Numerical study of enhanced boiling phenomena on vertically oriented surfaces with heterogeneous wettability: Lattice Boltzmann method

Abstract

Enhancing the heat transfer efficiency of exchanger tubes can reduce energy waste and lower the likelihood of tube rupture accidents. Employing mixed wettability treatment on the surface serves as a potent strategy to elevate heat transfer properties. This paper investigates the dynamic behavior of boiling bubbles adhering to a vertical surface, alongside assessing the associated heat transfer performance, utilizing the lattice Boltzmann method (LBM). The influences of hydrophobic region characteristics (spacing, width) and surface wettability, on bubble dynamics, and surface heat flux are investigated. The results show that at low superheat, the bubbles first nucleate and grow in the hydrophobic region, then slip into the hydrophilic region and leave the surface. At high superheat, the bubbles merge and form a vapor film. Driven by buoyancy, gravity, and surface tension, the vapor film moves in a wave-like manner across the surface, and a rewetting area appears at the hydrophilic-hydrophobic boundary. The heat flux at the surface increases with the increase of hydrophobic region width and spacing. It is important to note that the increase in hydrophobic region width promotes heat transfer only at low superheat, while the promotion effect of increasing the spacing is seen at high superheat. Additionally, a surface exhibiting moderate hydrophilicity demonstrates optimal heat transfer efficiency at high superheat conditions. Under the research conditions of this paper, the heat transfer enhancement rate of the mixed wetting surface is as high as 120.2 % compared to that of a purely hydrophilic surface.