Gas-liquid-noncatalytic solid reactions are typically conducted in three phase sparged reactors. Modeling of the particle size residence time distribution (RTD) and verification/validation of the models is essential for fundamental understanding and design of these multiphase reactors. A brief review and analysis of the RTD models reported in the literature is presented in this paper. Earlier investigations in this field typically employ the axial dispersion model to describe the RTD. It is shown that the tanks-in-series model can equally be applied in such cases. These single-parameter models are simplistic in nature and do not reflect accurately the flow behavior of solids in the three phase sparged reactors. Recent phenomenological approaches to modeling involve using a tanks-in-series model in parallel or countercurrent recycle mode with a plug flow reactor. These models have better accuracy but are also more complex and require specifications of several more parameters. Further developments in the field will be based on these models.