(152d) Flow Boiling Using a Piranha Pin Fin Heat Sink

Corey Woodcock, Xiangfei Yu, Yoav Peles¹ and Joel
Plawsky

Rensselaer Polytechnic Institute; ¹University of
Central Florida

The Piranha Pin Fin (PPF)
microdevice is a heat exchanger engineered to dissipate extreme thermal loads
using either dielectric fluids such as HFE7000 or water.  Fabrication of the
device is CMOS compatible and the first generations of the device have been
fashioned from silicon substrates. The PPF operates on the principle that heat
transfer would be more efficient if heated fluids could be removed nearly as
fast as they are created.  This process would keep the driving force as high as
possible.  Thus the heat exchanger is built as two layers; a primary substrate
that dissipates the bulk of the heat and shunts the heated fluids to a booster
section that continues to heat the fluid and extends the total surface area of
the device.  Three generations of devices were fabricated.  The first two generations
were single-layer systems designed to help understand the operation of the
primary layer and optimize the shape and location of the pin fins.  The third
generation was the first, two-layer system to be fabricated and tested.

Figure 1  Representative
PPF array

Correlations for the heat
transfer coefficient, h_tp, based on the Boiling Number and the Weber
Number in the PPF design was developed and validated with Gen II. The
discrepancy of heat transfer coefficient between predicted and measured values
was within 20%. The ratio of two-phase to single-phase pressure drop was
correlated with the Boiling Number (Bo) and the Jakob Number (Ja). The
discrepancy of the two-phase multiplier between prediction and experimental
measurements were within 12%.

                                                   (1)

The third generation PPF heat
sinks were the first series to provide both a primary substrate populated with PPFs,
as well as a booster substrate populated with solid micro pin fins. The
substrates are micro-aligned and fusion-bonded to provide a full three
dimensional (3D) architecture with bulk silicon properties. Experimental
results from the Gen III PPF microdevices provide a proof of concept of
the true PPF heat sink concept with fluid venting into multiple substrates.
At low flowrates (G = 670 [kg/s/m²]) the Gen III PPF heat
sink has been shown to dissipate heat loads approaching 1.1 [kW/cm²]
at an exit quality of 95%, while at higher flowrates (G = 3,300 [kg/s/m²])
the thermal limit of the heat sink remains unknown due to exceeding the
available power supply at >1.4 [kW/cm²].