• Journal of Biosystems Engineering
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• 제31권1호
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• pp.33-38
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• 2006

This work was conducted to find the operating characteristics of an efficient wet grinding system designed to obtain fine rice husk ash powder. Once the rice husk was combusted and the thermal energy was recovered from the furnace, the ash was fed and pulverized in the grinding system resulting a fine powder to be used as a supplementary adding material to the portland cement. Grinding time (15, 30, 45 min), impeller speed (250, 500, 750 rpm), and mixed ratio (6.7, 8.4, 11.l, 20.9) were three operating factors examined for the performance of a wet-type stirred ball mill grinding system. For the operating conditions employed, mean diameter of fine ash powder, specific energy input, and grinding energy efficiency were in the range of $2.83{\sim}9.58{\mu}m,\;0.5{\sim}6.73kWh/kg,\;and\;0.51{\sim}3.27m^2/Wh$, respectively. With the wet-type stirred ball mill grinding system used in this study, the grinding energy efficiency decreased with the increase in total grinding time, impeller speed, and mixed ratio. The difference in specific surface area of powder linearly increased with logarithm in total number of impeller revolution and the grinding energy efficiency linearly decreased. Grinding time of 45 min, impeller speed of 500 rpm, and mixed ratio of 6.7 were chosen as the best operating condition. At this condition, mean particle diameter of the fine ash, grinding energy efficiency, grinding throughput, and specific energy input were $2.84{\mu}m,\;2.28m^2/Wh,\;0.17kg/h$, and 2.03kWh/kg, respectively. Wet fine grinding which generates no fly dust causing pollution and makes continuous operation easy, is appeared to be a promising solution to the automatization of rice husk ash grinding process.

• 한국추진공학회지
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• 제20권5호
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• pp.9-18
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• 2016

일반적으로 다단 축류압축기는 부분 부하 조건에서 충분한 운전영역을 확보하기 위해 가변안내깃을 이용한다. 본 연구에서의 해석대상인 다단 축류압축기는 입구에서의 안내깃과 함께 1단과 2단 정익을 가변안내깃으로 하여 운전영역을 확보한다. 따라서 본 연구에서는 정격회전수의 70%와 90% 회전수 조건에서의 가변안내깃의 설치각이 다단 축류압축기의 성능에 미치는 영향에 대해 조사하였다. 다단 축류압축기의 성능은 3차원 정상상태 및 비정상상태 수치해석을 이용하여 확보하였다. 각 해석기법을 통해 확보한 결과를 비교하였으며 내부유동장의 특성을 파악하였다.

• Journal of Biosystems Engineering
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• 제39권1호
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• pp.39-46
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• 2014

Purpose: Monitoring and control of environmental condition is highly important for optimum control of the conditions, especially in greenhouses and plant factories, and the condition is not uniform within the facility. Objectives of the study were to investigate variability in soil water content and to provide information useful for better irrigation control. Methods: Experiments were conducted in a strawberry-growing greenhouse (greenhouse 1) and a cherry tomato-growing greenhouse (greenhouse 2) in winter. Soil water content, electrical conductivity (EC), and temperature were measured over the entire area, at different distances from an irrigation pump, and on ridge and furrow areas. Results: When measured over the entire greenhouse area, soil water content decreased and temperature and electrical conductivity increased over time from morning to afternoon after irrigation. Water content decreased by distance from the irrigation pump up to 70 m and increased after that, and temperature showed an inverse pattern. Soil water contents on the ridge were lower than those on the furrow, and the differences were 10.2~18.4%, indicating considerable variability. The lowest EC were observed on the furrow and highest values were observed on the ridge. Soil water contents were less and temperature levels were greater at the window side than in the center locations. Conclusions: Selection of number and location of soil water content sensor would be the first step for better water content monitoring and irrigation control. Results of the study would provide basic data useful for optimum sensor location and control for underground greenhouse environment.

• 한국유체기계학회 논문집
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• 제12권1호
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• pp.16-21
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• 2009

In the last five years, 91 accidents from portable gas ranges and non-refillable metallic gas cartridges have occurred. The gas cylinder installed with a relief valve was developed to prevent an explosive accident from the gas cartridge. In this study it was carried out to evaluate the safety of a gas cylinder mounted with a relief valve which can prevent an explosion. Under the real using condition and the extreme condition the gas cylinder is heated with an electric heater. Simultaneously, the operating pressure is checked and the suitability of releasing flux is evaluated. And the possibility of fire or explosion was tested when the gas was released from the relief valve at the real using condition. Using a numerical simulation method, the diffusion of butane gas released from a relief valve was visualized.

