• Journal of computational fluids engineering
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• v.22 no.1
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• pp.51-58
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• 2017

A penalized VIC method offers an efficient hybrid particle-mesh algorithm to simulate an incompressible viscous flow passing a solid body in an infinite domain. In this manner, the computational domain needs to be restricted to a relatively small region to reduce computational cost which would be very high in case of using a large domain. In this paper, we present how to dispose of far-field particles to avoid an unnecessarily large computational domain. The present approach constraints expansion of the domain and thus prevents the incremental computational cost. To validate the numerical approach, a flow around an impulsively started sphere was simulated for Reynolds numbers of 100 and 1000.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.611-619
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• 2010

The paper deals with the proper design of GGH(gas-gas heater) panel elements of desulfurization equipments in a thermoelectric power plant. When fossil fuels such as coal, petroleum et cetera are burnt to ashes, sulfur oxide compounds are produced, and calcareous sludges are deposited at GGH panel elements. In this case, operation of a power plant equipments is interrupted, and a tremendous economic loss comes into existence. One of the purposes of the paper is to find flow velocity distributions and regions of depositions when calcareous sludges pile up on the GGH panel elements through the fluid analysis. In the fluid analysis, flow velocity and position distributions of particles between GGH panel elements are demonstrated according to time variation for ammonia and calcium hydroxide particles.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.11
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• pp.861-869
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• 2015

In this study, wall to bed heat transfer and hydrodynamic characteristics in a conical fluidized bed combustor was investigated using computational fluid dynamics method. A two-fluid Eulerian-Eulerian model was used with applying the kinetic theory for granular flow(KTGF). The effects of the two drag models, Gidaspow and the Syamlal-O'Brien model, different inlet velocities($1.4U_{mf}{\sim}4U_{mf}$) and different particle sizes on the hydrodynamics and heat transfer were studied. The results showed that the hydrodynamic characteristics such as bed expansion ratio and pressure drop were not affected significantly by the drag models. But the heat transfer coefficient was different for the two drag models, especially at lower gas inlet velocities and small particle sizes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.8
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• pp.749-754
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• 2010

Knowledge of the characteristics of airflow in nasal cavities is essential to understand the physiological and pathological aspects of nasal breathing. In our laboratory, a series of experimental investigations on the nasal airflow was conducted; airflow in models of normal and deformed nasal cavities under both constant and periodic flow conditions was studied by PIV. Some of the patients with asymmetric nasal cavities experience pain or discomfort, while other patients with asymmetric nasal cavities do not experience pain. Airflows inside asymmetric nasal cavities with and without obstructions due to a bent nasal septum are investigated both experimentally by PIV and numerically by using the general-purpose FVM code in order to determine the reason for the above-mentioned discrepancy. The comparisons between two cases are tried. Heat and humidity distribution are investigated numerically.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.671-677
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• 2014

In this research, flow experiments and simulation of highly flowable concrete has been attempted using a viscoplastic particle method varying with dosages of SP admixture and water-cement (W/C) ratios. Rheological and flow characteristics of flowable concrete manufactured in domestic products of cement, aggregates, and SP admixtures were investigated by experimental programs varying with mix proportions. From experiment, the predictive model of rheological characteristics of flowable concrete has been newly proposed considering with the effects of the W/C ratio and the dosage of SP admixture, and the effect of mixing proportion has also been incorporated into shear stress and strain rate curve of flowable concrete in the current method. A series of L-box flow test of highly flowable concrete varying with dosages of SP admixture and W/C ratios was compared with the proposed model.

• The Korean Journal of Rheology
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• v.4 no.2
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• pp.138-147
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• 1992

사출성형충전공정에서 금형구조가 단섬유배향에 미치는 영향을 예측하기 위하여 수 치모사 프로그램을 개발하였다. 유한요소 /관찰 부피 방법에 복잡한 금형에서의 유동을 해 석하고 섬유와 섬유간의 상호작용을 고려한 섬유배향텐서 변화식을 이용하여 입자 추적법으 로 섬유배향분포를 구하였다. 수치모사 결과 금형 옆벽면과 내부 방해체의 주위에 있는 섬 유들이 전단변형의 영향으로 그들주위를 따라서 정렬되려는 경향을 보였다, 두 유동이 내부 방해체를 지나 접하면서 생성된 웰드라인을 따라서 단섬유들이 정렬되려는 경향을 나타내엇 다. 그리고 수축유동에서는 흐름방향으로 정렬되나 확장유동에서는 흐름방향에 수직으로 배 열되려는 경향을 확인하였다. 위아래 벽에 의한 전단변형의 영향으로 서로 다른두 배향구조 를 보여주는 skin-core 구조를 두께방향의 속도구배를 고려한 수치모사를 통하여 예측할 수 있었다. skin구조에서는 섬유들이 흐름방향으로 정렬되고 core 구조에서는 흐름방향에 수직 으로 배향되는 것을 확인하였으며 섬유상호계수값이 커질수록 임의 배향화하는 경향을 보였다.

• Proceedings of the KAIS Fall Conference
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• 2008.05a
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• pp.319-322
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• 2008

본 논문은 미분 반응기 및 유동층반응기에서 메탄의 열분해에 의한 수소 생산과 탄소 생성에 대한 연구를 수행하였다. 일반적으로 고온 분해시 사용되는 니켈과 철 성분을 대신할 철광석을 이용하여 분해특성을 고찰하였다. 환경에 대한 영향을 최소화한 상태에서 메탄의 전환반응을 메탄 분해촉매 활성에 영향을 미치는 인자에 대하여 연구하였다. 측정된 압력요동특성치의 해석을 통하여 유동층 열분해촉매의 유동화현상을 측정하였으며, 유동화특성에 따른 메탄열분해능을 측정하였다. 또한 고정층에서 공간속도, 입자크기, 비표면적이 미치는 영향을 고찰하여 철광석의 사용가능성을 타진하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.714-724
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• 1985

Two-phase(air-solid, air-liquid droplet) turbulent round jet has been analyzed numerically using two equation turbulence model. The mean motion of suspending particles in air has been treated as the secondary fluid with virtual density and eddy viscosity. In this paper, the local mean velocity of secondary fluid is not assumed to be the same as that of the primary one. Dissipation rate of turbulent kinetic energy which arises because the particles can not catch up with the turbulent fluctuations of the primary fluid has been modelled by using the concept of Kolmogorov's spectral energy transfer. Numerical computations were performed for flows with different volume fraction of the dispersed phase and the diameter of particle. Results show that the total rate of turbulent energy dissipation, turbulent intensities and spreading rate of jets are reduced by the increase of volume fraction of dispersed phase. However it does not show consistent tendency with increasing the particle diameter. This investigation also shows that presence of particles in the fluid modifies the structure of the primary fluid flow significantly. Predicted velocity profiles and turbulence properties qualitatively agree with available data.