• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.2
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• pp.93-103
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• 1981

It is well-known that nowadays heat resisting and anti-corrosive materials have been widely used as the components materials of gas turbines, nuclear power plants and engines etc. In the fields of machine production industry. And materials for engine components, like as the exhaust valve of internal combustion engine, have been required to operate under the high temperature range of $700^{\circ}C$-$800^{\circ}C$ and high pressured gas with repeated mechanical load for the high performance of engines. For these components, friction welding for bonding of dissimilar steels can be applied for in order to obtain process shortening, production cost reduction and excellent bonding quality. And age hardening recently has been noticed to the heat resisting materials for further strengthening of high temperature strength, especially high temperature fatigue strength. However, it is difficult to find out any report concerning the effects of age hardening for strengthening high temperature fatigue strength to the Friction welded heat resisting and anti-corrosive materials. In this study the experiment was carried out as the high temperature rotary bending fatigue testing under the condition of $700^{\circ}C$ high temperature to the friction welded domestic heat resisting steels, SUH3-SUS303, which were 10hr., 100hr. aging heat treated at $700^{\circ}C$ after solution treatment 1hr. at $1, 060^{\circ}C$ for the purpose of observing the effects of the high temperature fatigue strength and fatigue fracture behaviors as well as with various mechanical properties of welded joints. The results obtained are summarized as follows: 1) Through mechanical tests and micro-structural examinations, the determined optimum welding conditions, rotating speed 2420 rpm, heating pressure 8kg/mm super(2), upsetting pressure 22kg/mm super(2), the amount of total upset 7mm (heating time 3 sec and upsetting time 2 sec) were satisfied. 2) The solution treated material SUH 3, SUS 303, have the highest inclination gradient on S-N curve due to the high temperature fatigue testing for long time at $700^{\circ}C$. 3) The optimum aging time of friction welded SUH3-SUS 303, has been recognized near the 10hr. at $700^{\circ}C$ after the solution treatment of 1hr. at $1, 060^{\circ}C$. 4) The high temperature fatigue limits of aging treated materials were compared with those of raw material according to the extender of aging time, on 10hr. aging, fatigue limits were increased by SUH 3 75.4%, SUS 303 28.5%, friction welded joints SUH 3-SUS 303 44.2% and 100hr. aging the rates were 64.9%, 30.4% and 36.6% respectively. 5) The fatigue fractures occurred at the side of the base matal SUS303 of the friction welded joints SUH 3-SUS 303 and it is difficult to find out fractures at the friction welding interfaces. 6) The cracking mode of SUS 303, SUH 3-303 is intergranular in any case, but SUH 3 is fractured by transgranular cracking.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.877-882
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• 2014

The reduction of CO2 emission has been discussed in the Marine Environment Protection committee in the International Maritime Organization as the biggest causes of GHG for the purpose of indexing CO2 amounts released into the atmosphere from ships. Accordingly, various methods including the change in the hull design to improve energy efficiency, the coating development to reduce friction resistances, the additives development for improving thermal efficiency in an engine, the low-speed operation to reduce fuel consumptions, and etc. have been applied. The main engine of a ship is an electronic engine for improving the efficiency of the whole load area. However, marine generator engines still use mechanical drive engines in intake, exhaust, and fuel injection valve drive cams. In addition, most of marine generator engines in ships apply a part-load operation of less then 80% due to an overload protection system. Therefore, marine auxiliary diesel engine set at 100% load is necessary to readjust in order to efficient operation because of part-load operation. The objective of this study is to report the results of the part-load fuel consumption improvement by injection timing readjust to identifying the operational characteristics of a marine generator engine currently operated in a ship.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.719-725
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• 2017

Frozen milk products are commonly made in small refrigeration machines. R-502 has long been used as a refrigerant for soft ice cream machines, but it is being replaced with R-404A due to the issue of ozone layer depletion. However, R-404A has high global warming potential, so it also needs to be replaced. In this study, a mixture of R-290 and R-32 was considered as a new refrigerant. An optimization and performance evaluation of the mixture were conducted for a freezer volume of 2.8 liters. The focus of the optimization was the appropriate refrigerant charge and the opening of the expansion valve. At the optimized conditions, ice cream was produced in 6 minutes and 24 seconds with the mixture, and the COP was 0.83. For R-404A, the ice cream production time was 6 minutes and 22 seconds, and the COP was 0.90. The results may be used for the design of food refrigeration machines and to optimize other refrigeration cycles.

