• Nuclear Engineering and Technology
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• v.39 no.1
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• pp.9-20
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• 2007

Design study on the Gas Turbine High Temperature Reactor 300-Cogeneration (GTHTR300C) aiming at producing both electricity by a gas turbine and hydrogen by a thermochemical water splitting method (IS process method) has been conducted. It is expected to be one of the most attractive systems to provide hydrogen for fuel cell vehicles after 2030. The GTHTR300C employs a block type Very High Temperature Reactor (VHTR) with thermal power of 600MW and outlet coolant temperature of $950^{\circ}C$. The intermediate heat exchanger (IHX) and the gas turbine are arranged in series in the primary circuit. The IHX transfers the heat of 170MW to the secondary system used for hydrogen production. The balance of the reactor thermal power is used for electricity generation. The GTHTR300C is designed based on the existing technologies of the High Temperature Engineering Test Reactor (HTTR) and helium turbine power conversion and on the technologies whose development have been well under way for IS hydrogen production process so as to minimize cost and risk of deployment. This paper describes the original design features focusing on the plant layout and plant cycle of the GTHTR300C together with present development status of the GTHTR300, IHX, etc. Also, the advantage of the GTHTR300C is presented.

• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.831-840
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• 2009

In order to evaluate the start-up behavior and to identify, through abnormal operation occurrences, the transient behaviors of the Sulfur Iodine(SI) process, which is a nuclear hydrogen process that is coupled to a Very High Temperature Gas Cooled Reactor (VHTR) through an Intermediate Heat Exchanger (IHX), a dynamic simulation of the process is necessary. Perturbation of the flow rate or temperature in the inlet streams may result in various transient states. An understanding of the dynamic behavior due to these factors is able to support the conceptual design of the secondary helium loop system associated with a hydrogen production plant. Based on the mass and energy balance sheets of an electrodialysis-embedded SI process equivalent to a 200 $MW_{th}$ VHTR and a considerable thermal pathway between the SI process and the VHTR system, a dynamic simulation of the SI process was carried out for a sulfuric acid decomposition process (Second Section) that is composed of a sulfuric acid vaporizer, a sulfuric acid decomposer, and a sulfur trioxide decomposer. The dynamic behaviors of these integrated reactors according to several anticipated scenarios are evaluated and the dominant and mild factors are observed. As for the results of the simulation, all the reactors in the sulfuric acid decomposition process approach a steady state at the same time. Temperature control of the inlet helium is strictly required rather than the flow rate control of the inlet helium to keep the steady state condition in the Second Section. On the other hand, it was revealed that the changes of the inlet helium operation conditions make a great impact on the performances of $SO_3$ and $H_2SO_4$ decomposers, but no effect on the performance of the $H_2SO_4$ vaporizer.

• Korean Journal of Remote Sensing
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• v.19 no.4
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• pp.291-305
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• 2003

The cost of deploying Geological and Environmental information gathering systems, especially when such systems obtain remote sensing and photographic data through the use of commercial satellites and aircraft. Besides the high cost equipment required, adverse weather conditions can further restrict a researcher's ability to collect data anywhere and anytime. To mitigate this problem, we have developed a compact, multi-spectral automatic Aerial photographic system. This system's Multi-spectral camera is capable of the visible (RGB) and infrared (NIR) bands (3032*2008 pixel). It consists of a thermal infrared camera and automatic balance control, and can be managed by a palm-top computer. Other features includes a camera gimbal system, GPS receiver, weather sensor among others. We have evaluated the efficiency of this system in several field tests at the following locations: Kyongsang-bukdo beach, Nakdong river (at each site of mulkeum-namji and koryung-gumi), and Kyungahn River. Its tested ability in aerial photography, weather data, as well as GPS data acquisition demonstrates its flexibility as a tool for environmental data monitoring.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.330-330
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• 2016

