• Korean Chemical Engineering Research
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• v.49 no.2
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• pp.200-205
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• 2011

Axial and radial distributions of bubble holdup were investigated in a slurry bubble column with pilot plant scale(D=1.0 m). Effects of gas velocity, surface tension of continuous liquid medium and solid fraction in the slurry phase on the axial and radial distributions of bubble holdup were examined. The bubble holdup decreased with increasing radial dimensionless distance from the center of the column, while it increased with increasing dimensionless distance in the axial direction from the distributor, in all the cases studied. The radial non-uniformity of bubble holdup increased with increasing gas velocity but decreasing surface tension of liquid medium, while it was not dependent upon the solid fraction in the slurry phase. The axial non-uniformity of bubble holdup increased with increasing gas velocity, but it does not change considerably with variations of liquid surface tension or solid fraction in the slurry phase . The axial and radial distributions of bubble holdup were well correlated in terms of operating variables within this experimental conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.99-105
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• 2002

The performance test of an axial-type turbine is carried out with various axial gap distances between the stator and rotor. The turbine is operated at the low pressure and speed, and the degree of reaction is 0.373 at the mean radius. The axial-type turbine consists of ons-stage and 3-dimensional blades. The chord length of rotor is 28.2mm and mean diameter of turbine is 257.56mm. The power of turbo-blower for input power is 30kW and mass flow rate is $340m^3$/min at 290mmAq static-pressure. The RPM and output power are controlled by a dynamometer connected directly to the turbine shaft. The axial gap distances are changed from a quarter to three times of stator axial chord length, and performance curves are obtained with 9 different axial gaps. The efficiency varies about 8% of its peak value due to the variation of axial gap on the same non-dimensional mass flow rate and RPM, and experimental results show that the optimum axial gap is 1.6-1.9Cx.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.6 s.171
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• pp.30-39
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• 2005

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.6
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• pp.98-104
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• 2015

Excessive thrust acting on the rotor of pump can cause the damage of pump or the decrease of pump lifetime. Therefore, for ensuring the safety of LOX pump of a liquid rocket engine, the thrust of pump rotor is estimated by similarity tests. Axial thrust is indirectly measured by an axial thrust measurement unit positioned outside pump. Radial thrust is calculated based on pressure distribution of volute scroll. As a result, axial and radial thrust are increased when the flowrate of pump decreases. However, both thrusts do not affect the stability of pump rotor since their values are not large.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.98-103
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• 2002

초음파 비가진 시인 상용분무와 초음파가진 시인 개질분무, 간접진동분무, 간접진동 및 개질의 겸용분무의 네가지 경우 모두에서 분무액적의 평균직경 및 SMD가 전 영역에 걸쳐서 노즐 글에서 분무방향으로 멀어질수록 조금씩 증가했으며, 또한 초음파 비 가진시인 상용분무 경우가 초음파 가진 세경우에 비해 크게 나타났다. 초음파 가진 세가지 경우에서는 간접진동 및 개질법 겸용의 경우에서 분무액적의 미세화가 가장 우세하게 나타났다. 이는 초음파가 분무 축방향 전영역에 걸쳐서 분무액적의 미세화에 친화적임을 입증한다. 나. 분무 방향 축에서 반경 방향으로 갈수록 분무 액적의 평균 직경과 SMD는 감소하고 있으며, 반경방향 전 영역에 걸쳐서 상용 분무시의 액적이 가장 크게, 초음파겸용 경우에서 가장 작게 나타나고 있다. 이는 초음파가 분무 내부 전 영역에 걸쳐 액적의 미세화에 친화적임을 증명한다. 다. 분무액적의 크기에 따른 분무 분포도 비교에서 네가지 경우 모두에서 축 방향 거리가 멀수록 분무액적의 크기가 다소 증가함을 보였고, 축에서 반경 방향으로는 분무액적의 크기가 다소 감소함을 보이고 있다. 상용 분무와 초음파 분무의 비교에서 초음파 겸용 가진시는 상용 분무 때 보다 분무 영역 전반에 걸쳐서 미세화가 뚜렷이 우세함을 보였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.467-467
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• 2010

