• 한국항해항만학회지
• /
• 제37권2호
• /
• pp.129-135
• /
• 2013

동결농축폐수처리의 기술은 열역학적 효율이 높고 에너지 소비량이 작아 중소규모로 적합하며, 용수 재활용과 융해열의 냉열 재이용이 가능한 장점을 가지고 있다. 본 연구에서는 폐수 처리효율이 높은 동결농축폐수처리장치의 개발을 위해 수직원관 형태의 제빙관을 대상으로 염화나트륨수용액을 이용한 기초 실험을 통해 냉각면 온도, 기포 분사 방법에 따른 분리 성능을 확인 후 대표적 중금속인 Pb, Cr 수용액을 대상으로 냉각면 온도, 기포 직접 분사, 과냉각을 방지하기 위한 용질을 포함하지 않은 초기 빙층 두께의 영향에 따른 중금속 분리 성능을 실험 통해 확인하였다. 실험결과 두 수용액에서 모두 냉각면의 온도가 낮을수록 동결층의 성장속도가 빨라지고 용질의 분리효율이 저하되었다. 기포를 분사하는 방법 중에는 환모양의 노즐을 통해 동결계면에 직접 분사하는 방법이 원통벽면을 통해 간접 분사하는 것 보다 분리효율이 높게 나타났으며, 초기 빙층의 두께에 따른 실험에서는 1mm 보다는 5mm의 두께에서 분리효율이 더 우수한 것으로 나타났다.

• 한국해양공학회지
• /
• 제35권1호
• /
• pp.50-58
• /
• 2021

The demand for eco-friendly energy is expected to increase due to the recently strengthened environmental regulations. In particular, the flow inside the pipe used in a cargo handling system (CHS) or fuel gas supply system (FGSS) of hydrogen transport ships and hydrogen-powered ships exhibits a very complex pattern of multiphase-thermal flow, including the boiling phenomenon and high accuracy analysis is required concerning safety. In this study, a feasibility study applying the boiling model was conducted to analyze the multiphase-thermal flow in the pipe considering the phase change. Two types of boiling models were employed and compared to implement the subcooled boiling phenomenon in nucleate boiling numerically. One was the "Rohsenow boiling model", which is the most commonly used one among the VOF (Volume-of-Fluid) boiling models under the Eulerian-Eulerian framework. The other was the "wall boiling model", which is suitable for nucleate boiling among the Eulerian multiphase models. Moreover, a comparative study was conducted by combining the nucleate site density and bubble departure diameter model that could influence the accuracy of the wall boiling model. A comparison of the Rohsenow boiling and the wall boiling models showed that the wall boiling model relatively well represented the process of bubble formation and development, even though more computation time was consumed. Among the combination of models used in the wall boiling model, the simulation results were affected significantly by the bubble departure diameter model, which had a very close relationship with the grid size. The present results are expected to provide useful information for identifying the characteristics of various parameters of the boiling model used in CFD simulations of multiphase-thermalflow, including phase change and selecting the appropriate parameters.

