• Journal of Energy Engineering
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• v.7 no.1
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• pp.122-130
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• 1998

A simplified heat transfer model for the cooling capability of the AP 600 PCCS is proposed I this paper. As the PCCS domain is covered with very thin and long water film, it is phenomenologically divided into 3 regions; water entrance effect region, asymptotic region, and air entrance effect region. As the length of the asymptotic region is estimated to be over 90% of the whole domain, the phenomena in the asymptotic region is focused. Using the analogy between heat and mass transfer phenomena in a turbulent situation, a new dependent variable combining temperature and vapor mass fraction was defined. The similarity between the PCCs phenomena in the asymptotic region and the buoyant air flow phenomena on a vertical heated plate is derived. Using the similarity, the simplified heat transfer correlations for the interfacial heat fluxes and the ratios of latent heat transfer to sensible heat transfer were established. To verify the accuracy of the correlation, the results of this study were compared with those of other numerical analyses performed for the same configuration and they are well within the range of 15% difference.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.26-28
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• 2008

Soil moisture plays an important role in the land-atmosphere energy balance because it governs the partitioning of energy through latent heat fluxes or evapotranspiration. From the numerous studies, it is evident that the L-band radiometer is a useful and effective tool to measure soil moisture. The objective of the study is to develop and to verify the soil moisture retrieval algorithms for the L-band radiometer system. Through the radiometer-observed brightness temperature, surface emissivity and reflectivity can be derived, and, hence, soil moisture. We collect field and L-band airborne radiometer data from washita92, SGP97 and SGP99 experiments to assist the development of the retrieval algorithms. Upon launching the satellite L-band radiometer such as ESA-sponsored SMOS (Soil Moisture and Ocean Salinity) mission, the developed algorithms may be used to study and monitor globe soil moisture change.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.235-238
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• 2009

BaMg$Al_{10}O_{17}$ (BAM) co-doped with $Eu^{2+}$ and $Mn^{2+}$ was synthesized in a solid-state reaction and their luminescence properties were investigated as functions of the concentrations of the sensitizer and activator. BAM:$Eu^{2+}$ had a broad blue emission band at 450 nm and BAM:$Mn^{2+}$ exhibited green emission at 514 nm. The energy transfer from $Eu^{2+}$ to $Mn^{2+}$ was mainly of the resonance-type via an electric dipole-quadrupole interaction. Additionally, the addition of various fluxes such as $AlF_3$ and $BaF_2$ in the synthesis improves the moist and thermal stability. This is particularly important for the phosphor in white light emitting diodes (LEDs).

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.134.1-134.1
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• 2012

The radiation belt structure can be approximately reproduced by a form of diffusion equation, which takes into account the radial diffusion process as well as those in pitch angle and energy. The solution of the equation depends on several factors including initial and boundary conditions, diffusion coefficients, and plasmapause location. In this paper, we have attempted to determine a set of approximate functions for the energetic electron fluxes near the outer edge of the outer belt in terms of solar wind variable. We used the electron flux data from SST onboard the THEMIS spacecraft and determined its correlation with solar wind conditions in a systematic way. The functions were determined separately for different energy channels from ~30 keV up to 719 keV. Our determination of these functions allows us to predict the radial boundary condition for the electron flux, which can be implemented in a forecast model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.276-285
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• 1991

The transient heat transfer characteristics in the radiant heating panel were predicted by numerical analysis. Thermal behaviors of panel, such as temperature distributions in panel and convective and radiative heat fluxes in panel surface with respect to time were obtained. Heating hours per day, rate of energy supplied and maximum temperature differences at panel surface were also compared for several important parameters. The performance and thermal comfort of heating panel were studied and compared for various operating and design conditions such as pipe pitch, pipe location, pipe diameter and flow rate of hot water for the purpose of producing useful data, which can be used for the test and decision of efficient operating condition of the conventional heating systems or the optimal design of the new panel heating systems.

