Recent studies on jet penetration height in literature were reviewed. Double jet penetration in fluidized beds was investigated both experimentally and numerically. The experimental investigation was performed in a 300 x 51 mm two-dimensional gas-solids fluidized bed with two vertical jets, and the jet penetration height was measured. Different kinds of particles were tested in turn. The numerically predicted jet penetration heights were from the solution of a hydrodynamic model describing the gas-solids fluidization. The hydrodynamic model is based on the kinetic theory for fluidization and K-epsilon(k) turbulence model for gas phase. The governing partial differential equations were solved using the modified Inter Phase Slip Algorithm (IPSA) method. The formation mechanism of jets was analyzed and the interaction of two vertical jets was reconstructed using this model. Numerical results indicated that the flow pattern of a two jet system could be classified into three categories: isolated jets, transitional jets, and interacting jets. The criterions for those flow regions were found. The effects of jet characteristics (jet velocity, nozzle width, and the distance between two jets), particle properties (particle diameter, particle sphericity, and particle density), fluidizing gas characteristics (superficial gas velocity of bed, inlet gas density, and gas viscosity), and bed height on the jet penetration height were analyzed. It was found that the dominant factors affecting the jet penetration height are jet momentum, the drag between the two phases, entrainment near the jet neck, the distance between two jets, and the superficial gas velocity. Thus, the Froude number, Reynolds number, superficial gas velocity, the distance between the two jets, and jet nozzle width are used to propose algebraic empirical equations to estimate the jet penetration height of gas-solids fluidization at different jet regions. The empirical equations were compared with published experimental data or correlations. (C) 2003 Published by Elsevier B.V.