• 펄프종이기술
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• 제43권3호
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• pp.113-120
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• 2011

Precipitated calcium carbonate(PCC), particularly calcite crystal, is extensively used as a pigment, filler or extender in various industries such as paper, paint, textile, detergents, adhesives, rubber and plastics, food, cosmetics, and biomaterials. PCC is conventionally produced through the gas-liquid carbonation process, which consists on bubbling gaseous $CO_2$ through a concentrated calcium hydroxide slurry. This study is aimed to find some factors for controlling the morphology of engineered PCC in lab-scaled mixing batch. The experimental designs were based on temperature variables, $Ca(OH)_2$ concentration, $CO_2$ flow rate, and electrical conductivity. The model of engineered PCC morphology was finally controlled by adjustment of electrical conductivity(6.0~7.0 mS/cm) and $Ca(OH)_2$ concentration(10 g/L). Orthorhombic calcite crystals were mostly created at high concentration and electrical conductivity conditions because the increased ratio of $Ca^{2+}$ and $CO{_3}^{2-}$ ions affects the growth rate of orthorhombic faces. Excess calcium spices were contributed to the growth of faces in calcium carbonate crystal, and the non-stoichiometric reaction was occurred between $Ca^{2+}$ and $CO{_3}^{2-}$ ions during carbonation process.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.611-623
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• 2024

The ISP-47 TOSQAN experiment was analyzed with containmentFOAM which is an open-source CFD code based on OpenFOAM. The containment phenomena taking place during the experiment are gas mixing, stratification and wall condensation in a mixture composed of steam and non-condensable gas. The k-ω SST turbulence model was adopted with buoyancy turbulence models. The wall condensation model used is based on the diffusion layer approach. We have simulated the full TOSQAN experiment which had a duration 20000 s. Sensitivity studies were conducted for the buoyancy turbulence models with SGDH and GGDH and there were not significant differences. All the main features of the experiments namely pressure history, temperature, velocity and gas species evolution were well predicted by containemntFOAM. The simulation results confirmed the formation of two large flow stream circulations and a mixing zone resulting by the combined effects of the condensation flow and natural convection flow. It was found that the natural convection in lower region of the vessel devotes to maintain two large circulations and to be varied the height of the mixing zone as result of sensitivity analysis of non-condensing wall temperature. The computational results obtained with the 2D mesh grid approach were comparable to the experimental results.

• 한국화재소방학회논문지
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• 제32권1호
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• pp.7-15
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• 2018

구획실 내 프로판 가스화재에 대해 Fire Dynamics Simulator (FDS)를 이용한 수치계산을 수행하고 실험과의 비교를 통해 적용된 연소모델 예측성능을 평가하였다. 검토된 연소모델은 FDS v5.5.3의 혼합분율 연소모델과 FDS v6.6.3의 Eddy Dissipation Concept (EDC) 모델이며, EDC 모델에서 화학반응기구는 1-step Mixing Controlled, 2-step Mixing Controlled, 3-step Mixing Controlled 및 Mixing Controlled 반응과 유한화학반응이 혼합된 3-step Mixed 반응을 적용하였다. 구획실 내부의 온도에 대해서는 각 연소모델들 간의 예측성능 차이는 그다지 크지 않음을 확인하였다. 연소모델 차이에 의한 $O_2$와 $CO_2$ 농도에 대한 예측성능 차이보다는 CO에 대한 예측결과 차이가 크게 나타났다. CO 농도에 대해서는 EDC 3-step Mixing Controlled 모델이 가장 높게 예측하며 혼합분율 연소모델은 실험보다는 낮게 예측하였다. EDC 3-step Mixed 모델이 가장 예측성능이 좋았지만 EDC 2-step Mixing Controlled 모델도 충분히 합리적인 수준으로 예측하고 있음을 확인하였다. EDC 1-step Mixing Controlled 모델에 기존에 제안된 CO 수율을 적용할 경우 CO 농도에 대해서 너무 과소 예측하며 CO 예측 정확도를 높이기 위해 수율을 높이면 $CO_2$ 농도에 대한 합리적인 예측이 어려워지는 문제점이 있었다.

• 한국가스학회지
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• 제26권2호
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• pp.49-55
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• 2022