The quantification of dry season evaporation in regions, where the magnitude of dry season flows is key to the regional water supply, is essential for good water management. Also, tree transpiration has a significant role in the water balance of a catchment whenever it is tree populated, especially in water limited environments. Such is the case in the Middle Mountains of Nepal where dry season flows play a significant role in downstream water provisioning and their proper functioning is key to the welfare of millions of people. This research seeks to study the transpiration of a pine forest stand in the Jikhu Khola Watershed in the Middle Mountains of Nepal. To the author's knowledge, no single study has been made so far to estimate the dry season evaporation from the planted forest stand in the Middle Mountains of Nepal. The study was carried out in planted pine forest embedded within the Jikhu Khola Catchment. Field campaigns of sap flow measurements were carried out from September, 2010 to February, 2011 in the selected plot of 15*15m dimension, to characterize dry season evaporation. This was done by measuring sap fluxes and sapwood areas over the six trees of different Diameter at Breast Height (DBH) classes. The sap flux was assessed using Granier's thermal dissipation probe (TDP) technique while sapwood area was determined using several incremental core(s) taken with a Pressler borer and immediately dyeing with methyl orange for estimating the actual depth of sapwood area. Transpiration of the plot was estimated by considering the contribution of each tree class. For this purpose, sap flux density, sapwood area and the proportion of total canopy area were determined for each tree class of the selected plot. From these data, hourly and diurnal transpiration rates for the plot were calculated for experimental period. Finally, Cienciala model was parameterized using the data recorded by the ADAS and other terrain data collected in the field. The calibrated model allowed the extrapolation of Sap flux density (v) over a six month period, from September 2010 to February 2011. The model given sap flux density was validated with the measured sap flux density from Grainier method.

• Steel and Composite Structures
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• v.10 no.2
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• pp.129-149
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• 2010

The objective of this study is to formulate a general 3D material-structural analysis framework for the thermomechanical behavior of steel-concrete structures in a fire environment. The proposed analysis framework consists of three sequential modeling parts: fire dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of the structure. The first modeling part consists of applying the NIST (National Institute of Standards and Technology) Fire Dynamics Simulator (FDS) where coupled CFD (Computational Fluid Dynamics) with thermodynamics are combined to realistically model the fire progression within the steel-concrete structure. The goal is to generate the spatial-temporal (ST) solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST solutions are generated in a discrete form. Continuous FDS-ST approximations are then developed to represent the temperature or heat-flux at any given time or point within the structure. An extensive numerical study is carried out to examine the best ST approximation functions that strike a balance between accuracy and simplicity. The second modeling part consists of a finite-element (FE) transient heat analysis of the structure using the continuous FDS-ST surface variables as prescribed thermal boundary conditions. The third modeling part is a thermomechanical FE structural analysis using both nonlinear material and geometry. The temperature history from the second modeling part is used at all nodal points. The ABAQUS (2003) FE code is used with external user subroutines for the second and third simulation parts in order to describe the specific heat temperature nonlinear dependency that drastically affects the transient thermal solution especially for concrete materials. User subroutines are also developed to apply the continuous FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The proposed modeling framework is applied to predict the temperature and deflection of the well-documented third Cardington fire test.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.1
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• pp.35-41
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• 2008

The radiative heat loss from a receiver of a dish solar collector is numerically investigated. The dish solar collector considered in this paper consists of a receiver and multi-faceted mirrors. In order to investigate the performance comparison of dish solar collectors, six different mirror arrays and four different receivers are considered. A parabolic- shaped perfect mirror of which diameter is 1.40 m is considered as the reference for the mirror arrays. The other mirror arrays which consist of twelve identical parabolic-shaped mirror facets of which diameter are 0.405 m are suggested for comparison. Their reflecting areas, which are 1.545 $m^{2}$, are the same. Four different receiver shapes are a conical, a dome, a cylindrical, and a unicorn type. The radiative properties of the mirror surfaces and the receiver surfaces may vary the thermal performance of the dish solar collector so that various surface properties are considered. In order to calculate the radiative heat loss in the receiver, two kinds of methods are used. The Net Radiation Method that is based on the radiation heat balance on the surface is used to calculate the radiation heat transfer rate from the inside surface of the receiver to the environment. The Monte-Carlo Method that is the statistical approach is adopted to predict the radiation heat transfer rate from the reflector to the receiver. The collector efficiency is defined as the results of the optical efficiency and the receiver efficiency. Based on the calculation, the unicorn type has the best performance in receiver shapes and the STAR has the best performance in mirror arrays except the perfect mirror.

