• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.1-9
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• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.8
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• pp.1141-1151
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• 1998

An effective thermal conductivity measurement for suspensions of microparticles in oil mixture is conducted in order to evaluate the shear rate-dependence of the thermal conductivity of suspensions. Measurements are made for rotating Couette flows between two concentric cylinders. The rotating outer cylinder is immersed into a constant temperature water bath while the stationary inner cylinder is subject to a uniform heat fluff. Test fluids are made to be homogeneous suspensions, in which neutrally buoyant microparticles ($d=25{\sim}300{\mu}m$) are uniformly dispersed. The present measurements show strong shear-rate dependent thermal conductivities for the suspensions, which are higher than those at zero shear rate. The shear rate dependent thermal conductivity increases with the particle size and volume concentration.4 new model for shear rate-dependent thermal conductivity of microparticle suspensions is proposed; the correlation covers from zero shear rate value to asymptotic plateau value at moderately high shear rates.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.11a
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• pp.153-158
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• 2003

This study concerns the characteristics of helical flow in a concentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2％ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of 0∼500rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• Journal of KSNVE
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• v.6 no.4
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• pp.475-479
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• 1996

Recently, fiber optic hydrophone is a subject which has attracted as a underwater acoustic sensor. In this paper, a length of optical fiber is bonded to an end-capped hollow cylinder of some elastic material, e. g. aluminum and glass-pyres. The normalized sensitivity is derived according to the direction of polarization. Derived sensitivity equations are simulated for two different mandrel materials. The results are also compared to the McMahon's results which calculated for an average Pockel coefficient. Based on the numerical simulation normalized sensitivity is propotional to the inner to outer diameter ratio.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.984-989
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• 2009

The present study has been conducted to predict the temperature distribution in the core of the scraper type ice generator. The analytic model was simplified as the flow in the annular type cylinder, which had an inside wall moving in axial direction due to the rotation of screw and a fixed outside wall. The governing equations were arranged by the method of separation of variables. The results corresponded to the exact solutions of the Bessel function. The qualitative results such as general characteristics of heat transfer in annulus flow from outer cylinder wall to the inside wall were obtained. However the amount of the heat transfer was underestimated as low as $1/5{\sim}1/6$ of the designed value.

• Journal of computational fluids engineering
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• v.14 no.3
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• pp.95-105
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• 2009

We study time-periodic Taylor-Couette flow with the outer cylinder at rest and the inner one oscillating with a mean angular velocity. Varying the frequency of inner cylinder, we investigate the change of Taylor vortices at a given amplitude and a mean angular velocity. With a small frequency of modulation, we find that Taylor vortices appear and disappear periodically. With a higher frequency, Taylor vortices do not disappear, but the intensity of Taylor vortices modulates periodically. As the frequency increases, Taylor vortices modulate harmonically.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.110-115
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• 2017

Natural convection of a fluid with the Prandtl number of 7(water) in a horizontal annulus with constant temperature walls is numerically investigated. The inner cylinder is hotter than the outer cylinder. The flows are classified by the number of eddies in a half annulus. It is found that dual or triple solutions exists above a critical Rayleigh number for an annulus with a aspect ratio $D_i/L=4$. Transitions of $3{\rightarrow}1$ and $2{\rightarrow}1$ eddy flow occur with decrease of Rayleigh number. However, reverse transitions of $1{\rightarrow}3$ and $1{\rightarrow}2$ eddy flow do not occur with increase of Rayleigh number, and no hysteresis phenomenon is observed. In the regime of triple solutions, the 3 eddy flow has the largest mean Nusselt number value and the 1 eddy flow has the smallest value.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.898-904
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• 2006

A new method measuring thermal conductivity of fluids is proposed in this research. It is based on the steady state heat transfer from a hot central cylinder to a cold outer cylinder located concentrically. This method guarantees more stable measurement than conventional THM(transient hot-wire method) due to its simplicity of theoretical principle. Measurements was made for the three nanofluid samples with different particle concentration of pure, 2% and 4%. Nanofluids are made by mixing the pure transformer oil with AlN nano particles. Design of the sensor module and experimental procedures are explained and comparison of the measuring data between present method and THM was made in detail.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.115-123
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• 1997

The buckling strength, fatigue strength, stress corrosion cracking are considerably effected on one of initial imperfections, the residual stresses produced by a circumferential weld between axisymmetric cylinders. Therefore, we study the residual stresses, plastic strain and temperature distribution with using thermal elasto-plastic analysis which are generated by a circumferential weld between axisymmetric cylinders. It is investigated that welding residual stresses have an effect on the strength of cylinder for inner and outer shell under external pressure.

• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.244-249
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• 2000

Thermal gradient chemical vapor infiltration (TG-CVI) process, which is one of the CVI techniques to densify a porous fiber preform, requires for a heater to have uniform surface temperature distribution. Thus, it is essential to design the shape of the heater and to predict the temperature distribution when the heater has a profile which is not a simple cylinder. In this study, an analytical method has been used to design the inner profile of a conical heater showing uniform temperature distribution, if its outer shape is specified. Temperature distribution on the heater surface has been calculated with the finite difference method and compared with the experimental results. When a heater had a combined profile with a large cone and a small cylinder, temperature was higher in the cylindrical part. To reduce the temperature difference between these areas, a hole-machining method has been proposed including other possible ones. A shape design and optimization program has been made to improve the temperature uniformity of the TG-CVI heater better than that designed with the analytical method.