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

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.  

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 >900 W/cm2 with mass flux of ~300 kg/m2s and 3-8 oC temperature fluctuations. The improved performance is attributed to the microstructured surfaces which suppressed dry-out via capillarity within the microchannels.  

Advantages

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