Bubble departure phenomena on modified surfaces for enhanced pool boiling

Abstract

This research work explores bubble departure phenomena on different modified surfaces for enhanced pool boiling of water. Experiments were conducted for understanding bubble interaction with surfaces of different topography. The experiments were conducted in a controlled environment. Important parameters of pool boiling i.e. bubble departure diameter and bubble departure frequency were measured and analyzed to understand the mechanism of pool boiling and associated heat transfer. High speed video camera was employed to capture bubble phenomena on boiling surface. Three different surfaces have been used for experimentation as plain surface, pitted surface and finned surface. Copper is used as boiling surface and fin material. The setup was designed in such a way that the effect of surface topography can be precisely measured.

It has been observed that bubble departure phenomena not only depends on the supplied heat flux, but also on the surface topography, bubble merging and nucleation site density. Here it is revealed that with higher heat flux bubble departure diameter and bubble departure frequency generally increases along with heat transfer coefficient. But the increment is not linear as it seems. Although with the increase of heat flux, bubble departure diameter increases, there are other factors like surface tension, acting forces due to fluid motion, drag force and surface topography that affects the phenomena. These factors also affects the heat transfer coefficient of the system.

From the visual observation of the images of high speed video camera and analysis of obtained data, an empirical correlation has been proposed that can well predict the bubble departure diameter in pool boiling for different modified surfaces.