The two-fluid model based on the kinetic theory of granular flow is considered to be a fundamental tool for modeling gas-solid fluidized beds and has been extensively used for the last couple of decades. However its verification and quantitative validation still remain insufficient for a wide range of reactor geometries and operating conditions. In this study simulations were performed using the two-fluid model for two-dimensional (2D) bubbling gas-solid fluidized beds with and without immersed horizontal tubes. The bubble characteristics - aspect ratio, shape factor, diameter and rise velocity predicted by the simulation were compared and validated with experimental data obtained from pseudo-2D fluidized beds using digital image analysis technique. The predicted bubble shape and diameter were in good agreement with the experimental data for fluidized beds with and without immersed tubes. The simulation predicted higher bubble rise velocity compared to the experimental results obtained. This was due to the wall effect, which was not taken into consideration during the 2D simulation. In addition the influences of different drag laws, friction packing limits and solid-wall boundary conditions on the different bubble properties were investigated. The results showed that the choice of friction packing limits, drag laws and specularity coefficients have little influence on bubble properties. (C) 2011 Elsevier Ltd. All rights reserved.