• Journal of Powder Materials
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• v.30 no.6
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• pp.463-469
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• 2023

Aluminum alloys, known for their high strength-to-weight ratios and impressive electrical and thermal conductivities, are extensively used in numerous engineering sectors, such as aerospace, automotive, and construction. Recently, significant efforts have been made to develop novel aluminum alloys specifically tailored for additive manufacturing. These new alloys aim to provide an optimal balance between mechanical properties and thermal/electrical conductivities. In this study, nine combinatorial samples with various alloy compositions were fabricated using direct energy deposition (DED) additive manufacturing by adjusting the feeding speeds of Al6061 alloy and Al-12Si alloy powders. The effects of the alloying elements on the microstructure, electrical conductivity, and hardness were investigated. Generally, as the Si and Cu contents decreased, electrical conductivity increased and hardness decreased, exhibiting trade-off characteristics. However, electrical conductivity and hardness showed an optimal combination when the Si content was adjusted to below 4.5 wt%, which can sufficiently suppress the grain boundary segregation of the α-Si precipitates, and the Cu content was controlled to induce the formation of Al₂Cu precipitates.

• Journal of the Korean Institute of Landscape Architecture
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• v.44 no.4
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• pp.100-108
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• 2016

The climatic index for tourism(CIT) has recently been advanced, which includes complete human energy balance models such as physiological equivalent temperature(PET) and universal thermal climate index(UTCI). This study investigated human thermal sensation and comfort at Woljung-ri Beach, Jeju, Republic of Korea, in spring and summer 2015 for landscape planning and design in beach areas. Microclimatic data measurements and human thermal sensation/comfort surveys from ISO 10551 were conducted together. There were 869 adults that participated. As a result, perceptual and thermal preference that consider only physiological aspects had high coefficients of determination($r^2$) with PET in linear regression analyses: 92.8% and 87.6%, respectively. However, affective evaluation, personal acceptability and personal tolerance, which consider both physiological and psychological aspects, had low $r^2s$: 60.0%, 21.1% and 46.4%, respectively. However, the correlations between them and PET were all significant at the 0.01 level. The neutral PET range in perceptual for human thermal sensation was $25{\sim}27^{\circ}C$, but a PET range less or equal to 20% dissatisfaction, which was recommended by ASHRAE Standard 55, could not be achieved in perceptual. Only PET ranges in affective evaluation and personal tolerance affected by both aspects were qualified for the recommendation as $21{\sim}32^{\circ}C$ and $17{\sim}37^{\circ}C$, respectively. Therefore, the PET range of $21{\sim}32^{\circ}C$ is recommended to be used for the human thermal comfort zone of beach areas in landscape planning and design as well as tourism and recreational planning. PET heat stress level ranges on the beach were $2{\sim}5^{\circ}C$ higher than those in inland urban areas of the Republic of Korea. Also, they were similar to high results of tropical areas such as Taiwan and Nigeria, and higher than those of western and middle Europe and Tel Aviv, Israel.

• Geotechnical Engineering
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• v.10 no.4
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• pp.103-118
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• 1994

The rapid motion of granular material is microscopically observed, and investigated by continuum theory. From the binary collision phenomenon two different times are introduced : flying time and contact time. The former says the non -stationary motion and at a same time the variation of bulk volume. The latter is operative by a delayed time during the contact and describes the elastic properties of granular material. With both times a dynamic constitutive equation is postulated for four state variables : dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate. The balance laws of mass, momentum and energy which are represented through above four variabls, are applied to the model, in which due to the elastic property the relaxation and energy absorption are explained.

• Journal of the Korean Society of Combustion
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• v.19 no.4
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• pp.1-7
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• 2014

An experimental study on downwardly spreading flame over slanted electrical wire, which is insulated by Polyethylene (PE), was conducted with applied AC electric fields. The result showed that the flame spread rate decreased initially with increase in inclination angle of wire and then became nearly constant. The flame shape was modified significantly with applied AC electric field due to the effect of ionic wind. Such a variation in flame spread rate could be explained by a thermal balance mechanism, depending on flame shape and slanted direction of flame. Extinction of the spreading flame was not related to angle of inclination, and was described well by a functional dependency upon the frequency and voltage at extinction.