• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.385-388
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• 1997

As the environmental regulations become stricter, new machining technologies are being developed which takes envi ronmenta 1 aspects into account . Since cut t ing oi I has some impact on environment. many researches are being carried out to minimize the use of cutting oi I. The methods for minimizing cutting oil usage includes the following techniques: I ) Cooling of tools and work piece. 2) Useage of compressed cooling air for the removal of chip. 3) Minimal useage of environment-friendly vegetable cutt:ngoiI for lubrication between chip and tools. Since the turning machine is continuous, tools are under constant thermal load and tool wear increases as the lubricative performance degrades. Also surface roughnesses have a direct influence on turning. In order to examine the characteristics of turningmachining, this work investigates experimentally the degree of tool wear and characteristics of surface roughness in relation to machining conditions, supply methods, and cooling methods.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.108-118
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• 2000

This paper describes a design of the helium-recondensing system utilizing cascade Roebuck refrigerators. Superconducting generator or motor has the superconducting field wind-ing in its rotor that should be continuously cooled by cryogen. Since liquid helium transfer from the stationary system to the rotor is problematic, cumbersome, and inefficient, the novel concept of a rotating helium-recondensing system is contrived. The vaporized cold helium inside the rotor is isothermally compressed by centrifugal force and expanded sequentially in cascade refrigerators until the helium is recondensed at 4.2 K. There is no helium coupling between the rotor and the stationary liquid helium storage. Thermodynamic analysis of the cascade refrigeration system is performed to determine the key design parameters. The loss mechanisms are explained to identify entropy generation that degrades the performance of the system.

• 대한기계학회논문집B
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• 제35권5호
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• pp.517-524
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• 2011

볼텍스 튜브는 고압의 가스를 이용하여 고온 가스와 저온 가스를 분리하거나 입자상 물질의 분리에 사용 할 수 있는 장치이다. 본 연구에서는 직경 10mm의 볼텍스 튜브의 기본 설계 자료를 구축하기 위하여 에너지 분리 성능 실험을 수행하였다. 설계를 위한 기초 자료를 확보하기 위하여, 공급압력, 볼텍스 발생기의 오리피스 직경 및 튜브의 길이가 에너지 분리 특성에 미치는 영향력을 실험을 통하여 분석하였다. 결과적으로 오리피스 직경과 공급압력이 볼텍스 튜브의 성능의 지배적인 성능인자임을 확인하였다. 튜브길이가 성능에 미치는 영향은 미미하였다. Dc=0.7D, L=16D의 볼텍스 튜브에서 가장 우수한 에너지 분리효과를 얻을 수 있었다.

• 한국공작기계학회논문집
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• 제15권6호
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• pp.50-57
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• 2006

The investigation of microscopic precision in high speed endmilling is necessary for machinability evaluation, and the environmentally conscious machining technology have more important position in recent machining process. The microscopic precision of workpiece is influenced by machining environments variation as cutting fluid type and lubricant method. In this study, the cutting forces according to variation of cooling and lubrication are investigated by specially designed tool dynamometer. And the surface roughness, micro hardness and residual stress are evaluated according to machining environment. The characteristics of damaged layer in environmentally conscious machining and conventional machining using cutting fluid are compared experimentally.

• Journal of Periodontal and Implant Science
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• 제24권1호
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• pp.196-204
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• 1994

The purpose of this clinical trial was to study the effectiveness of 5% potassium nitrate dentifrice as a daily home treatment of dentinal hypersensitivity. Thirty subjects with dentinal hypersensitivity were included in a 4-week, double-blind, parallel, comparative study. Stimuli used included mechanical, cold water and compressed air blasts. A subjective assessment of the degree of hypersensitivity for each stimulus was recorded. The results indicated that 5% potassium nitrate dentifrice, in comparision with a conventional fluoride dentifrice, reduced dentinal hypersensitivity to a significant degree. The therapeutic response to potassium nitrate was apparent within 2 weeks and increased continuously for the length of the study period. We conclude that 5% potassium nitrate dentifrice is an effective agent for the daily home treatment of dentinal hypersensitivity.

