• Journal of Microbiology and Biotechnology
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• 제18권7호
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• pp.1257-1265
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• 2008

To lower the cost of ethanol distillation of fermentation broths, a high initial glucose concentration is desired. However, an increase in the substrate concentration typically reduces the ethanol yield because of insufficient mass and heat transfer. In addition, different operating temperatures are required to optimize the enzymatic hydrolysis (50$^{\circ}C$) and fermentation (30$^{\circ}C$). Thus, to overcome these incompatible temperatures, saccharification followed by fermentation (SFF) was employed with relatively high solid concentrations (10% to 20%) using a portion loading method. In this study, glucose and ethanol were produced from Solka Floc, which was first digested by enzymes at 50$^{\circ}C$ for 48 h, followed by fermentation. In this process, commercial enzymes were used in combination with a recombinant strain of Zymomonas mobilis (39679:pZB4L). The effects of the substrate concentration (10% to 20%, w/v) and reactor configuration were also investigated. In the first step, the enzyme reaction was achieved using 20 FPU/g cellulose at 50$^{\circ}C$ for 96 h. The fermentation was then performed at 30$^{\circ}C$ for 96 h. The enzymatic digestibility was 50.7%, 38.4%, and 29.4% after 96 h with a baffled Rushton impeller and initial solid concentration of 10%, 15%, and 20% (w/v), respectively, which was significantly higher than that obtained with a baffled marine impeller. The highest ethanol yield of 83.6%, 73.4%, and 21.8%, based on the theoretical amount of glucose, was obtained with a substrate concentration of 10%, 15%, and 20%, respectively, which also corresponded to 80.5%, 68.6%, and 19.1%, based on the theoretical amount of the cell biomass and soluble glucose present after 48 h of SFF.

• 한국수소및신에너지학회논문집
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• 제26권4호
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• pp.301-307
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• 2015

We present a study of hydrogen liquefaction using the CFD (Computational Fluid Dynamics) program. Liquid hydrogen has been evaluated as the best storage method because of high energy per unit mass than gas hydrogen, but efficient hydrogen liquefaction and storage are needed in order to apply actual industrial. In this study, we use the CFD program that apply navier-stokes equation. A hydrogen is cooled by heat transfer with the while passing gas hydrogen through Cu tube. We change diameter and flow rate and observe a change of the temperature and flow rate of gas hydrogen passing through Cu tube. As a result of, less flow rate and larger diameter are confirmed that liquefaction is more well. Ultimately, When we simulate the hydrogen liquefaction by using CFD program, and find optimum results, it is expected to contribute to the more effective and economical aspects such as time and cost.

• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.386-401
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• 2011

Mathematical models for various steps in coal gasification reactions were developed and applied to investigate the effects of operation parameters on dynamic behavior of gasification process. Chemical reactions considered in these models were pyrolysis, volatile combustion, water shift reaction, steam-methane reformation, and char gasification. Kinetics of heterogeneous reactions between char and gaseous agents was based on Random pore model. Momentum balance and Stokes' law were used to estimate the residence time of solid particles (char) in an up-flow reactor. The effects of operation parameters on syngas composition, reaction temperature, carbon conversion were verified. Parameters considered here for this purpose were $O_2$-to-coal mass ratio, pressure of reactor, composition of coal, diameter of char particle. On the basis of these parametric studies some quantitative parameter-response relationships were established from both dynamic and steady-state point of view. Without depending on steady state approximation, the present model can describe both transient and long-time limit behavior of the gasification system and accordingly serve as a proto-type dynamic simulator of coal gasification process. Incorporation of heat transfer through heterogenous boundaries, slag formation and steam generation is under progress and additional refinement of mathematical models to reflect the actual design of commercial gasifiers will be made in the near futureK.

• Advances in Energy Research
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• 제5권2호
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• pp.91-105
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• 2017

Thermal hydraulic (TH) analysis of nuclear power reactors is utmost important. In this way, the numerical codes that preparing TH data in reactor core are essential. In this paper, a subchannel analysis of a Russian pressurized water reactor (WWER1000) core with enhanced numerical code is carried out. For this, in fluid domain, the mass, axial and lateral momentum and energy conservation equations for desired control volume are solved, numerically. In the solid domain, the cylindrical heat transfer equation for calculation of radial temperature profile in fuel, gap and clad with finite difference and finite element solvers are considered. The dependence of material properties to fuel burnup with Calza-Bini fuel-gap model is implemented. This model is coupled with Isotope Generation and Depletion Code (ORIGEN2.1). The possibility of central hole consideration in fuel pellet is another advantage of this work. In addition, subchannel to subchannel and subchannel to rod connection data in hexagonal fuel assembly geometry could be prepared, automatically. For a demonstration of code capability, the steady state TH analysis of a the WWER1000 core is compromised with Thermal-hydraulic analysis code (COBRA-EN). By thermal hydraulic parameters averaging Fuel Assembly-to-Fuel Assembly method, the one sixth (symmetry) of the Boushehr Nuclear Power Plant (BNPP) core with regular subchannels are modeled. Comparison between the results of the work and COBRA-EN demonstrates some advantages of the presented code. Using the code the thermal modeling of the fuel rods with considering the fission gas generation would be possible. In addition, this code is compatible with neutronic codes for coupling. This method is faster and more accurate for symmetrical simulation of the core with acceptable results.

