• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.289-295
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• 2004

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flowmeter, an evaporator, and a gas cooler(test section). The main components of the water loop consist of a variable-speed pump, an isothermal tank, and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal stainless steel tube of the outer diameter of 9.53mm and of the inner diameter of 7.75mm. The length of the test section is 6m. The refrigerant mass fluxes were 200∼300kg/(m2$.$s) and the inlet pressure of the gas cooler varied from 7.5㎫ to 8.5㎫. The main results were summarized as follows : Pressure drop of CO2 increases with increasing gas cooler pressure. The friction factors of CO2 in a horizontal tube show a relatively good agreement with the correlation by Blasius. The heat transfer coefficient of CO2 in transcritical region increases with decreasing gas cooler pressure and decreasing mass flux of CO2. Most of correlations proposed in a transcritical region showed significant deviations with experimental data except for those predicted by Gnielinski.

• Journal of Energy Engineering
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• v.12 no.3
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• pp.223-230
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• 2003

A study was performed to measure and analyze the gas-side fouling of heat exchanger to cool the exhaust gas from sludge incinerator at ironworks. The incinerator gas passes through inside of the vertical tubes of heat exchanger to preheat the combustion air. This kind of fouling occurs at the entrance region of the heat exchanger and thus the perforated fouling plate was designed to measure the gas-side fouling and to analyze the particulate deposit. As a result of analysis, the particulate deposition rate was influenced by temperature, particulate composition and size and also the deposition patterns were different according to the location of perforated fouling plate. The computational analysis was performed to obtain the deposition rates at the perforated fouling plate and the calculation showed that the deposition rate was varied with the hole size and particulate size. It was proved that the fouling at the entrance region of heat exchanger could be measured by the perforated fouling plate designed in this study.

• Journal of Conservation Science
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• v.30 no.2
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• pp.149-156
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• 2014

Low oxygen treatment and heating treatment are used to prevent insects in the field of food science. These eco-friendly control methods can be applied to biological control technique in conservation treatment of organic cultural properties. To evaluate material stability, low-oxygen treatment and low oxygen treatment are applied to wood, pigment, paper and textile that are related to historical wooden buildings. As a result, wood moisture content declined after low oxygen treatment. But decline rate is a little, so it can be expected to turn back original state as time passes. And test result on pigment, paper, textile of chrominance and strength of test materials are stable. But after heating treatment, pigments are separated.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.25-32
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• 2012

Cold start driving cycles exhibit an increases in friction losses due to the low temperatures of metal components and media compared to the normal operating engine conditions. These friction losses are adversely affected to fuel economy. Therefore, in recent years, various techniques for the improvement of fuel economy at cold start driving cycles have been introduced. The main techniques are the upward control of coolant temperature and the fast warm-up techniques. In particular, the fast warm-up techniques are implemented with the coolant flow-controlled water pump and the WHRS (waste heat recovery system). This paper deals with an effect of fast ATF (automatic transmission fluid) warm-up on fuel economy using a recovery system of EGR gas waste heat in a diesel engine. On a conventional diesel engine, two ATF coolers have been connected in series, i.e., an air-cooled ATF cooler is placed in front of the condenser of air conditioning system and a water-cooled one is embedded into the radiator header. However, the new system consists of only a water-cooled heat exchanger that has been changed into the integrated structure with an EGR cooler to have the engine coolant directly from the EGR cooler. The ATF cooler becomes the ATF warmer and cooler, i.e., it plays a role of an ATF warmer if the temperature of ATF is lower than that of coolant, and plays a role of an ATF cooler otherwise. Chassis dynamometer experiments demonstrated the fuel economy improvement of over 2.5% with rapid increase in the ATF temperature.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.52-58
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• 2014

In the present work, design optimization of film-cooling hole array on the pressure side of high pressure turbine nozzle was conducted. There are four rows of fan-shaped film cooling holes on the nozzle pressure side surface and each row has a straight array of holes in the spanwise direction for baseline model. For design optimization, hole distributions in streamwise and spanwise directions for three rows of holes except first row are parameterized as a 2nd-order shape function. Three-dimensional compressible RANS equations are used for flow and thermal analysis around the nozzle surface and optimization technique using Design of Experiment, Kriging surrogate model and Genetic Algorithm is used. The results shows that averaged adiabatic wall temperature at the whole nozzle surface decreases about 2.7% and averaged film cooling effectiveness at the pressure side of nozzle increased about 8.2%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.289-296
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• 2016

