Numerical Simulation of Hydrodynamics Characteristics in a Tank with an Up-down Reciprocating Agitator

The hydrodynamics characteristics in a tank with an up-down reciprocating disc agitator were numerically investigated using computational fluid dynamics (CFD) simulations. A dynamic mesh technique along with a user-defined function (UDF) was used to solve the reciprocating movement of the disc agitator in the tank. The dynamic flow field and averaged values of some important parameters were obtained. The verification of the simulation was completed by comparing its results with experimental data in the literature. It is found that the flow pattern in the tank with a reciprocating agitator is characterized by two dynamic vortices, which are above and below the disc, respectively. Flow field, force acting on the disc and power requirement change periodically in the tank. The increase of frequency, amplitude and disc diameter leads to the increase of the averaged velocity in the tank as a whole. Nevertheless, the uniformity of velocity distribution is slightly improved, worsened and greatly improved respectively under the above operating conditions. The averaged values of the force acting on the disc and power consumption are in the second and the third power relations with the reciprocating frequency and amplitude, respectively. The ratio of fluid averaged velocity in one cycle to averaged disc speed, and Newton number are hardly affected by reciprocating frequency and amplitude, while they increase with the enlarged size of the disc agitator.