• 에너지공학
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• 제13권1호
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• pp.34-39
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• 2004

본 논문에서는 압축공기를 작동매체로 한 저압용 보텍스튜브에 대한 에너지 분리과정을 상세히 연구하였다 먼저 보텍스튜브에서 에너지 분리되어 나오는 온공기와 냉공기의 온도변화에 대하여 실험하였고, 보텍스튜브의 안쪽표면의 최대벽면온도 변화와 보텍스튜브 내의 온도분포를 통하여 보텍스튜브 내 유동장에서의 정체점의 위치에 대한 유용한 정보를 얻게 되었다. 이를 바탕으로 보텍스튜브의 노즐면적비와, 오리피스의 크기에 따른 에너지분리 과정 등을 실험을 통하여 알아보았다. 이러한 기하학적 형상의 변화실험을 통하여 저압용？대형 보텍스튜브의 에너지 분리과정이 고압형\ulcorner소형 보텍스튜브 보다 에너지 분리효과가 증대됨으로 인하여 최적의 노즐면적비와 오리피스지름비가 차이가 있음을 알 수 있었다.

• 터널과지하공간
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• 제2권1호
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• pp.116-122
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• 1992

A comprehensive, nonsteady state, computer simulation program for the environmental conditions in advancing tunnels (the HEADSIM simulation program) is constructed and successfully validated with heat balance amongst all heat sources, and with mass conservation amongst various airflows including the leakage air from ducts, under timedependent variations of inlet air conditions. which include sudden, diurnal and seasonal changes. Heat conduction in the wall strata and face strata is simulated with most complicated boundary conditions using the finite difference method, and the climatic conditions in roadway sections which contain air ducts, booster fan, spray cooler, compressed air pipes, cold water pipes, return water pipes, machinery and broken rock are simulated taking into account the variations of face operation and the heat storage mechanism in the strata. The limitations of simulation time steps and roadway section lengths are defined according to the stability criteria satisfying the principles of thermodynamics. Variations of heat transfer coefficients, which are newly set, and those of wetness factors are taken into account according to the variations of other parameters and the stepwise advance of the face. Newly-derived formulae are used for computing the air duct leakage and the pressure inside of the duct. A new concept of an 'imaginary duct' is introduced to simulate the climatic conditions in tunnels during holiday periods, which directly affect conditions on subsequent working days under the consideration of natural convection. A subsidiary program (the WALLSIM simulation program) is made to compute the dimensionless tunnel surface temperatures and to compare the results with those from analytical approaches, and to demonstrate the stability, convergence and accuracy of the strata heat conduction simulation, adopting the finite difference method. The WALLSIM also has wide applications, including those for the computation of age coefficients.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.225-226
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• 2006

As the technique of high-speed end-milling is widely adopted to machining field. The investigation for microscopic precision of workpiece is necessary for machinability evolution. The environmental pollution has become a big problem in industry and many researcher have investigated in order to preserve the environment. The environmentally conscious machining and technology have more important position in machining process. In the milling process, the cutting fluid has greatly bad influence on the environment. The damaged layer affect mold life and machine parts in machining. In this study, the cutting force, the surface roughness, micro hardness and residual stress is evaluated according to machining environment. Finally, it is obtained that the characteristics of damaged layer in environmentally conscious machining is better than that in conventional machining using cutting fluid.

• 에너지공학
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• 제11권3호
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• pp.276-282
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• 2002

본 논문에서는 압축공기를 작동매체로 한 저압용 vortex tube에 대한 에너지분리 과정을 상세히 연구하였다. 먼저 vortex tube에서 에너지 분리되어 나오는 온공기와 냉공기의 온도변화에 대하여 실험하였고, vortex tube의 안쪽표면의 최대벽면온도 변화와 vortex tube내의 온도분포를 통하여 vortex tube내 유동장에서의 정체점의 위치에 대한 유용한 정보를 얻게되었다. 이를 바탕으로 vortex tube의 최적 길이와 throttle의 형상, sleeve에 따른 에너지분리과정 등을 실험을 통하여 알아보았다. 또한 본 연구에서는 디젤기관의 배기에 적용하기 위한 외통을 사용하였다. 이때 vortex tube에서 나오는 은공기가 180$^{\circ}$돌아 나오면서 vortex tube의 바깥쪽 벽면을 가열하게 된다. 이러한 기하학적 형상을 통하여 에너지분리효과가 증대됨으로 인하여 디젤기관의 배기가스에 적용 시 고온유동의 온도를 높이고자함에 본 연구의 목적을 두고자한다.