• 한국정밀공학회지
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• 제19권5호
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• pp.126-132
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• 2002

Misaligned shafts of the rotating machinery have caused noise, vibration. bearing failures, and stress concentration of coupling parts which decrease the efficiency and life of shaft systems. Therefore the proper shaft alignment of those system should be monitored continuously in dynamic condition. To solve these problems under dynamic condition a telemetry system is used. In this study, the condition of the least bending moment which is known by analyzing the structure and stress induced by misalignment is found. After the shaft is aligned by dial gage, a telemetry system with strain gages is installed on shaft. The relationship between bearing displacement and moment of coupling part influenced by misalignment is investigated. The moment derived from two shaft strain at the nearby coupling is measured. The bending strain is measured 5 times for average in static state as well as in dynamic state with 100∼700 rpm.

• 한국신뢰성학회지:신뢰성응용연구
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• 제11권4호
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• pp.343-356
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• 2011

This paper proposes an accelerated life evaluation of drive shaft. The life test of drive shaft for independent suspension type AWD vehicle should be performed by use of the least test sample because many number of samples can't be used for the test because of its mass capacity and high price. We calculated the no failure test time by application of no failure test concept, and the already performed test data for drive shaft are applied for some kinds of reliability coefficients which are needed for calculation of life test time. And, for analysis of real driving condition of vehicle, the load spectrum is prepared using the needed road condition and vehicle data. The inverse power model is used for accelerated life test. The equivalent torque of load spectrum is achieved by use of Miner's Rule, and then the final accelerating condition is determined by decision of the accelerated test torque. This paper shows that the accelerated life test results corresponds with the target life and the proposed life test method can be very well applied to no failure life test for mass capacity machinery components.

• 한국유체기계학회 논문집
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• 제13권5호
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• pp.5-10
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• 2010

5MW, open pool type research reactor, is commonly used to education and experimental purpose. It is necessary to prepare a standardization of system designs for considering a demand. HANARO has prepared the standardization of 5MW research reactor system designs based on the design, installation, commissioning and operating experiences of HANARO. For maintaining an open pool type reactor safety, a primary cooling system (after below, PCS) should remove the heat generated by the reactor under a reactor normal operation condition and a reactor shutdown condition. For removing the heat generated by the reactor, the PCS should maintain a required coolant flow rate. For a verification of the required flow rate, a flow network analysis of the PCS was carried under a normal operating condition. Based on the flow network analysis result, this paper describes the PCS flow characteristics of a 5MW open pool type research reactor. Through the result, it was confirmed that the PCS met design requirements including design flow rate without cavitation.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.66-72
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• 2008

Fuel reforming technology for the fuel cell vehicles could be adopted to internal combustion engine for the reduction of engine out emissions. Since syngas which is reformed from fossil fuel has hydrogen as a major component, it has abilities to enhance the combustion characteristics with wide flammability and high speed flame propagation. In this paper, syngas was feed to 2.0 liter gasoline engine during the cold start and early state of idle condition. Not only cold start HC emission but also $NO_x$ emission could be dramatically reduced due to the fact that syngas has no HC and has nitrogen up to 50% as components. Exhaust gas temperature was lower than that of gasoline feeding condition. Delayed ignition timing, however, resulted in increased exhaust gas temperature approximated to gasoline condition. It is supposed that the usage of syngas in the gasoline internal combustion engine is an effective solution to meet the future strict emission regulations by the reduction of cold start THC and $NO_x$ emissions.

• 한국유체기계학회 논문집
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• 제10권6호
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• pp.17-23
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• 2007

In the present work, flow analysis has been performed in the steam turbine bypass control valve (single-path type) for two different cases i.e., case with steam only and case with both steam and water. The numerical analysis is performed by solving three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. The shear stress transport (SST) model and $k-{\varepsilon}$ model are used to each different case as turbulence closure. Symmetry condition is applied at the mid plane of the valve while adiabatic condition is used at the outer wall of the cage. Grid independency test is performed to find the optimal number of grid points. The pressure and temperature distributions on the outer wall of the cage are analyzed. The mass flow rate at maximum plug opening condition is compared with the designed mass flow rate. The numerical analysis of multiphase mixing flow(liquid and vapor) is also performed to inspect liquid-vapor volume fraction of bypass valve. The result of volume fraction is useful to estimate both the safety and confidence of valve design.

• 한국유체기계학회 논문집
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• 제14권4호
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• pp.38-44
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• 2011

This paper deals with the detail rotordynamic analysis for BB5 eight stages pump as development of API 610 BB5 type pump. Dry-run analytical model, not considering operating fluid, and wet-run analytical model, considering operating fluid are established. In addition, plain circular and pressure dam bearings are chosen and it was discussed that each bearing has an effect on dynamic characteristics of pump rotor system. A rotordynamic analysis includes the critical speed map, Campbell diagram, stability, and unbalance response. As results, it was predicted that rated speed of the pump rotor passes through 1st critical speed in dry-run condition regardless of bearings, however, it was verified that, in wet-run condition, the rotor system doesn't have critical speeds even if more than twice rated speed. Hence the resonance problem caused by the critical speeds does not happen since actual operating is in wet-run condition including operating fluid. As a result of unbalance response analysis, the pump rotor has stable vibration response at rated speed, regardless of operating fluid and the proposed bearing types.