Effects of micro-pin-fins on the bubble growth and movement of nucleate pool boiling on vertical surfaces

Abstract

Observing bubble behaviors on the heating surface during the boiling process is a convenient and effective method to study the boiling mechanism. In recent decades, many researchers have studied the bubble growth and departure processes on the boiling surface and proposed numerous theoretical models and empirical correlations. With the increasing demand on heat dissipation of the high-power equipment, various modified surfaces with great heat transfer performance have emerged. However, it is difficult to explain bubble behaviors on the surfaces with different structures by traditional bubble dynamics on smooth surfaces. In this paper, the pool boiling experiments on vertical surfaces under subcooled and near-saturated conditions were carried out. With the help of a high-speed camera with high temporal and spatial resolution, bubble behaviors on micro-pin-finned surfaces were observed. Different bubble growth modes on different surfaces were obtained and the influence of the micro-pin-fins on the bubble growth and departure processes was learned. The effects of heat transfer from the thermal boundary layer and the micro-pin-fins on the bubble growth rate were considered. The influence of the surface tension, inertia and reaction forces on the bubble movement was analyzed. Based on these two aspects, a bubble growth-movement model was established. The pin effect on the contact radius, the inertia induced by the variation of bubble growth rate and reaction force induced by the local differential pressure are the main mechanisms of the micro-pin-fins to promote the bubble departure.