• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.981-988
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• 2001

Characteristics of evaporation heat transfer in 6.2 and 5.1mm OD micro-fin tubes were investigated in the present study. The data were taken at evaporation temperatures of -5$^{\circ}C$ and 5$^{\circ}C$ and heat fluxes 5kW/$m^2$ to 10kW/$m^2$. Mass flux was consequently maintained at 210, 300 and 410kg/$m^2$s for the 6.2mm OD tube and 465, 500 and 600kg/$m^2$s for the 5.1mm OD tube. The effects of heat flux, mass flux, and outer diameter on the heat transfer coefficient are explored in the present study. The data showed that the evaporation heat transfer coefficient for the 6.2mm OD tube was averagly higher by 16% than that for a 7.0mm OD tube, while the 5.1mm OD tube had approximately 30% higher value than the 6.2mm OD tube.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.160-160
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• 2011

I-III-VI족 화합물 반도체인 $CuInS_2$(CIS) 박막은 Cu(In,Ga)$Se_2$에 비해서 독성원소를 사용하지 않으므로 환경 친화적이고 Ga, Se를 사용하지 않아 조성의 조절이 쉬우며 태양전지의 이상적인 밴드갭인 1.5 eV에 근접한 1.53 eV의 직접천이형 에너지 밴드갭을 가지고 있어 태양전지의 광흡수층으로써 유망한 재료이다. CIS 박막 증착에는 다양한 방법이 있으며 본 연구에서는 chamber를 진공으로 만들고 CIS를 구성하는 용액으로부터 미립자화 된 입자를 노즐을 통하여 팽창시켜 에어로졸을 생성하고 입자들의 운동에너지를 증착에 직접 이용 할 수 있는 Aerosol Jet Deposition (AJD)라는 방법을 이용하려고 한다. 이 방법은 높은 증착속도로 우수한 박막을 성장시킬 수 있는 저비용 및 단순공정으로 CIS를 증착 할 수 있는 새로운 방법이다. 물을 용매로 하여 수용액 상태의 $CuCl_2{\cdot}2H_2O$, $InCl_3$, $(NH_2)_2CS$를 혼합하여 CIS 용액을 제조하고 carrier gas를 주입하여 CIS 용액을 노즐로 이동시켜 팽창시킨다. 용액이 팽창되면서 온도가 감소하여 응축이 일어나며 이 응축된 용액이 가열된 기판 위에 충돌하여 용매가 증발하면서 결정화된 CIS가 증착이 된다. CIS의 특성은 용액의 전구체 비율, 기판 온도, 팽창 전 압력, chamber 압력 등의 영향을 받는데 본 연구에서는 기판 온도를 증착변수로 선택하여 CIS 박막을 증착하고 박막의 특성을 고찰하고자 한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.10
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• pp.930-938
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• 2001

In this study, evaporation pressure drop experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-22. An experimental refrigerant loop has been established to measure the evaporation pressure drop of R-22 in a vertical P&SHE. The flow channels were formed by adding three plates having a corrugated channel of a chevron angle of $45^{\circ}$. The R-22 flows down in one channel exchanging heat with the hot water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality were explored in detail. During the experiment, the quality change between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.15. The present data showed that two types of P&SHE have similar trends. The pressure drop increases with the vapor quality for both types of P&SHE. At a higher mass flux, the pressure drop is higher for the entire range of the vapor quality. Also, the increase in the average heat flux increases the pressure drop. Finally, at a higher system pressure, the pressure drop is found to be slightly lower.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2163-2165
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• 2001

화력 발전소 드럼수위의 제어는 보일러 시스템의 효율적인 운용을 위해 중요한 위치를 차지하고 있다. 드럼수위의 제어 목적은 드럼수위를 외란에 관계없이 항상 설정치로 유지하는 것이다. 정상 운전중에는 드럼의 중앙이하 부분에는 물이 차 있고, 상부에는 증기가 차 있으나 만일 수위가 너무 높아지면 carry over 현상이 발생하며 반대로 너무 낮으면 드럼 하부의 과열 및 튜브의 손상을 초래하여 대사고를 유발하게 되므로 드럼수위는 항상 정상으로 유지해야 한다. 드럼수위 제어루프는 처음에는 드림수위만을 제어입력으로 취하는 PI 제어기에 의해 이루어지다가, 주증기량이 일정량 이상 유지되면 드럼수위가 일정한 설정치를 유지하도록 급수량, 드럼수위, 주증기량에 의한 PI-PI 캐스케이드 형태의 제어로 절환되어 제어가 이루어진다. 또한 드럼 수위는 차압검출기에 의해서 측정되어지는데, 드럼의 압력에 따라 물과 증기의 밀도가 변하기 때문에 차압검출기에 의한 드럼수위 지시치는 드럼압력에 의한 보상도 요구되어진다. 본 논문에서는 중용량 화력발전소를 대상으로 드럼수위 보상과 드럼수위 제어기를 구현하고, 적용하여 실제 발전출력 증발시의 드럼수위 제어결과를 보임으로서 구현한 드럼수위 제어기의 효용성을 보인다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.3
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• pp.587-592
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• 2008

