• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.656-662
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• 2006

The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

• Tribology and Lubricants
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• v.39 no.6
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• pp.250-255
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• 2023

This study applies various surface patterns to minimize material loss in construction equipment that is subject to severe wear due to sand, such as the wear-resistant steel plates of dump trucks or the teeth of excavators. The relationship between surface morphology and wear behavior is investigated using PLA+ polymer to observe the effect of the surface pattern. Five types of samples - smooth, concave, convex, wavy concave, and wavy convex designs - are created using a 3D printer. A wear experiment is conducted for a duration of 3 h using 6.5 kg of abrasive particles. The mass loss of the samples after the experiment is measured to assess the extent of wear. Additionally, the surface morphology of the samples before and after the experiment is analyzed using SEM and confocal microscopy. The study results reveal that the smooth design exhibits the highest wear loss, whereas the concave and wavy concave designs show relatively lower wear loss. The convex and wavy convex designs exhibit varying contact areas with the abrasive particles depending on the surface pattern, resulting in different levels of wear. Furthermore, a comparison between the experimental results and DEM simulations confirms the observed wear trends. This study reveals the relationship between wear damage according to surface pattern shape and is expected to be of substantial help in the analysis of wear and tear on agricultural and heavy equipment.

• Journal of Computational Design and Engineering
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• v.1 no.2
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• pp.88-95
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• 2014

Because the cost of performance testing using actual products is expensive, manufacturers use lower-cost computer-aided design simulations for this function. In this paper, we propose using hexahedral meshes, which are more accurate than tetrahedral meshes, for finite element analysis. We propose automatic hexahedral mesh generation with sharp features to precisely represent the corresponding features of a target shape. Our hexahedral mesh is generated using a voxel-based algorithm. In our previous works, we fit the surface of the voxels to the target surface using Laplacian energy minimization. We used normal vectors in the fitting to preserve sharp features. However, this method could not represent concave sharp features precisely. In this proposal, we improve our previous Laplacian energy minimization by adding a term that depends on multi-normal vectors instead of using normal vectors. Furthermore, we accentuate a convex/concave surface subset to represent concave sharp features.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1098-1103
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• 2004

In this study, the effect of channel flow in the concave surface on local heat transfer characteristics of array jets was investigated experimentally. A TLC method is employed to determine local heat transfer coefficients on the target plate and also flow visualization has been conducted to investigate the behavior of a row of impinging jets and array of impinging jets. Two different array patterns of impinging array jets devices are tested for Reynolds number(Re=10,000). In a row of impinging jets, secondary vortex is strongly maintained by main vortex at nozzle-to-plate distance of H/d=2. Therefore, the Nusselt number slowly decreased at the mid-way region between adjacent jets. In array jets, the local maximum Nusselt number region move further in the downstream direction due to the increase of channel flow velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4013-4026
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• 1996

A numerical simulation has been carried out for the jet impinging on a flat plate and a semi-circular concave surface. In this computation finite volume method was employed to solve the full Navier-Stokes equation based on a non-orthogonal coordinate with non staggered variable arrangement. The standard k-.epsilon. turbulent model and low Reynolds number k-.epsilon. model(Launder-Sharmar model) with Yap's correction were adapted. The accuracy of the numerical calculations were compared with various experimental data reported in the literature and showed good predictions of centerline velocity decay, wall pressure distribution and skin friction. For the jet impingement on a semi-circular concave surface, potential core length was calculated for two different nozzle(round edged nozzle and rectangular edged nozzle) to consider effects of the nozzle shape. The result showed that round edged nozzle had longer potential core length than rectangular edged nozzle for the same condition. Heat transfer rate along the concave surface with constant heat flux was calculated for various nozzle exit to surface distance(H/B) in the condition of same jet velocity. The maximum local Nusselt number at the stagnation point occurred at H/B = 8 where the centerline turbulent intensity had maximum value. The predicted Nusselt number showed good agreement with the experimental data at the stagnation point. However heat transfer predictions along the downstream were underestimated. This results suggest that the improved turbulence modeling is required.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.868-872
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• 1997

The thermal deformation of a workpiece during grinding is one of the most important factors that affect a flatness of a grinding surface. The heat generated in one-pass surface grinding causes the convex deformation of a workpiece. Therefore, the ground surface represents a conacve profile. In the analysis a simple model of the temperature distribution,based on the result of a finite element method, is applied. The analyzed results are compared with experimental results in surface grinding. The main results obtained are as follows; (1) The temperature distibution of a workpiece by FEM is comparatively in good agreement with the experimental results. (2) The bending moment by generated heat cause a convex deformation of the workpiece and it reads to a concave profile of the grinding surface.

