Optimised hydrodynamic parameters for the design of photobioreactors using computational fluid dynamics and experimental validation

Bitog, J.P.P.,Lee, I.B.,Oh, H.M.,Hong, S.W.,Seo, I.H.,Kwon, K.S. Academic Press 2014 BIOSYSTEMS ENGINEERING Vol.122 No.-

A numerical simulation using computational fluid dynamics (CFD) was utilised to investigate the flow hydrodynamics of cylindrical bubble column type photobioreactors (PBRs) with a 30l culture medium. To establish the reliability of the simulation study, the CFD model was validated using particle image velocimetry (PIV) computed data under various air flow rates. There were 32 simulation cases for the study comprising two PBR designs, four air flow rates and four nozzle size diameters. Hydrodynamic analyses such as % volume of dead zones, average circulation time and turbulence intensity inside the simulated PBRs were evaluated. Results have shown that the most appropriate PBR for microalgae cultivation was a design with internal baffle and an extended cone-shaped bottom section. In addition, the recommended nozzle diameter was found to be 10 mm and a minimum air flow rate of 0.10 vvm. To eliminate dead zones inside the PBR, the flow rate can be slightly increased but should not exceed 0.15 vvm. Practical evaluation through laboratory experiments has further confirmed the results of the study where the biomass concentration of Chlorella vulgaris from the proposed PBR was significantly higher compared to the standard PBR design. Based on the numerical investigation and practical evaluation, the improved PBR can be seen to be more effective in culturing microalgae particularly for larger scale mass production.

A wind tunnel study on aerodynamic porosity and windbreak drag

J. P. Bitog,이인복,H.-S. Hwang,M.-H. Shin,홍세운,I.-H. Seo,E. Mostafa,Z. Pang 한국산림과학회 2011 Forest Science And Technology Vol.7 No.1

Natural windbreaks such as trees are very efficient barriers to high velocity winds. The windbreaks exert drag force causing a net loss of momentum and thus disturb the characteristics of flow. The main factors which can affect the efficiency of the windbreaks are tree height, width, tree arrangement, porosity, etc. However, tree porosity which is strongly related to the windbreak drag is very difficult to establish. In this study, the results of a wind tunnel test were introduced to find the aerodynamic porosity and resistance factor of a tree windbreak. Black pine tree (Pinus thunbergii), a typical tree windbreak in Korea was chosen as the experimental tree. With the main factors of wind velocity, static pressure and density of the tree, the aerodynamic porosity as well as the resistance factor of the tree was found. The average porosity at varied tree density were found to be 0.91, 0.69 and 0.42 for one, two and three trees, respectively. The resistance factors which can be equaled to the drag coefficient were 0.55, 0.82 and 1.08 for one, two and three trees, respectively. The determined aerodynamic porosity and windbreak drag will be used later as input data in computer simulation studies such as computational fluid dynamics (CFD). Moreover, the experimental procedure as well as the use of real trees in the wind tunnel experiment of finding the aerodynamic porosity and windbreak drag of various tree windbreaks was established through this study.

SIMULATION OF AN ARRAY OF FENCES IN SAEMANGEUM RECLAIMED LAND USING CFD TECHNOLOGY

( J. P. Bitog ),이인복 ( I. -b. Lee ),홍세운 ( S. -w. Hong ),황현섭 ( H. -s. Hwang ),서일환 ( I. -h. Seo ),유재인 ( J. -i. Yoo ),권경석 ( K. -s. Kwon ),최지선 ( J. -s. Choi ) 한국농공학회 2009 한국농공학회 학술대회초록집 Vol.2009 No.-

This paper discusses about the quantitative effect of windbreak fences on wind velocity in the reclaimed land at Saemangeum semi-arid desert in South Korea. Windbreak fences were constructed in the reclaimed land purposely to prevent the generation and diffusion of dust. Using CFD simulations, the effects of fence porosity, fence height, and the distance between the adjacent fences were investigated. A wind tunnel experiment was initially conducted and data gathered were used to develop the CFD models. From the experiments and CFD simulations, the overall percentage difference of the measured velocities was 7.81% which is generally acceptable to establishing the reliability of the CFD models. The reduction effect on wind velocity was measured in between the adjacent fences up to a height of 0.6 m from the ground surface. In terms of porosity (ε= 0, 0.2, 0.4, 0.6), 0.2 was found to be the optimum value. Conversely, the effect of fence height (0.6, 0.8 and 1.0 m) showed no significant difference; therefore, 0.6 m height is recommended. In addition, the effect of distance between the adjacent fences (2, 4 and 6 m) having a 0.2 porosity has decreased to about 75% regardless of the distance. In the case of the reclaimed land in Saemangeum, a decrease of 75% can prevent the generation and diffusion of dusts. However, the source of dusts is very large. Therefore, constructing an array of windbreak with 6 m distance between them is deemed necessary.

