• Wind and Structures
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• v.19 no.4
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• pp.389-404
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• 2014

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (${\beta}$=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

• Design & Manufacturing
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• v.18 no.2
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• pp.1-8
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• 2024

Unlike the roll-to-roll process that uses a steel roll and a nip roll, a vacuum roll can hold and transfer a thin film using a single roll. To precisely manufacture a vacuum roll, a thin outer cylinder must be machined, which is assembled on the outside of the roll and contacts the film via vacuum pressure. In this study, the effects of jaw width and chucking force on the deformation of the outer cylinder during the turning process were investigated using analysis, and a precision machining and burr removal process was developed. The deformation of the outer cylinder decreased almost linearly with increasing jaw width and increased with higher chucking force and larger cylinder diameter. Additionally, the deflection due to the weight of the outer cylinder was approximately three times greater than that caused by film tension. For the machined outer cylinder, a burr removal experiment was conducted, and concentricity and cylindricity were measured. Using a device that removes burrs by rotating a wheel connected to the main shaft at high speed, it was found that burrs generated on the inner diameter could be removed very efficiently. On the vacuum side, the concentricity errors of the inner and outer diameters were 0.015 mm and 0.014 mm, respectively, and on the opposite side, they were 0.006 mm and 0.010 mm, respectively. Additionally, the measurement of Total Indicator Runout (TIR) according to the angle showed that the maximum cylindricity of the outer and inner diameters was 0.02 mm and 0.025 mm, respectively. Finally, through burr-height measurement at the hole boundary, it was found that the heights were within 0.05 mm.

• Journal of the Korean Applied Science and Technology
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• v.32 no.4
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• pp.616-622
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• 2015

Current ballast water treatment technologies are applying chemical or electrical treatment technology which are not free from secondary environmental pollution. The purpose of this study is to treat the ballast water by shear stress without an additional environmental pollution and to find out the optimal treatment apparatus. We tried to treat ballast water by applying shear stress with two different type of combination of inner and outer cylinder, such as non-pattern type and groove type. In the case of non-pattern type of inner and outer cylinder, sterilization effect was comparatively low because of a slip between inner and outer cylinder. But in the case of groove type of inner and outer cylinder, sterilization effect was superior to the non-pattern type. With a same revolutional speed of 8000rpm, an extinction effect was acquired in the gap of 1 mm of inner and outer cylinder at non-pattern type, but 3mm of that of groove type.

• Journal of computational fluids engineering
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• v.6 no.3
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• pp.1-9
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• 2001

Mixed convection in a horizontal annulus is considered, and the effect of a forced flow on the natural convective flow is investigated. The inner cylinder is hotter than the outer cylinder, and the outer cylinder is rotating with constant angular velocity with its axis at the center of the annulus. The unsteady streamfunction-vorticity equation is solved with a finite difference method. For the fluid with Pr=0.7, there appear flows with two eddies, one eddy, or no eddy according the Rayleigh and Reynolds numbers. The rotation of the outer cylinder reduces the heat transfer rate at the wall of the annulus. The oscillatory multicellular flow of a low Prandtl number fluid with Pr=0.01 can be effectively suppressed by the forced flow.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.303-306
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• 1999

The paper describes a theoretical study on the speed of the torsional elastic waves propagating in a circular cylinder whose outer radius varies periodically as a harmonic function of the axial coordinate. The approximate solution for the phase speed has been obtained using the perturbation technique for sinusoidal modulation of small amplitude. It is shown that the wave speed in the cylinder with a corrugated outer surface is less than that in a smooth cylinder by the square of the amplitude of the surface perturbation. This theoretical prediction agrees reasonably with an experimental observation reported earlier. It is also shown that the wave speed reduction due to the surface corrugation becomes larger for a thinner cylinder and for a bigger density of corrugation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.551-561
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• 1997

Mixed convection of air in a horizontal concentric cylindrical annulus is investigated numerically. Isothermal boundary conditions are prescribed at the inner and outer cylinders, with the inner cylinder being warmer. The forced flow is induced by the outer cylinder which is rotating slowly with constant angular velocity with its axis at the center of the annulus. The effect of the forced flow on the flow pattern and heat transfer of natural convection is investigated for the annulus of (inner-cylinder radius/gap width) = 1. There appear two eddies, one eddy or no eddy according to the Rayleigh and Reynolds numbers. Map of the three flow regimes is constructed on the Ra-Re plane. (author). 28 refs., 9 figs., 2 tabs.

