• International Journal of Fluid Machinery and Systems
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• v.8 no.4
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• pp.304-310
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• 2015

Numerical simulation was applied to investigate the Taylor vortex flow inside the concentric cylinders with a constant radial temperature gradient. The reliability of numerical simulation method was verified by the experimental results of PIV. The radial velocity and temperature distribution in plain and 12-slit model at different axial locations were compared, and the heat flux distributions along the inner cylinder wall at different work conditions were obtained. In the plain model, the average surface heat flux of inner cylinder increased with the inner cylinder rotation speed. In slit model, the slit wall significantly changed the distribution of flow field and temperature in the annulus gap, and the radial flow was strengthen obviously, which promoted the heat transfer process at the same working condition.

• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.8-15
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• 2006

The existing approximations of diffusion flux in unstructured cell-centered finite volume methods are examined in detail with each other and clarified to have indefinite expressions in several respects. A new numerical approximation of diffusion flux at cell face center is then proposed, which is second-order accurate even on irregular grids and may be easily implemented in CFD code using cell-centered finite volume method with unstructured grids composed of arbitrary convex polyhedral shape.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.369-381
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• 1992

Characteristics of flow and heat transfer have been studied numerically in a square duct with a periodic pressure gradient. The flow in a duct was assumed to be fully developed and constant heat flux was imposed at the surfaces of a square duct. The distributions of axial velocity and time-space averaged temperature are investigated with angular velocity and amplitude ratio at a given Reynolds number 1000. When the periodic pressure gradient was imposed axially in a duct, the reverse flow may be occurred near the duct wall. The magnitude of this reverse flow increases as the amplitude ratio increases or as the angular frequency decreases. In the ranges of the amplitude ratio and the angular velocity in present investigation, the ratio of the periodic time space averaged temperature to the nonperiodic space averaged temperature has been found to be greater than one. This means that the cooling effect at the duct walls deteriorates with a periodic situation compared with nonperiodic one.

• Journal of Environmental Science International
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• v.10 no.5
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• pp.329-336
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• 2001

Characgcteristics of nocturnal boundary layer(NBL) were analyzed by the upper-air observations data using with the airsonde and pilot balloons from 1994 to 1999 in Kyungpook province. The automate weather boundary layer can become stably stratified when the surface is cooler than the air. Stable nocturnal boundary layer height were estimated from the top of surface stable layer where the vertical gradient of temperature and mixing ratio tend to zero or negative. The depth of the stable nocturnal boundary layer depended largely on the thermal effect rather than the wind effect at nighttime. The NBL was more developed on the land than on the coastal region. The stability index (bulk Richardson number) showed that the NBL was stable when the wind was weak and the vertical gradient of the temperature was strong. The heat budget in the NBL was studied by considering the effect of the radiative and the cooled by both the longwave radiative flux and the divergence of the heat flux, while NBL under the cloudy sky the longwave radiative flux played a role of the warming. It was noted that the heat was not conserved in both cases. To complete the heat budget in the NBL the warming/cooling by advection and subsidence must be considered.

• Journal of applied mathematics & informatics
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• v.32 no.5_6
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• pp.761-781
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• 2014

An exponentially accurate nonconforming spectral element method for elasticity systems with discontinuities in the coefficients and the flux across the interface is proposed in this paper. The method is least-squares spectral element method. The jump in the flux across the interface is incorporated (in appropriate Sobolev norm) in the functional to be minimized. The interface is resolved exactly using blending elements. The solution is obtained by the preconditioned conjugate gradient method. The numerical solution for different examples with discontinuous coefficients and non-homogeneous jump in the flux across the interface are presented to show the efficiency of the proposed method.