The availability of NMP, a solvent used in the manufacturing process of cathode material for lithium ion battery, depends on importation, and the price remains high because of the monopoly of BASF and ISP. For these reasons, most Lithium ion battery manufacturers reuse NMP after recovering it from the exhaust air in the drying process. In Korea, absorption method is mainly used for recovering NMP from the absorption tower using the hydrophilicity of NMP. However, this system has a few disadvantages, such as low purity (80％) of the recovered NMP and 100％ emission due to high water content of the treated gas. In this study, we develop a hybrid NMP recovery system by combining cooling condensation method with concentration method, by which it is possible to obtain an NMP recovery rate of 99.6％, and a high purity (96.1％) of the recovered NMP.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.303-303
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• 2013

표면에 부착된 나노/마이크로 입자는 다양한 분야에서 오염물질로 작용한다. 특히 형상이 미세하고 공정 단계가 복잡한 반도체 및 디스플레이 등의 전자 소자 공정에서 미치는 영향이 크다. 따라서 입자상 오염물질의 제거에 관하여 상용화된 습식 세정 방법이 다양하게 존재하지만 표면 손상, 화학 반응, 부산물, 세정 효율 등 여러 가지 문제점이 있어 새로운 세정 방법이 요구된다. 이에 건식 세정 방법, 그 중에서도 입자의 충돌을 통해 제거하는 방법인 에어로졸 세정, 필렛 세정 등이 개발되었으나 마이크로 크기로 생성되는 입자로 인하여 형상의 손상이 크다. 따라서 본 연구에서는 나노 단위로 기체/고체 혼합물만 생성하여 세정하는 가스 클러스터 세정 방법을 이용하여 이러한 문제점을 해결하고자 하였다. 클러스터 세정 장비를 이용한 표면 처리는 충돌에 의한 제거에 기반한다. 따라서 생성 및 가속되는 클러스터로부터 대상으로 전달되는 운동량의 정도가 세정 특성에 영향을 미치며 이는 생성되는 클러스터의 크기에 종속적이다. 생성 클러스터의 크기 분포는 분사 거리, 유량, 분사 각도, 노즐 냉각 온도 등의 변수에 관한 함수이다. 따라서 본 연구에서는 $CO_2$ 클러스터를 이용한 세정 특성을 정의 및 제어하기 위하여 생성되는 클러스터 특성에 관하여 이론적, 수치 해석적, 실험적 연구를 수행하였다. 먼저, $CO_2$의 물리적 특성 및 이를 이용한 특정 크기 오염 물질을 제거하는데 요구되는 임계 클러스터 크기 계산을 이론적으로 구하였다. 이는 오염물질의 부착력과 클러스터의 운동량 전달에 의한 제거력의 비교를 통해 이루어졌다. 두 번째로 클러스터 크기분포를 수치 해석적으로 예측하기 위하여 각 조건에 대하여 유동해석을 수행하고 이를 통해 구해진 노즐 내 기체의 냉각 속도를 GDE (General Dynamic Equation) 계산에 대입하여 구하였다. 마지막으로 PBMS(Particle Beam Mass Spectrometer)를 이용하여 실험적으로 클러스터 크기분포를 각 조건에 대하여 구할 수 있었다. 또한 크기 분포 경향에 대한 간접적 확인을 위하여 포토레지스트가 코팅된 웨이퍼에 클러스터의 충격으로 생성된 크레이터 크기의 경향을 분석하였다. 이와 같은 방법에 의하여 생성되는 클러스터는 노즐의 유량 증가, 온도 상승에 각각 비례하여 작아지는 것을 확인할 수 있었다.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.299-305
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• 2016

