• Nuclear Engineering and Technology
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• v.40 no.6
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• pp.477-488
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• 2008

The objective of the paper is to analyze the thermally induced density wave oscillations in water cooled boiling water reactors. A transient thermal hydraulic model is developed with a characteristics-based implicit finite-difference scheme to solve the nonlinear mass, momentum and energy conservation equations in a time-domain. A two-phase flow was simulated with a one-dimensional homogeneous equilibrium model. The model treats the boundary conditions naturally and takes into account the compressibility effect of the two-phase flow. The axial variation of the heat flux profile can also be handled with the model. Unlike the method of characteristics analysis, the present numerical model is computationally inexpensive in terms of time and works in a Eulerian coordinate system without the loss of accuracy. The model was validated against available benchmarks. The model was extended for the purpose of studying the flow-induced density wave oscillations in forced circulation and natural circulation boiling water reactors. Various parametric studies were undertaken to evaluate the model's performance under different operating conditions. Marginal stability boundaries were drawn for type-I and type-II instabilities in a dimensionless parameter space. The significance of adiabatic riser sections in different boiling reactors was analyzed in detail. The effect of the axial heat flux profile was also investigated for different boiling reactors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.7
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• pp.491-499
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• 2007

An architectural means of optimal daylight distribution is by using so-called light shelf systems, horizontal shading and redirecting devices. The overall performance of the daylighting system can be improved by the incorporation with electric lighting control devices. This paper aims to exemplify the benefit of daylighting in term of economic consideration. In such a case a reasonable technique to compare system costs is by life-cycle costing. Stated simply, a life-cycle cost represents the total cost of a system over its entire life cycle, that is, the sum of first cost and all future costs. Four different electric lighting system designs are proposed and a lighting control system that is continuously operating according to the level of daylight in the space has been adapted. The result shows clearly that although denser layout of lighting fixtures might be more effective to interface to the level of daylight ceaselessly changeable, its economic benefit may not meet the expected criterion the reason of increased initial investment and maintenance cost for the fixtures and control devices.

• The Journal of the Acoustical Society of Korea
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• v.2 no.1
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• pp.1-10
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• 1983

The presence of the sound tube and resonance cavity is unique in Korea Brahman Bells which is no examples in other country bells in the world. The sound tube erected in the crown is effective to emit the fundamental tone of the bell when the condition of resonant transmissibility is satisfied. The results of our analysis shows that the optimum length of the sound tube in the Bell Emile is 96cm but is not the present length, 77cm. The resonance cavity erected underneath the lip of the Bell Emile is found to be for the resonance of standing waves in the space including both bell cavity and resonance cavity and resonance cavity to the fundamental tone of the bell itself, in order that the strongest vibration can last long by least energy and lengthen the reverberation of the bell. Some historical remarks are also made on the magic flute, MANPASIKJUK, which was in existence in Shilla that can lull all evil waves, such as plagues, storms, droughts, famines and even enemies. The sound tube erected in the crown of the bell was originated in this magic flute. Finally, a strong proposal is advanced on the new national symbol of Korean traditional cultural assets. Indeed, it should be highly recommended that the Great King's Bell Emile would be the only real symbol of our national cultural assets by its own right of excellency and richness in every aspect of arts and sciences.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.243-256
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• 2011

This paper considers the concept of analog computing based on a cellular neural network (CNN) paradigm to simulate nuclear reactor dynamics using a time-dependent second order form of the neutron transport equation. Instead of solving nuclear reactor dynamic equations numerically, which is time-consuming and suffers from such weaknesses as vulnerability to transient phenomena, accumulation of round-off errors and floating-point overflows, use is made of a new method based on a cellular neural network. The state-of-the-art shows the CNN as being an alternative solution to the conventional numerical computation method. Indeed CNN is an analog computing paradigm that performs ultra-fast calculations and provides accurate results. In this study use is made of the CNN model to simulate the space-time response of scalar flux distribution in steady state and transient conditions. The CNN model also is used to simulate step perturbation in the core. The accuracy and capability of the CNN model are examined in 2D Cartesian geometry for two fixed source problems, a mini-BWR assembly, and a TWIGL Seed/Blanket problem. We also use the CNN model concurrently for a typical small PWR assembly to simulate the effect of temperature feedback, poisons, and control rods on the scalar flux distribution.

