• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.565-568
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• 2007

The high pressure hydrogen gas refueling system is required for fuel cell vehicle. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is adopted to investigate the gas flow characteristics inside the check valve for various refueling and tank pressures. The results showed that the choking phenomena can occur for certain refueling pressures, therefore refueling processes should be divided by multiple stages. And a design method to prevent the seal departure problem which reported in CNG usages is required.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.377-387
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• 2001

This paper presents leakage characteristics of a scroll compressor applying alternative refrigerants of R22 such as R407c and R410a under actual operating conditions. Because leakage in a scroll compressor produce significant losses and degradation of performance, those should be clarified to design a high efficient scroll compressor with alternative refrigerants of R22. However, flank and tip leakage characteristics of a scroll compressor with alternative refrigerants are very limited in open literature. In the present study, both experimentation and modeling of the leakages in the scroll compressor were performed. As a result, it was observed that the leakages of the scroll compressor with R407c increased by 15%, and that with R410a increased by 76% as compared to the compressor applying R22 under standard load conditions due to a higher upstream pressure and a higher pressure difference between pockets.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.39-46
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• 2008

The end plates of fuel cell assemblies are used to fasten the inner stacks, reduce the contact pressure, and provide a seal between Membrane-Electrode Assemblies (MEAs). They therefore require sufficient mechanical strength to withstand the tightening pressure, light weight to obtain high energy densities, and stable chemical/electrochemical properties, as well as provide electrical insulation. The design criteria for end plates can be divided into three parts: the material, connecting method, and shape. In the past, end plates were made from metals such as aluminum, titanium, and stainless steel alloys, but due to corrosion problems, thermal losses, and their excessive weight, alternative materials such as plastics have been considered. Composite materials consisting of combinations of two or more materials have also been proposed for end plates to enhance their mechanical strength. Tie-rods have been traditionally used to connect end plates, but since the number of connecting parts has increased, resulting in assembly difficulties, new types of connectors have been contemplated. Ideas such as adding reinforcement or flat plates, or using bands or boxes to replace tie-rods have been proposed. Typical end plates are rectangular or cylindrical solid plates. To minimize the weight and provide a uniform pressure distribution, new concepts such as ribbed-, bomb-, or bow-shaped plates have been considered. Even though end plates were not an issue in fuel cell system designs in the past, they now provide a great challenge for designers. Changes in the materials, connecting methods, and shapes of an end plate allow us to achieve lighter, stronger end plates, resulting in more efficient fuel cell systems.

• Journal of Energy Engineering
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• v.28 no.3
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• pp.10-17
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• 2019

According to South Korea's policy of supplying eco-friendly hydrogen vehicles, related industries are actively conducting research on the development of hydrogen cars and hydrogen charging station infrastructure. On the other hand, there is a lack of empirical research and assessment of the risk of non-metallic materials (such as liners, seals, gaskets) for classified materials that directly affect the durability and reliability of hydrogen vehicles and hydrogen charging stations. In this study, the risk factors for liners and seals of non-metallic parts used in high-pressure hydrogen installations were derived using FMEA, and the RPN values were calculated by converting the severity, frequency of occurrence and degree of detection into scores. The maximum value of the RPN 600, minimum value 63, average value 278.5 was calculated and periodic control of the liner and seal was identified as important. In addition, through hydrogen soakage and oxygen aging tests for non-metallic rubber products, physical test values that can be used as basic data were presented.

• Tuberculosis and Respiratory Diseases
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• v.57 no.5
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• pp.434-438
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• 2004

Background : An excessive endotracheal cuff pressure can cause tracheal injury, and insufficient cuff pressure may not generate an effective cuff seal. The peak inspiratory pressure influences the minimal occlusion pressure of the endotracheal tube cuff. However, the relationship between the minimal occlusion pressure and the tidal volume has not been investigated. This study was conducted to estimate the relationship between the tidal volume and the minimal occlusion pressure of the cuff. Methods : Ten mechanically ventilated patients were included. The minimal occlusion pressure of the cuff was measured using a pressure gauge. The basal tidal volume was increased and decreased as much as 10% whilst maintaining the same peak inspiratory pressure. The, minimal occlusion pressures were then measured in the high and low tidal volume state, respectively. Results : The peak inspiratory pressure was $32.6{\pm}4.72cmH_2O$ and the minimal occlusion pressure was $19.0{\pm}2.26$ mmHg in the basal ventilator setting. There was a significant relationship between the peak inspiratory pressure and the minimal occlusion pressure(r=0.77, p<0.01). The minimal occlusion pressure of the cuff was increased to $20.3{\pm}2.4$ mmHg in the high tidal volume state(p<0.05), and decreased to $16.8{\pm}3.01$ mmHg in the low tidal volume state (p<0.001). Conclusion : The minimal occlusion pressure of the cuff can be influenced by changes in the tidal volume as well as by the peak inspiratory pressure.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.492-498
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• 2012