• Journal of the Korean Solar Energy Society
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• v.24 no.4
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• pp.19-25
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• 2004

A numerical study is performed to investigate the effect of sun tracking on the thermal performance of the evacuated compound parabolic concentrator (CPC) collectors. The evacuated CPC collectors consist of a two-layered glass tube, a copper tube and a reflector. The collector has a copper tube as an absorber and a reflector inside a glass tube. The water is used as a working fluid. The length and the diameter of the glass tube are 1,700mm and 70mm, respectively. The length and the diameter of the copper tube are 1,700mm and 25.4mm, respectively. Ray tracing analysis is carried out in order to compare absorbed heat fluxes on the absorber surface of the stationary and tracking collectors. The collected energy is calculated and compared with that on a fixed surface tilted at $35^{\circ}$ on the ground and facing south. The results indicate that the collected solar energy of the sun tracking system is significantly larger than that of a stationary collector. The sun tracking evacuated CPC collectors show a better performance with an increase in the thermal efficiency of up to 14% compared with an identical stationary collector.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.202-204
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• 2009

Erosion is a common failure mode of materials frequently encountered in plant and power industry. Although the erosion resistance of Fe-base alloy has been inferior to the other expensive materials, it is expected that the strain-induced martensitic transformation can impart high erosion resistance to Fe-base alloy. The key technology to develop Fe-base metal cored welding wire for erosion resistant overlay welding may include the strain-induced metallurgy for hardening rate control and the welding flux metallurgy for dilution control. Sophisticated studies showed that the strain-induced martensitic transformation behavior was related to the critical strain energy which was dependent on the alloy composition. Dilution and bead shape of overlay weld were proved to be affected by metal transfer mode during gas tungsten arc welding and elements in welding fluxes. It was considered that the highly erosion resistant Fe-base overlay weld could be achieved by precise control of alloy composition to have proper level of critical strain energy for energy absorption and welding flux formulation to have small amount of deoxidizing metallic elements for dilution.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2607-2612
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• 2020

The present work was aimed to show the possibility of using hydrogel (acrylic/boric acid) for evaluation of the neutron radiation shielding. The influence of acrylic acid concentration, different gamma doses and relative contents of boric acid were studied. The physical properties and the thermomechanical stability of the studied samples were investigated. The shielding property of the composite for neutron was tested by Pu-Be neutron source (5 Ci) under room temperature. The neutron fluence rates and gamma fluxes were measured using a stilbene organic scintillator. The macroscopic effective removal cross-section Σ_R (cm^-1) of fast neutrons and total attenuation coefficient μ (cm^-1) of gamma rays has been studied experimentally. The transmission parameters, the relaxation length (??) and the half-value layer (HVL) were obtained. The obtained results indicated that the addition of boric acid to acrylic acid tends to increase the macroscopic effective removal cross-section Σ_R (cm^-1) to 0.141 compared to 0.094 of ordinary concrete.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.43.3-43.3
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• 2009

Our previous study showed the intensity of the long LBH (1600 - 1715 ${\AA}$) was enhanced very much compared to that of the short LBH (1400 - 1500 ${\AA}$) when the characteristic energy of the precipitating electrons increased from 1 keV to > 7 keV, in accordance with the theoretical models. In this presentation, we would like to present the results of our study for new modeling results about previous report and even higher energy electrons. We selected the events in which the fluxes both in the low energy (100 eV ~ 20 keV) and in the high energy (170 ~ 360 keV) were enhanced, and examined the auroral spectra for these events observed simultaneously by the imaging spectrograph on the same spacecraft. While the accurate characteristic energy could not be determined because of the gap in the energy range, our result showed the intensity ratio of the long LBH to the short LBH ranged from 1.2 to 2.0 in these events, in contrast to 1.0 or smaller for the events in which the highest enhancement was seen only in the low energy. Our study suggests that intense auroras might be accompanied by high energy electrons above 20 keV.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.8
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• pp.717-726
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• 2010

For the application into a 1 kWh flywheel energy storage system(FESS), this paper presents the design scheme of radial and axial hybrid magnetic bearings which use bias fluxes generated by permanent magnets. In particular, the axial hybrid magnetic bearing is newly proposed in this paper, in which a permanent magnet is arranged in axial direction so that it can support the rotor weight as well as provide a bias flux for axial magnetic bearing. Such hybrid magnetic bearings consume very low power, compared with conventional electromagnetic bearings. In this paper, to stably support a 140 kg flywheel rotor without contact, design process is explained in detail, and magnetic circuit analysis and three-dimensional finite element analysis are carried out to determine the design parameters and predict the performance of the magnetic bearings.