• Transactions of the Korean Society of Automotive Engineers
• /
• v.14 no.1
• /
• pp.129-137
• /
• 2006

This paper studies the effects of the swirl for the variation of intake port configuration that is key parameters in the flow field of direct injection diesel engines. In-cylinder flow characteristics is known to have significant effects on air-fuel mixing, combustion, and emissions. To investigate the effects of the swirl flow, various rpm(250, 500, 750) and two different intake port were used. And to evaluate the swirl motion in the flow field visualization engine, steady state flow test was conducted. Helical port intake port and SCV(Swirl Control Valve) were selected as the design parameters to increase the swirl flow and parametric study was performed. In the case of non-SCV, intake flow rate and non-dimensional swirl ratio were higher than those of SCV for the swirl head type. So, we could strengthen the swirl in the flow field with the swirl head type and don't using SCV. From the results of steady state flow test, non-swirl head type has the most good advantage for intake flow rate, and also the flow rate could be increased by using the SCV slightly. The effects of the type of engine head on intake air flow capability are dominant with respect to the existence of the SCV. We could measure the qualitative grade of swirl by capturing the scattering signal of microballoon from ICCD camera in the visualization diesel engine.

• Advances in pediatric surgery
• /
• v.8 no.1
• /
• pp.28-32
• /
• 2002

Meckel's diverticulum (MD) occurs in approximately 2 % of the population. The major complications of MD are bleeding, intestinal obstruction, infection and perforation. Perforation is the least common but most serious complication, the incidence od which is about 5-10 %. The causes of perforation are inflammatory diverticulitis and peptie ulceration. the purpose of study is to review the characteristics of perforated MD in children. Six patients with perforated MD who had been operated upon at the Department of Pediatric Surgery, Yeungnam University Hospital from April 1984 to July 2001 were included. Male predominated in a ratio of 5:1 and there were 2 neonates. The chief complaints were abdominal pain and distension. Half of the children showed a past history of bloody stools. The average age was 4 year and 9 months. The mean distance from the ileocecal valve to the diverticulum was 60 cm. Average length of the diverticulum was approximately 3 cm and width was 1.7 cm. The perforation site was the tip of the diverticulum in 3 cases, the base in 2 cases and along the lateral border in one. In two patients, ectopic gastric mucosa was found in the specimen. All of the patients were operated upon with a diagnosis of peritonitis of unknown etiology. In conclusion, when a child shows symptoms of acute abdomen or peritonitis, especially in boys, with the history of bloody stools and episodic abdominal pain, perforated MD should be suspected.

• Journal of ILASS-Korea
• /
• v.8 no.2
• /
• pp.1-6
• /
• 2003

The liquid phase LPG injection (LPLI) system (the third generation technology) has been considered as one of the next generation fuel supply systems for LPG vehicles, since it has a very strong potential to accomplish the higher power, higher efficiency, and lower emission characteristics than the mixer type(the second generation technology) fuel supply system However. when a liquid LPG fuel is injected into the inlet duct of an engine, a large quantity of heat is extracted due to evaporation of fuel. This leads to freezing of the moisture in the air around the outlet of a nozzle, which is called icing phenomenon. It may cause damage to the outlet nozzle of an injector or inlet valve seat. In this work, the experimental investigation of the icing phenomenon was carried out The results showed that the icing phenomenon and process were mainly affected by humidity of inlet air instead of air temperature in the inlet duel. Also, it was observed that the total ice formed around the nozzle weighs at about $150mg{\sim}260mg$ after injection for ten minutes. And some fuel species were found in the ice attached at the front side of a nozzle, while frozen ice attached at the back of a nozzle was mostly' consisted of moisture of inlet air. Therefore, some frozen ice deposit. detached from front nozzle of an injector, may cause a problem of unfavorable air fuel ratio control in the small LPLI engine.

• Journal of the Korean Magnetics Society
• /
• v.15 no.2
• /
• pp.61-66
• /
• 2005

In order to make submicron cell for spin-injection device, lift-off method using Pt stencil and wet etching was chosen. This approach allows batch fabrication of stencil substrate with electron-beam lithography. It simplifies the process between magnetic film stack deposition and final device testing, thus enabling rapid turnaround in sample fabrication. Submicron junctions with size of $200nm{\times}300nm$ and $500nm{\times}500nm$ 500 nm and pseudo spin valve structure of $CoFe(30{\AA})/Cu(100{\AA})/CoFe(120{\AA}$) was deposited into the nanojunctions. MR ratio was 0.8 and $1.1{\%}$, respectively and spin transfer effect was confirmed with critical current of $7.65{\times}10^7A/cm^2$.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.2
• /
• pp.79-85
• /
• 2007

An internal ballistic model to predict the performance of a Polyethylene-GOX (PE-GOX) hybrid motor was proposed and evaluated. A theoretical treatment of the model was followed by detail discussion of each of the factors affecting the overall performance. The present model consists of the governing equations by considering the unsteady burn-back rate of the fuel grain and on-off response characteristics of a oxygen-supply valve. The numerical results using the 4th order Runge-Kutta scheme with temporal physicochemical properties showed good agreements with test results and the global effects of the performance parameters, such as the burning area of the fuel grain, O/F ratio, and etc., on the performance of the motor were analyzed.

