Numerical investigation of bubble coalescence characteristics under nucleate boiling condition by a lattice-Boltzmann model

A numerical study was performed to investigate the characteristics of bubbl e growth, detachment and coalescence on vertical, horizontal, and inclined downward-facing surfaces. The FlowLab code, which is based on a lattice-Bol tzmann model of two-phase flows, was employed. Macroscopic properties, such as surface tension (sigma) and contact angle (beta), were implemented thro ugh the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potential s. The model predicted a linear relationship between the macroscopic proper ties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The simulat ion results on bubble departure diameter appear to have the same parametric dependence as the empirical correlation. Hydrodynamic aspects of bubble co alescence are investigated by simulating the growth and detachment behavior of multiple bubbles generated on horizontal, vertical, and inclined downwa rd-facing surfaces. For the case of horizontal surface, three distinct. reg imes of bubble coalescence were represented in the lattice-Boltzmann simula tion: lateral coalescence of bubbles situated on the surface; vertical coal escence of bubbles detached in a sequence from a site; and lateral coalesce nce of bubbles, detached from the surface. Multiple coalescence was predict ed on the vertical surface as the bubble detached from a lower elevation me rges with the bubble forming on a higher site. The bubble behavior on the i nclined downward-facing surface was represented quite similar to that in th e nucleate boiling regime on a downward facing surface. (C) 2000 Editions s cientifiques et medicales Elsevier SAS.