• Journal of Biosystems Engineering
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• v.39 no.2
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• pp.101-110
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• 2014

Purpose: The purpose of this study is to develop a system to optimize drying potential energy of the exhausted hot air by changing relative humidity of the air. This study modified the conventional drying method into a drying method changing exhaust cycle and time in order to control the relative humidity of the exhausted hot air during drying process. Method: A valve on the vent was controlled according to a preset time to change the exhaust cycle and time. This study analyzed the influence of the two different types of drying method on the drying characteristics, required energy, and quality of the dried peppers: conventional drying method exhausting hot air continuously and new drying method controlling exhaust cycle and time. Results: Drying characteristics based on exhaust time showed that drying time increased with exhaust time, and specific energy consumption was reduced by 28% from 18.39 MJ/kg (conventional method) to 13.24 MJ/kg when exhaust time was set to one minute. Drying characteristics based on heating time showed that drying time increased with heating time and specific energy consumption was reduced by 30% from 18.39 MJ/kg (conventional method) to 12.87 MJ/kg when exhaust time was set to 22 minutes. Drying characteristics based on exhaust cycle showed that drying time increased with exhaust cycle, and specific energy consumption was reduced by 31% from 18.39 MJ/kg (conventional method) to 12.69 MJ/kg when exhaust time was set to one minute and exhaust cycle was set to 22 minutes before drying and 40 minutes after drying. The quality of the dried red peppers showed that capsaicin, color, and sugar content were high as 34.87 mg/100g, 66.33, and 11.87%, respectively, when exhaust time was set to one minute and exhaust cycle was set to 22 minutes before drying and 40 minutes after drying. Conclusions: In order to utilize the drying potential energy of the exhausted air during drying process, the conventional drying method was modified into the drying method controlling exhaust cycle and time. The results showed that drying with exhaust cycle of one minute was more efficient in terms of drying time, required energy, and quality of the dried peppers than the one with exhaust cycle of 20~40 minutes.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.334-340
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• 2016

The combustion chamber of a diesel engine is often exposed to a more serious wear and corrosion environment than other parts of the engine because its temperature increases as a result of using heavy oil of low quality. Therefore, repair and built-up welding methods must be performed on worn or corroded parts of the piston crown, exhaust valve, etc. from an economical point of view. In this study, Inconel 718 filler metal was used in repair welding on the groove of a forged steel specimen for a piston crown, along with built-up welding on the surface of another forged steel specimen. Then, the corrosion characteristics of the weld metal zone for the repair welding and the deposited metal zone for the built-up welding were investigated using electrochemical methods in a 35% H₂SO₄ solution. The deposited metal zone indicated better corrosion resistance than the weld metal zone, showing a nobler corrosion potential, higher impedance, and smaller corrosion current density. It is considered that metal elements with good corrosion resistance were generally included in the filler metal, and these elements were also greatly involved in the deposited meta by built-up welding, whereas the weld metal consisted of metal elements mixed with both the filler metal and base metal elements because of the molten pool produced by the repair welding. Finally, it is considered that the hardness of the weld metal was increased by the repair welding, whereas the built-up welding improved the corrosion resistance of the deposited metal.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.924-930
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• 2018

