• Title/Summary/Keyword: micro scale

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Numerical simulation and experimental study of quasi-periodic large-scale vortex structures in rod bundle lattices

  • Yi Liao;Songyang Ma;Hongguang Xiao;Wenzhen Chen;Kehan Ouyang;Zehua Guo;Lele Song
    • Nuclear Engineering and Technology
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    • v.56 no.2
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    • pp.410-418
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    • 2024
  • Study of flow behavior within rod bundles has been an active topic. Surface modification technologies are important parts of the design of the fourth generation reactor, which can increase the strength of the secondary flow within the rod bundle lattices. Quasi-periodic large-scale vortex structure (QLVS) is introduced by arranging micro ribs on the surface of rod bundles, which enhanced the scale of the secondary flow between the rod bundle lattices. Using computational fluid dynamics (CFD) and water experiments, the flow field distribution and drag coefficient of the rod-bundle lattices are studied. The secondary flow between the micro-ribbed rod-bundle lattice is significantly enhanced compared to the standard rod-bundle lattice. The numerical simulation results agree well with the experimental results.

Fabrication and Characterization of Micro parts by Mechanical Micro Machining: Precision and Cost Estimation (기계식 마이크로 머시닝을 이용한 마이크로 형상의 특성과 비용 평가)

  • Kang, Hyuk-Jin;Choi, Woon-Yong;Ahn, Sung-Hoon
    • Journal of the Korean Society for Precision Engineering
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    • v.24 no.1 s.190
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    • pp.47-56
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    • 2007
  • Recently, demands on mechanical micro machining technology have been increased in manufacturing of micro-scale precision shapes and parts. The main purpose of this research is to verify the accuracy and cost efficiency of the mechanical micro machining. In order to measure the precision and feasibility of mechanical micro machining, various micro features were machined. Aluminum molds were machined by a 3-axis micro stage in order to fabricate microchips with $200{\mu}m$ wide channel for capillary electrophoresis, then the same geometry of microchip was made by injection molding. To evaluate the cost efficiency of various micro manufacturing processes, cost estimation for mechanical micro machining was conducted, and actual costs of microchips fabricated by mechanical micro machining, injection molding, and MEMS (Micro electro mechanical system) were compared.

Memory-Efficient Hypercube Key Establishment Scheme for Micro-Sensor Networks

  • Lhee, Kyung-Suk
    • ETRI Journal
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    • v.30 no.3
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    • pp.483-485
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    • 2008
  • A micro-sensor network is comprised of a large number of small sensors with limited memory capacity. Current key-establishment schemes for symmetric encryption require too much memory for micro-sensor networks on a large scale. In this paper, we propose a memory-efficient hypercube key establishment scheme that only requires logarithmic memory overhead.

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COMPUTATIONAL INVESTIGATION OF NOZZLE FLOWFIELD IN A MICRO TURBOJET ENGINE AND ITS SCALING CHARACTERISTICS (마이크로 터보제트 엔진 노즐 유동장에 관한 CFD 전산해석 및 스케일링 특성 연구)

  • Lee, H.J.;An, C.H.;Myong, R.S.;Choi, S.M.;Kim, W.C.
    • Journal of computational fluids engineering
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    • v.22 no.1
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    • pp.43-50
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    • 2017
  • Thermal flowfield of a micro turbojet engine was computationally investigated for exhaust nozzles with different aspect ratio and curvature. Special attention was paid to maximum and average temperature of the nozzle surface and the exhaust nozzle plume. The IR signatures of the micro turbojet engine nozzle were then calculated through the narrow-band model based on thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the sub-scale micro turbojet engine model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in sub-scale and full-scale cases.

A Study on Vehicle Big Data-based Micro-scale Segment Speed Information Service for Future Traffic Environment Assistance (미래 교통환경 지원을 위한 차량 빅데이터 기반의 미시구간 속도정보 서비스 방안 연구)

  • Choi, Kanghyeok;Chong, Kyusoo
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.21 no.2
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    • pp.74-84
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    • 2022
  • Vehicle average speed information which measured at a point or a short section has a problem in that it cannot accurately provide the speed changes on an actual highway. In this study, segment separation method based on vehicle big data for accurate micro-speed estimation is proposed. In this study, to find the point where the speed deviation occurs using location-based individual vehicle big data, time and space mean speed functions were used. Next, points being changed micro-scale speed are classified through gradual segment separation based on geohash. By the comparative evaluation for the results, this study presents that the link-based speed is could not represent accurate speed for micro-scale segments.

Fabrication and feasibility estimation of Micro Engine Component (미세 엔진 운용성 검증 및 요소 기술 개발)

  • Lee, Dae-Hoon;Park, Dae-Eun;Choi, Kwon-Hyoung;Yoon, Joon-Bo;Kwon, Se-Jin;Yoon, Eui-Sik
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.31-36
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    • 2001
  • As a part of micro engine development feasibility estimation was done through fabrication and test of down scaled combustor and MEMS fabricated spark electrode. In an experimental observation of the down scaled combustion phenomena where flame propagation was observed by optical method and pressure change in combustor which gives the information about the reaction generated thermal energy was recorded and analyzed. Optimal combustor scale was derived to be about 2mm considering increased heat loss effect and thermal energy generation capability. Through the fabrication and discharge test of MEMS electrode effects of electrode width and gap was investigated. Electrode was fabricated by thick PR mold and electroplating. From the result discharge voltage characteristic in sub millimeter scale electrode having thickness of $40{\mu}m$ was obtained. From the result base technology for design and fabrication of micro engine was obtained.

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Ion Beam Induced Micro/Nano Fabrication: Modeling (이온빔을 이용한 마이크로/나노 가공: 모델링)

  • Kim, Heung-Bae;Hobler, Gerhard
    • Journal of the Korean Society for Precision Engineering
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    • v.24 no.8 s.197
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    • pp.108-115
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    • 2007
  • 3D nano-scale manufacturing is an important aspect of advanced manufacturing technology. A key element in ability to view, fabricate, and in some cases operate micro-devices is the availability of tightly focused particle beams, particularly of photons, electrons, and ions. The use of ions is the only way to fabricate directly micro-/ nano-scale structures. It has been utilized as a direct-write method for lithography, implantation, and milling of functional devices. The simulation of ion beam induced physical and chemical phenomena based on sound mathematical models associated with simulation methods is presented for 3D micro-/nanofabrication. The results obtained from experimental investigation and characteristics of ion beam induced direct fabrication will be discussed.

A Study on the Modeling of Pt-Catalyzed Reaction and the Characteristics of Mass Transfer in a Micro-Scale Combustor (마이크로 스케일 연소기의 백금 촉매 반응 모델링과 물질 전달 특성에 대한 연구)

  • Lee, Gwang-Goo;Suzuki, Yuji
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.11
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    • pp.870-877
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    • 2008
  • Numerical analysis is applied to model Pt-catalyzed reaction in a micro-scale combustor fueled by butane. The reaction constants of catalytic oxidation are determined from plug flow model with the experimental data. Orders of magnitude between the chemical reaction rate and the mass transfer rate are carefully compared to reveal which mechanism plays a dominant role in the total fuel conversion rate. For various conditions of fuel flow rate and surface temperature, the profiles of Sherwood number are investigated to study the characteristics of the mass transport phenomena in the micro-tube combustor.

Analysis of Nano-contact Between Nano-asperities Using Atomic Force Microscopy (나노스케일 표면돌기 간의 미세접촉에 대한 해석)

  • Ahn, Hyo-Sok;Jang, Dong-Young
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.18 no.4
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    • pp.369-374
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    • 2009
  • In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and $Si_3N_4$ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

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