No abstract

A V-shaped punched baffle (VSPB) is developed to enhance fluid mixing in a stirred tank by producing impinging jet streams from face-to-face holes. Macromixing experiments and computational fluid dynamics (CFD) simulations are conducted with water and 0.5 wt % hydroxyethyl cellulose (HEC) solution as fluid to compare the performance of a standard baffle (SB), standard punched baffle (SPB) and VSPB. The experimental results show that the mixing time of VSPB is reduced by a maximum of 23 and 14.7% compared with those of SB and SPB at low speeds, respectively. With increasing stirring speed, the mixing time of all three baffles tends to be the same, but the power consumption of VSPB is less than that of SB and SPB with a Rushton turbine (RT). The simulation results show that the punched baffle can significantly increase the tangential velocity and turbulent kinetic energy of the fluid in the baffle region. Moreover, tiny vortices are at the back side of the punched baffles when the fluid is water. However, for a HEC solution, the flow field near the tank wall becomes disordered due to shear action caused by baffles and forms irregular vortices.

In this work, the gas dispersion and transport characteristics of three different disc turbines, namely, parabolic disc turbine (PDT), novel swept-back parabolic disc turbine (SPDT), and staggered fan-shaped parabolic disc turbine (SFPDT), are characterized by experiments and two-fluid model/RANS simulations. The physical explanation of the superior power characteristics of SFPDT and SPDT is elaborated using the pressure distribution and drag force coefficient on a blade surface. Gas−liquid performance parameters such as critical dispersion speed, relative power demand (RPD), and volumetric mass transfer coefficient are assessed under different conditions. The results show that SFPDT and SPDT can produce smaller flow separation regions and trailing vortices, resulting in smaller gas cavities under aeration conditions. SFPDT has the lowest critical dispersion speed under a high flow rate, while SPDT consumes the least power. Both SFPDT and SPDT exert roughly 7% higher gassed power input than PDT under aeration conditions and have higher efficiency on gas−liquid mass transfer than PDT. Moreover, empirical correlations from experimental data for SFPDT and SPDT are presented to provide a reference to the design of industrial stirred tanks.