• 대한토목학회논문집
• /
• 제4권4호
• /
• pp.79-93
• /
• 1984

수중조류(水中藻類) 제거(除去)하기 위한 공법(工法)의 하나로 가압부상법(加壓浮上法)은 아주 효과적(効果的)이다. 이러한 가압부상법(加壓浮上法)의 효율(効率)에 영향을 미치는 요소(要素)로는 시료수(試料水)에 대(對)한 가압수(加壓水)의 체적비율(體積比率), 가압수(加壓水)의 압력(壓力), 접촉시간(接觸時間), 응집제(凝集劑)의 종류(種類) 및 투여량, 수온(水溫), 반응조내(反應槽內)의 물의 흐름상태, 기포(氣泡)의 크기 및 상승속도(上昇速度), 그리고 기포(氣泡)와 입자(粒子)간의 접착(接着) 등이다. 본(本) 연구(硏究)에 있어서는 모형조내(模型槽內)에서 실제의 기포(氣泡) 상승속도(上昇速度)와 이론적(理論的)인 상승속도(上昇速度)와의 비교, 기포(氣泡)와 입자(粒子)간의 접착현상(接着現象) 규명 기포(氣泡)의 크기 및 상승속도(上昇速度)가 수중조류(水中藻類) 제거공정(除去工程)에 미치는 영향 등을 규명함으로써 가압부상법(加壓浮上法)의 합리적(合理的)인 적용방법(適用方法)을 검토(檢討)하였다. 수중조류(水中藻類) 제거(除去)를 위하여 기포(氣泡)의 발생(發生)과 기포(氣泡)의 크기 변화(變化)과정 및 기포(氣泡)의 부상속도(浮上速度), 기포(氣泡)와 입자(粒子)간의 접착현상(接着現象), 연속식(連續式) 가압부상(加壓浮上) 실험(實驗)의 이론적(理論的) 고찰과 실험적(實驗的) 증명에 의(依)하여 얻은 결과(結果)는 다음과 같다. 기포(氣泡) 상승속도식(上昇速度式)은 스톡스 방정식(方程式)보다 아이브스 식(式)이 더 적합(適合)하다. 기포(氣泡)와 조류(藻類)와의 결합(結合)은 컨벡티브 타입이었으며 부착현상(附着現象)과 충돌현상(衝突現象)보다 흡수현상(吸收現象)에 의(依)한 접착(接着)이 많았다. 기포(氣泡)와 크기는 $100{\mu}m$ 보다 작으며 반응조내(反應槽內)의 유동(流動)이 적을 때가 처리효율(處理効率)이 좋았다. 또한, 본(本) 실험(實驗)에 사용(使用)된 연속식(連續式) 가압부상(加壓浮上) 장치의 최적조건(最適條件)으로는 시료수(試料水)에 대(對)한 가압수(加壓水)의 체적비(體積比)가 15%, 반응조내(反應槽內) 체류시간은 15분(分), 가압수(加壓水) 압력(壓力) $4kg/cm^2$, 가압수(加壓水) 분사기(噴射機)의 시료수(試料水) 유입구(流入口)와의 거리는 30cm 이었으며 온수(水溫)의 변화(變化)에 따른 처리효율(處理効率)의 변동은 거의 없었으며 처리효율(處理効率)은 85~91% 였다.

• Elastomers and Composites
• /
• 제58권4호
• /
• pp.208-215
• /
• 2023

In this study, the properties of polyurethane-polydimethylsiloxane (PU-PDMS) hybrid foams containing different types and contents of physical blowing agents (PBAs) were investigated. Two types of blowing agents, namely physical blowing agents and thermally expandable microspheres (TEM), were applied. The apparent density was measured using precisely cut foam samples, and the pore size was measured using image software. In addition, the microstructure of the foam was confirmed via scanning electron microscopy and transmission electron microscopy. The thermal conductivities related to the microstructures of the different foams were compared. When 0.5 phr of the hydrocarbon-based PBA was added, the apparent density and pore size of the foam were minimal; however, the pore size was larger than that of neat foam. In contrast, the addition of 3 phr of TEM effectively reduced both the apparent density and pore size of the PBAs. The increase in resin viscosity owing to TEM could enhance bubble production stability, leading to the formation of more uniform and smaller pores. These results indicate that TEM is a highly efficient PBA that can be employed to decrease the weight and pore size of PU-PDMS hybrid foams.

• 한국전자파학회논문지
• /
• 제22권9호
• /
• pp.833-839
• /
• 2011

본 논문에서는 다양한 변조 신호에 대한 1.8 GHz 대역 VSWR을 구하는 방법을 제시하였다. 방향성 결합기를 이용하여 입사 전력과 반사 전력을 측정하였으며, 측정 회로 크기와 비용을 최소화하기 위해 SPDT(Single Pole Double Throw) 스위치를 사용하여 한 개의 검파기와 한 개의 AD(Analog to Digital) 변환기로 회로 구현이 가능하게 되었다. MCU(Micro Control Unit)를 이용하여 전압 반사 계수와 VSWR을 계산하였으며, 다양한 변조 신호에 대한 측정오차를 줄이고 MCU의 처리 시간 및 부하를 최소화하기 위해, 간단한 버블정렬 알고리즘을 적용하여 비적용한 경우보다 0.2의 VSWR 오차를 개선할 수 있었다.