The objective of this study was to investigate heating performance characteristics of electric heat pump system in a fuel cell electric vehicle (FCEV). In order to analyze heating performance characteristics of electric heat pump system with plate-type heat exchanger using stack coolant to evaporate the refrigerant, R-134a, each component was installed and tested under various operating conditions, such as air inlet temperature of inner condenser and compressor speed. When the air inlet temperature of inner condenser was varied from $0.0^{\circ}C$ to $-20.0^{\circ}C$, heating capacity was not quite different due to similar temperature gap between inlet and outlet of inner condenser with electric-driven expansion valve (EEV). However, COP increased until certain EEV opening, especially under 45.0%, because of decreasing power consumption. According to the compressor speed variation from 2,000 to 4,000 RPM, heating capacity and COP were found to have opposite trend. In the future works, stack coolant conditions as the heat source for tested heat pump system were analyzed with respect to heating performance, such as heating capacity and COP.

• Clean Technology
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• v.16 no.3
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• pp.213-219
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• 2010

Vortex tube is the device that can separate small particles from the compressed gas, as well as compressed gas into hot and cold gas. Due to energy and particle separation ability, a vortex tube can be used as the main component of the $CO_2$ absorption device. In this study, experimental approach has been performed to analyze the energy separation characteristics of the vortex tube. To obtain the preliminary design data, energy separation characteristics of the vortex tube has been tested for orifice diameter, nozzle area ratio, and tube length. As a result, the orifice diameter is the major factor of the vortex tube design. The nozzle area ratio and tube length have a minor effect on the energy separation performance. For Dc=0.6D, AR=0.14~0.16, and L=16D, maximum energy separation has been occurred. The result from this study can be used as the basic design data of the $100Nm^3$/hr class vortex tube applied to the $CO_2$ absorption device. Compared with the $CO_2$ absorption process containing an absorption tower, the process with a vortex tube is expected to have a huge advantage of saving the installation space and the operating cost.

• Journal of Chest Surgery
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• v.32 no.6
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• pp.525-531
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• 1999

Background: We analyzed five hundred patients who underwent either isolated or concomitant coronary artery bypass grafting(CABG) between November 1981 and June 1997. Material and Method: There were 330 males and 170 females with a mean age of 57.4$\pm$8.9 years. To evaluate the preoperative status, we performed electrocardiograghy, echocardiography, MIBI scan, Duplex sonogram, common blood test including CK and LDH and coronary angiography. Result: Preoperative clinical diagnoses were unstable angina in 282 (56.4%), stable angina in 141 (28.2%), postinfarction angina in 58 (11.6%), acute myocardial infarction in 8 (1.6%), variant angina in 7 (1.4%) and failed percutaneous transluminal coronary angioplasty in 4 (0.8%) patients. Preoperative angiographic diagnoses were three-vessel disease in 263 (52.6%), two-vessel disease in 93 (18.6%), one-vessel disease in 71 (14.2%), left main disease in 68 (13.6%), and others in 5 (1.0%) patients. Patients had various risk factors for coronary disease, and the frequency of the risk factors such as hypertension, diabetes and smoking showed increasing tendency year by year. We used saphenous vein grafts in 1143, internal thoracic artery grafts in 442, radial artery graft in 17, and gastroepiploic artery graft in 1 anastomosis. The mean number of grafts was 3.2$\pm$1.2 per patient. Concomitant operations were prosthetic valve replacement or valvuloplasty in 31, coronary endarterectomy and angioplasty in 27, left main coronary angioplasty in 13, carotid endarterectomy in 5, and neurologic problems, bleeding, and perioperative myocardial infarction. The mean follow-up period was 25$\pm$23 months and there were 5 cases of reoperation. Conclusion: We hope that the surgical results would improve with the accumulation of experience, application of new myocardial protection technique, and timely intervention of mechanical assisted devices.