• Journal of the Korean Society of Visualization
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• v.6 no.2
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• pp.33-38
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• 2008

The effect of the radial temperature gradient and the presence of slits in the wall of outer of two cylinders involved in creating a Taylor-Couette flow was investigated by measuring the velocity field inside the gap. The slits were azimuthally located along the inner wall of the outer cylinder and the number of slits used in this study was 18. The radius ratio and aspect ratio of the models were 0.825 and 48, respectively. The heating film wrapped around the inner cylinder was used for generating the constant heat flux and we ensured the constant temperature condition at the outer space of the outer cylinder. The velocity fields were measured by using the PIV(particle image velocimetry) method. The refractive index matching method was applied to remove image distortion. The results were compared with plain wall configuration of Taylor-Couette flow. From the results, the presence of slits in the wall of outer cylinder and temperature gradient increased the flow instability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.689-696
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• 1996

A comparison is made of the heat loss from a hollow cylinder, computed using an one-dimensional analytic method and a two-dimensional separation of variables scheme. For a two-dimensional analysis, the temperature of the inner surface as a boundary condition can be varied along the length of the cylinder by varing the temperature variation factor, b. Comparisons of the heat loss from the hollow cylinder using these two methods are given as a function of non-dimensional cylinder length, the ratio of the outer radius to the inner radius, temperature variation factor and Biot number. The result shows that the value of the heat loss from the hollow cylinder obtained using the one-dimensional analytic method becomes close to the value given by the two-dimensional separation of variables scheme as the value of Biot number and the non-dimensional hollow cylinder length increase and as the ratio of the outer radius to the inner radius decreases.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.630-635
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• 2016

In the prior work, we studied a ballast water treatment apparatus, which is secondary pollution free by using physical treatment of shear stress. The principle of this apparatus is smashing various microorganisms by shear stress generated between stationary outer cylinder and revolving inner cylinder. Because of various magnitude of shear stress according to the inner cylinder surface type and revolution speed, an appropriate surface type and optimum revolution speed should be studied by consecutive experiment to determine the reference data for commercial apparatus. Through a comparative study of disk type and cylinder type of ballast water treatment apparatus, cylinder type is turned out to be superb to disk type. In this study, we studied to determine the superior collaboration of cylinder type, groove type and knurling type of inner cylinder to non patterned outer cylinder, and to optimize the revolution speed and flow rate according to the gap between inner cylinder and outer cylinder. As a result, we could get perfect sterilization effect at groove type under the conditions of 250 mL/min of flow rate at 8,000 rpm and 500 mL/min of flow rate at 10,000 rpm respectively.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.328-335
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• 1988

Natural convection in annuli between the horizontal and vertical concentric cylinders for ratio of the inner to the outer radius, $R_1$=0.85, 0.35 has been studied by the numerical analysis. Governing equations are numerically sloved by means of Successive over-relaxation methods. It is found that maximum local Nusselt number, $Nu_{1.max}$ at the inner cylinder and $Nu_{2.max}$ at the outer cylinder for $R_2$=0.35 have maxima at ${\phi}=0^{\circ}$, ${\phi}=180^{\circ}$ ${\xi}=0.4$, 1.6 for horizontal cylinder and at bottom, top for vertical cylinder, respectively. In the present study, mean Nusselt numbers at the vertical cylinder increased more than that at the horizontal cylinder by about 64% for $R_1$=0.35.