Stirring of material in biogas plant needs to be done to provide desirable contact between microorganisms and substrate which can improve digestion process. In the present study, computational fluid dynamics (CFD) was used to determine a suitable mechanical stirrer for biogas plant and simulate the flow pattern of cow manure. In order to select optimum design of impeller, three types of impeller including six-blade turbine, four-blade turbine and six-flat-blade disc turbine were evaluated. Simulations were undertaken utilizing Fluent 15.0 software with a multiple reference frame approach via standard k-ε turbulence model under steady-state conditions. According to the simulation results, six-blade turbine impeller is more appropriate than the two other impellers. The results further indicated that, this type of stirrer offers suitable mixing both at the center and on the lateral walls of the reactor, reducing dead spaces and improving mass and heat transfers inside the reactor.
