• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.952-964
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• 1992

The interaction of natural convection and radiation heat transfer in a two dimensional square enclosure containing absorbing, emitting and linear anisotropically scattering gray medium is numerically analyzed. P-1 and P-3 approximation is introduced to calculate radiation heat transfer. The effects of scattering albedo, wall emissivity, scattering anisotropy, and optical thickness on the characteristics of the flow and temperature field and heat transfer are investigated. Temperature and velocity profiles depend a great deal on the scattering albedo, and the importance of this effect increases with decrease in albelo. Planck number is another important parameter in radiation heat transfer. The increase in scattering albedo increases convection heat transfer and decreases radiation heat transfer at hot wall. However, the increase in scattering albedo decreases both convection and radiation heat transfer at cold wall. The increase in optical thickness decreases radiation heat transfer. The scattering anisotropy has important effects on the radiation heat transfer only. The highly forward scattering leads to an increase of radiation heat transfer whereas the highly backward scattering leads to an decrease of radiation heat transfer. The effect of scattering anisotropy decreases when reducing the wall emissivity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1051-1056
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• 2014

After hot rolling, a high-temperature steel plate with a temperature higher than $800^{\circ}C$ is rapidly cooled by multiple circular water jets. In this cooling process, because the temperature of the steel plate is much higher than the boiling point of the cooling water, film-boiling heat transfer occurs and a very thin steam layer forms between the plate surface and the cooling water. The steam layer acts as a thermal resistance that prevents heat transfer between the cooling water and the steel plate. In addition to the film-boiling heat transfer, complex physical phenomena such as the free-surface flow of residual water that accumulated on the material and the material's high-speed motion also occur in the cooling process. In this study, the simultaneous cooling process of the upper and lower sides of a running hot steel strip is investigated using a three-dimensional numerical model and the cooling performances and characteristics of the upper-side cooling and lower-side cooling are compared.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2628-2634
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• 2014

Vehicle washer heater system is more widely adopted to defrost a window or to clear the windshield glass in winter season. The washer heater system should be designed to heat up washer fluid rapidly to the target temperature for only a short time. A numerical analysis has been carried out to analyze the heat transfer characteristics with materials of inside parts in vehicle washer heater system with filler and flow path. ANSYS - FLUENT software is employed for the analysis. The axial symmetry model is three-dimensional and unsteady. It applies to the coupled method which is one of pressure based. Through this result, it was obtained to find the optimal material condition for the filler and flow path in washer system. For material of filler, the air with lower density was heated more rapidly rather than silicon carbide(SiC). For material of flow path, copper with the heat transfer coefficient of approximately four times greater than the nickel gives us higher efficiency. That is the reason why the heating time of methanol was reduced to make uniform temperature in washer heater system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.4
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• pp.319-345
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• 2011

In case of tunnels in cold regions, a freeze of groundwater around tunnel may act as a barrier of tunnel drainage in winter, or may cause the inner extrusion of lining. In spite of that, a design of insulation for preventing the frost damage of tunnel lining has not been introduced in Korea, while foreign countries such as Norway and so on have a standard on insulation. In this study, a few freezing cases of road tunnels have been reviewed, and the results show that the freezing protection is necessary. In order to characterize the thermal distribution in the tunnel, following measurements have been performed at Hwa-ak tunnel; the temperature distribution by longitudinal lengths, the internal temperature of lining and the temperature distribution of the ground under pavement. From these measurements, the characteristics of the tunnel's internal temperature distribution due to temperature change in the air has been analyzed. Based on the measurement results on the temperature distribution at Hwa-ak tunnel, thermal flow tests on the rock specimen with and without insulation have been performed in the artificial climate chamber to investigate the performance of the insulation. Also, a number of 3D numerical analyses have been performed to propose appropriate insulation and insulation thicknesses for different conditions, which could prevent the frost damage of tunnel lining. As a result of the numerical analysis, air freezing index of 291$^{\circ}C{\cdot}$ Hr has been suggested as the threshold value for freezing criteria of groundwater behind the tunnel lining.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.357-366
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• 1986

The flow characteristics of two-dimensional turbulent offset jet which is discharged parallel to a solid wall has been studied experimentally and numerically. In the experiment, 3-hole pitot tube and 2 channel constant temperature hot-wire anemometer are used to measure local mean velocity, turbulence intensity and Reynolds stress while scannivalve is used to measure the wall pressure distribution. It is confirmed experimentally that local mean velocity is closely related to wall pressure distribution. It is also verified that for large Reynolds numbers and fixed step height there exists a similarity in the distribution of wall pressure coefficient. The maximum values of turbulence intensity occur in the top and bottom mixing layers and the magnitude of Reynolds stress becomes large in the lower mixing layer than in the top mixing layer due to the effect of streamline curvature and entrainment. In the numerical analysis, standard k-.epsilon. model based on eddy viscosity model and Leschziner and Rodi model based on algebraic stress model are adopted. The numerical analyses predict shorter reattachment lengths than the experiment, and this difference is judged to be due mainly to the problem of turbulence model constants and numerical algorithm. This also causes the inconsistency between the two results for other turbulence quantities in the recirculation region and impingement region, which constitutes a subject of a continued future study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.223-233
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• 2011

