Research Papers: Evaporation, Boiling, and Condensation

Mechanistic Considerations for Enhancing Flow Boiling Heat Transfer in Microchannels

[+] Author and Article Information
Satish G. Kandlikar

Mechanical Engineering Department,
Rochester Institute of Technology,
Rochester, NY 14623
e-mail: sgkeme@rit.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 13, 2015; final manuscript received September 2, 2015; published online October 13, 2015. Assoc. Editor: Amy Fleischer.

J. Heat Transfer 138(2), 021504 (Oct 13, 2015) (16 pages) Paper No: HT-15-1028; doi: 10.1115/1.4031648 History: Received January 13, 2015; Revised September 02, 2015

Research efforts on flow boiling in microchannels were focused on stabilizing the flow during the early part of the last decade. After achieving that goal through inlet restrictors and distributed nucleation sites, the focus has now shifted on improving its performance for high heat flux dissipation. The recent worldwide efforts described in this paper are aimed at increasing the critical heat flux (CHF) and reducing the pressure drop, with an implicit goal of dissipating 1 kW/cm2 for meeting the high-end target in electronics cooling application. The underlying mechanisms in these studies are identified and critically evaluated for their potential in meeting the high heat flux dissipation goals. Future need to simultaneously increase the CHF and the heat transfer coefficient (HTC) has been identified and hierarchical integration of nanoscale and microscale technologies is deemed necessary for developing integrated pathways toward meeting this objective.

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Fig. 1

The HTC versus the quality in a microchannel under flow boiling of water at an inlet temperature of 22 deg, heat flux expressed in kW/m2 [4]

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Fig. 2

A schematic of the vapor venting microchannel assembly developed by David et al. [54]. (Redrawn from Ref. [54].)

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Fig. 3

The principle of operation for removing vapor bubbles through a hydrophilic membrane by eliminating the liquid inertia forces by Fazeli et al. [55], and by two-phase flow as proposed by Xu et al. [53] and David et al. [54]. (Image courtesy Moghaddam [56].)

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Fig. 4

Pin fins covered by the PTFE membrane and surrounded by liquid supply trenches, with nucleation sites along the fins and channel bottom wall [55]: (a) fins and substrate with nucleation cavity channels and (b) fins covered with hydrophobic membrane for vapor transport. (Images courtesy Moghaddam [56].)

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Fig. 5

The boiling performance of the biphilic micro/nanostructure device with water at different liquid pressures [55]. (Image courtesy Moghaddam [56].)

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Fig. 6

The localized venting from the nucleation sites within “piranha” fins [57]. (Image courtesy Peles [58].)

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Fig. 7

The expanding microchannel geometry to suppress explosive bubble growth and flow reversal [64]: (a) stepped microchannels and (b) diverging microchannels

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Fig. 8

The expanding flow area by progressively removing fins along the flow length by Balasubramanian et al. [68]. Flow direction from the bottom up. All dimensions are in millimeter.

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Fig. 9

Schematic representation of stepped microchannel with a stepwise reduced fin height in the flow direction. (Adapted from Ref. [69].)

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Fig. 10

A schematic of the open microchannels with TM for stable enhanced flow boiling. (Adapted from Kandlikar et al. [70].)

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Fig. 11

(a) The performance of an open microchannel geometry for (a) TM and UM for flow rates of 40 and 225 mL/min [70]. The corresponding mass fluxes (G) for different configurations: UM—for a volumetric flow rate V = 40 mL/min, mass flux G = 305 kg/m2s; and for V = 225 mL/min, G = 1717 kg/m2s; tapered (200 μm) manifold, TM—for V = 40 mL/min, inlet mass flux, Gin = 305 and outlet mass flux Gout = 159 kg/m2s; for V = 225 mL/min, Gin = 1717 and Gout = 896 kg/m2s, CHF was not reached for the TM configurations in this testing, (b) new test results with TM at a flow rate of 80 mL/min for the same microchannel and taper configuration.

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Fig. 12

The spreading of liquid from the corner region to the channel walls with a hydrophilic surface structure (Kandlikar [74])




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