In this study, hydrodynamics such as solid circulation rate and voidage in the desulfurizer and the reaction characteristics of Zn-based solid sorbents were investigated using lab-scale high pressure and high temperature desulfurization process. The continuous HGD (Hot Gas Desulfurization) process consist of a fast fluidized bed type desulfurizer (6.2 m tall pipe of 0.015 m i.d), a bubbling fluidized bed type regenerator (1.6 m tall bed of 0.053 m i.d), a loop-seal and the pressure control valves. The solid circulation rate was measured by varying the slide-gate opening positions, the gas velocities and temperatures of the desulfurizer and the voidage in the desulfurizer was derived by the same way. At the same gas velocities and the same opening positions of the slide gate, the solid circulation rate, which was similar at the temperature of $300^{\circ}C$ and $550^{\circ}C$, was low at those temperatures compared with a room temperature. The voidage in the desulfurizer showed a fast fluidized bed type when the opening positions of the slide gate were 10~20% while that showed a turbulent fluidized bed type when those of slide gate were 30~40%. The reaction characteristics of Zn-based solid sorbent were investigated by different desulfurization temperatures at 20 atm in the continuous operation. The $H_2S$ removal efficiency tended to decrease below the desulfurization temperature of $450^{\circ}C$. Thus, the 10 hour continuous operation has been performed at the desulfurization temperature of $500^{\circ}C$ in order to maintain the high $H_2S$ removal efficiency. During 10 hour continuous operation, the $H_2S$ removal efficiency was above 99.99% because the $H_2S$ concentration after desulfurization was not detected at the inlet $H_2S$ concentration of 5,000 ppmv condition using UV analyzers (Radas2) and the detector tube (GASTEC) which lower detection limit is 1 ppmv.

• Nuclear Engineering and Technology
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• v.31 no.1
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• pp.17-28
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• 1999

A thermal-hydraulic analysis is conducted on the loss-of-coolant-accident (LOCA) during shutdown operation of YGN Units 3/4. Based on the review of plant-specific characteristics of YGN Units 3/4 in design and operation, a set of analysis cases is determined, and predicted by the RELAP5/MOD3.2 code during LOCA in the hot-standby mode. The evaluated thermal-hydraulic phenomena are blowdown, break flow, inventory distribution, natural circulation, and core thermal response. The difference in thermal-hydraulic behavior of LOCA at shutolown condition from that of LOCA at full power is identified as depressurization rate, the delay in peak natural circulation timing and the loop seal clearing (LSC) timing. In addition, the effect of high pressure safety injection (HPSI) on plant response is also evaluated. The break spectrum analysis shows that the critical break size can be between 1% to 2% of cold leg area, and that the available operator action time for the Sl actuation and the margin in the peak clad temperature (PCT) could be reduced when considering uncertainties of the present RELAP5 calculation.

• Tunnel and Underground Space
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• v.23 no.1
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• pp.13-30
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• 2013

Increase of pore fluid pressure resulting from injection of $CO_2$ may reactivate pre-existing faults, and the induced seismic activities can raise the safety issues such as seal integrity, restoration of storage capacity, and, in the worst case, removal of previously injected $CO_2$. Thus, fault stability and potential for $CO_2$ leakage need to be assessed at the stage of site selection and planning of injection pressure, based on the results of large-scale site investigations and numerical modeling for various scenarios. In this report, studies on the assessment of fault stability during injection of $CO_2$ were reviewed. The seismic activities associated with an artificial injection of fluids or a release of naturally trapped high-pressure fluids were first examined, and then site investigation methods for the magnitude and orientation of in situ stresses, the distribution and change of pore fluid pressure, and the location of faults were generally summarized. Recent research cases on possibility estimation of fault reactivation, prediction of seismic magnitude, and modeling of $CO_2$ leakage through a reactivated fault were presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.397-402
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• 2016

To produce adequate electricity in nuclear and thermal power plants, an optimal amount of steam should be supplied to a generator connected to high- and low-pressure steam turbines. A turbine output control device, which is a special steam valve employed to supply or interrupt the steam to the turbine, is operated using a hydraulic servo actuator. In power plants, the performance of servo actuators is degraded by the air generated from the hydraulic system, or causes frequent failures owing to an increase in the wear of the seal. This is due to the seal being burnt as generated heat using the produced compressed air. Some power plants have exhausted air using a fixed orifice, and thus they encounter power loss due to mass flow exhaust. Failures are generated in hydraulic pumps, electric motors, and valves, which are frequently operated. In this study, we perform modeling and analysis of the load-sensing air-exhaust valves, which can be passed through very fine flow under normal use conditions, and exhaust mass flow air at the beginning stage as with existing fixed orifices. Then, we propose a method to prevent failures due to the compressed air, and to ensure the control accuracy of hydraulic servo actuators.

• Restorative Dentistry and Endodontics
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• v.27 no.1
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• pp.24-33
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• 2002

Leakage studies have been performed frequently, since a fluid-tight seal provided by various dental fill-ing materials has been considered clinically important. The leakage of the various root-end filling materials has been widely investigated mostly dye penetration method. These dye studies cannot offer any information about the quality of the seal of a test material over a long period of time The purpose of this study was to evaluate the microleakage of root end cavities in blood contamination filed amalgam, intermediate restorative material(IRM), light cured glass ionomer cement(GI) and mineral trioxide aggregate(MTA) by means of a modified fluid transport model. Fifty standard human root sections, each 5mm high and with a central pulp lumen of 3mm in diameter, were and filled with our commonly used or potential root end fill ing materials after they were contaminated with blood. At 24h. 72h, 1, 2, 4, 8, and 12 weeks after filling, leakage along these filling materials was determined under a low pressure of 10KPa(0.1atm) using a fluid transport model. The results were as follows : 1 MTA group showed a tendency of decreasing percent of gross leakage (20m1/day) in process of time, whereas the other materials showed a tendency of increasing in the process time. 2. At the all time interval, GI group leaked significantly less than amalgam group and IRM group (p＜0.05). 3. At the 4 weeks, the percentage of gross leakage in MTA group decreased to 0% thereafter, the low per-centage of gross leakage was maintained in MTA group until the end of the experiment, whereas the percentage in IRM group increased to 100% 4. At the 12 weeks, percentage of gross leakage was significantly low in MTA group(0%), comparison with GI group(40%), amalgam group(90%) and IRM group(100%), but there was no significant difference between latter two materials.