Experimental characterization of flow boiling heat dissipation in a microchannel heat sink with different orientations

Experimental characterization of FC-72 flow boiling in a microchannel heat sink is presented for three different orientations: vertical upflow (VU), vertical downflow (VD) and horizontal flow with horizontal facing (HH). The heat sink consisted of 21 microchannels in parallel, with the channel dimensions of 0.2mm (W) times 2mm (H) times 15mm (L). The heat sink was attached onto a flip chip BGA package with a thermal grease at the interface to minimize the contact resistance. The experiments were conducted based on a subcooling around 31 degC and inlet thermodynamic equilibrium quality x=-0.4 with varying flow rates and power inputs. Boiling with bubbles was observed at the heat sink outlet even if the exit quality x<0. It was found that the flow boiling regime can be represented by isolated bubble flow, slug flow in the present microchannels. Both the junction to inlet thermal resistances and pressure drops are presented as functions of the power input. The effect of the flow orientations on both thermal and hydraulic performances was examined and discussed