• Polymer(Korea)
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• v.25 no.6
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• pp.855-865
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• 2001

The optimization condition of injection molding for a commercial product of TV speaker grille of A Company was induced using a CAE software of Moldflow. The flow and packing phase analysis was performed by using flow balance, runner balance, and the intermediate one by using the above two balances, which were used for controlling the amount of packing resins into the cavity, Later, the analysis performed by using the measured viscosity (local database) at various shear rates and the results were compared with the computer simulation using the standard database. Flow balance induced minimized weld line resulted in a better appearance and physical properties of the were line, but exhibited a disadvantage of large deformation and gas formation due to over-packing of the molten resin in the center of the speaker grille. Runner balance improved the disadvantage of the flow balance by controlling the amount of molten resin injected from the gate, however resulted reduced mechanical properties and poor appearance of the weld line. However, the modified method induced from the flow and runner balance improved the disadvantages by changing the runner size. In addition, the analyses based on the local database and the standard database were compared. Although the measured viscosity was slightly higher and the temperature distribution was broader than the standard database, no distinct difference was obtained from the analysis using the two different databases.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2042-2052
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• 2003

An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000∼70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.3
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• pp.655-663
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• 2024

In order to meet the technological demand for indoor heating systems that ensure winter thermal comfort during the transition from internal combustion engines to electrification, a localized proximity heating module using surface heating elements was developed. The operational performance of heating module was tested in the low temperature chamber. The experiment conditions were varied by changing the chamber temperature (-10, 0℃), the air flow rate (6.2, 6.0, 4.2m³/h), the heater power (100, 80, 60, 40W). Thermal comfort model was confirmed using the CBE Thermal Comfort Tool applying ASHRAE standard 55. Under -10℃ condition, thermal comfort was satisfied at 23.4, 23.2℃ at power of 100W and air flow rate 6.0, 4.6m³/h. Under 0℃ condition, at power of 80W, air flow rate 6.2, 6.0m³/h, and at power of 60W, air flow rate 4.6m³/h showed results of 25.7, 26.1, 23.0℃, respectively, satisfying thermal comfort. This study analyzed the operating performance of the local proximity heating module in the low temperature chamber and applied thermal comfort model to prove applicability of local proximity heating module using surface heating elements and how to utilize the thermal comfort model.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.149-156
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• 2016

The hypersonic flow on the stagnation streamline of a blunt body is analyzed with quasi one-dimensional (1-D) Navier-Stokes equations approximated by adopting the local similarity to the two-dimensional (2-D)/axisymmetric Navier-Stokes equations. The governing equations are solved using the implicit finite volume method. The computational domain is confined from the stagnation point to the shock wave, and the shock fitting method is used to find the shock position. We propose a boundary condition at the shock, which employs the shock wave angle in the vicinity of the stagnation streamline using the shock shape correlation. As a result of numerical computation conducted for the hypersonic flow over a sphere, the proposed boundary condition is shown to improve the accuracy of the prediction of the shock standoff distance. The quasi 1-D Navier-Stokes code is efficient in computing time and is reliable for the flow analysis along the stagnation streamline and the prediction of heat flux at the stagnation point in the hypersonic blunt body flow.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.30-36
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• 2005

This paper reports the experimental study of the heat transfer characteristics of the wake region behind a cylinder in cross flow. Local heat transfer coefficient was measured from the stagnation point (θ=0°) to 180°, and the variation of Nu in the axial direction along the cylinder was also studied. The results show that the heft transfer rate at the rear (θ=180°) near the duct wall can increase as much as 58% over the 2 dimensional value at the center of the duct. The heat transfer profiles in the wake region also show distinct effects of the aspect ratio and the heat transfer boundary condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.523-534
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• 1998

The convection heat transfer on horizontal circular tube is studied as a conjugated heat transfer problem. With uniform heat generation in a cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer are investigated for the case of forced convection around horizontal circular tube in cross flow of air and water. Non-dimensional conjugation parameter $ K^*$ which can be deduced from the governing energy differential equation should be used to express the effect of circumferential wall heat conduction. Two-dimensional temperature distribution$ T({\gamma,\theta})$ is presented. The influence of circumferential wall heat conduction is demonstrated on graph of local Nusselt number.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.39-45
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• 2001

With uniform heat generation from the inner surface of the cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer is investigated for the case of forced convection around horizontal circular tube in cross flow of air. The wall conduction number which can be deduced from the governing energy equation should be used to express the effect of circumferential wall heat conduction. It is demonstrated that the circumferential wall heat conduction influences local Nusselt numbers of one-dimensional and two-dimensional solutions.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.667-676
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• 2005

In this research, the reasonable local scour estimates considered conditions of the bed material and the flow was accomplished on two piers P14 and P17 of Il-san bridge. Especially, the Il-san bridge was located on the lower Han-river where is influenced by the tides of In-chon, and it has hydraulic condition that can cause the bridge piers local scour because of tides at ordinary times, as well as a flood. Therefore, the local scour depth has been presented influenced by the maximum velocity of the flow when a flood after construction and the tides on construction on the basis of the standards of river design and road design, furthermore, the results was made a comparative analysis. According to the results, the local scour depth on the basis of the standards of river design was higher than it on the basis of the standards of road design(SRICOS), and the local scour depth influenced by the maximum velocity of the flow when a flood after construction was determined the final local scour depth of P14 and P17 at the Il-san bridge. It was ascertained that the local scour depth did not exceed the inserted depth of bridge foundation.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.363-369
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• 2002

Orifice meter is the most widely used flowmeter in custody transfer between KOGAS and city gas companies. Absolute pressure value is needed to calculate the gas flow of orifice metering system, but the gauge pressure transmitters are mainly used in the field. In case that the gauge pressure transmitters are used, the fixed value as standard atmospheric pressure(101.325kPa) is applied for the absolute pressure value. The real, local atmospheric pressures of each metering station are different from the standard condition as the altitude and weather conditions. In this study the flow calculation errors were quantitatively analyzed through examining the atmospheric pressures of 50 stations of KOGAS. The data for analysis are such like the time data of supplied gas amount, the altitude of each metering station, the time data of atmospheric pressures and altitudes of each weather observatory. The results showed that the local atmospheric pressures were different from the standard value and the gas flow calculation errors were distributed between $-0.024\%{\~}0.025\%$ based on the supplied gas amount in the year 1999 and 2000.

• Ocean Systems Engineering
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• v.11 no.1
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• pp.43-58
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• 2021

In the present work, a 3D numerical model is proposed to study local scouring around single vertical piers with different cross-section shapes under steady-current flow. The model solves the flow field and sediment transport processes using a coupled approach. The flow field is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in combination with the k-ω SST turbulence closure model and the sediment transport is considered using both bedload and suspended load models. The proposed model is validated against the empirical measurements of local scour around single vertical piers with circular, square, and diamond cross-section shapes obtained from the literature. The measurement of scour depth in equilibrium condition for the simulations reveal the differences of 4.6%, 6.7% and 13.1% from the experimental measurements for the circular, square, and diamond pier cases, respectively. The model displayed a remarkable performance in the prediction of scour around circular and square piers where horseshoe vortices (HSVs) have a leading impact on scour progression. On the other hand, the maximum deviation was found in the case of the diamond pier where HSVs are weak and have minimum impact on the formation of local scour. Overall, the results confirm that the prediction capability of the present model is almost independent of the strength of the formed HSVs and pier cross-section shapes.