The Climate chamber system is an essential facility for aerodynamic performance development of commercial vehicles to investigate air flow field characteristics in different climatic conditions. In particular, the analysis of airflow fields within the chamber system is an essential consideration for optimal design. In this study, the pressure characteristics and velocity uniformity in the test section area were predicted with blower impeller rotational speed using CFD. The velocity uniformity is affected by the distance from the blower nozzle outlet, reaching up to 72.7% at 695 RPM. The pressure differential between 300 RPM and 740 RPM shows an approximate difference of 2651 Pa, with a high-pressure distribution observed along the right side wall of the blower. These results are expected to be used as design data applicable for improving the performance of environmental chamber systems.

Recently injection mold processing is necessary for the development of efficient solar concentrator system with a Fresnel lenses. Heat transfer mechanism in the Fresnel lens manufacturing process have a significant influence on precision machining and optical performance of solar power generation. In this study, we analyzed the thermal characteristics of temperature and heat flux distributions near the lens for transient molding process using CFD method. Initially for one second fast temperature variation on the upper surface of the lens leads to high heat flux distribution. It is gradually cooled to around 128℃ over a period of 60 seconds which is largely affected by the mold structure and the characteristics of the cooling lines. There is also high heat flux occurred on the lens upper side and lower surfaces with rapid temperature change. These results can be applied as fundamental design data for the manufacturing process in the development of Fresnel lenses.

본 논문은 슬로싱 상태에 놓인 포화 상태 액체수소탱크에서 열 유속 및 BOG(Boil-off gas)의 경향을 다루고 있다. 특히, 액체-기체 간의 침투 및 혼합에 의한 열 교환에 관심을 두었다. 먼저, VOF(Volume of fluid)와 Eulerian 기반의 다상 유동모델로 모형 슬로싱 실험 을 모사하여 압력을 예측하고 계측된 값과 비교하였다. 자유 수면 및 충격 압력 실험 결과와 해석 결과를 비교하였으며, 유체의 속도 예측에서 정확할 수 있음을 간접적으로 증명하였다. 그리고 2차원의 Type-C 원통형 수소탱크를 대상으로 다상열유동해석을 수행하 였다. 이때 포화상태에 놓인 액체 및 기체수소를 가정하고, 해석을 통해 각 상간의 혼합에 의한 열 교환의 수준을 확인하고자 하였다. 단, 상간의 열 교환만을 관심으로 두고 있었으므로 질량전달 및 기화모델은 해석에서 제외하였다. 최종적으로 상의 혼합으로 인해 액 체수소로 유입되는 열 유속의 기여도에 대하여 정리하였다. 또한 액체수소로 유입되는 열 유속과 집중 질량 기반의 간이식을 통해 BOG 발생량 및 경향을 예측하고 분석하였다.

In this study, we propose a flow velocity evaluation scheme based on pressure measurement in pressurized pipeline systems. Conservation of mass and momentum equations can be decomposed into mean and perturbation of pressure head and flowrate, which provide the pressure head and flowrate relationship between upstream and donwstream point in pressurized pipeline system. The inverse impedance formulations were derived to address measured pressure at downstream to evaluation of flow velocity or pressure at any point of system. The convolution of response function to pressure head in downstream valve provides the flow velocity response in any point of the simple pipeline system. Simulation comparison between traditional method of characteristics and the proposed method provide good agreements between two distinct approaches.

This paper reports critical heat flux(CHF) performance on wire heater according to material, thickness, length, cross sectional shape. Water was employed as the working fluid, which was saturated at 1 atm. By comparison of CHF values with difference conditions of wire length, contact resistance inherent in the experimental apparatus could be analyzed, which had made the bias error in many research groups. So, exact value of CHF could be measured, which was consistent with the literatures. The CHF value showed decrease tendency, as the cross sectional area increased and reach to the capillary length of the working fluid. Meanwhile, the effect of thermal properties on CHF was not observed in the experimental cases. This data would be used as a reference data in research field of CHF using wire heater, i.e. reactivity initiative accident(RIA).

