This research focuses on performing multiphase solid/liquid/gas CFD simulations of a UASB reactor in order to obtain a validated model that provides a clearer understanding of the hydrodynamic behaviour of the three phases in UASB reactors. Eulerian–Eulerian, laminar, three-dimensional, multiphase simulations are carried out using Fluent 16.2. The liquid phase velocity and flow profile are validated through PIV experiments. A liquid mean velocity difference of 8.45% is found between the experimental and numerical results, thus validating the CFD model. Shadowgraphy is applied successfully to validate the biogas phase velocity and bubble size. Based on the hydrodynamic analysis results, the reactor can be divided into four regions, according to its mixing conditions. For the flow rates studied, minimal solids washout is observed. In the present research, only 0.02% of the volume are dead zones within the reactor, which indicates good mixing conditions. The reactor shows a recirculation stream at the centre that has an important role in relation to the mixing conditions. The validated model can be used for further studies on the optimisation of UASB reactors.
