Visualization-based nucleate pool boiling heat transfer enhancement on different sizes of square micropillar array surfaces

Abstract

Visualization-based nucleate pool boiling experiments are carried out on different sizes of square micropillar array surfaces (SMAS) and plain surface using deionized water as working fluid at atmospheric pressure. The quantitative measurements of the bubble dynamics, including the nucleation site density, the bubble departure diameter and the frequency, are obtained using a high-speed camera with microscope. The obtained results show that the SMAS, with square micropillar in the range of 0.2–0.8 mm height and width (the pitch between the micropillar is equal to the micropillar width), has a considerably lower wall superheat, which enhanced the heat transfer coefficient (HTC) by 32–203% compared to the plain surface. Generally, the boiling heat transfer intensifies with the increase in the square micropillar height keeping the width constant. But the tendency reverses at high heat flux levels. The high-speed visualization reveals that the higher square micropillar has faster bubble departure frequency at low heat flux, because higher micropillar is conducive to induce capillary flow and aids in separating the paths of departing bubble and replenishment liquid. However, the increase of bubble diameter at high heat flux restrains bubble departure with higher square micropillar. In addition, the increase of square micropillar width is conducive to enhancing the boiling heat transfer and the tendency is reversed at high heat flux levels when the square micropillar height is kept constant. The bubble dynamics are compared with the predictions using various correlations from the literature.