정삼투 공정(forward osmosis, FO)은 역삼투 공정(reverse osmosis, RO)에 비해 저압으로 운영되므로 오염 제어, 유지 보수, 막 세정 및 잠재적 에너지 저감 측면에서 큰 이점이 있어 다양한 분야에 적용할 수 있는 기술이다. 특히, 정삼투 공정의 막오염층이 비교적 느슨하고 분산된 특성을 가지므로 역삼투 공정과 달리 물리세정만으로도 충분한 막오염 제어가 가능하다. 하지만 기존 연구들의 경우 정삼투 물리세정에 적합한 세정 유속을 적용하지 않아 최적화 운전을 하지 못했다는 한계가 있다. 따라서 이 연구는 경제적인 에너지량으로 높은 효율의 세정을 보일 수 있는 적절한 유속의 정당성 평가를 목적으로 한다. 정삼투 공정 막오염 실험을 8.54 cm/s 순환 유속으로 유지하고 세 가지 세정유속으로 회복률과 SEC(specific energy consumption) 비교 평가하였다. 이 실험의 결과로 2배속 세정이 3배속 세정의 수투과도 회복률 만큼의 높은 효율을 보 이는 동시에, 2배속 세정이 높은 세정효율 및 경제적인 SEC를 보이는 적절한 유속이라는 것을 확인하였다.

본 연구는 난방온실의 온도분포 균일화를 위한 기초자료 제공을 목적으로 온수난방 방식의 토마토 재배 온실 에서 난방실험을 통하여 난방배관의 표면온도와 실내기온 사이의 상관관계를 분석하고, 난방배관의 열전달특성 분석과 난방배관 배치의 개선을 통하여 난방배관 표면온도의 편차를 줄이고 균일도를 향상시키기 위한 방안을 도출하였다. 서로 다른 두 온실의 온도분포를 분석하여 최대편차와 균일도를 검토한 결과, 온수의 유량이 많고 난방배관의 길이가 짧게 배치된 온실의 온도편차가 작고, 균일도는 높은 것으로 나타났다. 또한 순환팬을 가동한 경우에 온도편차는 작아지고 균일도가 개선되는 것을 확 인할 수 있었다. 난방배관의 표면온도와 실내기온 사이의 상관관계를 분석한 결과, 두 온실 모두에서 유의적인 (p<0.01) 정적 상관관계가 있는 것으로 나타났다. 온수난방 온실에서 실내기온의 분포는 난방배관 표면온도의 분포에 영향을 받는다는 것을 확인할 수 있었고, 온도편차 가 최소화 되도록 난방배관을 배치함으로써 실내기온 분포의 균일도를 개선할 수 있는 것으로 판단되었다. 난방 배관의 열전달 특성을 분석한 결과 배관의 길이가 길어 지면 온도편차는 커지고, 관내의 유속이 빨라지면 온도 편차는 작아지는 것으로 나타났다. 따라서 지선배관의 길이가 짧아지도록 난방배관을 배치하고, 관내의 유속을 제어함으로써 온실의 온도분포와 환경의 균일성을 개선 할 수 있을 것으로 판단되었다. 국내 온실에서 가장 많 이 사용하고 있는 튜브레일(40A) 방식의 온수난방시스 템에서 하나의 지선배관에서의 온도편차를 3oC 이내로 조절하기 위해서는 관내의 유속이 0.2, 0.4, 0.6, 0.8, 1.0m·s-1일 때 난방배관의 길이는 각각 40, 80, 120, 160, 200m 이내로 제한해야 하는 것으로 분석되었다.

