• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.901-906
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• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.75-79
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• 1999

순환유동층은 주탑에서 비말 동반된 입자를 cyclone과 같은 입자 포집장치에서 회수하여 다시 주탑으로 재 주입함으로써 입자의 순환이 일어나는 외부 순환계와 종래의 유동층내에 원형관(Draft tube)이나 평판을 설치하여 두개의 층으로 분리한 후 가스 분산판 위의 간격을 통해 입자들을 두 구역 사이로 강제 순환시키는 내부순환계로 분류할 수 있다. 드래프트 관을 갖는 내부순환유동층 반응기는 기체와 고체의 적절한 접촉을 통해 반응이 이루어지는 반응기 형태이다.(중략)

• Journal of Energy Engineering
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• v.2 no.1
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• pp.1-15
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• 1993

내부순환유동층이란 전형적인 기-고체 유동층 내부에 보조장치로서 원형관(draft tube) 또는 평판(partition plate)을 삽입하여 단일용기를 두 개의 층으로 분리하고 층 사이의 개방면적(opening area)을 통하여 입자의 순환이 일어나도록 하는 반응기 형태이다. (중략)

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.8
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• pp.633-643
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• 2015

In this study, we develop a highly efficient conical-air diffuser that generates fine bubble. By inserting a sufficient number of aerotropic microorganisms with dissolved oxygen from an air diffuser and minimizing the air-channel blockages within the air diffuser, we expect to improve the efficiency and durability of the decomposition process for organic waste. To upgrade the conventional air diffuser, we perform experiments and numerical analysis to develop a conical-type that generates fine bubble, and which is free from nozzle blockage. We complement the air-diffuser design by numerically analyzing the internal air-flow pattern within the diffuser. Then, by applying the diffuser to a mockup bioreactor, we experimentally and numerically study the bubble behavior observed in the diffuser and the 2-phase fluid flow in the bioreactor. The results obtained include statistics of the cord length and increased velocity, and we investigate the mechanisms of the fluid-flow characteristics including bubble clouds. Throughout the study, we systemize the design procedures for the design of efficient air diffusers, and we visualize the fluid-flow patterns caused by bubble generation within the mockup bioreactor. These results will provide a meaningful basis for further study as well as the detection of oxygen transfer and fluid-flow characteristics in real-scale bio-reactors using sets of air diffusers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.11-11
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• 1999

액체 램제트 연소기는 흡입공기와 분무, 혼합 그리고 이에 따른 연소 등 일련의 과정에 따라 다수의 복잡한 현상들이 상호 밀접하게 관련되어 있다. 본 연구에서는 액체 램제트 연소기내의 유동특성을 파악하기 위해서 2차원 및 3차원 연소기 형상에 대해서 수치적 실험을 수행하였으며, 격자구성은 연소기에 공기를 공급하고 연료를 분무하는 공기 유입관 영역과 연소실 영역, 그리고 출구 대기 영역으로 나누어 독자적으로 격자를 생성시켰다. 2차원과 3차원 유동해석을 비교하였고 분무모델의 적용에 따른 연소특성 및 분사위치에 따른 연소특성을 비교하였다. 유동해석 결과 2차원과 3차원의 유동특성은 달랐으며, 분무모델을 적용해야 정확한 연소 유동 현상을 예측할 수 있음을 알 수 있었다. 그리고 유입관의 안쪽에 연료의 분사위치를 준 경우가 연소의 안정화에 필요한 재순환영역으로의 연료의 혼합이 잘 되어 유입관 바깥쪽에 연료를 분사시키는 것보다 좋은 분사위치임을 알 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.2
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• pp.18-24
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• 1999

Liquid ramjet combustor is closely connected with complex phenomena due to a series of processes such as intake air, spray, mixing, and combustion. The present numerical experiments were peformed to investigate these flow characteristics for two and three dimensional liquid ramjet combustor. Grid system was made with three domains: intake region where air is supplied and fuel is injected, combustor and nozzle region, and exit atmosphere region. The numerical results showed that two and three dimensional flow patterns in recirculation region of combustor were significantly different each other and spray model was necessary to predict correctly the chemical reaction flow characteristics. Numerically examined for two different location of fuel injector, one is located on the bottom position of curved intake and the other is located on the top position. We found that bottom position of fuel injector is better than top position because fuel influx to the recirculation region which is need to sustain chemical reaction is more than the latter.

• Journal of Energy Engineering
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• v.12 no.4
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• pp.289-301
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• 2003

To develop a chemical-looping combustion technology, conceptual design of 50 kW thermal chemical-looping combustor, which is composed of two interconnected pressurized circulating fluidized beds, was performed by means of mass and energy balance calculations. A riser type fast fluidized bed was selected as an oxidizer and a bubbling fluidized bed was selected as a reducer by mass balance for the chemical-looping combustor. Calculated values of bed mass, solid circulation flux, and reactor dimension by mass and energy balance calculations were suitable for construction and operation of chemical-looping combustor. It is concluded from the comparison of the design results and operating values of commercial circulating fluidized bed that the process outline is realistic. Moreover, the previous results support that oxygen carrier particle, NiO/bentonite, fulfills the conversion rates needed for the proposed design. The effects of system capacity, metal oxide content in a oxygen carrier particle, amount of steam input, gas velocity, and solid depth on design values were investigated and the changes in the system performance can be estimated by proposed design tool.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.15-15
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• 1999

램 가속기에 대한 연구는 램 가속기의 작동 조건이 고온, 고압, 초고속이라는 점과 가속기 내부에서 급격한 화학반응이 수반된다는 특성으로 인하여 실험과 해석상의 상당한 어려움이 존재한다. 램 가속기는 작동 모드에 따라 탄체 후방의 열적 질식 조건을 이용한 열적 질식 모드(Thermally Choked Mode)와 탄체 표면에 형성되는 데토네이션파를 이용한 초폭굉모드(Superdetonative Mode)로 나뉘어진다. 본 연구는 초폭굉 모드로 작동하는 램 가속기의 작동 성능 향상을 위한 방법으로 수치 최적화 기법을 이용한 램 가속기 내부 예 혼합기의 조성비 최적화를 수행하였다. 설계 변수로는 수소와 질소의 조성비를 선정하였으며, 최적 설계 목표는 일정한 질량과 형상을 갖는 탄체를 초기속도 2500m/s에서 3000m/s로 가속시키기 위하여 필요한 최소 램 가속관의 길이로 정하였다. 본 연구에서는 구베법에 기반한 Simplex 방법 및 SLP(Sequential Linear Programming)등의 수치 최적화 기법을 적용하였고, 가속기 내부의 유동장은 해석의 효율성을 고려하여 이차원 비점성 유동으로 가정하였고, 비평형 화학반응 해석을 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.225-232
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• 2012

A chemical reactor network (CRN) was developed for a lean premixed gas turbine combustor to predict the emission of pollutants such as NOx and CO. In this study, the predictions of NOx and CO emissions from lean premixed methane-air combustion in the gas turbine were carried out using CHEMKIN and a GRI 3.0 methane-air combustion mechanism, which includes the four NO formation mechanisms for various load conditions. The calculated results were compared with experimental data obtained from a modified test combustor to validate the model. The contributions of the four NO pathways were investigated for various load conditions. The effects of nonuniformity of the mass flux and of the equivalence ratio of the injector on the NOx formation were investigated, and a method of reducing the pollutant formation was suggested for the development of a sub-10 ppm gas turbine combustor.