Mixing behaviour of miscible liquid-liquid multiphase flow in stirred tank with different marine propeller installment by computational fluid dynamics method

This paper presents a three-dimensional and transient computational fluid dynamics (CFD) simulation of the miscible liquid-liquid system (water-molasses) in a stirred tank operated in turbulence regime. The mixing process is crucial role when the viscosity and density of the solution are different, even though the solution mutually dissolved. There are two configurations used in the modelling. The first configuration is a conicalbottomed cylindrical tank equipped with a side-entry marine propeller and the second one is equipped with the top-entry marine propeller. The geometry of tank (D = 0.26 m and H = 0.363 m) and propeller (d = 0.033 m) are the same in both configurations. The transient calculations were conducted using the mixture model multiphase flow approach coupled with RANS (Standard k ϵ) turbulence model with time step is 0.01 s. A multiple refference frame approach was applied to modelling propeller motion. The mixing behaviour and the prediction of the moment of impeller and shaft are compared between top-entry and side-entry configuration. Some simulation results included the flow pattern recognition and distribution of molasses was discussed. The flow pattern in the top-entry configuration was indicating a stable double loop circulation. Whereas the flow patterns in side-entry configuration showing loop circulation around the marine propeller, some unstable and disordered flow pattern also formed around the tank wall. The variation of the flow pattern which happened showed the instability of the mixing process in side-entry configuration. There is a significant different mixing process produced from the side entering and top entering based on the distribution of molasses inside the tank. The result of CFD-simulation shows that the moment of impeller and shaft decrease for the side-entry configuration, and increase for top-entry configuration toward complete mixing.