High-speed visualization of boiling from an enhanced structure

Using high-speed photography (1500 frames/s) bubble growth data on microporous structures immersed in a pool of dielectric coolant (FC-72) were obtained. Wafer dicing and wet etching was used to fabricate a net of interconnected microchannels on a 10 mm. x 10 mm piece of silicon wafer. The resultant structure has pores that communicate the interior of microchannels to the liquid pool. The pore diameter was varied in a range 0.12-0.20 mm, and the pore pitch in 0.7-1.4 mm. The data were collected maintaining the system pressure at one atmosphere and increasing the wall superheat up to 12 K. Among the geometrical parameters, the pore diameter was found to be most influential on the bubble departure diameter. The findings about the bubble growth rate, the bubbling frequency, and the bubble site density were largely in accord with the previously reported data. However, the coverage of wider ranges of wall superheat and the structural parameters in the present study revealed new bubble characteristics that was used in implementing an analytical model for boiling heat transfer on the porous structure. (C) 2002 Elsevier Science Ltd. All rights reserved.