• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.290-295
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• 2000

An experimental study was carried out in a cavity with upper channel and square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. The visualization system consists of 2-dimensional sheet light by Argon-Ion Laser with cylindrical lens and flow picture recording system. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000). Obtained result showed various flow patterns. Severe unsteady flow fluctuation within the cavity are remarkable and sheared mixing layer phenomena are also found at the region where inlet flow is collided with the counter-clockwise rotating main primary vortex. Photographs of Mach-Zehnder are also compared in terms of constant heat flux.

• KSBB Journal
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• 제6권2호
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• pp.147-156
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• 1991

Diazotized chitin (CHITN) was synthesized reacting with NaN3 and HCl to alkaline hydrolyzed chitin for the support of immobilized enzyme. Immobilized $\beta$-glucosidase on diazotized chitin(CHITN-Gase) was produced reacting with glutaraldehyds as bifunctional reagent. CHITN-Gase activities were determined reacting with p-nitrophenol-$\beta$-D-glucopyranoside in plug flow reactor as a reference. Optimum temperature, optimum pH, reaction constant and deactivation rate were determined with variation of flow rate and H/D. The particle size of immobilized enzyme in the best was, 35 mesh (CHITN35-Gase). The optimum conditions of immobilized enzyme were $70^{\circ}C$ in temperature and 5.0 in pH. Diameter and flow rate of plug flow reactor in the best was 8.5mm in diameter and 0.8ml/min in flow rate. Reaction constant was mainly influenced by electrostatic force. The best glucose hydrolizing activities of CHITN3 5-Gase was 3.34$\times$10-5 M/1. while that of native-$\beta$-glucosidase was 2.44$\times$10-5 M/1.

• 한국전산유체공학회지
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• 제4권2호
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• pp.1-8
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• 1999

Natural convection in a horizontal annulus with the inner cylinder heated by the application of a constant heat flux and the isothermally cooled outer cylinder is considered, and the transition of flows and the bifurcation phenomenon are numerically investigated for air with Pr=0.7. The zero initial condition always induces a crescent-sheped eddy flow. A bicellular flow in which the fluid descends along the vertical central plane of the annulus can be obtained at high Rayleigh number by introducing artificial numerical disturbances. Dual solutions are found above a certain critical Rayleigh number. Hysteresis phenomena have not been observed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1358-1363
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• 2004

The objective of this work is to propose calibration facility in which a thin film type heat flux sensor can be calibrated under convective flow condition by using a small wind tunnel with the constant temperature plate condition. A small wind tunnel has been built to produce a boundary layer shear flow above a constant temperature copper plate. 12-independent copper blocks, thin film heaters, insulators and temperature controllers were used to keep the temperature of flat plate constant at a specified temperature. Three commercial thin film-type heat flux sensors were tested. Convective calibrations of these gages were performed over the available heat flux range of $1.4{\sim}2.5kW/m^2$. The uncertainty in the heat flux measurements in the convective-type heat flux calibration facility was ${\pm}2.07%$. Non-dimensional sensitivity is proposed to compare the sensitivity calibrated by manufacturer and that of experiment conducted in this study.

• 멤브레인
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• 제22권5호
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• pp.332-341
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• 2012

실리카 콜로이드 용액의 정유량 한외여과에서 중력 방향에 대한 막모듈의 위치(경사각) 변화에 따라 발생되는 자연대류 불안정 흐름의 막오염 저감효과를 차압의 변화 정도를 측정하여 규명하였다. 막표면에 케이크 층을 형성함으로서 막오염을 발생시키는 나노 사이즈의 실리카 입자(평균 크기 = 7, 12, 22, 50 nm 및 78 nm)가 함유된 5가지 종류의 콜로이드 용액을 사용하여 중력 방향에 대한 막모듈의 위치(경사각 = $0^{\circ}{\sim}180^{\circ}$)에 따른 차압의 변화를 교반이 없는 dead-end 정유량 한외여과 실험을 통해 측정하였다. 상대적으로 크기가 작은 실리카 입자(7, 12 nm 및 22 nm)가 함유된 콜로이드 용액의 정유량 한외여과에서 막모듈 경사각을 $30^{\circ}$ 이상으로 유지하면 막모듈에 자연대류 불안정 흐름이 발생되어 막오염 형성을 크게 억제시켜 차압의 증가가 거의 나타나지 않았다. 이 자연대류 불안정 흐름의 발생은 막표면에 형성된 실리카 케이크층의 벌크용액으로의 역이동(back transport)을 유발시킴으로서 차압의 증가를 억제시키는 막성능 개선 효과를 나타내었다. 그러나 상대적으로 크기가 큰 실리카 입자(50 및 78 nm)가 함유된 콜로이드 용액의 정유량 한외여과에서는 자연대류 불안정 흐름 발생의 효과가 거의 없었다. 임계 플럭스 측정 결과 실리카 입자의 크기가 작을수록 그리고 막모듈 경사각이 클수록 막모듈에의 자연대류 불안정 흐름의 발생 강도가 커져 막오염 형성이 억제되었으며, 이로 인해 임계 플럭스가 증가하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.266-272
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• 2000

