Experimental study on convective boiling flow and heat transfer in a microgap enhanced with a staggered arrangement of nucleated micro-pin-fins

The boiling flow and heat transfer of FC-72 in a microgap channel are experimentally addressed. The heated surface of the microgap with a test area of 10 mm × 10 mm was enhanced using a staggered array of 613 columnar micro pin fins. Inside the micro pin-fins are nucleated with a 60 μm pore and opening of 45 μm. The test surface of the channel is a square of 10 mm, and the height of the channel is 100 μm. The saturation working temperatures of FC-72 is 50 °C, the surface heat flux was up to 60 kW/m², and the mass flux was selected in the range of 94–275 kg/m² s. The on nucleated boiling temperatures (ONB), convective heat transfer coefficient, outlet dryness, and pressure drop are measured and reported. The boiling behavior of FC-72 is also recorded using an image capturing device and reported. A comparison between the superheat temperature of nucleated pin fins and plane pin fins (with no nucleation) shows that nucleation of pin fins reduces the superheat temperature. The outcomes reveal that for a high mass flux, 196–275 kg/m² s, the superheat temperature is high, and the degree of superheat increases as the surface heat flux increases. When the surface heat flux is high (q″ > 30 kW/m²), the convective heat transfer is almost independent of mass flux. At the initiation flow boiling, a notable jump in the pressure drops can be seen. After that, the pressure drop increases gradually by the increase in surface heat flux. The boiling images reveal that the boiling flow initiated inside the nucleation pores of micro pin-fins.