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Research Papers

Two-Phase Microchannel Heat Sinks: Theory, Applications, and Limitations

[+] Author and Article Information
Issam Mudawar

Boiling and Two-Phase Flow Laboratory (BTPFL),  Purdue University International Electronic Cooling Alliance (PUIECA), Mechanical Engineering Building, 585 Purdue Mall, West Lafayette, IN 47907

J. Electron. Packag 133(4), 041002 (Dec 08, 2011) (31 pages) doi:10.1115/1.4005300 History: Received July 11, 2011; Revised September 30, 2011; Published December 08, 2011; Online December 08, 2011

Boiling water in small channels that are formed along turbine blades has been examined since the 1970s as a means to dissipating large amounts of heat. Later, similar geometries could be found in cooling systems for computers, fusion reactors, rocket nozzles, avionics, hybrid vehicle power electronics, and space systems. This paper addresses (a) the implementation of two-phase microchannel heat sinks in these applications, (b) the fluid physics and limitations of boiling in small passages, and effective tools for predicting the thermal performance of heat sinks, and (c) means to enhance this performance. It is shown that despite many hundreds of publications attempting to predict the performance of two-phase microchannel heat sinks, there are only a handful of predictive tools that can tackle broad ranges of geometrical and operating parameters or different fluids. Development of these tools is complicated by a lack of reliable databases and the drastic differences in boiling behavior of different fluids in small passages. For example, flow boiling of certain fluids in very small diameter channels may be no different than in macrochannels. Conversely, other fluids may exhibit considerable “confinement” even in seemingly large diameter channels. It is shown that cutting-edge heat transfer enhancement techniques, such as the use of nanofluids and carbon nanotube coatings, with proven merits to single-phase macrosystems, may not offer similar advantages to microchannel heat sinks. Better performance may be achieved by careful optimization of the heat sink’s geometrical parameters and by adapting a new class of hybrid cooling schemes that combine the benefits of microchannel flow with those of jet impingement.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Comparisons of (a) boiling curves and (b) pressure drop characteristics for microchannel and minichannel heat sinks with identical inlet conditions using R-113. (Adapted from Bowers and Mudawar [13])

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Figure 2

Two-phase water cooling of turbine blades using open-tipped cooling passages. (Adapted from Mudawar [23-24])

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Figure 3

(a) International thermonuclear experimental reactor (ITER) [25] and schematics of microchannel cooling of first-wall of fusion reactor blanket. (b) Variation of CHF for water flow boiling through single tube with inlet temperature and outlet pressure based on Hall and Mudawar’s high-flux inlet conditions correlation [29].

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Figure 4

(a) Schematic of rocket engine microchannel cooling. (b) Photograph of NASA combustion chamber utilizing high aspect ratio cooling channels [32]

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Figure 5

Vapor removal from concave heated wall of small rectangular channel by centrifugal forces [36]

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Figure 6

(a) Schematic of avionics enclosure housing multiple two-phase clamshell cooling modules [45]. (b) Construction of microchannel cooling module [46]

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Figure 7

(a) Propulsion system components for hybrid vehicle [47-48]. (b) Microchannel cooling of electronic power device

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Figure 8

Serpentine microchannel heat exchanger for HPMH hydrogen storage [53]

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Figure 9

(a) Direct-refrigeration-cooling and (b) indirect-refrigeration-cooling systems

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Figure 10

Examples of systems demanding predictive models for effects of gravitational field on two-phase flow and heat transfer

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Figure 11

CHF data for μge and horizontal 1 ge flow boiling. (Adapted from Zhang [72])

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Figure 12

(a) Basic CPL configuration and circuit board attachment to tubular CPL evaporator; (b) evaporator construction; and (c) evaporator cross-section and groove detail showing axial growth of first bubble during CPL startup. (Adapted from LaClair and Mudawar [80] and Cullimore [82])

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Figure 13

(a) Schematic of single microslot module used for micro-PIV measurement of single-phase water flow; (b) micro-PIV system; (c) comparison of measured and numerically predicted centerline velocity along flow direction; and (d) comparison of measured pressure drop and predictions based on numerical analysis and macrochannel correlations [90].

