The time, t_C, elapsed from bubble contact to the rupture of the liquid film between two bubbles in a quasi two-dimensional column was measured to investigate the effects of the particle diameter on bubble coalescence. The particle diameter ranged from 60 to 150 µm and the particle volumetric concentration ranged from 0 to 0.50 (50%). The effects of particle diameter on bubble coalescence were evaluated through the experiments and were implemented into a bubble coalescence model for a multi-fluid model. Distributions of the gas holdup in a three-dimensional slurry bubble column were also measured using an electrical conductivity probe to obtain experimental data for validation of the coalescence model. The conclusions obtained are as follows: (1) t_C decreases, in other words, bubble coalescence is enhanced with decreasing the particle diameter, which results in the reduction of the gas holdup of the slurry bubble column, (2) the particle-effect multiplier to t_C is of great use to take into account the effects of the particle concentration and diameter in multi-fluid simulations of slurry bubble columns, and (3) the interaction between the bubble interfaces and particles in the bubble coalescence process after bubble contact is a local phenomenon and rarely depends on the macroscopic behavior of the interface, which allows us to develop a correlation for particle-induced enhancement of bubble coalescence for three-dimensional bubble columns even with a small experimental setup like a Hele–Shaw cell.