본 연구에서는 종결정 크기, 종결정 코팅양, 수열 용액 숙성시간을 조절함으로써 분리층 두께가 제어된 모데나이트 제올라이트 분리막을 제조하고, 분리층 두께가 투과증발 물 투과유속에 미치는 영향을 90 wt.% 에탄올 수용액에서 고찰 하였다. 유성 밀을 이용해 종결정을 분쇄시켜 20~30 nm 크기의 종결정을 제조하였고, 진공여과코팅 중에 종결정 용액의 농도와 통과된 양을 바꿔주면서 코팅양을 조절하였다. 제조된 분리막은 분리층 두께가 얇을수록 더 높은 물 투과유속을 나타내었으며, 약 4 μm 두께를 갖는 분리막의 경우, 760의 높은 물/에탄올 선택도와 1.0 kg/m2h의 높은 물 투과유속을 나타내었다. 이는 나노크기 종결정을 사용하여 4 μm 두께로 분리층을 얇게 만들었기 때문으로 판단된다. 따라서 본 연구로부터 종결정의 크기와 진공여과 코팅양, 수열 용액 숙성시간을 조절하는 것은 분리 층의 두께를 효과적으로 조절할 수 있는 방법임을 알았 다. 또한, 모데나이트 제올라이트 분리층의 두께를 얇게 하는 것이 분리막의 물 투과유속을 증진시키는 중요한 방법임을 확인 하였다.

하천의 생태 환경적인 측면을 고려하여 여러 가지 친환경적인 호안공법이 적용되어 시공되는 사례가 증가하고 있다. 친환경적인 호안공법으로는 식생공이 대표적이나 중량물을 시공하는 호안공법과 달리 식생매트를 고정핀으로 고정하는 방식의 식생매트와 같은 호안공법의 경우 중량물을 설계하는 여타의 공법과 달리 적합한 설계방법이 없어 경험적인 방법을 통해서 제 품의 개발과 시공이 이루어지고 있는 실정이다. 따라서 본 연구에서는 식생매트공법에 사용되는 고정핀과 고정핀이 정착된 지반을 모델링하고 유한요소법을 활용하여 호안식생매트의 안전성을 평가하였다. 해석결과 핀의 상단 부분에서 인발에 저항하기 위해 인장응력이 유발되고 있으며, 헤드 부분은 거의 응력이 작용하지 않는 것으로 나타났고, 핀의 Von Mises 응력값이 인장강 도에 비해 낮게 나타나 파괴모드가 재료 자체의 항복 또는 파쇄에 의한 파괴가 아닌 핀과 지반사이의 뽑힘이 전체 거동을 지배 한다고 평가하였다. 본 연구는 유한요소법을 통해서 식생매트공법의 안전성을 변위와 발생응력에 대하여 평가하였다.

Recently, copper alloy netting has been proposed as a material for aquaculture facilities that can be set in harsh offshore environments. To design a cage made of copper alloy netting, it is necessary to calculate the flow of water through the netting and force of external sources on the netting. Therefore, this study measured and analyzed the current velocity reduction after passing through the netting and the hydrodynamic forces acting on the netting using copper alloy netting with nine solidity ratios. As a result of the reduction rate of the flow velocity through the netting, the flow reduction rate was increased as the solidity ratio of netting was increased. The flow reduction rate was also increased as the attack angle on the netting was decreased. In analyzing the resistance on the netting, we also discovered that resistance was increased with increase in the flow velocity and solidity ratio. An analysis of the hydrodynamic coefficient acting on the netting is shown that the drag coefficient tends to increase as the attack angle increases. We also analyzed the hydrodynamic coefficient according to the variation of the Reynolds number. When the drag coefficients acting on the netting were analyzed with the different Reynolds numbers, the Reynolds number increased from over 0.3 m/s to a relative constant. Finally, the copper alloy nettings had a smaller velocity reduction rate when comparing the flow velocity reduction rate between copper alloy nettings and nylon nettings.

