Experimental study of boiling heat transfer in a microchannel with nucleated-shape columnar micro-pin-fins

The boiling regime and flow field patters of boiling heat transfer of FC-72 dielectric fluid in a microchannel are experimentally studied. The inner surface of the test section of the microchannel is covered with nucleated columnar fins of height 100 mu m. Each fin is nucleated with the core diameter of 60 mu m and opening of 45 mu m, which the fin openings is aligned opposite to the flow direction. The experiments are performed for two saturation temperatures of T-sat = 35 degrees C and T-sat = 50 degrees C. The heat flux and mass velocity are in the range of 0.67-4.5 W/cm(2), and 94-138 kg/m(2) s, respectively. The results are reported for the on boiling temperature difference and pressure drop. The flow-field behavior of formation of bubbles at the nucleated fins, single-pore nucleation, and boiling flow regime are addressed. The results reveal that the increase in the mass velocity increases the subcooled temperature difference. The flow-behavior images in the test-section show that cell flow, block flow, droplet/block flow, droplet flow, and annular flow patterns can be formed by the increase of the surface heat flux. The on boiling phase change induces about three-fold of pressure-drop in the microchannel, Besides, the rise of the working fluid saturation temperature raises the pressure-drop.