The influence of surface roughness on flow boiling heat transfer and pressure drop in microchannels is experimentally explored. The microchannel heat sink employed in the study consists of 10 parallel, 25.4 mm long channels with nominal dimensions of 500 μm × 500 μm. The channels were produced by saw-cutting. Two of the test piece surfaces were roughened to varying degrees with electrical discharge machining (EDM). The roughness average, Ra, varied from 1.4 μm for the as-fabricated, saw-cut surface to 3.9 and 6.7 μm for the two roughened EDM surfaces. Deionized water was used as the working fluid. Experiments indicate that the surface roughness has little influence on boiling incipience and only a minor impact on saturated boiling heat transfer coefficients at lower heat fluxes. For wall heat fluxes above 1500 kW/m2, the two EDM surfaces (3.9 and 6.7 μm) have similar heat transfer coefficients that were 20 to 35% higher than those measured for the saw cut surface (1.4 μm). Analysis of the pressure drop measurements indicates that only the roughest surface (6.7 μm) has an adverse effect on the two-phase pressure drop.

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