Bubble dynamics and heat transfer characteristics on a micropillar-structured surface with different nucleation site positions

Abstract

Microstructured surfaces have been extensively employed to enhance nucleate boiling. However, enhancement mechanisms have not been fully understood. In this work, a three-dimensional numerical model is developed to investigate growth and departure dynamics of a single bubble for nucleate boiling on a micropillar-structured surface. In the model, the volume of fluid method is used to capture vapor–liquid interfaces, and evaporations in both vapor–liquid interface and microlayer are taken into account. Moreover, a pressure outlet boundary condition is proposed to reasonably describe the inflow and outflow on side surfaces of the computational domain. The focus of this work is to answer how the location of nucleation site affects bubble dynamics and the resultant heat transfer characteristics. Two typical locations are considered: the center in the micropillar gap and the corner between the micropillar and substrate, referred to as the center nucleation and corner nucleation. The results show that the bubble with the center nucleation exhibits symmetric growth and departure, whereas the symmetry is broken up for the bubble with the corner nucleation. Asymmetric growth and departure induce asymmetric temperature profiles inside/around the bubble, leading to a faster departure and a smaller departure diameter for the bubble with the corner nucleation. Moreover, contributions of microlayer evaporation and vapor–liquid interface evaporation for the two nucleation locations are also discussed.