Pool boiling heat transfer on artificial micro-cavity surfaces in dielectric fluid FC-72

Abstract

The boiling performance and flow mechanism on artificial micro-cavity surfaces with different geometric parameters are presented in the present study. The test surfaces are manufactured on a 625 mu m thick, 10 mm x 10 mm square silicon plate. The treated cavities are all cylinders with three diameters (200, 100 and 50 mu m) and two depths (200 and 110 mu m). The densities of the cavities were designed to be 33 x 33, 25 x 25 and 16 x 16 arrays with 100, 200 and 400 mu m spacings, respectively. The characteristics of heat transfer for pool boiling of FC-72 on artificial micro-cavity surfaces were also examined. In this paper, visualization of the flow patterns was conducted to investigate the characteristics of the bubbles in the growth and departure process. The results indicated that boiling incipience and temperature excursion of silicon-based surfaces are more significant than those of metal-based surfaces reported in the literature. The effects of cavity density are stronger in the high heat flux region than in the low heat flux region because of the bubble/ vapor coalescence near the heating surface. The heat transfer coefficient increases with heat flux and cavity density but a denser cavity will suppress the value of critical heat flux (CHF). Besides, in moderate and high heat flux regions, a larger cavity diameter surface shows earlier decay and a lower peak value of the heat transfer coefficient. The maximum value of CHF on the base area was 3 x 10(5) Wm(-2) (30 W m(-2)) for the test surface with a 33 x 33 cavity array, which is almost 2.5 times that of the plain silicon surface.