• Title/Summary/Keyword: Microchannel

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Investigation of Heat Transfer in Microchannel with One-Side Heating Condition Using Numerical Analysis (수치 해석을 이용한 단일 마이크로채널의 단면 가열 조건의 열전달 특성에 관한 연구)

  • Choi, Chi-Woong;Huh, Cheol;Kim, Dong-Eok;Kim, Moo-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.12
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    • pp.986-993
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    • 2007
  • The microchannel heat sink is promising heat dissipation method far high density electronic devices. The cross-sectional shape of MEMS based microchannel heat sink is limited to triangular, trapezoidal, and rectangular due to their fabrication method. And heat is added to one side surface of heat source. Therefore, those specific conditions make some complexity of heat transfer in microchannel heat sink. Though many previous research of conjugate heat transfer in microchannel was conducted, most of them did not consider heat loss. In this study, numerical investigation of conjugate heat transfer in rectangular microchannel was conducted. The method of heat loss evaluation was verified numerically. Heat distribution was different for each wall of rectangular microchannel due to thermal conductivity and distance from heat source. However, the ratio of heat from each channel wall was correlated. Therefore, the effective area correction factor could be proposed to evaluate accurate heat flux in one side heating condition.

Study of Wettability Effect on Pressure Drop and Flow Pattern of Two-Phase Flow in Rectangular Microchannel (사각 마이크로채널 내의 2 상유동 압력강하와 유동양식에 대한 젖음성의 영향에 대한 연구)

  • Choi, Chi-Woong;Yu, Dong-In;Kim, Moo-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.12
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    • pp.939-946
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    • 2009
  • Wettability is a critical parameter in micro-scale two-phase system. Several previous results indicate that wettability has influential affect on two-phase flow pattern in a microchannel. However, previous studies conducted using circular microtube, which was made by conventional fabrication techniques. Although most applications for micro thermal hydraulic system has used a rectangular microchannel, data for the rectangular microchannel is totally lack. In this study, a hydrophilic rectangular microchannel was fabricated using a photosensitive glass. And a hydrophobic rectangular microchannel was prepared using silanization of glass surfaces with OTS (octa-dethyl-trichloro-siliane). Experiments of two-phase flow in the hydrophilic and the hydrophobic rectangular microchannels were conducted using water and nitrogen gas. Visualization of twophase flow pattern was carried out using a high-speed camera and a long distance microscope. Visualization results show that the wettability was important for two-phase flow pattern in rectangular microchannel. In addition, two-phase frictional pressure drop was highly related with flow patterns. Finally, Two-phase frictional pressure drop was analyzed with flow patterns.

Effects of External Voltages and Widths on Fluid Velocity in Microchannel (외부전압 및 너비 변화에 따른 마이크로채널의 유체 속도 변화)

  • Kim, Jin-Yong;Lee, Hyo-Song;Kim, Jeong-Soo;Rhee, Young Woo
    • Applied Chemistry for Engineering
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    • v.16 no.2
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    • pp.238-242
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    • 2005
  • In this work, Polydimethylsiloxane (PDMS) and SU-8 (Microchem, USA) photoresist were used to make the microchannel by soft lithographic method. To investigate the effects of external voltages and widths of the microchannel, we made the microchannel by soft lithographic method. To investigate the effects of external voltages and widths of the microchannel, we made the microchannel with various widths: $100{\mu}m,\;200{\mu}m$ and $300{\mu}m$. And each micorchannel was supplied with external voltage, respectively. As a result, the fluid velocity increased with an increase of the external voltage at the same width. It was speculated that the electrical double layer was condensed and the zeta potential increased with increase of the external voltage. The fluid velocity increased with the microchannel width increase at the same external voltage. It is concluded that the resistance in the microchannel decreased as the microchannel width increased.

Cooling Performance of a Microchannel Heat Sink with Nanofluids (나노유체를 냉각유체로 사용하는 마이크로채널 히트 싱크의 냉각효율)

  • Jang, Seok-Pil
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.9
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    • pp.849-854
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    • 2005
  • In this paper, the cooling performance of a microchannel heat sink with nano-particle-fluid suspensions ('nanofluids') is numerically investigated. By using theoretical models of thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion respectively, we investigate the temperature contours and thermal resistance of a microchannel heat sink with nanofluids such as 6nm copper-in-water and 2nm diamond-in-water. The results show that a microchannel heat sink with nanofluids has high cooling performance compared with the cooling performance of that with water, the classical coolant. Nanofluids reduce both the thermal resistance and the temperature difference between the heated microchannel wall and the coolant.

Variation of Flow Rates in Heterogeneous Microchannel Systems (비균일계 마이크로채널에서의 유량 변화 특성)

  • Kim, Jin-Yong;Lee, Hyo-Song;Yu, Jae-Keun;Kim, Ki-Ho;Rhee, Young Woo
    • Applied Chemistry for Engineering
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    • v.17 no.1
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    • pp.28-32
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    • 2006
  • This study investigated the variation of flow rates in microchannels that consisted of polydimethyl siloxane (PDMS) and glass using various external voltages. Three different microchannel widths and two different depths. PDMS and negative photoresist (SU-8) were used to make the microchannels by the soft lithographic method. For each depth of microchannel ($50{\mu}m$ and $100{\mu}m$), three different widths ($100{\mu}m$, $200{\mu}m$ and $300{\mu}m$) were made. In each case, several different external voltages were applied (0.3 kV, 0.35 kV, 0.4 kV and 0.45 kV) to examine the flow rates. Our results indicated that flow rate increased with an increase of the external voltage at the same microchannel width. This was because the electrical field was increased as the external voltage increased. For the same external voltage, the flow rate increased as the microchannel's width increased. These results showed that the resistance in the microchannel decreased as the microchannel's width increased. Also, to investigate the effect of microchannel's depth and width, the cross-sectional area of the microchannel was increased to the double in area. As a result, the effect of the microchannel's depth was higher at a low external voltage, and the effect of the microchannel's width was higher at a high external voltage.