• Journal of Korea Water Resources Association
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• v.46 no.2
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• pp.139-153
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• 2013

For analyzing shallow-water flows over the uneven bottom, the HLLL scheme and the divergence form for bed slope source term (DFB) technique, respectively were applied to the flux gradient and the bottom gradient source terms in a finite-volume model for the shallow water equations. And also the model incorporated the volume/free-surface relationship (VFR) to consider the partially submerged cells (PSC). It was identified that a simpler version of the weighted surface-depth gradient method in the MUSCL was equivalent to the original one in the accuracy for 1D steady flows. It was verified that the flux gradient term and the bottom gradient source term were well-balanced exactly by the VFR for the 1D PSC. The VFR for the triangular PSC settled the problem which the governing equations were not well-balanced by the DFB technique for the 2D PSC. There were good agreements in simulations and experiments for 2D dam-break flows over a triangular sill and a round bump. In addition, the partial dam-break flow was successfully simulated for flooding of roughnesses in an irregular bottom as well as a sloping one. Therefore, this model is expected to be applied to the real river with uneven topography.

• KSBB Journal
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• v.14 no.2
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• pp.230-234
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• 1999

To improve the crossflow untrafiltration flux, we applied periodic oscillations in transmembrane pressure gradient in order to promote fluid turbulence by inducing repeated compression and relaxation of the cake/gel layer. The oscillatory forms used were square-, sine-, triangle-wave, and pumping interruption. The permeate flux profiles were mathematically simulated and compared with the experimental data. The result showed the periodic pumping interruption most effectively improved the overall flux by up to about 32%. Enough pumping off-time, at least on the order of tens of seconds, was needed to allow the solutes in the layer to diffuse back to the bulk phase. It was better to start the oscillations earlier before the layer was fully established. The square-wave oscillation yielded about 11% increase, which was particularly pronounced in the later part of the filtration. Either the amplitude or the period of the oscillations resulted little influence on flux.actate ester, and lactate ester produced in esterification reaction was distilled simultaneously with hydrolysis reaction into lactic acid. When the yields of lactic acid recovered by batch reactive distillations with various alcohols were compared, the yield of lactic acid was increased as the volatility of lactate ester was increased. In this batch reactive distillation, because the mixtures condensed in partial condensor were flown to reboiler through distillation column, the recovery yield of lactic acid was affected by operation temperature of partial condensor. Hydrolysis reaction into lactic acid in distillation column rarelyoccurred because of short retention time of lactate ester and water. Lactate ester was reacted into lactic acid in reboiler.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.19-33
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• 2024

In nuclear thermal-hydraulic system codes, most correlations used for vertical pipes, under downward two-phase flow, have been developed considering small pipes or pool systems. This suggests that there could be uncertainties in applying the correlations to accident scenarios involving large vertical pipes owing to the difference in the characteristics of two-phase flows, or flow conditions, between large and small pipes. In this study, we modified the Multi-dimensional Analysis of Reactor Safety KINS Standard (MARS-KS) code using correlations, such as the drift-flux model and two-phase multiplier, developed in a plant-scale air-inflow experiment conducted for a pipe of diameter 600 mm under downward two-phase flow. The results were then analyzed and compared with those based on previous correlations developed for small pipes and pool conditions. The modified code indicated a good estimation performance in two plant-scale experiments with large pipes. For the siphon-breaking experiment, the maximum errors in water flow for modified and original codes were 2.2% and 30.3%, respectively. For the air-inflow accident experiment, the original code could not predict the trend of frictional pressure gradient in two-phase flow as / increased, while the modified MARS-KS code showed a good estimation performance of the gradient with maximum error of 3.5%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.61-68
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• 2003

This study deals with the use of the conjugate gradient method for the simultaneous estimation of two unknown boundary heat fluxes on the slab in reheating furnace. Temperature measurements by the experiment are used in the inverse analysis. The heat flux estimations for three different cases of measurement locations in the slab are performed: non-skid, skid, and shift-skid zones. The estimated heat fluxes for three cases indicated the three regions having local peak values of heat fluxes. The estimated temperatures at measurement locations were in good agreements with the measured temperatures within 5% relative error.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.3046-3056
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• 1994

To design and develop a turbocharged engine, it needs that many studies must be preceded about the characteristics of engine performance and thermal flow. To accomplish this purpose, turbocharger was equipped to 1.3 liter naturally aspirated gasoline engine. The temperature probe of plate type was designed and it was installed into the combustion chamber wall to measure unsteady temperature. The unsteady heat flux at combustion chamber wall was evaluated using one dimensional unsteady conduction equation with the wall temperature and temperature gradient.