• 한국화재소방학회논문지
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• 제29권2호
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• pp.33-38
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• 2015

고압과 정량 흡상을 목적으로 클리어런스가 없는 초고압 회전용적형 헬리컬기어 펌프의 개발을 진행하였다. 펌프의 내부 압력과 토출 유속을 검증하기 위해 CFD 해석을 수행하였다. 이에 따라 FVM 기법으로 유동해석을 수행하였는데 클리어런스가 없는 완전히 밀폐된 형태의 FVM 유동해석은 격자가 연속하게 구성되지 않아 유체영역이 분리되어 정상적인 결과를 얻어낼 수 없었다. 이러한 문제로 격자 구성이 필요치 않은 MPS 기법으로 유동해석을 수행하였고, MPS 유동해석을 통해 펌프의 내부 압력과 토출 유속을 확인할 수 있었다. 로터의 회전속도 1,000 rpm에서 펌프 내부의 압력은 최소일 때 19.5 bar, 최대일 때 44.6 bar이고, 평균 압력은 33.9 bar로 확인되었다. 토출 유속은 최소일 때 64.5 m/s, 최대일 때 84.8 m/s이고, 평균 유속은 76.1 m/s로 확인되었다. 본 연구를 통해 클리어런스가 없는 해석 모델의 유동해석은 FVM 기법보다는 MPS 기법이 더 적합하였음을 확인할 수 있었다. 또한 초고압 회전 용적형 헬리컬기어 펌프의 압력의 변화에 따른 유속과의 관계를 본 연구를 통해 규명할 수 있었다.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.426-430
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• 2009

In order to investigate the design method for a micro centrifugal compressor, which is the most important component of an ultra micro gas turbine, an impeller having the outer diameter of 20mm was designed, manufactured and tested. The designed rotational speed is 500,000 rpm and the impeller has a fully 3-dimensional shape. The impeller was rotated at 250,000 rpm in the present study. The experimental results of the tested compressor with the vaned and the vaneless diffusers were compared. It was found that the vaned diffuser attained the higher flow rate than the vaneless diffuser at the maximum pressure ratio. In addition the maximum pressure ratio was higher for the diffuser having a larger diffuser divergence angle at the high flow rate. These results were compared with those obtained by the prediction method used at the design stage.

• 한국정밀공학회지
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• 제26권1호
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• pp.51-56
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• 2009

Recently, with the increasing lightness and miniaturization of high resolution camera phones, the demand for aspheric glass lens has increased because plastic and spherical lens are unable to satisfy the required performance. An aspheric glass lens is fabricated by the high temperature and pressure molding using a tungsten carbide molding core, so precision grinding and coating technology for the molding core surface are required. This study investigates the effect of diamond-like carbon (DLC) and rhenium-iridium (Re-Ir) coating For aspheric molding core surface. The grinding conditions of the tungsten carbide molding core were obtained by design of experiments (DOE) for application in the ultra precision grinding process of the tungsten carbide molding core of the aspheric glass lens used in 5 megapixel, $4{\times}$ zoom camera phone modules. A tungsten carbide molding core was fabricated under this grinding condition and coated with the DLC and Re-Ir coating. By measurements, the effect of DLC and Re-Ir coating on the form accuracy and surface roughness of molding coer was evaluated.

• 한국공작기계학회논문집
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• 제17권2호
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• pp.1-6
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• 2008

In recent years, developments in the semiconductor and electronic industries have brought a rapid increase in the use of large size silicon wafer. For further improvement of the ultra precision surface and flatness of Si wafer necessary to high density ULSI, it is known that polishing is very important. However, most of these investigation was experiment less than 300mm diameter. Polishing is one of the important methods in manufacturing of Si wafers and in thinning of completed device wafers. This study reports the machining variables that has major influence on the characteristic of wafer polishing. It was adapted to polishing pressure, machining speed, and the slurry mix ratio, the optimum condition is selected by ultra precision wafer polishing using load cell and infrared temperature sensor. The optimum machining condition is selected a result data that use a pressure and table speed data. By using optimum condition, it achieves a ultra precision mirror like surface.

