• Title, Summary, Keyword: Aspect Ratio

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EFFECT OF ASPECT RATIO ON SLIP FLOW IN RECTANGULAR MICROCHANNELS

  • Islam, Md.Tajul;Lee, Yeon-Won
    • Proceedings of the KSME Conference
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    • pp.2803-2810
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    • 2007
  • Three dimensional numerical studies were carried out to investigate the effect of aspect ratio on gas slip flow in rectangular microchannels. We focused on aspect ratio effect on slip velocity, pressure distribution and mass flow rate. As aspect ratio decreases the wall slip velocity also decreases. As a result nonlinearity of pressure distribution increases. The slip velocities on sides and top/bottom walls are different and this difference decreases with increasing aspect ratio. These two velocities are equal when aspect ratio is 1. The ratios of slip mass flow rate over noslip mass flow rate increases with increasing aspect ratios.

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Influence of an Aspect Ratio of Rectangular Channel on the Cooling Performance of a Multichip Module

  • Choi, Min-Goo;Cho, Keum-Nam
    • Journal of Mechanical Science and Technology
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    • v.14 no.3
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    • pp.350-357
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    • 2000
  • Experiments were performed by using PF-5060 and water to investigate the influence of an aspect ratio of a horizontal rectangular channel on the cooling characteristics from an in-line $6{\times}1$ array of discrete heat sources which were flush mounted on the top wall of the channel. The experimental parameters were aspect ratio of rectangular channel, heat flux of simulated VLSI chip, and channel Reynolds number. The chip surface temperatures decreased with the aspect ratio at the first and sixth rows, and decreased more rapidly at a high heat flux than at a low heat flux. The measured friction factors at each aspect ratio for both water and PF-5060 gave a good agreement with the values predicted by the modified Blasius equation within ${\pm}7%$. The Nusselt number increased as the aspect ratio decreased, but the increasing rate of Nusselt number reduced as the aspect ratio decreased. A 5:1 rectangular channel yields the most efficient cooling performance when the heat transfer and pressure drop in the test section were considered simultaneously.

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High-Aspect-Ratio Nanoscale Patterning in a Negative Tone Photoresist

  • Ryoo, Kwangki;Lee, Jeong Bong
    • Journal of information and communication convergence engineering
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    • v.13 no.1
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    • pp.56-61
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    • 2015
  • The demand for high-aspect-ratio structures has been increasing in the field of semiconductors and other applications. Here, we present the commercially available negative-tone SU-8 as a potential resist that can be used for direct patterning of high-aspect-ratio structures at the submicron scale and the nanoscale. Such resist patterns can be used as polymeric molds to create high-aspect-ratio metallic submicron and nanoscale structures by using electroplating. Compared with poly (methyl methacrylate) (PMMA), we found that the negative tone resist required an exposure dose that was less than that of PMMA of equal thickness by a factor of 100-150. Patterning of up to 4:1 aspect ratio SU-8 structures with a minimum feature size of 500 nm was demonstrated. In addition, nanoimprint lithography was studied to further extend the aspect ratio to realize a minimum feature size of less than 10 nm with an extremely high aspect ratio in the negative resist.

A Proton Beam Shaping using an Extreme Aspect Ratio Micro-hole (극대세장비 마이크로 홀을 이용한 양성자 빔 집적 응용)

  • Kim, Jin-Nam;Kwon, Won-Tae;Lee, Seong-Gyu
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.7
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    • pp.737-744
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    • 2012
  • EDM is the manufacturing process that uses the thermal energy to machine electrically conductive part. Despite a lot of research has been conducted for decades, the best aspect ratio of the micro hole using micro-EDM has not been over 30, yet. In the present study, new fabrication scheme was introduced to increase the aspect ratio of micro hole dramatically. Micro holes with less than 10 aspect ratio were aligned and welded together to manufacture a micro hole with extreme aspect ratio. Alignment of the micro hole with over 380 aspect ratio was conducted by the home-made apparatus installed with microscope and laser beam. The micro hole with extreme aspect ratio was used to shape pencil beam from proton beam generated from MC-50 cyclotron. The pencil beam was utilized to machine test specimen whose result was compared with GEANT4 computer simulation. It was shown that the experimental and simulation result were closer as the aspect ratio of the micro hole was bigger.

A technique to avoid aspect-ratio locking in QUAD8 element for extremely large aspect-ratios

  • Rajendran, S.
    • Structural Engineering and Mechanics
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    • v.37 no.6
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    • pp.633-648
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    • 2011
  • This paper investigates the aspect-ratio locking of the isoparametric 8-node quadrilateral (QUAD8) element. An important finding is that, if finite element solution is carried out with in exact arithmetic (i.e., with no truncation and round off errors), the locking tendency of the element is completely avoided even for aspect-ratios as high as 100000. The current finite element codes mostly use floating point arithmetic. Thus, they can only avoid this locking for aspect-ratios up to 100 or 1000. A novel method is proposed in the paper to avoid aspect-ratio locking in floating point computations. In this method, the offending terms of the strain-displacement matrix (i.e., $\mathbf{B}$-matrix) are multiplied by suitable scaling factors to avoid ill-conditioning of stiffness matrix. Numerical examples are presented to demonstrate the efficacy of the method. The examples reveal that aspect-ratio locking is avoided even for aspect-ratios as high as 100000.