나무의 공극률과 방풍 효과에 대한 풍동 실험

제시비톡 ( J. P. Bitog ),이인복 ( I. -b. Lee ),황현섭 ( H. -s. Hwang ),홍세운 ( S. -w. Hong ) 한국농공학회 2010 한국농공학회 학술대회초록집 Vol.2010 No.-

Natural windbreaks such as trees are very efficient barriers to high velocity winds. The windbreaks exert drag force causing a net loss of momentum and thus disturb the characteristics of flow. The main factors which can affect the efficiency of the windbreaks are tree height, width, tree arrangement, porosity, etc. However, tree porosity which is strongly related to the windbreak drag is very difficult to establish. Recently, computational fluid dynamics (CFD) have been actively used to investigate wind flow characteristics around artificial and natural windbreaks such as trees. As a first step in the simulation, the CFD model had to be designed as a porous media because of the complexity of the physical structure. In this study, the results of wind tunnel test were introduced to find the porosity and aerodynamic resistance of a tree windbreak. Black pine tree (Pinus thunbergii), a typical tree windbreak in Korea was chosen as the experimental tree. With the main factors of wind velocity, static pressure, and density of the tree, the aerodynamic porosity as well as the resistance factor of the tree was found. The average porosity at varied tree density were found to be 0.91, 0. 69 and 0.42 for one, two and three trees, respectively. The resistance factors which can be equaled to the drag coefficient were 0.55, 0.82 and 1.08 for one, two and three trees, respectively. The determined aerodynamic porosity and windbreak drag will be used later as input data of CFD models. Moreover, the experimental procedure as well as the use of real tree in the wind tunnel experiment of finding the aerodynamic porosity and windbreak drag of various tree windbreaks was established through this study.

광생물 반응기 설계를 위한 CFD 입자추적기술

제시비톡 ( Jessie P. Bitog ),이인복 ( In-bok Lee ) 한국농공학회 2011 한국농공학회 학술대회초록집 Vol.2011 No.-

Photobioreactors has been widely considered to be the most effective and efficient growth vessel for mass production of photosynthetic microorganisms such as microalgae for various purposes. However, practicable photobioreactor designs are still in the process of development. This can be observed from the rapid increase of numerical simulation studies on the design and development photobioreactors. Among the numerical methods, a computational fluid dynamic (CFD) technique holds the greatest potential considering its wide and practical application in multiphase flow systems. In this study, particle tracking technique of CFD was used to evaluate the performance of a 30L bubble type photobioreactor where the cells are considered as fine particles. The commercial CFD model Flow-3D was used in all tests. Flow-3D allows the release of particles from a user-defined source. A circular plane was defined as a source of particles in any part of the computational grid, with a given generation rate expressed in particles/second. The particles are passively transported by the flow and they do not interact with each other or with the fluid. The particles are assumed as spherical and defined by properties such as diameter and density. The locations of the particles were continuously tracked and the average amounts of light received by the particles were theoretically computed. The average growth of the cells was then computed based on the amount of light intensity distribution in the photobioreactor utilizing the Lambert-Beer Law proposed earlier by Lou and Al- Dahhan (2003). Results of the simulation study on growth of cells revealed good agreement with the growth of cells grown in a 30L photobioreactor.