• Applied Science and Convergence Technology
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• 제23권3호
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• pp.103-112
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• 2014

The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM; Section II, Figs. 1 and 2) for a low vacuum, a static expansion system (SES; Section III, Figs. 3 and 4) for a medium vacuum, and an orifice-type dynamic expansion system (DES, Section IV, Figs. 5 and 6) for high and ultra-high vacuum systems. For each system, explicit measurement model equations with multiple variables are given. According to ISO standards, all of these system variable errors were used to calculate the expanded uncertainty (U). For each system, the expanded uncertainties (k = 1, confidence level = 95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) levels are summarized in Table 4. Within the uncertainty limits, our bilateral and key comparisons [CCM.P-K4 (10 Pa to 1 kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table 5).

• FOCUS: LIFE SCIENCE
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• 제1호
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• pp.8.1-8.3
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• 2024

Ultra-high performance liquid chromatography (UHPLC) systems are integral to modern analytical laboratories, necessitating careful maintenance and operation protocols to ensure optimal performance. This document provides comprehensive guidelines for the proper shutdown and reactivation of UHPLC systems to prevent damage and maintain operational efficiency. • Shutdown: Remove the column and replace it with a union to avoid blockages. Flush the system with a compatible solvent mix, clean mobile phase reservoirs to prevent microbial growth, flush the pump with storage solvent, and clean the autosampler, including the needle and injection port. • Reactivation: Inspect the system for wear or damage, gradually reintroduce mobile phases starting with a weak solvent, reinstall the column securely, and perform system checks on baseline stability, pressure consistency, and detector performance. By adhering to these guidelines, laboratories can ensure the longevity and reliability of their UHPLC systems, maintaining high analytical performance and minimizing downtime. These procedures help prevent common issues such as blockages, contamination, and component wear, thereby supporting efficient and accurate analytical operations.

• Bulletin of the Korean Chemical Society
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• 제22권2호
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• pp.159-163
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• 2001

Si3N4 powder has been analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The sample was dissolved by high-pressure acid digestion with HF, H2SO4 (1+1), and HNO3 mix ture. This technique is well suited for the impurity analysis of Si3N4 because the matrix interference is eliminated. A round-robin samples trace elements, such as Ca, W, Co, Al, Fe, Mg, and Na, were determined. For the direct analysis, slurry nebulization of 0.96 mm Si3N4 powder also has been studied by ICP-AES. Emission intensities of Fe were measured as ICP operational conditions were changed. Significant signal difference between slurry particles and aqueous solution was observed in the present experiment. Analytical results of slurry injection and high-pressure acid digestion were compared. For the use of aqueous standard solution for calibration, k-factor was determined to be 1.71 for further application.

• Computers and Concrete
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• 제7권2호
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• pp.191-202
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• 2010

A laboratory investigation was conducted to characterize the constitutive property behavior of Cor-Tuf, an ultra-high-performance composite concrete. Mechanical property tests (hydrostatic compression, unconfined compression (UC), triaxial compression (TXC), unconfined direct pull (DP), uniaxial strain, and uniaxial-strain-load/constant-volumetric-strain tests) were performed on specimens prepared from concrete mixtures with and without steel fibers. From the UC and TXC test results, compression failure surfaces were developed for both sets of specimens. Both failure surfaces exhibited a continuous increase in maximum principal stress difference with increasing confining stress. The DP tests results determined the unconfined tensile strengths of the two mixtures. The tensile strength of each mixture was less than the generally assumed tensile strength for conventional strength concrete, which is 10 percent of the unconfined compressive strength. Both concretes behaved similarly, but Cor-Tuf with steel fibers exhibited slightly greater strength with increased confining pressure, and Cor-Tuf without steel fibers displayed slightly greater compressibility.

• 한국약용작물학회:학술대회논문집
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• 한국약용작물학회 2008년도 추계학술발표회
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• pp.483-484
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• 2008

• 대한화학회지
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• 제38권6호
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• pp.411-417
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• 1994

난용성 신소재 중의 하나인 파인 세라믹의 분석을 위하여, 알칼리 용융법과 고압 산분해법 등의 시료 전처리법을 유도결합원자발광분석기(ICP-AES)를 이용하여 연구하였다. Al2O3 분말을 분석하여 본 결과, 고압 산분해법이 알칼리 용융법보다 재현성 있는 측정치를 얻을 수 있었다. SiC분말의 경우에서는 고압산분해법으로 처리한 후 Si매트릭스를 Si-F형태로 증발시켜서 분석하여 본 결과 분말 중의 ppm 농도 범위의 불순물들이 매트릭스에 의한 간섭없이 분석되었다. 일본 인증기준물인 JCRM022, JCRM023 초미립 분말을 고압 산분해법으로 분석하여 본 결과, 좋은 재현성과 높은 정확성을 나타내었다.