Experimental Study of Boiling Phenomena by Micro/Milli Hydrophobic Dot on the Silicon Surface in Pool Boiling

Abstract

Many pool boiling experiments to enhance the nucleate boiling condition have been conducted and could get brilliant and challengeable results. A consensus was that CHF and heat transfer were affected by a modified heating surface. One of the efforts was the nanofluids experiments, and they have exhibited an incredible enhancement of CHF when nanofluids have been used as a working fluid in pool boiling. The results also have showed clearly that such large CHF enhancement came from the deposition of nanoparticles on the heating surface changing the surface condition. The surface covered by oxidized metal nanoparticles has a high wettability, and so it affects CHF. The fact that the wettability effect is significant to the enhancement of CHF is also supported by other kinds of boiling experiments. In addition, many researchers reported that wettability enhances not only CHF but also nucleate boiling heat transfer coefficient. In this regard, the excellent boiling performance (a high CHF and a high heat transfer coefficient) in pool boiling could be achieved through some favorable surface modification which satisfies the optimized wettability condition. For finding the optimized condition, we design the special heaters to examine how two materials, which have different wettabilities, affect the boiling phenomena. The special heaters have hydrophobic dots on the silicon surface. The hydrophobic dots lead to an early bubble inception. The bubble interface is bounded on the material boundary. The peculiar teflon(AF1600) is used as the hydrophobic material. The contact angle of the heating surface which is made by teflon is 120° to water at the room temperature. The contact angle of the silicon surface is 60° at the room temperature. The experiments using the micro hydrophobic dots and milli hydrophobic dot are performed, and the results are compared with the reference surface.