• Korean Chemical Engineering Research
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• 제40권6호
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• pp.681-686
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• 2002

산업 현장에서 이론적인 건조방법이 실제와는 차이가 많고 또한 배기가스의 재순환이 폐열을 이용하는 목적으로 열원의 절감에는 경제적이지만 이들 파라미터에 따른 요소수지 성형화에 미치는 영향을 연구한바가 없다. 따라서 요소 수지 성형재료의 경화 특성을 건조와 성형 공정 중의 건조온도와 시간, 배기가스 재 순환률 및 성형온도에 따라 실험하여 다음과 같은 결과를 얻었다. 성형재료의 수분함량은 건조 시간과 건조 온도가 증가함에 감소하고, 건조속도는 배기가스 재 순환률이 증가하면 감소한다. 특히 경화유동도는 배기가스의 재 순환량, 건조온도 및 성형온도가 증가하면 감소한다. 또한 건조온도, 건조시간, 배기가스의 재 순환량 및 성형온도에 따라 수분함량과 경화유동도에 대한 상관식을 구하여 재현성있는 최적의 조건을 구명하였다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.

• Steel and Composite Structures
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• 제36권5호
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• pp.603-615
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• 2020

The present manuscript focuses on the flow and heat transfer of the dusty fluid along exponentially stretching cylinder. Enormous attempts are made for fluid flow along cylinder but the study of fluid behavior along exponentially stretching cylinder is discussed lately. Using appropriate transformations, the governing partial differential equations are converted to non-dimensional ordinary differential equations. The transformed equations are solved numerically using Shooting technique with Runge-Kutta method. The influence of the physical parameters on the velocity and temperature profiles as well as the skin fraction coefficient and the local Nusselt number are examined in detail. The essential observations are as the fluid velocity decreases but temperature grows with rise in particle interaction parameter, and both the fluid velocity and temperature fall with increase in mass concentration parameter, Reynold number, Particle interaction parameter for temperature and the Prandtl number.

• 공업화학
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• 제7권2호
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• pp.308-314
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• 1996

경막형 결정화기에서 벤젠-시클로헥산 혼합물로부터 벤젠의 결정성장속도가 조사되었다. 결정성장속도는 경막결정화기의 냉각벽에 부착되는 결정의 양으로부터 얻어진 결정두께와 시간에 대한 상관관계식으로부터 결정되었다. 결정성장속도와 결정의 표면온도와, 용융액의 온도의 차로 정의되는 과냉각정도와의 상관관계가 얻어졌다. 이 이성분 공융계에 대한 결정성장속도는 과냉각정도의 2승에 비례하였다. 경막결정화기의 열전달 및 물질전달 속도에 근거하여 결정의 표면온도 및 결정두께를 예측할 수 있는 모델식이 제시되었다. 5wt% 및 10wt%의 시클로헥산을 포함한 벤젠-시클로헥산 혼합물에 대하여 여러 다른 냉각온도에서 실험적으로 얻어진 결정두께의 자료와 모델식으로 계산된 결과가 비교되었다.

• 대한기계학회논문집B
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• 제35권1호
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• pp.9-15
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• 2011

본 연구에서는 3 차원 전산 열유동해석을 통하여 형상법칙에 근거하여 개발된 냉각판의 열수력학적인 특성을 분석하였다. 서펜타인 형상을 포함하여 최적화, 최적화되지 않은 1, 2 차 형상 총 5 개 형상을 대상으로 동일한 구속조건을 부여함으로써 유동저항, 열저항 및 분지유로에서의 유동균일도를 상호 비교함으로써 냉각판의 성능평가를 수행하였다. 그 결과, 최적화된 1, 2 차 형상 구조가 최적화되지 않은 경우와 비교하여 훨씬 적은 압력손실을 나타내었으며, 압력손실을 기준으로 최적화된 2 차 형상 구조가 가장 우수한 유동 구조를 나타내었다. 또한, 최적화된 1, 2 차 형상구조의 열저항 및 유동 분배성능도 기존에 사용되는 유로형상과 비교하여 모두 우수한 성능을 보였다.

• 한국안전학회지
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• 제35권6호
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• pp.32-45
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• 2020

The problem of determining the discharge rates of gases from pressurized vessels through pressure relief devices was dealt with comprehensively. First, starting from basic fluid flow equations, detailed modeling procedures were presented for isentropic nozzle flows and frictional flows in a pipe, respectively. Meanwhile, physical explanations were given to choking phenomena in terms of the acoustic velocity, elucidating the widespread use of Mach numbers in gas flow models. Frictional flows in a pipe were classified into adiabatic, isothermal, and general flows according to the heat transfer situation around the pipe, but the adiabatic flow model was recommended suitable for gas discharge through pressure relief devices. Next, for the isentropic nozzle flow followed by adiabatic frictional flow in the pipe, two equations were established for two unknowns that consist of the Mach numbers at the inlet and outlet of the pipe, respectively. The relationship among the ratio of downstream reservoir pressure to upstream pressure, mass flux, and total frictional loss coefficient was shown in various forms of MATLAB 2-D plot, 3-D surface plot and contour plot. Then, the profiles of gas properties and velocity in the pipe section were traced. A method to quantify the relationship among the pressure head, velocity head, and total friction loss was presented, and was used in inferring that the rapid increase in gas velocity in the region approaching the choked flow at the pipe outlet is attributed to the conversion of internal energy to kinetic energy. Finally, the Levenspiel chart reproduced in this work was compared with the Lapple chart used in API 521 Standatd.