강화되는 환경 규제에 따라 석탄 화력발전소에서는 암모니아를 환원제로 사용하는 선택적 촉매 환원법을 이용하여 질소산화물의 발생량을 감소시키고 있다. 본 연구에서는 전산유동 해석을 수행하여 암모니아 혼합 관에서 희석 공기와 암모니아를 효과적으로 혼합하기 위한 혼합 장치를 도출하는 것을 목적으로 수행하였다. 혼합 장치가 없는 기존 혼합 관 형상인 Case 1-1 형상을 기준으로 혼합 관내의 후류 단면과 16개 출구에서 암모니아 농도의 %RMS를 비교하여 혼합 효과를 비교하였다. 혼합 장치는 암모니아 공급 관 후류에 사각 판과 혼합 관 벽면에 원호 모양의 판의 위치를 변경하여 수행하였다. 기존 형상의 경우(Case 1-1)에 16개 출구에서 암모니아 농도의 %RMS는 29.50%로 나타났다. 혼합 장치 형상이 암모니아 공급 관 후류에 사각 판이 있는 것과 인접한 곳에 원호 판을 설치한 Case 3-2 형상의 16개 출구에서 암모니아 농도의 %RMS는 2.08%로 나타났으며 암모니아 혼합에 가장 효과적인 혼합 형상임을 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.42.2-42.2
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• 2005

• 한국자동차공학회논문집
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• 제16권6호
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• pp.192-199
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• 2008

The key issues for the reduction technologies of the exhaust gas from diesel engine being developed are to reduce particulate matters and NOx. The SCR system is known to be one of the most efficient and stable technologies to remove NOx through the mixing of NOx and urea solution. In the present research, the effects of mixer configurations of SCR system have been investigated to enhance the SCR performance. First, a Schlieren technique is employed to visualize the mixing characteristics of urea solution and exhaust gas. The results show that a mixer is essential to obtain proper fluid mixing. In addition, numerical studies have been made to understand the mixing characteristics through the comparison of the mal-distribution index of concentration at the several locations of the diffuser. In particular, the effects of number of blade and mixer angles on mixing characteristics were studied. The results show that the blade angle has a larger effect on the mixing characteristics than the number of blades.

• 한국가스학회지
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• 제21권4호
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• pp.1-5
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• 2017

밀폐된 거주공간에서 주성분이 메탄으로 이루어진 천연가스 누출은 가연성 분위기를 형성여 폭발사고로 이어진다. 밀폐공간에서 폭발을 일으키기 위한 최소 매탄 누출양은 혼합정도에 크게 의존한다. 본 논문에서는 가우스분포모델과 폭발실험에 근거하여 폭발 사고가 발생할 수 있는 최소한의 메탄 누출량을 예측하기 위한 방법을 제시하고자 한다. 밀폐공간에서 높이에 따라 가연성가스의 농도분포는 가우스분포를 가지는 것을 가정하여 연소범위에 있는 가스의 최대량을 예측하고, 일정한 부피에서 예측된 가스가 연소되어 단열 또는 등온 혼합과정을 통하여 최종 폭발압력을 예측할 수 있다. 폭발사고에 의한 건물의 피해 정도에 대응하는 최소가스 누출양을 예측할 수 있다. 연구결과 건물 내 밀폐공간에서 아주 적은 양의 메탄가스가 누출되어도 심각한 폭발사고를 일으킬 수 있다. 이는 안전장치 개발에 있어서 적절한 조치를 취하기 전에 최소허용 가스 누출량을 설정하는 것에 유용하게 사용될 수 있을 뿐 만 아니라 폭발사고 조사에도 활용 될 수 있다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.287-289
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• 2012

The research and development history of the gas turbine combustor in Korea is introduced briefly. It is very important to understand the fuel spray, mixing phenomena in achieving combustion performance. In this paper, two kinds of fuel injection system such as duplex fuel injector and rotary spray system are introduced in developing gas turbine combustor in Korea. The extensive experimental research of fuel spray, ignition, performance and endurance rig test makes gas turbine combustor successfully in Korea.

• 한국연소학회지
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• 제17권4호
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• pp.60-65
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• 2012

The MILD combustion and pollutant emission characteristics were investigated computationally. The temperature of supplying air-stream and mixing rate (${\Omega}$) of exhaust gas in the air-stream were adjusted to investigate the effects of those parameters on the MILD combustion in jet flow field. The emission indices for NO (EINO) and CO (EICO) were introduced to quantify the amount of those species emitted from the combustion. The high-temperature region disappeared gradually as the mixing rate increased for fixed air-stream temperature. The EINO increased as the air-stream temperature became higher for fixed mixing rate, and the EINO decreased dramatically with increasing the mixing rate for each air-stream temperature condition. The EICO also decreased with increasing the mixing rate and it was nearly independent of air-stream temperature except for near ${\Omega}$ = 0.7. It was found that the CO supplied in the air-stream can be destroyed in the MILD combustion over the certain mixing rate.

• The Korean Journal of Ceramics
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• 제4권3호
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• pp.235-239
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• 1998

Ultrafine $SnO_2$ powder was prepared by the diffusion mixing gas-phase reaction of $SnCl_4$(g) and water vapor. The effects of reaction variables, such as the chloride partial pressure, the reaction temperature, and the residence time is the reactor, on the powder size were examined systematically. Calculated concentration and distribution of chemical species, using the Burke-Schumann diffusion mixing model, were compared with the experimetal results. The effects of the reaction variables on the powder size were also discussed qualitatively.