Etienne Costa-Patry

Flow Boiling of R134a in a Multi-Microchannel Heat Sink With Hotspot Heaters for Energy-Efficient Microelectronic CPU Cooling Applications

This paper focuses on two-phase flow boiling of refrigerant R134a inside a copper multi-microchannel heat sink for microelectronic central processing unit cooling applications. The heat sink is composed of 100 parallel microchannels, 100 μm wide, 680 μm high, and 15 mm long, with 72-μm-thick fins separating the channels. The base heat flux was varied from 2.57 to 189 W/cm2 and the mass flux from 205 to 1000 kg/m2s, at a nominal saturation temperature of 63°C. Over 40 000 local heat transfer coefficients were measured at 35 locations using local heaters and temperature sensors, for which different heat transfer trends were identified. The main ones were that the heat transfer coefficient increased with heat flux and was independent of mass flow rate. Heat transfer coefficients as high as 270 000 W/m K (relative to the base area) were reached, keeping the chip under 85°C with a maximum of 94 kPa of pressure drop, for no inlet subcooling and a coolant flow rate of 1000 kg/m2s.

On-Chip Two-Phase Cooling With Refrigerant 85

Hot-spots are present in micro-electronics and are challenging to cool effectively. This paper presents highly nonuniform heat flux measurements obtained for a pseudo-CPU with 35 local heaters and temperature sensors cooled by a silicon multi-microchannel evaporator with 85 μm wide and 560 μm high channels separated by 46 μm wide fins. A low pressure dielectric refrigerant, R245fa, was used as evaporating test fluid. The base heat flux was varied from 6 to 160 W/cm2 and the junction temperature always remained below 65°C, while the fluid inlet saturation temperature was 30.5°C. On-chip two-phase cooling was found to very effectively cool the hot-spots without inducing flow instabilities. Building on analogous uniform heat flux tests made on the same test section, the effects of position, orientation size, and strength of the hot-spots were analyzed.

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Hot-spots are present in micro-electronics and are challenging to cool effectively. Using a copper micro-evaporator mounted on a pseudo-chip, on-chip two-phase cooling was found to very effectively cool the hot-spots without inducing flow instabilities. Building on a flow pattern-based prediction method developed for uniform heat flux conditions, the experimental results could be well predicted.