• International Journal of Fluid Machinery and Systems
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• v.2 no.3
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• pp.206-214
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• 2009

Alternate blade cavitation, rotating cavitation and cavitation surge in rocket turbopump inducers were simulated by a three dimensional commercial CFD code. In order to clarify the cause of cavitation instabilities, the velocity disturbance caused by cavitation was obtained by subtracting the velocity vector under non-cavitating condition from that under cavitating condition. It was found that there exists a disturbance flow towards the trailing edge of the tip cavity. This flow has an axial flow component towards downstream which reduces the incidence angle to the next blade. It was found that all of the cavitation instabilities start to occur when this flow starts to interact with the leading edge of the next blade. The existence of the disturbance flow was validated by experiments.

• The KSFM Journal of Fluid Machinery
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• v.14 no.2
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• pp.25-28
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• 2011

The control rod assemblies do freely fall into the reactor core by the gravity from the control rod drive mechanism. In order to achieve a rapid shutdown and control the reactor power, it is required to insert control rod assemblies as soon as possible. In this paper, we evaluated the drop time and flow characteristics caused around guide tube for SMART(System-integrated modular advanced reactor) control rod assembly. Numerical analyses are carried out with FLUENT program of computational fluid dynamics. This study results show that the drop time of the control rod assembly in the operating condition of SMART is more 20 percent rapidly than the drop time of the room temperature and ambient atmosphere condition.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.68.5-68
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• 2002

For the performance test of rechargeable electric tools, it is necessary to test under the same condition as the actual operation condition. They are necessary to control the load torque and to acquire the test data with a computer, and it should be convenient to fix the tool on the test equipment for rechargeable electric tools. It consists of torque loading parts, sensing parts and control software. Two hysteresis brakes, connected serially with flexible coupling, were applied to control the load for the test. The sensing part consists of a torque sensor, a rpm detector and a power analyzer. The torque and the rpm were measured in order to calculate the output of the rechargeable electric...

• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.76-84
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• 2011

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.35-41
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• 2010

Experimental study on the flow field inside the nozzle for radial turbine was performed. At design point, the pressure is high and the Mach number is low at the pressure side of the nozzle inlet semi-vaneless space as the flow turns through the nozzle vanes. As the flow accelerates through the nozzle passage to the throat the pressure level at the pressure and suction sides becomes similar. The flow continued accelerating from the throat to the inlet of turbine wheel and the pressure field became uniform in the circumferential direction in the vaneless space. In high expansion ratio condition, strong favorable pressure gradient band region occurred just after the throat in the semi-vaneless space in the circumferential direction and the pressure became uniform in the circumferential direction after this band. In low expansion ratio condition, core flow acceleration is dominant after the throat and this non-uniform pressure field reached to the inlet of turbine wheel.

• The KSFM Journal of Fluid Machinery
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• v.12 no.2
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• pp.31-38
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• 2009

The valve performance has been evaluated from the theoretical equation based on design information such as packing thrust, spring preload and friction coefficient(${\mu}$). The accuracy of those data can be lower than that of vendor's initial design data. Especially, the friction coefficient can be degraded with time than the original condition and the valve performance calculated using the previous friction coefficient can not be available. Accordingly, this paper is describing a new performance evaluation method of valve based on diagnostic test data which are acquired from a site valve tested in static and dynamic conditions. Especially, this paper provides a new method using friction coefficient(${\mu}$) which is derived from the diagnostic test data acquired in the valve's design basis condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.130-130
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• 2010

Thin Si films were grown by a plasma-enhanced chemical vapor deposition (PECVD, SNTEK, Korea) system. Two different deposition condition were applied and formed a fully amorphous Si (a-Si) film and a micromorph mixing of microcrystalline Si (mc-Si) and a-Si film. Under one sun illumination, the micromorph device provided the enhanced open circuit voltage and fill factor values. It presents the fabrication of the micromorph Si film and the a-Si film by modulating a deposition condition. The performances of the Si thin film Schottky solar cells are discussed.

• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.5-8
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• 2004

A low cost MOD processing using YBCO oxide powder as a starting precursor was employed for fabrication of YBCO thin films. YBCO oxide is advantageous over metal acetates or TFA salts which are popular starting precursors for conventional MOD-TFA process. YBCO thin films were prepared by oxide-precursor-based MOD process and annealing condition was optimized. The YBCO thin film annealed at 78$0^{\circ}C$ shows no transport $I_c$ and poor microstructure. However, the YBCO thin film annealed at higher temperature shows improvement in microstructure and current transport property. In order to improve critical current, YBCO thin film was prepared by double coating method. YBCO thin film prepared with double coating approach shows enhanced superconducting performance ($I_c$>100A/cm-w).

• Journal of the Korean Society of Industry Convergence
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• v.23 no.6_2
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• pp.1075-1080
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• 2020

The control on temperature and humidity on the cow-house is essential to assure production efficiency and the control on disease of cows. Fog system and screen fence are typical methods to drop the temperature inside of cow-house during the summer season. This study focused on the change in temperature and humidity under the condition of application of those methods. The results indicate that the installation of atomizer and insulation curtain cause decrease in temperature and increase in humidity. However, Using both of methods at the same time doesn't make any additional meaningful effects on temperature and humidity.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.26 no.2
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• pp.61-69
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• 2020

As post-harvest processes of onions are carried by a 20 kg-net package which results in high-cost and low-efficiency, especially, the insufficient drying and physical damage of onions after harvesting leads to a huge second loss in storage, we had developed a low-cost, high-efficiency post-harvest bulk handling machinery system by collecting onions on a farm using ton-bags, drying with forced air circulation, and sorting/packaging. The post-harvest bulk handling machinery system consisted of 6 devices, and this study designed an automatic feed hopper with a feeding rate control device, an inclined belt conveyor with a two-step chute, and an automatic pallet unloading device for feeding onions into the sorting/packing line. This study also analyzed the performance and control of the total system. The device had 1-ton handling capacity, but the operational condition was set to increase the capacity. The three-step filling method of pallet by the velocity control of the inclined belt conveyor was applied in the post-harvest bulk handling machinery system for the prevention of physical damage. If one worker was set to operate the total system, the time required to complete one palletized load was approximately 5 minutes and 5 seconds. The calculated daily handling capacity was approximately 94 tons, when the daily actual working time was 8 hours. When the developed system was applied to the managerial size of 2,000 ton, the processing cost per ton of the system was decreased by 19.5%, compared with the existing 20 kg-net package-based handling. The developed post-harvest bulk handling machinery system would be a good substitute for the rapid decline and aging of rural labor.