• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.567-576
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• 1999

An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

• Solar Energy
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• v.15 no.1
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• pp.53-71
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• 1995

Experiments have been conducted on a planar, free surface jet of water to investigate the effects of aspect ratios(AR=6.67, 15, 26.67), average nozzle velocity($V_0=3.3m/s{\sim}78m/s$) and nozzle-to-plate spacings($Z/W=6{\sim}40$) on the characteristics of heat transfer, when 3 rectangular waterjets impinging on a flat plate which has the uniform heat flux. the scondary peaks which produced by circular jets also produced by rectangular water jets. The position of the scondary peaks depends upon the aspect ratio of nozzle. The heat transfer coefficient was subjected to the influence of aspect ratio. The heat transfer correlations and best position of nozzles which produced maximum heat transfer coefficient at stagnation point are provided.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.6
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• pp.272-280
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• 2021

The influence of acetylene flow rates on the carburizing behavior of an AISI 4115 steel in 1 ton-class mass production-type vacuum carburizing furnace has been studied through microstructure, carbon concentration, hardness analyses. The AISI 4115 steels were carburized with various flow rates (20, 32.7, 60 l/min) and locations in the furnace (top, center, bottom) at 950℃. The acetylene flow rate played an important role in controlling the carburizing properties of carburized samples, such as effective case depth and uniformity carburizing according to location in the furnace. At an acetylene flow rate of 20 l/min, the carburized samples had a shallow average hardened layer (0.645 mm) compared to the target hardening depth (1 mm) due to low carbon flux and spatial uniformity of carburization (17.8%) in the furnace. At a flow rate of 60 l/min, the carburized samples showed an average hardened layer (1.449 mm) deeper than the target hardening depth and had the spatial uniformity of carburization (98.8%). In particular, at a flow rate of 32.7 l/min, the carburized samples had an average hardened layer (1.13 mm) close to the target hardening depth and had the highest carburizing uniformity (99.1%). As a result, an appropriate flow rate of 32.7 l/min was derived to satisfy the target hardening depth and to have spatial uniform hardened layer in the furnace.

• Journal of Environmental Science International
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• v.1 no.2
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• pp.119-124
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• 1992

Cloud streets were successfully simulated by numerical model (RAMS) including an Isolated mountain near the coast, large sensible heat flux from the sea surface, uniform stratification and wind velocity with low Froude number (0.25) in the inflow boundary The well developed cloud streets between a pair of convective rolls are simulated at a level of 1 km over the sea. The following five results were obtained: 1) port the formation of the pair of convective rolls, both strong static instability and a topographically induced mechanical disturbance are strongly required at the same time. 2) Strong sensible heat flux from the sea surface is the main energy source of the pair of convective rolls, and the buoyancy caused by condensation in the cloud is negligibly small. 3) The pair o( convective rolls is a complex of two sub-rolls. One is the outer roll, which has a large radius, but weak circulation, and the other is the inner roll, which has a small radius, but strong circulation. The outer roll gathers a large amount of moisture by convergence in the lower marine boundary, and the inner roll transfers the convergent moisture to the upper boundary layer by strong upward motion between them. 4) The pair of inner rolls form the line-shaped cloud streets, and keep them narrow along the center-line of the domain. 5) Both by non-hydrostatic and by hydrostatic assumptions, cloud streets can be simulated. In our case, non-hydrostatic processes enhanced somewhat the formation of cloud streets. The horizontal size of the topography does not seem to be restricted to within the small scale where non-hydrostatic effects are important.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.99-104
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• 2001

Thermally induced vibration response of solar array is investigated. The solar array model consists of composite thin walled beam and solar blanket, spreader bar. The composite thin walled beam incorporates a number of nonclassical effects of transverse shear, primary and secondary warping, rotary inertia and anisotropy of constituent materials. The solar blanket is a membrane subjected to uniform tension in the z direction. The spreader bar is a rigid member. A coupled thermal structure analysis that includes the effects of structural deformations on heating and temperature gradient is investigated. A stability criterion given in parameters for establishes the conditions for thermal flutter.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.399-406
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• 2001

Thermally induced vibration response of composite thin walled beams is investigated. The thin-walled beam model incorporates a number of nonclassical effects of transverse shear, primary and secondary warping, rotary inertia and anisotropy of constituent materials. Thermally induced vibration response characteristics of a composite thin walled beam exhibiting the circumferentially uniform system(CUS) configuration are exploited in connection with the structural bending-torsion coupling resulting from directional properties of fiber reinforced composite materials and from ply stacking sequence. A coupled thermal structure analysis that includes the effects of structural deformations on heating and temperature gradient is investigated.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1195-1202
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• 2004

In this paper an experimental study was investigated for two-phase flow distribution in compact heat exchanger header. A test section was consisted of the horizontal bottom dividing header($\phi$: 5 mm, L: 80 mm) and 10 upward circular mini channels ($\phi$: 1.5 mm, L: 850 mm) using an acrylic tube. Three different types of tube intrusion depth were tested for the mass flux and inlet mass quality ranges of 50 - 200 kg/$m^2$s and 0.1 - 0.3, respectively. Air and water were used as the test fluids. The distribution of vapor and liquid is obtained by measurement of the total mass flow rate and the calculation of the quality. Two-phase flow pattern was observed, and pressure drop of each channel was measured. By adjusting the intrusion depth of each channel an uniform liquid flow distribution through the each channel was able to solve the mal-distribution problem.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1120-1132
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• 2003

A problem of a circular elastic inhomogeneity interacting with a crack under uniform loadings (mechanical tension and heat flux at infinity) is solved. The singular. integral equations for edge and temperature dislocation distribution functions are constructed and solved numeric-ally, to obtain the stress intensity factors. The effects of the material property ratio on the stress intensity factor (SIF) are investigated. The computed SIFs are used to predict the kink angle of the crack when the crack grows.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.4
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• pp.33-41
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• 2008

The prelaunch thermal transients in the cryogenic oxidizer tank of liquid propulsion rocket subjected to uniform heat flux from outside are numerically analyzed through thermodynamic equations and heat and mass transfer relations. The prelaunch stage is assumed to be composed of five idealized sub-stages including pressurization process by helium gas injection. The Peng-Robinson equation of state is utilized in the lumped analysis of ullage gas. The liquid region is divided into a number of horizontal layers of uniform properties to account for the thermal stratification. The computational result for the typical case shows that the temperature rise of liquid oxidizer is less than 1K and the adsorbed helium into the liquid is approximately 10g.

• Steel and Composite Structures
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• v.38 no.2
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• pp.189-211
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• 2021

An analytical solution is presented to analyze the thermoelastoplastic response of a rotating thick-walled cylindrical pressure vessel made of functionally graded material (FGM). The analysis is based on Tresca's yield condition, its associated flow rule and linear strain hardening material behaviour. The uncoupled theory of thermoelasticity is used, and the plane strain condition is assumed. The material properties except for Poisson's ratio, are assumed to vary nonlinearly in the radial direction. Elastic, partially plastic, fully plastic, and residual stress states are investigated. The heat conduction equation for the one-dimensional problem in cylindrical coordinates is used to obtain temperature distribution in the vessel. It is assumed that the inner surface is exposed to an airstream and that the outer surface is exposed to a uniform heat flux. Tresca's yield criterion and its associated flow rule are used to formulate six different plastic regions for a linearly hardening condition. All these stages are studied in detail. It is shown that the thermoelastoplastic stress response of a rotating FGM pressure vessel is affected significantly by the nonhomogeneity of the material and temperature gradient. The results are validated with those of other researchers for appropriate values of the system parameters and excellent agreement is observed.