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Figure 14

Schematic diagrams of microchannel heat sinks with (a) rectangular, (b) inverse-trapezoidal, (c) triangular, (d) trapezoidal, (e) diamond-shaped, and (f) circular cross-sections. (Adapted from Kim and Mudawar [97-98])

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Figure 15

(a) Appearance of departing bubbles along microchannel cross-section, (b) stream-wise deformation of bubble. Dimensionless (c) liquid velocity, (d) liquid temperature contours at microchannel exit; and (e) comparison of incipience model predictions with experimental data for water. (Adapted from Qu and Mudawar [103]).

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Figure 16

(a) Test module for adiabatic microchannel two-phase flow regimes study. (b) Construction of nitrogen-water mixer. (c) Photographs and schematics of two-phase flow regimes. (d) Two-phase regime map. (e) Comparison of flow regime map with macro-channel map of Mandhane [116]. (f) Comparison of flow regime map with macrochannel map of Taitel and Dukler [117]. (Adapted from Qu [115]).

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Figure 17

Top view depictions of two neighboring microchannels and temporal records of inlet and outlet pressures during (a) severe pressure drop oscillation and (b) mild parallel channel instability. (Adapted from Qu and Mudawar [120])

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Figure 18

Components of a complete two-phase microchannel flow pressure drop model

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Figure 19

Flow regimes, heat transfer regimes, and variations of wall temperature and convective heat transfer coefficient along microchannel flow

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Figure 20

Variation of subcooled boiling pressure drop with base heat flux. (Adapted from Lee and Mudawar [67])

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Figure 21

Comparison of predictions of Lee and Mudawar correlation [64] for saturated boiling pressure drop with (a) Lee and Mudawar’s R134a data [64] and (b) Qu and Mudawar’swater data [120]. (Adapted from Lee and Mudawar [64])

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Figure 22

Comparison of predictions of Lee and Mudawar correlation [65] for saturated boiling heat transfer coefficient with (a) Lee and Mudawar’s R134a data [65] and (b) Qu and Mudawar’s water data [62]. (Adapted from Lee and Mudawar [65])

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Figure 23

Premature CHF and flow oscillations in heat sink with Dh  = 415.9 µm for Tin  = 0°C, G = 670 kg/m2 s, and qbase" > 250.0 W/cm2 : (a) initial vapor pocket buildup in upstream plenum, (b) growth of vapor mass, (c) complete blockage of inlet plenum by vapor mass, and (d) purging of vapor mass along microchannels. (Adapted from Lee and Mudawar [67])

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Figure 24

(a) Variations of mean microchannel base temperature and pressure drop with hydraulic diameter. (b) Variations of mean microchannel base temperature and pressure drop with channel aspect ratio. (c) Variations of hydraulic diameter and aspect ratio with channel width for constant channel height. (b) Variations of mean channel base temperature and pressure drop with channel width for constant channel height. All results are based on channel wall thickness equal to channel width. (Adapted from Lee and Mudawar [150]).

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Figure 25

(a) Flow boiling curve at measurement downstream location tc4 for pure water and 1% Al2 O3 . (b) Photograph of particles after being removed from microchannels. (Adapted from Lee and Mudawar [154])

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Figure 26

Variation of CHF with time for CNT-coated surfaces for three mass velocities and Tin  = 30°C. (Adapted from Khanikar [158])

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Figure 27

SEM images of CNT-coated surface after five boiling tests at G = 368 kg/m2 s and Tin  = 30°C. (a) CNT cellular formations observed over isolated regions of the surface. (b) Dominant fish-scale pattern observed over most of the surface. (Adapted from Khanikar [158])

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Figure 28

Smart, passive (pump-free) cooling concept and boiler microchannel enhancement features. (Adapted from Mukherjee and Mudawar [160-161]).

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Figure 29

(a) Comparison of pumpless loop CHF variation with gap width for FC-72 and water. (b) Photographs of nucleate boiling in FC-72 and in water. (Adapted from Mukherjee and Mudawar [160-161])

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Figure 30

Construction of hybrid microchannel/jet-impingement cooling module [164-165]

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Figure 31

Schematic representation of vapor growth along microchannel in hybrid microchannel/jet-impingement cooling module, and boiling curves corresponding to two jet velocities. (Adapted from Sung and Mudawar [167])

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