조립된 KAERI ECR(Electron Cyclotron Resonance Ion Source) 이온원의 중요한 성능을 결정하는 ECR 챔버 내의 자장구조를 3차원 가우스 메타를 이용하여 측정하였다. ECR 이온원의 자장은 축방향 (빔인출 방향) 자장 Bz와 반경방향 자장 Br (Bx, By)로 이루어지는 데, KAERI에서 개발한 ECR 이온원의 경우 Bz는 요크 구조체들을 포함한 3개의 전자석들에 의해 만들어지고, Br은 영구자석들로 구성된 헥사폴에 의해 만들어진다. 헥사폴에 의한 자장은 ECR 챔버 벽(R=34 mm)의 위치에서 최대 값을 측정하여 계산결과와 비교하였고, 챔버 내부 R=30 mm 위치에서 축방향과 반경방향의 자장구조를 측정하였다. 전자석 만에 의한 자장은 헥사폴 결합 요크와 챔버 내의 요크를 제거한 상태에서 자장을 측정하여 계산된 결과와 비교하였다. 전자석과 헥사폴에 의한 통합 자장구조는 ECR 챔버와 챔버 내의 요크 구조물을 제거한 상태로 R=30mm 위치에서 전자석의 정격전류에 의한 자장구조를 측정하였고, 최종적으로 이온원 자석구조물들을 모두 장착한 상태에서 축 중심(R=0mm)에서의 축방향 자장 값들을 측정하여 설계한 값과 비교하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.140-148
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• 2002

Anisotropic elastic constants of Zr-2.5Nb pressure tube materials were determined by a high temperature resonant ultrasound spectroscopy (RUS). The resonant frequencies were measured using alumina wave-guides and wide band ultrasonic transducers in a small furnace. The rectangular parallelepiped specimens were fabricated along with the axial, radial and circumferential direction of the pressure tube. A nine elastic stiffness tensor for orthotropic symmetry was determined in the range of room temperature ${\sim}500^{\circ}C$. As the temperature increases, the elastic constant tensor, cij gradually decreases. Higher elastic constants along the transverse direction compared to those along the axial or radial direction are similar to the case of Young's modulus or shear modulus. A crossing of shear elastic constants along axial direction and radial direction was observed near $150^{\circ}C$. This fact corresponds to the crossing of c44 and c66 of single crystal zirconium.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.4
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• pp.439-444
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• 2011

Purpose: To represent the shape of toric corea in the elliptical function for the determination of curvature distribution and lacrimal thickness between cornea and contact lens when the lens is fitted. Methods: Topography measurements of corneal curvature and curvature equation derived from the assumed elliptical function were evaluated using the Excel program which included the necessary equation derived. Results: Mathematical expressions for the cornea whose ribbon shaped-topography image, in which the center does not coincide with the corneal apex, can be determined. Conclusions: For the application where the higher accuracy on the cornea is not required, such as higher order aberration, the cornea cal be expressed in the simple elliptical function.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.141-144
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• 2008

Atomization characteristics and spatial distribution of the spray emanating from an injector of liquid-propellant thruster are investigated by using dual-mode phase Doppler anemometry (DPDA). Spray characteristic parameters such as the mean velocity, Sauter mean diameter (SMD), and velocity fluctuation are measured at various locations along the spray axis as well as on the radial direction. Those data are quantified in radial profile and also used to scrutinize the correlation between diameter and turbulence intensity of spray droplets. For the better visual grasp, dynamic behavior of spray droplets along the spray stream is presented through the velocity vectors projected on the plane of geometric axis of nozzle orifice and radial coordinate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.848-855
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• 2019

Eco-friendly gas turbine combustors are getting attention due to emission regulations. Swirler is important design factor for flame stability and flashback inside the combustor. Design methods of the axial swirler and the radial swirler were discussed and the suitability of the swirl number calculation considering the geometric design variables and the flow loss was examined in the radial swirl for gas turbine combustor. The swirl number of flow was calculated by computational fluid dynamics and compared with swirl number according to each design method.