• 대한기계학회논문집B
• /
• 제21권6호
• /
• pp.747-757
• /
• 1997

A numerical investigation of the fuel concentration field in a fluidized bed has been carried out for the scale-up of a fluidized bed combustor (FBC). A two-dimensional transient model is developed using the two-phase fluidization, a simple chemical reaction, and lateral solid mixing theories. The uniformity of fuel concentration distributions is controlled by the location and the number of fuel feeders, fluidizing velocities and the bed-heights. While larger bubbles owing to greater fluidizing velocities enhance the fuel-dispersion in the bed, they have adverse effects on fuel combustion and thus result in the increase of fuel concentration, since a greater bubble means a larger bypass which reduces gas-exchange rates between bubble and emulsion phases. Average or maximum values of the bed fuel concentration are utilized as criteria for the scale-up from a pilot/lab-scale to a commercial-size bed.

• 상하수도학회지
• /
• 제32권5호
• /
• pp.381-388
• /
• 2018

Microbubbles oxygen transfer to water was simulated based on experimental results obtained from the bubbles generation operated under varying liquid supply velocity to the multi-step orifices of the generator. It had been known that liquid supply velocity and bubble size are inversely related. In the oxygen transfer, a non-steady state was assumed and the pseudo stagnation caused the slow movement of bubbles from the bottom to the water surface. Two parameters were considered for the simulation: They represent a factor to correct the pseudo stagnation state and a scale which represented the amount of bubbles in supply versus time. The sum of absolute error determined by fitting regression to the experimental results was comparable to that of the American Society of Civil Engineers (ASCE) model, which is based on concentration differential as the driving force. Hence, considering the bubbles formation factors, the simulation process has the potential to be easily used for applications by introducing two parameters in the assumptions. Compared with the ASCE model, the simulation method reproduced the experimental results well by detailed conditions.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.497-501
• /
• 2000

Flow over a sphere is controlled experimentally at $Re=10^5$ using electro-magnetic actuators. The electro-magnetic actuator developed in this study is composed of the permanent magnet electro-magnet membrane and slot. Eight actuators are placed inside the sphere at equally spaced intervals on a latitudinal plane and the position of the control slot is 76 from the stagnation point. Each actuator generates a periodic blowing and suction through the slot at variable frequencies of $10{\sim}140Hz$ and variable amplitudes by controlling electric signals applied to the electro-magnet. Drag on the sphere measured using a load cell is significantly reduced with control at the forcing frequencies larger than the natural shedding frequency $({\approx}14Hz\;at\;Re=10^5)$, whereas drag is slightly increased at the forcing frequency of 10Hz. It is shown from pressure measurement that the static pressure in the rear surface of the sphere is significantly increased with control, indicating that the separation is delayed due to control. Flow visualizations also show that the detaching shear layer is more attracted to the sphere center with control, the separation bubble size is significantly reduced, and motion inside the bubble is very weak, as compared to the case of uncontrolled flow.

• 한국안전학회지
• /
• 제20권1호
• /
• pp.42-48
• /
• 2005

The present study investigates the effect of balcony on external smoke movement of high rise building through the fire tests of the 1/10 reduced model scale using Froude scaling. A hexane pool fire is used to examine the smoke movement for various opening sizes of balcony and temperature distributions are measured by T-type thermocouples. Also, hydrogen bubble technique is applied to visualize the smoke movement near the balcony. Measured temperatures of the closed balcony is 2.5 times higher than those of the open balcony because the external smoke in case of the closed balcony rise along the vertical wall. The maximum vertical temperature of partially closed balcony is similar with fully closed balcony and mean temperature inside of balcony increases as opening size of balcony decreases. The experimental results show that the balcony space plays an important roles in preventing fire propagation and cooling of smoke layer. In order to ensure the fire safety in high rise building design, a series of systematic researches are required to examine the various type of balconies.

• 대한조선학회논문집
• /
• 제43권2호
• /
• pp.177-185
• /
• 2006

Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.