• The Korean Journal of Rheology
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• v.11 no.2
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• pp.122-127
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• 1999

The characteristics of thermal boundary layer flow of a micropolar fluid in the vicinity of a wedge has been studied with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions are presented for the heat transfer characteristics with Pr=1 using the fourth-order Runge-Kutta method and their dependence on the material parameters is discussed. The distributions of dimensionless temperature and Nusselt number across the boundary layer are compared with the corresponding flow problems for a Newtonian fluid over wedges. Numerical results show that for a constant wedge angle with a given Prandtl number, Pr=1, the effect of increasing values of K results in an increasing thermal boundary thickness for a micropolar fluid, as compared with a Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for a micropolar fluid is lower than that of a Newtonian fluid.

• Water for future
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• v.26 no.4
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• pp.97-105
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• 1993

This paper presents the results of a study conducted to improve the understanding of the characteristics of cylindrical capsule flow in a pipeline by taking into account of the effect of capsule density uniformity. The effect of capsule density variation in the axial direction was studied both experimentally and anaytically. The experiments were conducted in a 190mm diameter straight pipe 17m long. The velocity, gap and tilt of capsules were measured under various conditions, In order to interpret the data on various capsule density conditions, the stability index given in the dimensionless number was introduced. The motion of capsules in pipelines is strongly affected by the stability of the capsules characterized by the stability index. The experiments conducted prover that the stability index is a valid criterion for explaining and correlating data on the capsule motion and the capsule density uniformity.

• Solar Energy
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• v.10 no.1
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• pp.22-30
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• 1990

Steady laminar natural convection heat transfer from a square beam with a horizontal adiabatic plate has been studied numerically for various Grashof numbers and beam shapes. The heat transfer from a square beam increases as the dimensionless beam width W / L decreases. The mean Nusselt number of the upper surface is minimum at W / L = 1.0, maximum at W / L = 0.25 and that of the side surface is minimum at W / L = 0.25, maximum at W / L = 1.0. The increases of the total mean Nusselt number with increasing Grashof number is dominated by the beam width.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.846-857
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• 1995

An experimental study is made of turbulent shear flows in a nearly two-dimensional 90.deg. curved duct by using the hot-wire anemometer. The Reynolds normal and shear stresses, triple velocity products, integral length scales, Taylor micro length scales and dissipation length scales are measured and analyzed. For a positive shear at the inlet, the afore-mentioned turbulence quantities are all suppressed. However, when the inlet shear flow is negative, they are augmented, i.e., the convex curvature suppresses the turbulence whereas the concave curvature augments it. It is found that the curvature effects are rather sensitive to the triple velocity products than the Reynolds stresses. The evolution of turbulence under the curvature with the different shear conditions is well described by the modified curvature parameter S' and the non-dimensional development time ${\tau}$.'

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.430-439
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• 1985

Conjugate natural convection in double enclosed annuli between horizontal concentric cylinders has been studied by the numerical analysis and experimental measurements. The interface conditions between the liquid and the solid of middle shell are obtained through the correlation factor based on the ratio of solid to fluid thermal conductivities and the Prandtl number. The characteristics of conjugate heat transfer are discussed under various dimensionless parameters such as conductivity ratios, shell thickness, diameter ratios, Prandtl number, and Rayleigh number. It is found that the average equivalent conductivity K over var $_{eq}$ does not depend on the conductivity ratios and shell thickness. The K over bar $_{eq}$ however, depends on the Prandtl number and the Rayleigh number.

• Proceedings of the Korea Water Resources Association Conference
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• 1993.07a
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• pp.483-490
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• 1993

This paper presents the results of a study conducted to improve the understanding of the characteristics of cylindrical capsule flow in a pipeline by taking into account of the effect of capsule density uniformity. The effect of capsule density variation in the axial direction was studied both experimentally and analytically. The experiments were xonducted in a 190mm diameter straight pipe 18m long. The velocity, tilt of capsules and the gap between the capsule bottom and the pipe bottom were measured under various conditions. In order to interpret the data on the various capsule density conditions, the stability index given in the dimensionless numberwas introduced. The motion of capsules in pipelines is strongly affected by the stability of the capsules characterized by the stability index. The experiments conducted proved that the stability index is a valid criterion for explaining and correlating data on the capsule motion and the capsule density uniformity.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.153-160
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• 1989

A numerical and experimental study has been performed on natural convection heat transfer from a horizontal annulus with spacers. The mode of heat transfer in the annulus is changed from conduction to convection at Ra = 10$^{3}$. By increasing wall conductivity, mean Nusselt number is apparently increased at $K_{w}$/K$_{f}$ .leg. 48, but at /K$_{w}$/K$_{f}$ > 48, slightly increased for no spacers, and decreased for vertical spacers and horizontal spacers. The mean Nusselt number can be represented in an exponential function of Grashof number at all conditions. The characterics of natural convection heat transfer show similiarity for no spacers and vertical spacers but show difference for horizontal spacers. The presence of the horizontal spacers increased the convective heat transfer by an average 6 percent over that for the no forced cooling to outer cylinder. The maximum local Nusselt number appears at .theta. = 150.deg. in a conducting tube and .theta. = 30.deg. in an outer cylinder for vertical spacers, and appears at .theta. = 180.deg. in a conducting tube and .theta. = 0.deg. in an outer cylinder for horizontal spacers.spacers.

• Water for future
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• v.24 no.2
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• pp.81-95
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• 1991

For investigation of the interaction of tide and river flow, the derived equations are solved analytically using the approximation method of perturbation. The convective inertia and nonlinear bottom friction terms are included in the derivations. The harmonic analysis is applied to decompose the complicated interaction of the freshwater discharge with various constituents of tide into its individual interaction with each constituent. In this study, four main constituents(M2, S2, Kl, 01) are included. The relations of dimensionless parameters of the tide, especially the dimensionless damping modulus, are then determined for each solution. The results show that analytical solution of dimensionless damping modulus underestimates the measured value obtained from harmonic analysis. Results of water level obtained by applying the analytical model to a tidal reach of the Keum River in the years 1981 and 1982 show very good agreement with those obtained from the harmonic analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.881-887
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• 2006

The objective of this study are to analyze the flow characteristics of R22 flowing through EEVs and to develop an empirical correlation to predict the refrigerant flow rate. The mass flow rates of EEVs with different geometries were measured at various condensing temperatures, subcoolings, and EEV openings. Based on the experimental data, an empirical correlation for mass flow predictions in EEVs was developed by modifying the orifice equation. The correlation showed good agreement with the measured data for R22 with average and standard deviations of 1.4% and 6.1%, respectively. Approximately 90% of the measured data were within ${\pm}10%$ of the predictions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.5
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• pp.169-175
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• 2022

Scour in a flow field affected by waves, such as river estuaries or shallow waters, is more difficult to predict than scour in a currents. The main issue in predicting the scour around circular files, such as undersea bridges, is the maximum scour depth and the point of occurrence. In the case of two or more adjacent circular piles, the location and depth of maximum scour according to the spacing between piles and the arrangement method show a lot of difference compared to the case of a single pile. In this paper, the KC number are calculated as dimensionless variables representing the strength of the flow. And the correlation between pile gap size and relative scour depth was analyzed.