Effects of size and number density of micro-reentrant cavities on boiling heat transfer from a silicon chip immersed in degassed and gas-dissolved FC-72

Boiling heat transfer of FC-72 from newly developed treated surfaces with m icro-reentrant cavities was studied experimentally. The surface structure w as fabricated on a silicon chip by use of microelectronic fabrication techn iques. Four kinds of treated surfaces with the combinations of two cavity m outh diameters (about 1.6 mu m and 3.1 mu m) and two number densities of th e micro-reentrant cavities (811/cm(2) and 96 x 10(3) l/cm(2)) were tested a long with a smooth surface. Experiments were conducted at the liquid subcoo lings of 3 K and 25 K with degassed and gas-dissolved FC-72. While the wall superheat at boiling incipience was strongly dependent on the dissolved ga s content; it was little affected by the cavity mouth diameter and the liqu id subcooling. The heat transfer performance of the treated surface was con siderably higher than that of the smooth surface. The highest performance w as obtained with a treated surface with a larger cavity mouth diameter and a larger cavity number density. The results were compared with those for pr eviously developed treated surfaces.