Enhanced Flow Boiling Heat Transfer in Microchannels with Structured Surfaces

Technology #16829

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Schematic of the microchannel design. The microchannel has length of 10 mm, width of 500 μm, and height of 500 μm. The micropillars incorporated into the microchannel were etched in Si with heights of 25 μm, diameters of 5-10 μm and pitches of 10-40 μm. The 8.5 mm (length) × 250 μm (width) platinum (Pt) heater and four resistance temperature detectors (RTDs) were fabricated along the channel on the back side.Schematic of the fabrication process for the microchannels with integrated micropillars. (a) Micropillars of 25 μm height were etched in Si using DRIE. (b) A 500 μm thick Si wafer was etched through using DRIE (c) The two wafers were bonded together using Si-Si fusion bonding (d) Inlet and outlet holes were laser-drilled on a 500 μm thick Pyrex glass wafer (e) After a 500 nm SiO2 layer was grown on the Si surfaces, the Pyrex wafer was bonded to the Si wafers as a cover. (f) A 250 nm thick Pt layer was deposited on the backside of the microchannel using E-beam evaporation and patterned to form heater and temperature sensors.Images and SEM of fabricated microchannel. (a) Top and (b) bottom view image. (c) SEM of the cross section image of a representative, fabricated microchannel and magnified view of micropillars on the channel bottom surface (inset).
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Inventors
Professor Evelyn Wang
Department of Mechanical Engineering, MIT
External Link (drl.mit.edu)
Dion Antao
Department of Mechanical Engineering, MIT
Kuang-Han Chu
Department of Mechanical Engineering, MIT
Yangying Zhu
Department of Mechanical Engineering, MIT
External Link (mit.edu)
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Enhanced Flow Boiling Heat Transfer Through Microstructures to Decouple Heat Transfer and Flow Instabilities

US Patent Pending 2016-0033212
Publications
Suppressing High-Frequency Temperature Oscillations in Microchannels with Surface Structures
Applied Physics Letters, 110(3), p. 033501, 2017
Surface Structure Enhanced Microchannel Flow Boiling
Journal of Heat Transfer, 138(9), p. 091501, 2016
Reducing Instability and Enhancing Critical Heat Flux Using Integrated Micropillars in Two-phase Microchannel Heat Sinks
2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems , Anchorage, AK, June 21-25, 2015
Enhanced Flow Boiling Heat Transfer in Microchannels with Structured Surfaces
International Heat Transfer Conference, Aug. 10-15, 2014

Applications

Two-phase microchannel heat sinks can be used for thermal management of electronic devices such as central processing units (CPUs), concentrated photovoltaics, power electronics, and laser diodes.

Problem Addressed

Electronic systems such as power electronics and laser diodes typically exceed heat fluxes of 1000 W/cm2. Current thermal management systems including heat pipes, and pool boiling have achieved heat fluxes of 100-250 W/cm2, which is not high enough for many systems. This two-phase microchannel heat sink in a custom closed loop test setup demonstrated heat flux ~735 W/cm2 with mass flux of ~1849 kg/m2s and 3-8 oC temperature fluctuations. The improved performance is attributed to the microstructured surfaces within the microchannels.

Technology

The two-phase microchannel consists of channels filled with micropillars, fabricated out of a Si wafer using deep reactive ion etching (DRIE) and a Pyrex glass wafer with inlet and outlet holes. The fabricated microchannels were 500µm x 500µm x 10mm with micropillar arrays (heights of ~25µm, diameters of 5-10µm and pitches of 10-40µm) on the bottom channel wall, where heat is applied. This design suggests that two-phase heat transfer and fluid flow behavior can be decoupled allowing the overall heat flux to increase. Bubbles are generated via the less hydrophilic sidewalls while the superhydrophilic microstructures at the bottom of the channel enhance the capillary wicking capability to prevent dryout.

Advantages

  • Increased critical heat flux
  • Thermal management solution for high performance electronic devices