Abstract-The following study concentrates on two-phase flow boiling
of refrigerant R134a inside two similar copper multimicrochannel
heat sinks, one of which was designed for singlephase
water cooling of microprocessors. The two-phase heat sink
was composed of 100 parallel microchannels, 100 µm wide, 680
µm high, 15 mm long with 72 µm-thick fins, and 63 parallel microchannels.
Base heat fluxes and channel-based mass fluxes were
varied from 2.57 to 190 W/cm2
and from 205 to 1000 kg/m2
s, all at
a nominal saturation temperature of 63ºC. Local heat transfer
coefficients were measured at 35 locations using localized heaters
and temperature sensors. The main trend identified was that the
heat transfer coefficient increased with heat flux at all vapor qualities
and mass fluxes tested. Heat transfer coefficients as high as
250’000 W/m2
K (relative to the base area) were reached, keeping
the chip under 85ºC. Backflow and flow instabilities were the
main issues with the single-phase heat sink when used in flow boiling,
leading to flow mal-distribution and jet impingement effects.