The past, present and future of CFD for agro-environmental applications

Lee, I.B.,Bitog, J.P.P.,Hong, S.W.,Seo, I.H.,Kwon, K.S.,Bartzanas, T.,Kacira, M. Elsevier 2013 Computers and electronics in agriculture Vol.93 No.-

Computational fluid dynamics (CFD) is a proven simulation tool which caters to almost any field of study. The CFD technique is utilized to simulate, analyze, and optimize various engineering designs. In this review, the discussion is focused on the application of CFD in the external atmospheric processes as well as modeling in land and water management. With respect to its application in environmental investigations, numerous CFD studies have been done in the atmospheric processes where generally only the fluid flow characteristics are investigated. The application of CFD to soil and water management is still limited. However, with the present demand for conservation and sustainable management of our soil and water resources, CFD application in this field is fast emerging especially in structure designs of dams and reservoirs where CFD offers fast reliable results with less labor and cost. Every CFD model should be validated in order to be considered accurate and reliable. However, a benchmark or standard procedures in validating CFD models is not yet available. This probably answers why the success of the CFD models is still mostly attributed to the user's skills and experience. At present, the degree of application of CFD to the agro-environmental field is limited by the computing power and software used, however, the fast ever computing power of PCs continually expands the potential of CFD and can be generally more flexible at accounting for the unique aspects of every CFD project. This allows easy access to conduct simulation studies from simple to complex models. In this paper, after a state of art analysis of the past and present application of CFD in the agro-environmental applications, its future directions were discussed, in order to potentially serve as a guide for researchers and engineers on what project or investigations can be conducted.

축산악취의 확산 예측을 위한 전산유체역학 모델의 개발

이인복,홍세운,황현섭,서일환,J. Bitog,권경석 한국기상학회 2010 한국기상학회 학술대회 논문집 Vol.2010 No.4

소형 풍력 발전을 위한 축산 배기팬의 후류 평가

홍세운 ( Sewoon Hong ),이인복 ( Inbok Lee ),( J. P. Bitog ),송상현 ( Sanghyeon Song ),이성복 ( Sungbok Lee ),김용희 ( Yonghee Kim ) 한국농공학회 2010 한국농공학회 학술대회초록집 Vol.2010 No.-

풍력 발전은 풍속의 세제곱에 비례하여 에너지를 생산할 수 있으므로 풍속이 높고 일정할수록 높은 발전효율을 보인다. 풍속이 낮고 변동이 큰 자연풍과 달리 팬에 의하여 인위적으로 생성된 기류는 이러한 관점에서 최적의 적용 대상이라 할 수 있다. 농업 분야에서 축산 시설에서 사용되는 배기팬은 축사 내부의 유해 가스 배출 등의 목적으로 최소환기 이상의 환기량으로 연중 가동되고 있으므로, 본 연구에서는 이에 의해 형성되는 배기팬 후류의 양질의 바람을 발전에 사용하고자 발전 가능성 및 발전 시 배기팬에 나타날 수 있는 부하의 가능성을 사전에 평가해 보고자 하였다. 축산 농가에서 주로 사용되고 있는 50인치 배기팬을 사용하여 실험을 한 결과, 배기팬으로부터 약 3 m정도 거리에서 약 5~7 m/s의 풍속이 유지되었으며, 5 m 이후부터는 풍속이 약 4 m/s 이하로 급격히 감소되는 것으로 나타났다. 배기팬 뒤에 장애물을 설치하여 장애물에 의한 부하를 측정한 결과, 배기팬의 1 m 뒤에 장애물 판을 설치한 경우에는 약 20% 정도의 배기유량이 감소되는 결과를 보였으나, 거리가 증가함에 따라 그 부하는 점차 감소하였다. 배기팬의 소비전력 또한 약 1 m 거리일 때에는 10 % 정도 증가하였지만, 그 이후의 거리들에서는 약 5 % 미만으로 점차 부하는 감소하는 결과를 보였다. 약 3 m 정도의 거리에서는 배기유량과 소비전력에서 장애물이 없을 때와 비교하여 약 5 % 내외의 차이를 보이고 있으며, 실험에 사용된 장애물 판에 비하여 실제 풍력 터빈은 솔리디티가 훨씬 작으므로 부하에 의한 역효과는 더욱 감소할 것으로 예상된다. 이러한 풍력 발전의 가능성에 따라 적정 풍력 터빈의 형상과 위치 등을 결정하고자 전산유체역학 시뮬레이션 툴을 사용하여 배기팬에서 형성되는 복잡한 후류를 모의하고자 하였다. 해석 결과의 검증과 보정을 위하여 실험을 통하여 배기팬 후류의 수평적 풍속 분포를 측정하였고, 배기팬 후면에 다수의 짧은 실을 프로브로 설치하여 유동을 가시화하였다. 실험을 통하여 측정된 수직, 수평적 풍속 분포들은 시뮬레이션에 의한 기류 분포와 비교하여 배기팬에서 생성되는 기류의 프로파일을 생성하는데 활용되었다.