The High Temperature Superconducting power cables (HTS power cables) become increasingly longer to commercialize the HTS power cable system. Accordingly, demands on refrigerators of large cooling capacity per a unit system have been increased. In Korea, it is currently imported from abroad with the high price due to insufficient domestic technologies. In order to commercialize the HTS power cables, it is necessary to develop the refrigerators with large cooling capacity. The Brayton refrigerators are composed of recuperative heat exchangers, compressors and cryogenic turbo expanders. The most directly considering the efficiency of the Brayton refrigerator, it depends on performance of the cryogenic turbo expander. Rotating at high speed in cryogenic temperature, the cryogenic turbo expanders lower temperature by expanding high pressure of a helium or neon gas. In this paper, the reverse Brayton cycle is designed and the cryogenic turbo expander is designed in accordance with the thermodynamic cycle.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.236-236
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• 2013

비냉각 적외선 검출기는 산업용 군사용으로 최근 각광을 받고 있다. 이는 주야간 빛이 없는 곳에서도 사물의 열을 감지할 수 있어 인체감지 및 보안감시, 에너지 절감 등에 응용될 수 있는 핵심부품이다. 비냉각 적외선 검출기로는 재료의 저항의 변화를 감지하는 마이크로볼로미터형이 가장 많이 사용된다. 감지재료로는 비정질 실리콘(a-Si)과 산화바나듐(VOx)이 가장 많이 사용된다. VOx 박막은 일반적으로 RF sputtering 방법으로 증착이 되며, 저항이 낮고, 저항의 온도변화 계수(TCR)가 크며 신호 대 잡음 특성이 우수한 반면 산소(oxygen) phase가 다양하여 갓 증착된 상태의 박막은 재현성이 떨어지는 단점이 있다. 본 연구에서는 기존의 V 타겟을 사용한 VOx 박막을 증착하는 방법을 개선하여 ZnO 나노박막을 중간에 삽입하여 저항 특성을 조절할 뿐만 아니라 열처리에 의해 TCR 값을 향상시키고, VO2 phase 가 주로 나타나는 박막 증착 및 공정 방법을 소개한다. RF sputtering 장비를 이용하여 산소와 아르곤 가스의 혼합비를 4.5로 하였으며, VOx 증착 시 플라즈마 Power는 150 W 로 하여 상온에서 증착하였다. 갓 증착된 VOx 다층박막의 XRD 스펙트럼은 V2O5 피크가 주된 상을 이루고 있었으며, 산소열처리에 의해 VO2 상이 주로 나타남을 알 수 있었다. TCR 값은 갓 증착된 샘플에서 -0.13%/K의 값을 얻었으며, $300^{\circ}C$에서 50분간 열처리 후 -3.37%/K 으로 급격히 향상됨을 알 수 있었다. 저항은 열처리 후 약 100 kohm으로 낮아져 검출소자를 위한 조건에 적합한 특성을 얻을 수 있었다. 또한 산소열처리의 온도 및 시간에 따라 TCR 및 표면 거칠기 특성을 조사하였으며, 최적의 열처리 조건을 얻고자 하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.65-74
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• 2004

The heat transfer coefficient and pressure drop of $CO_2$(R-744) during gas cooling Process of carbon dioxide in a horizontal tube were investigated experimentally and theoretically. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop consist of a receiver. a variable-speed pump. a mass flowmeter, an evaporator. and a gas cooler(test section). The main components of the water loop consist of a variable-speed Pump. an constant temperature bath. and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus The test section consists of smooth, horizontal stainless steel tube of 9.53 mm outer diameter and 7.75 mm inner diameter. The length of test section is 6 m. The refrigerant mass fluxes were 200 ~ 300 kg/($m^2{\cdot}s$) and the inlet pressure of the gas cooler varied from 7.5 MPa to 8.5 MPa. The main results were summarized as follows : The predicted correlation can evaluated the R-744 exit temperature from the gas cooler within ${\pm}10%$ for most of the experimental data, given only the inlet conditions. The predicted gas cooley capacity using log mean temperature difference showed relatively food agreement with gas cooler capacity within ${\pm}5%$. The pressure drop predicted by Blasius estimated the pressure drop on the $CO_2$ side within ${\pm}4.3%$. The predicted heat transfer coefficients using Gnielinski's correlation evaluated the heat transfer coefficients on the $CO_2$ side well within the range of experimental error. The predicted heat transfer coefficients using Gao and Honda's correlation estimated the heat transfer coefficients on the coolant side well within ${\pm}10\;%$. Therefore. The predicted equation's usefulness is demonstrated by analyzing data obtained in experiments.