In this study, the effects of operating conditions on the formation of reversible and irreversible fouling were investigated in the filtration using ceramic membrane for water treatment process. The effect of coagulation pretreatment on fouling formation was also evaluated by comparing the performance of membrane filtration both with and without addition of coagulant. A resistance-in-series-model was applied for the analysis of membrane fouling. Total resistance (RT) and internal fouling resistance (Rf) increased in the membrane filtration process without coagulation as membrane flux and feed water concentrations increased. Internal fouling resistance, which was not recovered by physical cleaning, was more than 70% of the total resistance at the range of the membrane flux more than 5 m3/m2･day. In the combined process with coagulation, the cake layer resistance (Rc) increased to about 30-80% of total resistance. As the cake layer formed by coagulation floc was easily removed by physical cleaning, the recovery rate by physical cleaning was 54~90%. It was confirmed from the results that the combined process was more efficient to recover the filtration performance by physical cleaning due to higher formation ratio of reversible fouling, resulted in the mitigation of the frequency of chemical cleaning.

When the heat flux on the heating surface following changing heat condition in the boiling heat transfer system exceeds critical heat flux, the critical heat flux phenomenon is going over to immediately the film boiling area and then it is occurred the physical destruction phenomenon of various heat transfer systems. In order to maximize the safe operation and performance of the heat transfer system, it is essential to improve the CHF(Critical Heat Flux) of the system. Therefore, we have analysis the effect of improving CHF and characteristics of heat transfer following the nanoparticle coating thickness. As the results, copper nanocoating time are increased to CHF, and in case of nano-coatings are increased spray-deposited coating times more than in the fure water; copper nanopowder is increased up to 6.40%. The boiling heat transfer coefficients of the pure water are increased up to 5.79% respectively. Also, the contact angle is decreased and surface roughness is increased when nano-coating time is increasingly going up.

In this study, a direct contact membrane module was manufactured to be used in a pilot scale membrane distillation process to treat 3 m3/day of the digestate produced from anaerobic digestion of livestock manure. In order to investigate the performance of the membrane module, permeate flux was measured with and without spacer inside the module under various condition of temperature difference and cross flow velocity (CFV) through the membrane surfaces. Flux recovery rate after chemical cleaning was also investigated by applying three different cleaning methods. Additionally, thermal energy consumption was theoretically simulated based on actual pilot plant operation conditions. As results, we observed flux of the module with spacer was almost similar to the theoretically predicted value because the installation of spacer reduced the channeling effect inside the module. Under the same operating condition, the permeate flux also increased with increasing temperature difference and CFV. As a result of chemical in-line cleaning using NaOCl and citric acid for the fouled membranes, the recovery rate was 83.7% compared to the initial flux when NaOCl was used alone, and 87% recovery rate was observed when only citric acid was used. However, in the case of using only citric acid, the permeate flux was decreased at a rapid rate. It seemed that a cleaning by NaOCl was more effective to recover the flux of membrane contaminated by the organic matter as compared to a cleaning by citric acid. The total heat energy consumption increased with increasing CFV and temperature difference across the membrane. Thus, further studies should be intensively conducted to obtain a high permeate flux while keeping the energy consumption to a minimum for a practical application of membrane distillation process to treat wastewater.

In this study, we designed the 3-dimensional tire mold according to the A automobile company’s tire model, and analysed the distribution of temperature of mold using the numerical method when the heat flux and heat transfer time at the surface of tire mold were changed. A analysis region of mold was the 1/16 of entire mold, and the grid number was about more than 880 thousand. In order to analyze the temperature change of mold, the thinnest part of the mold was chosen as the research object, and then the temperature of 6 points on the vertical downward direction of the thinnest part was analyzed with the time change. While the numerical condition was that heat flux was 321,200 W/m2, 440,000 W/m2 and 880,000 W/m2, and measuring time was 0.1 second, 0.2 second, 0.5 second and 1 second, respectively. As a result, the temperature difference between the surface temperature and the lowest temperature of mold was 7.3℃ when the heat transfer time was 0.1 second. Also, the minimum temperature difference was almost 0.11℃ when the heat transfer increased to 1 second. It can be explained that the main material of tire mold was aluminum and its thermal conductivity was high (k=140 W/m·K). In addition, when the heat transfer time was more than 1 second, the heat flux of mold surface will be transmitted at the inside of the thinnest part, and the heat transfer will be a marked difference according to the shape of the thinnest part.