Fabrication of a novel micromachined measurement device for temperature distribution measurement in the microchannel (마이크로채널 내의 온도 분포 측정을 위한 미소 측정 구조물의 제작)

  • Park, Ho-Joon;Lim, Geun-Bae;Son, Sang-Young;Song, In-Seob;Pak, James-Jung-Ho
    • Proceedings of the KIEE Conference
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    • pp.1921-1923
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    • 2001
  • In this work, an array of resistance temperature detector(RTD) was fabricated inside the microchannel in order to investigate in-situ flow characteristics. A rectangular straight microchannel, integrated with RTD's for temperature sensing and a heat source for generating the temperature gradient along the channel. were fabricated with the dimension of $200{\mu}m(W){\times}{\mu}m(D){\times}$48mm(L), while RTD measured precise temperatures at the inside-channel wall. 4" $525{\pm}25{\mu}m$ thick P-type <100> Si wafer was used as a substrate. For the fabrication of RTDs. 5300$\AA$ thick Pt/Ti layer was sputtered on a Pyrex glass wafer. Finally, glass wafer was bonded with Si wafer by anodic bonding, therefore RTD was located inside the microchannel. The temperature distribution inside the fabricated microchannel was obtained from 4 point probe measurements and Dl water is used as a working fluid. Temperature distribution inside the microchannel was measured as a function of mass flow rate and heat flux. As a result, precise temperatures inside the microchannel could be obtained. In conclusion, this novel temperature distribution measurement system will be very useful to the accurate analysis of the flow characteristics in the microchannel.

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STUDY ON TWO-DIMENSIONAL LAMINAR FLOW PAST A VERTICAL PLATE IN A MICROCHANNEL (마이크로채널 내의 수직 평판을 지나는 2차원 층류유동장에 대한 연구)

  • Yoon, Seok-Hyun;Jeong, Jae-Tack
    • 한국전산유체공학회:학술대회논문집
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    • pp.233-238
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    • 2010
  • A two-dimensional laminar flow past a vertical plate in a microchannel is investigated. At far upstream and downstream from the plate in the microchannel, the plane Poiseuille flow exists. The Stokes flow for this microchannel is investigated analytically and then the laminar flow by numerical method. For the Stokes flow analysis, the method of eigenfunction expansion is used. From the results, the streamline pattern and the pressure distribution are plotted, and the additional pressure drop induced by the plate and the force exerted on the plate are calculated as functions of the length of the plate. For the laminar flow, finite difference method (FDM) is used to obtain the vorticity and the stream function. When the Reynolds number exceeds a critical value, a pair of viscous eddies appears behind the plate.

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Comparison of Performance Characteristics with Heat Exchanger Type in $CO_2$ Cycle (이산화탄소 사이클에서 열교환기의 형태 변화에 따른 성능특성 비교)

  • Bae, Kyung-Jin;Cho, Hong-Hyun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.10
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    • pp.657-664
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    • 2010
  • The theoretical analysis of performance characteristics in a $CO_2$ cycle with the heat exchanger type was carried out. The size and performance of the fin-tube and microchannel heat exchanger were compared with operating conditions. As a result, the performance of the fin-tube gascooler and evaporator were more sensitive to the variation of operating condition compared to that of the microchannel gascooler and evaporator. Beside, the sizes of microchannel gascooler and evaporator could be decreased by 73% and 76%, respectively, compared to those of the fin-tube type gascooler and evaporator with the similar capacity. The COP and reliability of the $CO_2$ system can be increased by using a microchannel heat exchanger.

Manipulation of Microfluid Width in a Microchannel Using Gas Boundary (미세 채널에서 가스 경계면을 이용한 미세 유체의 폭 조절)

  • Son, Sang-Uk;Lee, Seung-Seob
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.8
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    • pp.1190-1195
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    • 2004
  • A novel manipulation of microfluid width in a microchannel was presented by controlling inflation of a gas boundary. The gas boundary was formed by heating water with a microheater in a semicircular shape from a chamber which was connected symmetrically to the microchannel. The formed gas boundary inflated perpendicularly to the flow direction and, consequently, the microfluid width was narrowed. The inflation and contraction were flexibly like a virtual wall and dependent on two factors: one is the flow velocity of the microfluid and the other is the pressure inside the gas boundary. Dimensions of the chamber and the microchannel width were determined empirically as same of $300\;{\mu}m$ for stable operation. The width of microfluid was manipulated manually with the microheater and could be maintained as up to $22\;{\mu}m$. The stable focusing began to be distorted when the flow velocity exceeded 17.8 mm/s.

The flow Analysis in a Microchannel using the Lattice Boltzmann Method (격자볼츠만방법(LBM)을 이용한 마이크로채널 내의 유동해석)

  • Cho K. J.;Jeong J. T.
    • 한국전산유체공학회:학술대회논문집
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    • pp.79-82
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    • 2004
  • As an alternative numerical method, the lattice Boltzmann method (LBM) is used to simulate a 2-dimensional pressure driven microchannel flow which comes from frequently in MEMS problems. The flow is assumed to be isothermal ideal gas flow. The flow field is calculated with various Knudsen numbers, pressure ratios and aspect ratios of the microchannel. The LBM can show the fundamental characteristics in microchannel flow such as velocity slip and nonlinear pressure drop.

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