A ceramic monolithic catalyst is a honeycomb structure that consists of two layers. The honeycomb structure is regarded as a continuum in structure and heat-flow analysis. The equivalent mechanical properties of the honeycomb structure were determined by performing finite element analysis (FEA) for a test specimen. Bending strength experiments and FEA of the test specimen used in ASTM C1674-08 standard test were performed individually. The bonding coefficient between the cordierite ceramic layer and the washcoat layer was almost zero. The FEA test specimen was modeled on the basis of the bonding coefficient. The elastic modulus, Poisson's ratio, and the thermal properties of the ceramic monolithic substrate were determined by performing the FEA of the test specimen.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.599-607
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• 2015

In this study, we theoretically investigate the thermal performances of heat pipes that have different nano-fluid properties. Two different types of nano-particles have been used: $Al_2O_3$ and CuO. The thermal performances of the heat pipes are observed for varying nano-particle aggregations and volume fractions. Both the viscosity and the conductivity increase as the volume fraction and the aggregation increase, respectively. Increasing the volume fraction helps increase the capillary limit in the well-dispersed condition. Whereas, the capillary limit is decreased under the aggregate condition, when the volume fraction increases. The dependence of the heat pipe thermal resistance on the volume fraction, aggregation, and conductivity of the nano-particles is analyzed. The maximum thermal transfer of the heat pipe is highly dependent on the volume fraction because of the high permeability of the heat pipe. For the proposed heat pipe, the optimum volume fraction of the nano-particle can be seen through 3D graphics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.103-112
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• 1991

In this study, a numerical model was established and applied to simulate the steady-state groundwater and heat flow in an isotropic, heterogeneous, three dimensional aquifer system with uniform thermal properties and no change of state. This model was developed as an aid in screening large groundwater-flow systems as prospects for underground waste storage. Driving forces on the system are external hydrologic conditions of recharge from precipitation and fixed hydraulic head boundaries. Heat flux includes geothermal heat-flow, conduction to the land surface, advection from recharge, and advection to or from fixed-head boundaries. The model uses an iterative procedure that alternately solves the groundwater-flow and heat-flow equations, updating advective flux after solution of the groundwater-flow equation, and updating hydraulic conductivity after solution of the heat-flow equation. Dierect solution is used for each equation. Travel time is determined by particle tracking through the modeled space. Velocities within blocks are linear interpolations of velocities at block faces. Applying this model to the groundwater-flow system located in Jigyung-ri. Songla-myun, Youngil-gun. Kyungsangbuk-do, the groundwater-flow system including distribution of head, temperature and travel time and flow line, is analyzed.

• Journal of Korea Foundry Society
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• v.20 no.5
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• pp.290-299
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• 2000

A three-dimensional model was developed in order to simulate heat and fluid flow of a continuous casting billet. The model was coded with the general-purpose CFD program FIDAP, using the finite element method. The present model consists of 2 individual calculation schemes, named model 1 and model 2. Mold region only was calculated to check the pouring stream through submerged nozzle with model 1. Entire region, which consists of mold, secondary cooling, radiation cooling was calculated to predict crater end position, temperature profile and solid shell profile(model 2). Standard $k-{\bullet}\hat{A}$ turbulence model has been applied to simulate the turbulent flow induced by submerged nozzle. Enthalpy method was adopted for the latent heat of solidification. Fluid flow in mushy zone was treated using variable viscosity approach. The more casting speed and superheat increased, the more metallurgical length increased. The shell thickness at the mold exit is proved to be mainly controlled by superheat by the present simulation. It may be concluded that the present model can be successfully applied far the prediction of heat and fluid flow behavior in the continuous casting process.

• Solar Energy
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• v.14 no.2
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• pp.3-16
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• 1994

The major objectives of the study are to suggest the optimal basic design conditions for the horizontal storage tank system. For this purspose computer simulation has been carried out to find the characteristics of flow patterns in horizontal storage tank, and experiments have been carried out for the duration of one turnover, Experimental parameters are volume flow rate(1 LPM to 4 LPM), amount of heat generated from heat sources(0 W to 100 W), and inlet and outlet port types of the storage tank(DD type, DO type, ID type, IO type).