• 제목/요약/키워드: Microchannel

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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.

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.

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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    • 2001.07c
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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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A Numerical Analysis on Cooling Performance of Microchannel Waterblock for Electronic Devices Cooling (전자기기 냉각용 마이크로채널 워터블록의 냉각성능에 관한 수치해석)

  • Choi, Mi-Jin;Kwon, Oh-Kyung;Cha, Dong-An;Yun, Jae-Ho;Lee, Chan
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2426-2431
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    • 2007
  • The microchannel waterblock has a good capability in the cooling of electronic devices. The object of this paper is to estiblish the scheme of design for the microchannel waterblock. The effects of flow rate and channel size on the cooling performances are investigated. It was found that the optimum flow rates were ragned from 0.7 lpm to 1.4 lpm. The thermal resistance at 2.0 lpm and 100 W was 0.13 $^{\circ}C$/W. Decrease in the width of channels is more effective for the improvement in the cooling performances of microchannel waterblock than increase in the height of channels. The increase of pressure drop resulted from decrease in the width of channels can be decreased by increasing the hight of channels.

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An Experimental Study on Cooling Performance of Microchannel Waterblock for Electronic Devices Cooling (전자기기 냉각용 마이크로채널 워터블록의 냉각성능에 관한 실험적 연구)

  • Kwon, Oh-Kyung;Choi, Mi-Jin;Cha, Dong-An;Yun, Jae-Ho
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2432-2437
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    • 2007
  • The demand of high speed and miniaturization of electronic devices results in increased power dissipation requirement for thermal management. In this work, the effects of microchannel width, height and liquid flowrate on the cooling performances of microchannel waterblock are investigated experimentally. The microchannel waterblock considered ranged in width from 0.5 to 0.9 mm, with the channel height being nominally 1.7 to 9 times the width in each case. The experiments were conducted using water, over a liquid flow rate ranging from 0.2 to 2.0 lpm. The base temperature, thermal resistance and pressure drop increase with increasing of liquid flow rate. The measured thermal resistances ranged from 0.10 to 0.23 $^{\circ}C$/W for the channel 5.

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Numerical Study of Heat Transfer Enhancement on Microchannel Plate Heat Exchanger with Channel Shape (채널 형상에 따른 마이크로채널 판형 열교환기 열전달 성능 향상에 관한 수치 연구)

  • Jeon, Seung-Won;Kim, Yoon-Ho;Lee, Kyu-Jung
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.1888-1893
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    • 2007
  • In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

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Averaging Approach for Microchannel Heat Sinks Subjected to the Uniform Wall Temperature Condition (등온 경계 조건을 가지는 마이크로채널 히트 싱크의 열성능 해석을 위한 평균 접근법)

  • Kim, Dong-Kwon;Kim, Sung-Jin
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.1247-1252
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    • 2004
  • The present paper is devoted to the modeling method based on an averaging approach for thermal analysis of microchannel heat sinks subjected to the uniform wall temperature condition. Solutions for velocity and temperature distributions are presented using the averaging approach. When the aspect ratio of the microchannel is higher than 1, these solutions accurately evaluate thermal resistances of heat sinks. Asymptotic solutions for velocity and temperature distributions at the high-aspect-ratio limit are alsopresented by using the scale analysis. Asymptotic solutions are simple, but shown to predict thermal resistances accurately when the aspect ratio is higher than 10. The effects of the aspect ratio and the porosity on the friction factor and the Nusselt number are presented. Characteristics of the thermal resistance of microchannel heat sinks are also discussed.

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