.(Phase Chang Material) : Its melting point is the range of required operation temperature. It has large specific latent heat and is chemically stable compared to other organic or inorganic substances. It is cheap and easy to treat. This study represents experimental results of heat transfer characteristics of P.C.M. under the outward melting process in a vertical cylinder. We experimented with twelve combinations of conditions, i.e., three different inlet temperatures($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$), two working fluid directions(upward and downward), and two aspect ratios, H/R(4 and 2). At the inlet temperature of $7^{\circ}C$ and $4^{\circ}C$, there was temperature stagnation region where the temperature of P.C.M. remains constant at $4^{\circ}C$ regardless of aspect ratio and direction of working fluid. This temperature stagnation occurs as the water, at its maximum density, flows down to the lower region. The phase change interface formed bell-shaped curve as the melting process continued. With a new set of conditions(4H/R, inlet temperature $4^{\circ}C$ and $1^{\circ}C$, downward/upwerd inlet direction), the movement of phase change interface was faster when the working flued inlet direction was downward. With the same set of conditions, melting rate and total melting energy were larger when the working fluid inlet direction was downward. The results were reversed when the other sets of conditions were applied.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.9
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• pp.793-802
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• 2009

Adsorption properties were estimated for the organic silicon compounds (siloxanes) in an actual landfill gas (LFG) using adsorbents such as coconut activated carbon, coal activated carbon, silica gel, sulfur adsorbent, carbonized sludge, and molecular sieve 13X. Coconut activated carbon showed the highest removal efficiency of more than 95%. The desorption of hexamethyldisiloxane (L2) from the adsorbent, however, resulted in the remarkable concentration variation of the compound in the treated gas. Silica gel, which had high adsorption capacity for L2 in single substance adsorption experiment in the other study, could not remove the component in the actual landfill gas while it adsorbed well octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) in the LFG. Therefore the elimination of hexamethyldisiloxane is an important factor to determine the level of total organosilicon compound in pretreated landfill gas. Moreover, the L2 from the actual landfill gas was effectively adsorbed by the serial adsorption test using two columns packed with coconut activated carbon which has the great capacity of siloxanes removal among others. In order to utilize efficiently LFG as a renewable energy, the emission and adsorptive characteristics of the substance to be treated should be considered for the organization, operation, and management of pretreatment process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.29-36
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• 2017

In this study, acombined cogeneration power plant produced two types of thermal energy and electric or mechanical power in a single process. The performance of each component of the gas turbine-combined cogeneration system was expressed as a function of the fuel consumption of the entire system, and the heat and electricity performance of each component. The entire system consisted of two gas turbines in the upper system, and two heat recovery steam generators (HRSG), a steam turbine, and two district heat exchangers in the lower system. In the gas turbine combined cogeneration system, the performance test after 10,000 hours of operation time, which is subject to an ASME PTC 46 performance test, was carried out by the installation of various experimental facilities. The performance of the overall output and power plant efficiency was also analyzed. Based on the performance test data, the test results were compared to confirm the change in performance. This study performed thermodynamic system analysis of gas turbines, heat recovery steam generators, and steam turbines to obtain the theoretical results. A comparison was made between the theoretical and actual values of the total heat generation value of the entire system and the heat released to the atmosphere, as well as the theoretical and actual efficiencies of the electrical output and thermal output. The test results for the performance characteristics of the gas turbine combined cogeneration power plant were compared with the thermodynamic efficiency characteristics and an error of 0.3% was found.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.55-62
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• 2008

This study investigated the status and problems of marine-related environmental impact assessment and a utilization-consultation system in Korea and suggested improvement of the review organization. Also, it conducted SWOT analysis based on evaluation of functions, roles and performance of the marine environmental impact assessment center and proposed development strategies of the center through introduction of expert opinions and advanced systems. The performance statement-review by the center in 2007 included 358 cases in total; 165 (46.1%) for consultation on utilization of sea area, 104 for environmental impact assessment (29.0%), and 89 (24.9%) for prior environmental review. The consultation on utilization of sea area can be divided into that for public water surface-use (41%) and reclamation (32%), and sea aggregate extraction process (21%). Although bad impacts on marine environment are reducing under the current system, there are some limits and problems to supplement it in terms of content, system and operation. Review system on sea area utilization-impact(marine environmental impact assessment center) by marine environmental management law needs to obtain expertise, fairness and efficiency and, to do so, have operational supports and institutional improvement to maximize its own functions and roles. At the same time, it is necessary for the center to establish identity and the status as a professional review organization by setting active development strategies inside the center. Finally, it should strengthen an consultation system of marine environmental impact assessment led by the related ministry to achieve effective coastal management.