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RESEARCH PAPERS: Micro/Nanoscale Heat Transfer

Suppression of Boiling Flow Oscillations in Parallel Microchannels by Inlet Restrictors

[+] Author and Article Information
Ali Koşar, Chih-Jung Kuo

Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180

Yoav Peles

Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180pelesy@rpi.edu

J. Heat Transfer 128(3), 251-260 (Sep 27, 2005) (10 pages) doi:10.1115/1.2150837 History: Received May 12, 2005; Revised September 27, 2005

Geometrical effects of MEMS-based microfabricated inlet orifices on the suppression of parallel channel and upstream compressible volume instabilities commonly exhibited during flow boiling in parallel microchannels have been investigated. The heat fluxes at the onset of unstable boiling have been obtained over effective heat fluxes ranging from 9 to 614Wcm2 and mass fluxes from 115to389kgm2s. A dimensionless parameter M, which accounts for the pressure drop increase imposed by the inlet restrictors, has been used to correlate the extent of flow instability suppression. It has been shown that the onset of unstable boiling asymptotically increases with M. At sufficiently high M values, parallel channels and upstream compressible volume instabilities are completely eradicated although it gives way to another instability to develop, namely, the critical heat flux conditions. A correlation has been developed in terms of M to predict the conditions leading to unstable boiling.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) CAD model of the microchannel device, (b) Geometry of a sample orifice configuration, (c) Flow distributive pillars (units in μm)

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Figure 2

Experimental setup

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Figure 3

Dependence of friction factor on the Reynolds number

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Figure 4

Dependence of M on the Reynolds number

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Figure 5

Experimental and theoretical (38) friction factors across orifices: (a) Device 2R50, (b) Device 3R200, (c) Device 4R400

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Figure 6

Pressure multiplier as a function of xe: (a) Device 2R50, (b) Device 3R200, (c) Device 4R400

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Figure 7

Pressure drop fluctuations in device 1NR at G=389kg∕m2s: (a) Adiabatic condition, (b) Impeding OUB, (c) At OUB

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Figure 8

Average surface temperatures of the devices: (a) G=115kg∕m2s; (b) G=265kg∕m2s; (c) G=389kg∕m2s

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Figure 9

Time sequence of images at OUB (G=265kg∕m2s) recorded for device 1NR at the inlet

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Figure 10

Comparison of qoub″ data with CHF correlations

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Figure 11

qoub″∕qoub,400μm″ as a function of M

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