The importance of variable displacement piston pump is recently increasing in industrial applications, as it is widely used for raising the energy level of the fluid in hydraulic system. The regulator is the device that controls the pump output flow depending on the machine load and engine speed, and that regulates the discharge flow of the piston pump by controlling the swivel angel. This work deals with constant power control of a regulator system in bent-axis type piston pump. In order to use engine power effectively, it is important to keep the horsepower from the engine to the pump constant. Therefore, optimum power usage is obtained by accurately following the power hyperbola. First, the governing equations of the regulator are derived, and analysis is performed by numerical simulation in which significant parameters of regulator are identified. Also, we designed and manufactured the prototype of the constant power control regulator for experiments. The experimental results show the responsibility and pressure-flowrate characteristics and these are compared with the theoretical analysis. As the result, it is confirmed that the characteristics of the designed regulator correspond to the numerical simulation.

• Journal of Astronomy and Space Sciences
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• 제20권3호
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• pp.163-174
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• 2003

The motion of 3C 120 Jet relative to the core is reasonably uniform and the VLBI scale jet connects outwards to a VLA ~ 100kpc scale. We measured the jet width variation from the center and found some indication of a power law which indicates the jet expands roughly with a constant opening angle and a constant flow velocity, $V_{f}{\cong}c$, from subparsec scales to ~ 100 kpc. With such a constant flow velocity and based on other physical parameters deduced from observed emission characteristics of the jet, we have established an equipartition jet model which might accommodate the basic parameters of the jet on subparsec scales, with which one can fit the radio intensities over all the scale of the jet even to ~100 kpc.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제16권3호
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• pp.181-192
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• 2012

Here in this paper, the steady paint film flow on a vertical wall of a non-Newtonian pseudo plastic fluid for drainage problem has been investigated. The exact solution of the nonlinear problem is obtained for the velocity profile. Also the average velocity, volume flux, shear stress on the wall, force to hold the wall in position and normal stress difference have been derived. We retrieve Newtonian case, when material constant ${\mu}_1$ and relaxation time ${\lambda}_1$ equal zero. The results for co-rotational Maxwell fluid is also obtained by taking material constant ${\mu}_1$ = 0. The effect of the zero shear viscosity ${\eta}_0$, the material constant ${\mu}_1$, the relaxation time ${\lambda}_1$ and gravitational force on the velocity profile for drainage problem are discussed and plotted.

• Advances in concrete construction
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• 제10권5호
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• pp.381-391
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• 2020

This study aimed to develop reference materials (RMs) for mortar that can simulate the initial flow characteristics with constant quality over a long period. Through the previous research on the development of RMs for cement paste, the combination of limestone, glycerol, and water was used as the basic matrix for developing RMs for mortar in this study. In addition, glass beads of three particle sizes (0.5, 1.0, and 2.0 mm) and ISO standard sand were selected as tentative candidates to derive fine aggregate substitutes. The mixture of glass beads could simulate the initial flow characteristics of mortar, but under the same mixing ratio, replicates showed an unstable tendency to indicate inconsistent values due to the generation of electrostatic properties between materials and equipment. On the other hand, the mixture using ISO standard Sand not only simulates the constant flow characteristics for a long period of time, but also shows stable results with little error in replicates. Therefore, limestone, glycerol, ISO standard sand, and water were finally determined as components that met the required properties of RMs for mortar. The effect of each component on the flow characteristics of RMs was analyzed. It was found that glycerol increased the cohesion between the particles of standard sand, resulting in a constant increase both in the plastic viscosity and yield stress. Both limestone and standard sand had a dominant effect on the yield stress. The relationships between various mortar mixing ratios and the corresponding mixing ratios of RMs were established. In addition, the results of the verification experiment showed that the rheological properties of the RMs obtained through the relationships correlated with various water/cement ratios and the fine aggregate volume fractions of mortar obtained with same manner. In other words, the RMs for mortar developed in this study can be used as standard samples because they can simulate the initial flow characteristics of mortar of various mixing ratios for a long period without any chemical changes.

• 대한기계학회논문집B
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• 제23권8호
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• pp.969-977
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• 1999

A similarity solution of a steady laminar flow of micropolar fluids past wedges has been studied. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions of the equations are then obtained using the fourth-order Runge-Kutta method and the distribution of velocity, micro-rotation, shear and couple stress across the boundary layer are obtained. These results are compared with the corresponding flow problems for Newtonian fluid past wedges with various wedge angles. Numerical results show that, keeping ${\beta}$ constant, the skin friction coefficient is lower for a micropolar fluid, as compared to a Newtonian fluid. For the case of constant material parameter K, however, the velocity distribution for a micropolar fluid is higher than that of a Newtonian fluid.