• Journal of Chest Surgery
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• v.29 no.11
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• pp.1218-1222
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• 1996

The reported incidence of postcardiotomy cardiogenic shock not responding to conventional therapy is still 0.1 to 0.8%. For this group of patients, more aggressive form of circulatory support must be employed. Centrifugal pumps are a ventricular assist device most commonly used on this purpose, due to low cost and easy availability. Currently, however, clinical experience of centrifugal pumps as a ventricular assist device is rarely reported in Korea. From January 1992 to January 1996, 2986 patients underwent cardiac operations on cardiopulmonary bypass at Seoul National University Hospital. Refractory postcardiotomy cardiac failure requring ventricular support with a Biomedicus centrifugal pump developed in ten of these patients. There were eight men and two women, ranged in age from nine years to 77 years with a mean of 50$\pm$20 years. The primary surgical procedures consisted of isolated coronary revascularization in four patients, combined coronary revascularization and aortic valve replacement in two, aortic dissection repair in two, pulmonary embolectomy in one, and heart transplantation in one. Of the ten patients, five had left ventricular assistance, one had right ventricular assistance, and four had biventricular assistance. Duration of ventricular assistance ranged from 24 to 175 hours, with a mean of 76$\pm$51 hours. Seven patients were weaned from ventricular assistance, and four of them discharged. The causes of death for nonsurvivors were progressive cardiac failure in two patients and multiorgan failure, intractable ventricular fibrillation, irreversible brain injury, and mechanical problem, respectively, in the other four. Survival was not predicted by time on cardiopulmonary bypass, aortic cross-clamp time, or duration of ventricular support. Major complications included bleeding(7), renal failure(6), infection(3) and neurologic complication(2). These results indicate that a centrifugal pump can provide reasonably satisfactory short-term circulatory support.

• Journal of Chest Surgery
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• v.39 no.1 s.258
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• pp.18-27
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• 2006

Background: Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a rare congenital anomaly, but is one of the most common causes of myocardial ischemia which would result in high mortality within the first year of life. This is our early result of the surgical management for these patients. Material and Method: From June 1989 to July 2003, 6 patients with ALCAPA and one patient with ARCAPA (Anomalous origin of the Right coronary artery from the pulmonary artery) underwent surgical repair. We have reviewed the all medical records, electrocardiogram, chest X-ray and echocardiography retrospectively. Result: Three of the patients were boys and four were girls. The median age at the operation was 5.4 months (Range: 3$\∼$33 months). The average body weight of at the operation was 6.7 kg (Range: 3.7$\∼$11.3 kg). A mean follow up period was 18 months. Only 3 patients were initially diagnosed as ALCAPA. And 3 patients had moderate mitral regurgitation. Immediate coronary artery reimplantation on diagnosis with the aim of restoring a two-coronary system circulation was done. The average bypass time was 114$\pm$37 minutes, and the average aortic cross clamping time was 55$\pm$22 minutes. The average stay of intensive care unit was 5$\pm$3 days, the mean mechanical ventilator time was 38$\pm$45 hours and the hospital stay after operation was 12$\pm$5 days. There were significant improvements in electrocardiogram and chest X-ray of the all patients except one late death patient. The ventricular function showed almost normal recovery after operation; the EF (Ejection Fraction) increased from 41.2$\pm$ 10.3$\%$ to 60.5$\pm$ 15.8$\%$ within 1 month and to 59.8$\pm$13.9$\%$ within 1 year after operation, the SF (Shortening Fraction) increased from 23.6$\pm$4.7$\%$ to 38.6$\pm$8.4$\%$ within 1 month and to 37.4$\pm$7.9$\%$ within 1 year after operation, LVEDDI (Left Ventricular End-diastolic Dimension Index) decreased from 100.8$\pm$25.6 mm/$m^{2}$ to 90.3$\pm$ 19.2 mm/$m^{2}$ within f month and to 79.3$\pm$ 15.8 mm/$m^{2}$ within 1 year after operation. Concomitant mitral repair was done in two patients with anterior mitral leaflet prolapse. In every patient, mitral valve showed less than mild regurgitation during follow up. One late death occurred in which patient Dor procedure was applied 10 months after initial operation due to the dilated cardiomyopathy Conclusion: In the management of this rare and could be fatal Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA), early suspicion and correct diagnosis is of most important. But, after diagnosis, immediate restoration of 2 coronary systems could result in good outcome.