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1669-1679
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• 2017

Background: Steam generator (SG) is one of the significant components in the nuclear steam supply system. A variety of SGs have been designed and used in nuclear reactor systems. Every SG has advantages and disadvantages. A brief account of some of the existing SG designs is presented in this study. A high surface to volume ratio of a SG is required in small modular reactors to occupy the least space. In this paper, performance improvement for SGs of integral small modular reactor is proposed. Aims/Methods: For this purpose, cross-grooved microfins have been incorporated on the inner surface of the helical tube to enhance heat transfer. The primary objective of this work is to investigate thermal-hydraulic behavior of the proposed improvements through modeling in RELAP5-3D. Results and Conclusions: The results are compared with helical-coiled SGs being used in IRIS (International Reactor Innovative and Secure). The results show that the tube length reduces up to 11.56% keeping thermal and hydraulic conditions fixed. In the case of fixed size, the steam outlet temperature increases from 590.1 K to 597.0 K and the capability of power transfer from primary to secondary also increases. However, these advantages are associated with some extra pressure drop, which has to be compensated.

• Journal of Digital Convergence
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• v.10 no.11
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• pp.449-457
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• 2012

The purpose of this study is to investigate the relationship between radiation origin and health professionals, and to reduce exposed dose of radiation through efficient management. Increasing exposed dose of radiation to health professionals are caused by the increase of PET/CT use and a radioactive isotope. Hence, in this study, space dose from each origin of radiation generating was analyzed and the use of personnel protective clothing and shields was compared. As a result of this study, we confirmed that the exposed dose of radiation was much higher in case of wearing personnel protective clothing(0.5 mm pb) than no wearing personnel protective clothing under high energy gamma radiation(511 keV) of the position emitter($^{18}F$).

• Nuclear Engineering and Technology
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• v.4 no.4
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• pp.280-293
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• 1972

The differential fast neutron spectra above 0.5 Mev at particular spatial positions in tile reactor(TRIGA MARK-II) core has been determined experimentally using several threshold activation detectors. The series expansion technique utilizing the concept of least squares optimization was used to obtain an approximate solution to the set of integral equations which are defined by the experimentally determined activation data. The influence of use of different weighting functions in the solution was analyzed in each measurement. To carry out the necessary mathematical calculations, a computer code for the UNIVAC 1106 digital computer has been prepared. Good agreement was achieved between the differential fast neutron spectra determined in this work and the computed flux determined independently using space-independent multigroup transport theory.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.226-231
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• 2011

This study set out to review the air current fluidity in exhaust common ducts by installing an inlet pipe at a leisure space in the PS(Pipe Shaft)room for the sake of wind power generation with kitchen and bathroom exhaust common ducts of all the equipment and air conditioning shafts in high-rise apartment. The air current functionality of kitchen and bathroom exhaust common ducts was reviewed by analyzing wind velocity changes according to changes to the area of exhaust common ducts through a simulation, changes to the wind velocity of the kitchen hood by applying an external inlet pipe, changes to the usage factor of exhaust common ducts, and changes to wind velocity by altering the form of the ventilator at the bottom of the old exhaust common duct. It was a basic study on the utilization of exhaust wind velocity in exhaust common ducts.

• Journal of Surface Science and Engineering
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• v.36 no.2
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• pp.148-154
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• 2003

Short ($\tau$=40 $mutextrm{s}$) and high-voltage ($U_{sub}$=2~8 kV) negative substrate bias pulses were used to assist pulsed magnetron sputtering DLC films deposition. Space- and time-resolved probe measurements of the plasma characteristics have been performed. It was shown that in case of high-voltage substrate bias spatial non-uniformity of the magnetron discharge plasma density greatly affected DLC deposition process. By Raman spectroscopy it was found that maximum percentage of s $p^3$-bonded carbon atoms (40 ~ 50%) in the coating was attained at energy $E_{c}$ ~700 eV per deposited carbon atom. Despite rather low diamond-like phase content these coatings are characterized by good adhesion due to ion mixing promoted by high acceleration voltage. Short duration of the bias pulses is also important to prevent electric breakdowns of insulating DLC film during its growth.wth.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.79-83
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• 2014

Dye-sensitized solar cells (DSSCs) are applied in the emerging fields of building integrated photovoltaic and electronics integrated photovoltaic like small portable power sources as demands are increased with characteristic advantages. Highly flexible dye-sensitized solar cells (DSSCs) prepared on single stainless steel mesh were proposed in this paper. Single mesh DSSCs structure utilizing the spraying the chopped glass paper on the surface treated stainless steel mesh for integrating the space element and the electrode components, counter electrode component and photoelectrode component were coated on each side of the single mesh. The fabricated single mesh DSSCs showed the energy-conversion efficiency 0.50% which show highly bendable ability. The new single mesh DSSCs may have potential applications as highly bendable solar cells to overcome the limitations of TCO-based DSSCs.