Boiling of FC-72 on silicon chips with micro-pin-fins and submicron-scale roughness

Experiments were conducted to study the effects of micro-pin-fins and submicron-scale roughness on the boiling heat transfer from a silicon chip immersed in a pool of degassed and gas-dissolved FC-72. Square pin-fins with fin dimensions of 50 × 50 × 60 μm³ (width × thickness × height) and submicron-scale roughness (RMS roughness of 25 to 32 nm) were fabricated on the surface of a square silicon chip (10 × 10 × 0.5 mm³) by use of microelectronic fabrication techniques. Experiments were conducted at the liquid subcoolings of 0, 3, 25 and 45 K. Both the micro-pin-finned chip and the chip with submicron-scale roughness showed a considerable heat transfer enhancement as compared to a smooth chip in the nucleate boiling region. The chip with submicron-scale roughness showed a higher heat transfer performance than the micro-pin-finned chip in the low-heat-flux region. The micro-pin-finned chip showed a steep increase in the heat flux with increasing wall superheat. This chip showed a higher heat transfer performance than the chip with submicron-scale roughness in the high-heat-flux region. The micro-pin-finned chip with submicron-scale roughness on it showed the highest heat transfer performance in the high-heat-flux region. While the wall superheat at boiling incipience was strongly dependent on the dissolved gas content, it was little affected by the liquid subcooling.