Effect of surface structure and coating on the heat transfer deflection behavior in the early stage of nucleate boiling

Abstract

This paper presents the effects of surface structure and coating on the heat transfer deflection point (HTDP) when the rate of increase of the heat transfer coefficient (HTC) changes during the early stage of nucleate boiling. Two types of micro-cylinder arrays were fabricated on a Si substrate using microelectromechanical system techniques. A SiO2 thin film was deposited on the microstructured surfaces to reveal how the surface coating affects the boiling behavior. The HTDP differs from the minimum nucleation criteria indicating that the HTDP occurs at a slightly higher heat flux than the minimum nucleation criteria. A deflection occurs at a specific value of the HTC on each surface, namely, similar to 3.27 kW/(m(2).K) with a SiO2 layer and 4.67 kW/(m(2).K) without a SiO2 layer, regardless of the surface structures. In the after deflection regime, instantaneous slopes of the boiling curves are governed by the surface structure. Regardless of the surface coating, the final slopes increase as the surface roughness increases, namely, 31.2, 63.5, and 87.0 kW/(m(2).K) for flat, coarse, and dense surface structures, respectively. These results will contribute to a better understanding of the behavior of the HTDP during boiling. (C) 2018 Elsevier Ltd. All rights reserved.