• Proceedings of the KSME Conference
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• 2001.11a
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• pp.766-771
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• 2001

Gas-assisted injection molding is an innovative low-pressure injection molding technique that can provide numerous benefits such as reduced part warpage, excellent surface quality without sink marks, low injection pressure, and greater design flexibility. However, the adoption of gas-assisted injection molding may cause unexpected defects if the gas channel design is not conducted properly. The objective of this paper is to broaden the understanding of gas-assisted injection molding by summarizing the design procedures and experimental results of the gas-assisted injection molding of a 17" flat monitor front cover. The gas channels were designed by using Moldflow(MF/GAS) simulations and a 450 ton injection molding machine with a 5 stage pressure control gas kit was used in the experiments.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.839-842
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• 2002

Some open jet wind tunnels have been operating under limitations due to large pressure fluctuations at some wind tunnel speeds. The Hyundai Aero-acoustic full scale Wind Tunnel (HAWT), which was completed in 1999, shows that most of the specifications were fulfilled but wind tunnel pulsations at some wind speeds were observed. Hyundai Motor Company started the wind tunnel modification in order to solve this problem in 2001. After the modification work the amplitude of pressure fluctuation was reduced and below required level over full wind speed range. Aero-acoustic performance, e.g. background noise, as well as aerodynamic performance were improved after this work.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1999-2011
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• 1995

Computer simulation was conducted to study performance characteristics of air-cooled condenser of a double effect absorption heat pump with variations of saturation pressures and mass flow rates of the refrigerant ; volume flow rates, relative humidities and temperatures of the air The vertically installed condenser had the staggered tube array with continuous plate fins of wavy type. When the saturation pressure of the condenser was decreased from 760 torr to 20 torr, heat transfer rates and condensing rates of refrigerant were decreased. If excess refrigerant flows in the condenser, the pressure and saturation temperature of the condenser were increased which makes the refrigerating capacity of an absorption heat pump reduced.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.688-692
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• 2001

Three-dimensional experimental analyses were conducted in the pulverizer simplified isothermal model. The experimental model was constructed on a 1/3.5 scale of 500MW pulverized coal boiler. The purpose of this study is to investigate the characteristics of coal particle separator and the pressure loss in the pulverizer models with dynamic classifier. Without regards a shape of separator top, the results showed that the increase of dynamic classifier rpm was induced in finer coal particle. But the capacity of total mass per minute was reduced. Also, the increase of dynamic classifier rpm had no effect on total pressure loss, but an increase of inlet velocity was induced that the rise of total pressure loss in the pulverizer models with dynamic classifier.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.382-389
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• 2000

The purpose of present study is to investigate for reducing pressure fluctuations in tile case of installing tile air-shafts on the side wall of the tunnel with small cross-sectional area on conventional line. Experiments were performed with a 1/61-scale moving model rig for the tunnel of 0.764km length in the condition of tunnel cross-section area of 28 ㎡ According to the results, the maximum pressure fluctuation is reduced by 45% for 19 air-shafts. This results have the speed-up effects of about 33.4km/h for the train running in tunnel.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1166-1171
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• 2009

Fin-tube heat exchangers are widely used in refrigeration systems. To improve the performance of fin-tube heat exchangers, the shape of plain fin was developed in slit fin and louver fin. These pins have higher heat transfer performance as well as larger pressure drop. Recent studies of a delta winglet vortex generators(DWVG) show less heat transfer capacity than louver fin. However, the DWVG have very small pressure drop. This paper compares the performance for the plain fin and DWVG fin in terms of flow characteristics and heat transfer based on CFD analyses. The DWVG generate vortex and delayed flow separation and leads to a reduction of a wake region behind a tube. The results show that the DWVG produce improved heat transfer and reduced pressure drop compared to a plain fin. This result is opposite to the Reynolds analogy.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.598-603
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• 1996

When locked rotor event. occurs, instantaneously affected loop and core flow were quickly reduced, which resulted in an increase in coolant temperature and system pressure. Analysis method of this event was that constant core inlet temperature and system pressure as well as change in core flow calculated from COAST code were statically used as an input variable to HERMITE code, because of no tools to simulate NSSS behavior and 1-D core neutronics transient coincidently. With employing TASS code revised with 1-D neutronics model, this event was analyzed in point of DNBR. By doing so, analysis procedure could be simplified and unreasonable conservatism might be removed in DNBR calculation by consideration of pressure increase.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.11 no.1
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• pp.31-39
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• 2007

A pedagogic model for blood flow is introduced to help medicine majors understand a simplified version of Navier-Stokes equations which is known to be a good tool for interpreting the phenomena in blood flow. The pressure gradient consists of a time-independent part known as Hagen-Poiseuille's gradient and a time-dependent part known as Sexl's, and the model formula for the volume rate of blood flow is reduced to a very simple form. For demonstration, the blood rate in human aorta system is analyzed in connection with the time-dependence of pressure gradient. It is shown for Sexl's part that the flow rate lags the pressure gradient by ${\pi}/2$, which is thought to be due to the relaxation process involved.

• 연구논문집
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• s.32
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• pp.15-22
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• 2002

In offset or intaglio printing machine, it's operated with combination of blanket cylinder and impression cylinder. The blanket cylinder has some number of grooves to attach the blanket on surface. In case of operating the printing machine, it has generate mechanical impact noise when the two cylinders encounter with the grooves. So, in this study, we developed a printing pressure control algorithm with hydraulic servo control system. We also proposed simulation model of experimental device to analysis the throw on force response of hydraulic servo actuator. Finally, we have reduced the mechanical impact noise and improved printing quality with a groove detecting signal and PI control of hydraulic servo actuator.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.528-533
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• 2005

This paper presents the study of flows at T-junction pipe with orifices. Experiments were carried out for several flow rates, orifice sizes, and pressure differences. Numerical simulations were also done to get more data for the wide range of flow rates. Experimental results and numerical ones are in a good agreement. Due to the effect of T-junction part, the flow rates at the lateral pipe are greater than those at straight pipe for the same pressure differences. When orifices were added, the effects of T-junction part on the ratio of flow rates and the ratio of loss coefficients reduced.