In order to investigate the performance of an internal heat exchanger for $CO_2$ refrigerant system, the experiment was performed. Four kinds of internal heat exchangers(IHX) were used. The effects on the IHX length, the number of tube, the operating condition and the type of IHX were investigated. With increasing of the IHX length, the capacity and efficiency increased. The pressure drop of the low-side was larger compared with that of the high-side. As the temperature of the gas cooler increased, the capacity and efficiency increased linearly. The operation condition of evaporator was suggested as two phase region rather than superheat region. The capacity and efficiency of the micro-channel was larger about 90% and 75% than those of the tube. But the pressure drop of the micro-channel was more larger, compared with that of the tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.658-668
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• 1999

The objective of the present study is to investigate the effect of experimental parameters on the hydrodynamic characteristics in a horizontal tee-type evaporator using R-22. The experimental apparatus consisted of an unheated tee-type test section, a liquid-vapor separator, a preheated, mass flow meters, a plate heat exchanger, pump, and other measurement devices. The experimental parameters were mass flux(500 and 600kg/$m^2$s), inlet quality(0.1~0.3) and separation ratio(0.3~0.7). Absolute pressure at the inlet of the test section was 0.652 MPa. The branch-to-inlet inner diameter ratio was 0.61. Pressure gradient at the branch section was larger than that at the run section at the same separation ratio. Pressure drop per unit length increased at the run section and decreased at the branch section as the separation ratio increased. Pressure drop predicted by the separated flow model agreed with experimental data within -35 to +16%. Generally, predicted values showed similar trend with the data. Mass flow ratio of vapor refrigerant was affected by the inlet quality more than the mass flux.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.213-213
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• 2022

본 논문은 슬로싱(Sloshing) 거동에 놓인 극저온 액체수소 화물창의 BOG 예측을 위한 CFD 해석 절차를 다루고 있다. 특히, 적재율(Filling Ratio)에 따라 달라지는 열 유입과 그에 따른 액체수소의 기화 경향을 파악하기 위한 목적으로 수행되었다. 액체수소와 기체수소의 혼재에 의한 다상 열유동(Multiphase-Thermal flow) 특성을 반영하고 유동에 따른 강제 대류 현상을 열유속에 반영하기 위한 CFD 해석을 수행하였다. 다상 유동 모델의 정확성을 검증하기 위하여 슬로싱 실험의 압력 계측 값과 해석의 압력 값 및 자유수면(Free surface) 형상을 비교하였다. 소형 C-Type 독립형 액화수소 탱크를 대상으로 슬로싱 유동과 BOG 발생을 수치적으로 예측하였다. 해석 과정에서 VOF(Volume of fraction) 모델과 Eulerian 모델을 모두 적용하여, 액체수소에 유입되는 열 유속(Heat flux)의 예측 정확성을 비교하였다. 슬로싱 유무에 따라 액체수소에 유입되는 열 유속을 비교하여 슬로싱 유동의 포함 여부에 따른 BOG 발생량의 변화를 제시하였으며, 최종적으로 액체수소의 충전율(Filling ratio) 별로 BOG 발생량의 경향성을 제시하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.12
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• pp.4721-4726
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• 2010

The performance characteristics of water-chilling heat pump using CO2 for the control of inverter frequency was investigated experimentally. An experimental apparatus is consisted of a compressor, a gas cooler, an expansion valve, an evaporator and a liquid receiver. All heat exchangers used in the test rig are counter flow type heat exchangers with concentric dual tubes, which are made of copper. The gas cooler and the evaporator consist of 6 and 4 straight sections respectively arranged in parallel, each has 2.4m length. The experimental results summarize as the following: for constant inlet temperature of evaporator and gas cooler, as mass flow rate, compression ratio and discharge pressure increases with the inverter frequency. And heating capacity and compressor work increases, but coefficient of performance(COP) decreases with the inverter frequency of compressor. As inlet temperature of secondary fluid in the evaporator increases from $15^{\circ}C$ to $25^{\circ}C$, compression ratio and compressor work decreases, but mass flow rate, heating capacity and COP increases with the inverter frequency of compressor. The above tendency is similar with performance variation with respect to the variation of inverter frequency in the conventional vapor compression refrigeration cycle.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.232-237
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• 2011

Recently, continuous research on cryogenic valves is being carried out with the rapid development of the cryogenic valve-related industry, and especially, high performance of cryogenic valves is being promoted due to the breakthrough development and demand of users, etc., of the mechanical, shipbuilding, semiconductor and display industry and the aerospace industry field, but it is the reality that technical development and research on cryogenic application equipment on vacuum insulation are insufficient. The present research focused on interception of heat exchange with the outside by keeping low pressure after installing a jacket pipe outside a stem and also considered heat transfer properties on changes in pressure of a vacuum part and radius of a jacket which can reduce heat exchange for effective heat transmission control by studying it in a three-dimensional numerical analysis method.

• Resources Recycling
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• v.3 no.1
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• pp.32-37
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• 1994

Mercury in spent button type batteries can be separated and recovered with vacuum distillation method. It was found that mercury in the battery began to distill at $150^{\circ}C$ and organic substanced like a packing material was decomposed at$ 300^{\circ}C$. More than 99.9% of mercury contained in the battery was distiled and separated at about $250^{\circ}C$ and 20 torr with 8 hours' reaction time. The dissolution tests of the residue after distillation showed that mercury concentration in the solution were lower than 5 ppb and this values satisfied the environ-mental condition. Also as the furnace heating rate was above $15^{\circ}C$/min, it was found that the spent battery was destroyed because of increased pressure in the battery inside.