Experimental data on bubble characteristics-averaged size and rise velocity-were obtained using digital image analysis methods from two-dimensional (thin) bubbling fluidized beds with and without simulated horizontal tube bundles, These data were used to develop semiempirical correlations for bubble size and rise velocity. These mechanistic correlations can be extrapolated readily to three-dimensional fluidized beds, and calculations for bubble size, velocity and bubble fraction compare favorably with relevant literature data. Application of these correlations for bubble behavior in the interpretation of experimental data on the mixing of solids-in two- and three-dimensional fluidized beds containing horizontal tubes-is illustrated in an accompanying paper.