• Journal of the Korean Wood Science and Technology
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• v.32 no.6
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• pp.50-56
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• 2004

This study was conducted to investigate the performance of sound absorption type-noise barriers manufactured with a combination of wood particles used for particleboard, recycled waste newspaper, and cement. An average density of wood-combined cement board was in the range from 0.83 to 0.96 g/cm³, showing relatively low-density board. Regardless of types of cement bonded board or wooden board, the board with concave holes(凹)-formed surfaces showed greater sound absorption coefficient compared to those of flat surface boards. The board density was not related with those coefficients. Accordingly, it was concluded that concave or deep corrugated surface structure has played an important role in sound absorption for the application of sound absorption type-noise barrier.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.324-333
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• 1998

Measurements of the local heat transfer coefficients on a hemispherically concave surface with a round oblique impinging jet were made. The liquid crystal transient method was used for these measurements. This method, which is a variation of the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystal for the surface temperature measurements. The Reynolds number used was 23,000 and the nozzle -to -jet distance was L/d=2, 4, 6, 8 and 10 and the jet angle was $\alpha$=0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$and 40$^{\circ}$. In the experiment, the maximum Nusselt number at all region occurred at L/d(equation omitted)6 and Nusselt number decreases as the inclined jet angle increases. For the normal jet the contours of constant Nusselt number are circular and as the jet is inclined closer and closer to the surface the contours become elliptical shape. The decreasing rate of the Nusselt number at X/d＞ 0(upstream) on a surface curvature are higher than those on a flate plate and the decreasing rate of the Nusselt number at X/d ＜0(downstream) on a surface curvature are lower than those on a flate plate. And also, the decreasing rate of local Nusselt number distribution at X/d ＜0(upstream) exhibit lower than with X/d ＜0(downstream) as jet angle increases. The second maximum Nusselt number occurred at long distance from stagnation point as jet angle increases.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.35-38
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• 2020

Airfryer is used to heat a food up by convecting hot air upward around the food. In this study, we investigated the effect of the bottom-shape of the food container in airfryer on the upward convection velocity of hot air to find an optimal bottom-shape by computational fluid dynamics. Numerical experiments were performed by solving the incompressible Navier-Stokes equations with turbulence model. We found that the maximum upward velocity with concave flow-passage on the bottom was bigger than that with the flat bottom and that the maximum upward convection velocity was achieved when the number of concave flow-passage with fan-shape is around six. The pressure drop by the internal flow was found to increase as the number of the concave flow-passage on the bottom increased probably due to increase of the surface area of the bottom. Therefore, it can be said that the optimal number of the concave flow-passage is around six for the flow rate considered in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.691-699
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• 1997

The effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds number ranges from Re=11,000 to 50,000, the nozzle-to- surface distance from L/d=2 to 10, and the surface curvature from D/d=6 to 12.The present results are also compared to those for the flat plate case. In the experiment, the local Nusselt numbers tend to increase in all regions with an increasing surface curvature. The maximum Nusselt number for all Reynolds numbers occurred at L/d .ident. 6 and a second maximum in the Nusselt number occurred at R/d .ident. 2 for both Re=23,000 and Re=50,000 in the case of L/d=2 and for Re=50,000 only in the case of L/d=4. Meanwhile, as the surface curvature increases, the value of the secondary maximum Nusselt number decreases. All the other cases exhibit monotonically decreasing values of the Nusselt number along the curved surface. The stagnation point Nusselt numbers are well correlated with Re, L/d, and D/d.