The Influences of Process Parameters in Piercing with a High Aspect Ratio for Thick Aluminum Sheet (알루미늄 판재의 고 세장비 피어싱가공을 위한 작업변수의 영향)

  • Kim, J.G.;Kim, J.B.;Kim, J.H.
    • Transactions of Materials Processing
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    • v.23 no.1
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    • pp.23-28
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    • 2014
  • The aspect ratio of a hole is defined as the ratio of the thickness to the diameter of the sheet metal. Most holes in the sheet metal industry are made by piercing. However, for thick sheets, which have an aspect ratio greater than 2, a machining process like drilling instead of piercing is usually used to make holes. In the current study, piercing, which is a shearing process, is evaluated to punch a hole with a high aspect ratio by using a newly designed die set-up. The piercing die was manufactured to prevent the punch from buckling and also to improve the alignment between the die components. An aluminum alloy sheet was selected for the experiments. The influence of several process parameters such as sheet thickness, clearance and stripping force were investigated. Experimentally, a hole with an aspect ratio of 5 was pierced. The resulting hole had a clean surface and the dimensional accuracy of pierced hole was considerably improved with decreasing clearance between punch and die. It is also shown that the larger penetration depth of the effective sheared surface can be achieved for high aspect ratio piercing relative to conventional piercing with a low aspect ratio.

Electrical Conductivity of Carbon Fiber-Polymer Composite (Carbon 화이버-폴리머 복합체의 전기적 특성)

  • 이재연;최경만
    • Journal of the Korean Ceramic Society
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    • v.35 no.6
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    • pp.603-609
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    • 1998
  • The composites of insulating polymer filled with conducting carbon-fiber were fabricated by molding press method. To understand the fiber aspect-ratio dependence of electrical conductivity the aspect ratio was varied from 4 to 10 The percolation thresholds of transition from the insulator to the conductor de-creased as the fiber aspect ratio increased. The percolation threshold of fiber-segregated composite in this study was smaller than that of fiber-random composite shown in other study. When the electrical con-ductivity curves were fitted by general effective medium equation morphological variable(t) decreased as the fiber aspect-ratio increased.

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The Effect of Aspect Ratio on Aerodynamic Characteristics of Flapping Motion (날개의 종횡비가 날개 짓 운동의 공기역학적 특성에 미치는 영향)

  • Oh, Hyun-Taek;Choi, Hang-Cheol;Kim, Kwang-Ho;Chung, Jin-Taek
    • 유체기계공업학회:학술대회논문집
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    • pp.217-220
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    • 2006
  • The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from $10^{\circ}$ to $40^{\circ}$ regardless of aspect ratio, and the mean drag coefficients above angle of attack $50^{\circ}$ were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.

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A Study on Prediction of Young's Modulus of Composite with Aspect Ratio Distribution of Short Fiber (장단비 분포를 갖는 단섬유 복합재의 영계수 예측에 대한 연구)

  • Lee, J.K.
    • Journal of the Korea Society For Power System Engineering
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    • v.10 no.4
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    • pp.99-104
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    • 2006
  • Young's modulus of composite has been predicted by Eshelby's equivalent inclusion method modified with Mori-Tanaka's mean field theory, where short fibers of aspect ratio distribution are assumed to be aligned. Young's modulus of the composite is predicted with the smallest class interval for simulating the actual distribution of fiber aspect ratio, which is compared with that computed using different class intervals. Young's modulus of the composite predicted with mean aspect ratio or the largest class interval is overestimated by the maximum 10%. As the class interval of short fibers for predicting Young's modulus decreases, the predicted results show good agreements with those obtained using the actual distribution of fiber aspect ratio. It can be finally concluded from the study that if and only if the class interval of short fiber normalized by the maximum aspect ratio is smaller than 0.1, the predicted results are consistent with those obtained using the actual distribution of aspect ratio.

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Effects of Aspect Ratio on Local Heat/Mass Transfer in Wavy Duct (열교환기 내부 유로 종횡비 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang In Hyuk;Hwang Sang Dong;Cho Hyung Hee
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.6
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    • pp.569-580
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    • 2005
  • The present study investigates the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger. The effects of duct aspect ratio and flow velocity on the heat/mass transfer are investigated. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The aspect ratios of the wavy duct are 7.3, 4.7 and 1.8 with the corrugation angle of $145\Omega$. The Reynolds numbers, based on the duct hydraulic diameter, vary from 300 to 3,000. The results show that at the low Re(Re $\leq$ 1000) the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, non-uniform heat/mass transfer coefficients distributions appear. As the aspect ratio decreases, the number of cells formed by secondary vortices are reduced and secondary vortices and comer vortices mix due to decreased aspect ratio at Re$\leq$1000. At Re >1000, the effects of corner vortices become stronger. The average Sh for the aspect ratio of 7.3 and 4.7 are almost same. But at the small aspect ratio of 1.8, the average Sh decreases due to decreased aspect ratio. More pumping power (pressure loss) is required for the larger aspect ratio due to the higher flow instability.