• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.31 no.7
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• pp.45-52
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• 2002

1991년에 Maryland 대학에 Dr. Reinhard Rader-macher에 의해 환경에너지공학연구소(CEEE)가 설립되었다. 이 연구소는 환경 및 경제적인 관점에서 에너지 변환 시스템을 개발하는데 선두적인 역할들 수행해왔다. 환경 에너지 공학 연구소는 산업체, 정부,및 연구소에서 지원 받는 컨소시엄 형태의 연구 센터이다. 대체 냉매, $CO_2$초월임계 사이클에 관한 연구를 1993년에 시작한 이래, 현재 세계적으로 40여 개의 회사가 지원을 하고 있다. 2단 압축 $CO_2$ 사이클 최적화, 초월 임계 사이클에서의 오일에 따른 열전달 영향, 초월$CO_2$임계 시스템에서의 오일 정체, $CO_2$압축기 모델링, 자동차에서의 $CO_2$기후 조절 시스템, $CO_2$냉매를 이용한 에어컨, $CO_2$저온 냉동 시스템 등에 관한 연구를 수행하고 있다. CEEE는 향후 연구로 구성요소 및 시스템 최적화, 효율향상, 시스템 적용확대에 관한 연구를 할 예정이다. 센터는 보고서, 컨소시엄 미팅. 워크샵, 교과목 개설, 당문 연구자 초청들을 통해 산업계 및 기술을 전달하고 있다. 본 고에서는 환경에너지 공학 연구소에서 $CO_2$ 초월임계 사이클에 초점을 맞추어 연구소의 연구활동을 기술한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.874-882
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• 2013

Kerosene(Jet A-1), one of the propellants for each stage's engine of the Korea Space Launch Vehicle-II(KSLV-II), functions as coolant at the same time as it flows inside the cooling jacket of the combustion chambers and is injected through the film cooling holes. A physical surrogate mixture model to reproduce the thermophysical characteristics of Jet A-1 has been selected and the thermodynamic/transport properties of the model fuel under high pressure including supercritical conditions have been estimated using SUPERTRAPP(NIST SRD4). Comparisons with the measured properties suggest that proposed database can be used to extract properties of Jet A-1 for conjugate heat transfer analysis of liquid propellant rocket engine thrust chambers. Predicted combustion/cooling performance of regeneratively cooled thrust chambers shall be validated through comparisons with upcoming firing test results.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.27-32
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• 2019

In this study, the vorticity distribution and the temperature distribution change around a circular cylinder were compared and analyzed with time for constant inlet velocity and periodic inlet velocity. Also, the frequency characteristics of the flow were analyzed by analyzing the time variation of lift and drag and their PSD(power spectral density). In the case of constant inlet velocity, the well known Karman vorticity distribution was shown, and vortices were alternately generated at the upper and lower sides of the circular cylinder. In case of periodic inlet velocity, it was observed that vortex occurred simultaneously in the upper and lower sides of the circular cylinder. In both cases, it was confirmed that the time dependent temperature distribution changes almost the same behavior as the vorticity distribution. For the constant inlet velocity, the vortex flow frequency is 31.15 Hz, and for the periodic inlet velocity, the vortex flow frequency is equal to the preriodic inlet velocity at 15.57 Hz. The mean surface Nusselt number was 99.6 for the constant inlet velocity and 110.7 for the periodic inlet velocity, which showed 11.1% increase in surface heat transfer.

• Journal of the Korean Society of Visualization
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• v.18 no.3
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• pp.23-34
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• 2020

Two-phase flow and heat transfer characteristics during the reflood phase of a single heated rod in the KHU reflood experimental facility were examined. Two-phase flow behavior during the reflooding experiment was carefully visualized along with transient temperature measurement at a point inside the heated rod. By numerically solving one-dimensional inverse heat conduction equation using the measured temperature data, time-resolved wall heat flux and temperature histories at the interface of the heated rod and coolant were obtained. Once water coolant was injected into the test section from the bottom to reflood the heated rod of >700℃, vast vapor bubbles and droplets were generated near the reflood front and dispersed flow film boiling consisted of continuous vapor flow and tiny liquid droplets appeared in the upper part. Following the dispersed flow film boiling, inverted annular/slug/churn flow film boiling regimes were sequentially observed and the wall temperature gradually decreased. When so-called minimum film boiling temperature reached, the stable vapor film between the heated rod and coolant was suddenly collapsed, resulting in the quenching transition from film boiling into nucleate boiling. The moving speed of the quench front measured in the present study showed a good agreement with prediction by a correlation in literature. The obtained results revealed that typical two-phase flow and heat transfer behaviors during the reflood phase of overheated fuel rods in light water nuclear reactors are well reproduced in the KHU facility. Thus, the verified reflood experimental facility can be used to explore the effects of other affecting parameters, such as CRUD, on the reflood heat transfer behaviors in practical nuclear reactors.

• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.154-162
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• 1998

A planar Bi-Sb multijunction thermal converter with high thermal sensitivity and small ac-dc transfer error has been fabricated by preparing the bifilar thin film Pt-heater and the hot junctions of thin film Bi-Sb thermopile on the $Si_{3}N_{4}/SiO_{2}/Si_{3}N_{4}$-diaphragm, which functions as a thermal isolation layer, and the cold junctions on the dielectric membrane supported with the Si-substrate, which acts as a heat sink, and its ac-dc transfer characteristics were investigated with the fast reversed dc method. The respective thermal sensitivities of the converter with single bifilar heater were about 10.1 mV/mW and 14.8 mV/mW in the air and vacuum, and those of the converter with dual bifilar heater were about 5.1 mV/mW and 7.6 mV/mW, and about 5.3 mV/mW and 7.8 mV/mW in the air and vacuum for the inputs of inside and outside heaters, indicating that the thermal sensitivities in the vacuum, where there is rarely thermal loss caused by gas, are higher than those in the air. The ac-dc voltage and current transfer difference ranges of the converter with single bifilar heater were about ${\pm}1.80\;ppm$ and ${\pm}0.58\;ppm$, and those of the converter with dual bifilar heater were about ${\pm}0.63\;ppm$ and ${\pm}0.25\;ppm$, and about ${\pm}0.53\;ppm$ and ${\pm}0.27\;ppm$, respectively, for the inputs of inside and outside heaters, in the frequency range below 10 kHz and in the air.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.850-859
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• 2012

Devolatilization is an important mechanism in the gasification and pyrolysis of woody biomass, and has to be accordingly considered in designing a gasifier. In order to describe the devolatilization process of wood particle, there have been proposed a number of empirical correlations based on experimental data. However, the correlations are limited to apply for various reaction conditions due to the complex nature of wood devolatilization. In this study, a simple model was developed for predicting the devolatilization of a wood particle in a fluidized bed reactor. The model considered the drying, shrinkage and heat generation of intra-particle for a spherical biomass. The influence of various parameters such as size, initial moisture content, heat transfer coefficient, kinetic model and temperature, was investigated. The devolatilization time linearly increased with increasing initial moisture content and size of a wood particle, whereas decreases with reaction temperature. There is no significant change of results when the external heat transfer coefficient is over 300 $W/m^2K$, and smaller particles are more sensitive to the outer heat transfer coefficient. Predicted results from the model show a similar tendency with the experimental data from literatures within a deviation of 10%.

• Journal of Bio-Environment Control
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• v.18 no.4
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• pp.341-347
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• 2009

Experiments and computations were conducted to investigate the heat insulation characteristics of multi layer materials for cultivation greenhouse. In case of the experiments, measurements of temperature were carried out with a K-type thermocouples and data logger to research the heat transfer in the experimental module generated by the heat source. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of multi layer materials. The numerical analyses were performed by commercial code CFX-11 according to the variation of multi layer materials without air layer. The experimental results showed that the heat insulation of multi layer materials was higher than single layer materials by 50~90%. It was found that the effect of heat insulation was raised by the combination of multi layer materials.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.33-37
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• 2019

In this study, the graded thermal properties of composites are obtained by difference in specific gravity of fillers including Cu, h-BN and GO powders in epoxy. Relatively heavy powders such as Cu and h-BN compared to GO mostly at the bottom layer, while light GO powders were dispersed in the top layer in the composites. The thermal conductivity of composites was gradually increased from 0.55 (0.52) W/mK to 2.82 (1.37) W/mK for GO/h-BN (GO/Cu) epoxy composites from surface to bottom. On the contrary, the coefficient of thermal expansion was decreased from 51 ppm/℃ to 23 ppm/℃ and from 57 ppm/℃ to 32 ppm/℃ for GO/Cu and GO/h-BN, respectively. The variation of thermal properties in composites is attributed due to intrinsic material properties of filler including thermal conductivity, morphology and the distribution by the specific weight of fillers. This simple strategy for realizing graded thermal composites by introducing different filler materials would be effective heat transfer at interface of heterostructure with large thermal properties such as inorganic semiconductor/plastic, metal/plastic, and semiconductor/metal.

• Journal of Energy Engineering
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• v.23 no.2
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• pp.207-216
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• 2014

The energy loss can be divided into the loss caused by heat transfer and the loss caused by air flow. Heat transfer is the loss resulting from the heat transmittance of external wall, roof, and floor, and represents one of the most vulnerable elements of existing buildings. To prevent such loss, it is necessary to increase the mean heat transmittance of entire external wall, including the window, to a level above the standard regional value and ensure the air-tightness of window. The old buildings have the structure which is prone to the loss of greater air flow due to the air infiltration through the exit/entrance door upward along the stairway by the stack effect and simultaneous suction of air from each floor, and becomes even vulnerable to the loss of heat insulation for each floor, although the external wall and windows are the most vulnerable parts. The improvement plans for each floor need to be submitted in tandem with the diagnosis of whole building, regarding the diagnosis plan and energy improvement measures based on the survey of site, rather than adhering to the misconception that the replacement of window alone will result in energy-savings.

• Journal of the Korean Geotechnical Society
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• v.26 no.2
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• pp.45-54
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• 2010

The SCW numerical model described in the companion paper was used to carry out a comprehensive parametric study to evaluate the performance of the SCW. The five ground related parameters, which are porosity, hydraulic conductivity, thermal conductivity, specific heat, geothermal gradient, and five SCW design parameters, which are pumping rate, well depth, well diameter, dip tube diameter, bleeding rate, were used in the study. Two types of numerical simulations were performed. The first type was used to perform short-term (24-hour) simulation, while the second type 14 day simulation. The study results indicate that the parameters that have important influence on the performance of SCW were hydraulic conductivity, thermal conductivity, geothermal gradient, pumping rate, and bleeding rate. The thermal conductivity had the most important influence on the performance of the SCW. With the increase in the geothermal gradient, the performance increased in the heat mode, but decreased in the cooling mode. The hydraulic conductivity influenced the performance when the value was larger than $10^{-4}m/s$. The depth of the well increased the performance, but at the cost of increased cost of boring. The bleeding had an important influence on SCW, greatly enhancing the performance at a limited increased cost of operation. Overall, this study showed that various factors had a cumulative influence on the performance of the SCW, and a numerical simulation can be used to accurately predict the performance of the SCW.