• Journal of Welding and Joining
• /
• v.25 no.5
• /
• pp.58-63
• /
• 2007

The relationship between GMA welding conditions and the bead shape of overlay weld was studied by using ${\Phi}1.6mm$ hypo-eutectic metal-cored wire designed for hardfacing against the severe metal-to-metal wear. As the welding voltage increased, the dilution also increased but the sudden drop of dilution was observed at $30{\sim}33V$. It was considered to be due to the decrease of penetration resulting from the change of transfer mode, from short circuit to spray. It was also found that the behavior of penetration with welding current was dependant on the transfer mode. The short circuit mode exerted the penetration to decrease while the spray mode did it to increase with increase of welding current. The former was considered to be responsible for the remarkable decrease in dilution at low welding voltage region. The change of transfer mode also had an effect on the behavior of bead width with welding current but it did not on the bead spreadability defined as W/H ratio. It was considered that the optimal welding conditions for multi-pass overlay welding could be obtained from the bead spreadability suitable for bead lapping and the dilution as low as possible in the spray transfer mode.

• Journal of Korean Society of Water and Wastewater
• /
• v.29 no.3
• /
• pp.395-406
• /
• 2015

This research carried out an analysis on input cost and leakage reduction effect by leakage reduction method, focusing on the project for establishing an optimal water pipe network management system in the Taebaek region, which has been executed annually since 2009. Based on the result, optimal cost-benefit analysis models for water distribution network rehabilitation project were developed using DEA(data envelopment analysis) and multiple regression analysis, which have been widely utilized for efficiency analysis in public and other projects. DEA and multiple regression analysis were carried out by applying 4 analytical methods involving different ratios and costs. The result showed that the models involving the analytical methods 2 and 4 were of low significance (which therefore were excluded), and only the models involving the analytical methods 1 and 3 were suitable. From the result it was judged that the leakage management method to be executed with the highest priority for the improvement of revenue water ratio was installation of pressure reduction valve, followed by replacement of water distribution pipe, replacement of water supply pipe, and then leakage detection and repair; and that the execution of leakage management methods in this order would be most economical. In addition, replacement of water meter was also shown to be necessary in case there were a large number of defective water meters.

• Journal of the Korean Magnetics Society
• /
• v.18 no.6
• /
• pp.227-231
• /
• 2008

Magnetic and structural properties of CoFeZr alloy films as a function of Zr concentration and magnetoresistive properties of spin valves incorporated with amorphous CoFeZr alloy films have been studied. Magnetization and coercivity of CoFeZr alloy films decreased as the Zr content increased. A single amorphous CoFeZr phase was formed when the Zr content is about above 18 at%. Magnetoresistance ratio and exchange coupling field of spin valves with amorphous CoFeZr were reduced slightly as compared with spin valves with CoFe because the resistance of amophous CoFeZr is higher than that of crystalline CoFe. However, the ${\Delta}{\rho}$ of spin valves with amorphous CoFeZr was improved due to reduction of current shunting.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.4
• /
• pp.299-305
• /
• 2017

Re-engineering is gaining attention due to severe environmental pollution and economic crisis. Although re-engineering in shipbuilding has been carried out steadily, technological advancements, domestic ship repair and maintenance industries are not as prevalent as shipbuilding industries. In order to solve this problems, laser cladding can significantly aid with technical development. Laser cladding produces an outstanding clad layer with minimal dilution and little porosity. In this study, prior to applying laser cladding to an exhaust valve face, the effects of various parameters that affect the characteristics of the 1 pass clad layer were investigated. When laser power was increased, the clad layer width became broader and the height was decreased. In addition, it was identified that the hardness of the clad layer was inversely proportional to the power, and the entire clad layer was diluted through an EDS chemical composition analysis.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.2
• /
• pp.1032-1037
• /
• 2011

In this study, simulation and optimization works for a demethanizer column have been performed to obtain ethane and heavier products from a pretreated natural gas stream. Pretreated natural gas feed stream was partially condensed after being precooled by exchanging heat with demethanizer top vapor stream and by using an external refrigeration cycle with a propane refrigerant. Vapor stream was cooled further and partially condensed through a turbo-expander. The power generated from the expansion of turbo-expander was delivered to the compressor for the residue gas compression. Liquid stream was cooled by Joule-Thomson expansion valve and was fed to the middle section of the demethanizer. Recovery percent of ethane for feed natural was set to 80% and methane to ethane molar ratio was fixed as 0.0119. On the other hand, some of the cold heat could be recovered by splitting the feed stream and by exchanging heat with side reboiler in order to reduce the heat duty in the propane refrigeration cycle.