제3발표장 : 생물생산시설 및 환경공학 분야 ; CFD를 이용한 광생물반응기 구조에 따른 바이오매스 생산성 예측

서일환 ( Il Hwan Seo ),이인복 ( In Bok Lee ),JPBitog ( J P Bitog ),권경석 ( Kyung Seok Kwon ),박하아린 ( Ha A Rin Park ) 한국농업기계학회 2013 한국농업기계학회 학술발표논문집 Vol.18 No.1

신시-야미도 매립 공사 현장의 비산 먼지 영향 예측

황현섭 ( Hyunseon Hwang ),이인복 ( Inbok Lee ),홍세운 ( Sewoon Hong ),서일환 ( Ilhwan Seo ),( Jessiepascualpiog Bitog ),권경석 ( Kyeongseok Kwon ),김용희 ( Yonghee Kim ),최지선 ( Jisun Choi ),송상현 ( Sanghyeon Song ) 한국농공학회 2010 한국농공학회 학술대회초록집 Vol.2010 No.-

신시-야미도 매립공사 지역에서는 공사 진행 되면서 현장으로부터 야미도로 유입되는 비산 및 부유 먼지로 인하여 인근 주민과의 마찰이 예상되었다. 매립공사의 면적은 약 200ha로서 연구 시기는 2009년 12월 매립공사가 완료되는 시점까지 수행하였다. 본 연구는 1. 야미도에의 마을에 영향을 미치는 풍향 및 풍속을 파악하고, 2. 그 위험 기상 조건으로 중심으로 농도 지수를 표현하여 이를 분석하였다. 또한, 민원 대비의 목적으로 사람의 시야 및 영향 정도를 고려할 수 있도록 지상 1m 높이의 조건에서 이를 비교하였다. 매립공사로 인한 영향을 분석한 결과는 다음과 같다. 현장 기상분석 결과, 야미도 마을로 유입되는 유입풍의 발생빈도가 매우 낮았으며, 그 중 빈도가 높은 시기는 우기와 밤과 새벽 시간으로 마을 주민에게 직접적인 영향이 매우 적을 것으로 판단되었다. 공사가 이루어지는 매립지에서 멀어질수록 입자의 농도가 감소하는 경향을 보이고 있으며, 각 지점의 경우 농도는 TSP가 200~400 ㎍/㎥ 범위이었으며, PM10은 95~200 ㎍/㎥로 나타났으며, 최대 농도를 보이는 측정지점은 매립공사가 이루어지는 현장 내부에서 나타났다. 그 원인으로 매립지 공사 지역에 측정 지점이 위치하고 있어 차량 및 공사 장비의 작업과 이동에 의하여 발생된 먼지들이 포집된 것으로 판단된다. 1m 높이에서 분석한 시뮬레이션 결과, 높은 풍속보다 낮은 풍속에서 더 큰 영향을 미치는 것으로 나타났다. 그러나 확산 거리는 퐁속이 높을수록 더 멀리 확산되는 것으로 나타났다. 이는 10㎛ 입경 분석 결과에서도 유사한 경향을 보이는 것으로 나타났다. 10㎛ 입경의 비산거리는 낮은 풍속에서 경계에서부터 약 300m 내에서 침착되는 것으로 나타났다. 신시-야지 매립 공사의 야미도 주거 지역에 대한 영향빈도 분석 결과, 풍향에 따라 남(S)> 남동(SE)>남서(SW) 로 나타났다. 현장 측정에서 남풍(S), 남동풍(SE)의 빈도가 낮으므로, 실제 야미도 주거 지역으로 유입되는 비산 먼지는 매우 적을 것으로 판단된다. 풍속이 높아지면서 먼지가 상승기류와 함께 더 높은 높이로 비산되는 것으로 파악되었다. 또한, 대부분 남풍이 피해가 크게 주는 것으로 나타났으며, 다음이 남동, 남서로 나타났다. 유입풍이 불어올 경우 발생된 먼지의 40% 정도가 마을을 통과하는 것으로 분석되었다.