Influence of the vessel shape on the performance of a mechanically agitated system

Numerical Study and Geometric Investigation of the Influence of Rectangular Baffles over the Mixture of Turbulent Flows into Stirred Tanks

The present work aims to define strategies for numerical simulation of the mixture of turbulent flows in a stirred tank with a low computational effort, and to investigate the influence of the geometry of four rectangular baffles on the problem of performance. Two computational models based on momentum source and sliding mesh are validated by comparison with experimental results from the literature. For both models, the time-averaged conservation equations of mass, momentum and transport of the mixture are solved using the finite volume method (FVM) (FLUENT® v.14.5). The standard k–ε model is used for closure of turbulence. Concerning the geometrical investigation, constructal design is employed to define the search space, degrees of freedom and performance indicators of the problem. More precisely, seven configurations with different width/length (L/B) ratios for the rectangular baffles are studied and compared with an unbaffled case. The momentum source model leads to valid results and significantly reduces the computational effort in comparison with the sliding mesh model. Concerning the design, the results indicate that the case without baffles creates the highest magnitude of turbulence kinetic energy, but poorly distributes it along the domain. The best configuration, (L/B)o = 1.0, leads to a mixture performance nearly two times superior than the case without baffles.

Investigation of the flow patterns and power requirements in agitated systems: effects of the design of baffles and vessel base

The flow patterns and power consumption of a six-blade Rushton turbine (RT) in a cylindrical vessel are characterized in this paper. We focus on the effects of the shape of the vessel base by studying two cases: a conical and a dished shape. In addition, the effects of the height of the vessel base (h2) are explored and four cases are considered, namely: h2/D = 1/10, 1/6, 1/5 and 1/3 (D: vessel diameter). In the second part of our investigation, a new design of baffles (a triangular-shaped baffle) is suggested and a comparison is made between the performance of the standard and the triangular baffles. The main findings revealed that the conical shape of the vessel base provides a slight enhancement in the axial circulation at almost the same power input for the dished bottomed vessel. For Re < 2 × 104, the power required by both types of baffles is the same; however, above this value of Re, a reduction by about 4% in power consumption is given by the standard baffles. Also, and for all shapes of baffles and vessel bases, a reduction in power consumption may be obtained by increasing the height of the vessel base.