Enhanced boiling heat transfer of FC-72 over micro-pin-finned surfaces with submerged jet impingement

The experiment was made of boiling heat transfer of FC-72 on micro-pin-finned chips with submerged jet impingement. The experimental conditions cover two different liquid subcoolings (25, 35 K), three different jet velocities (V_j=0.5, 1.0, 1.5 m/s) in the direction perpendicular to chip surface. The dimension of the silicon chips is 10 mm × 10 mm × 0.5 mm (length × width × thickness) on which micro-pin-fins with the two dimensions of 50 μm × 50 μm × 60 μm (width × thickness × height, named PF50-60) and 50 μm × 50 μm × 120 μm (named PF50-120) were fabricated using the dry etching technique. For micro-pin-fins, the critical heat flux qchf increases with jet velocity and liquid subcooling. Increasing liquid subcooling and jet velocity can decrease the size of bubbles' separation, increase the detachment frequency and thus decrease the wall superheat and increase the critical heat flux. The heat transfer process is dominated by the forced convection in single-phase heat transfer region, and the heat flux increases linearly with increasing wall superheat. In the nucleate boiling region, the heat transfer is affected by both the forced convection and nucleate boiling heat transfer. The slope of nucleate boiling curve is larger than that in single-phase region when the jet velocity is small, indicating better heat transfer performance of boiling.