Particles(including solid particles,liquid drops and gas bubbles)are ubiquitous in a large number of natural processes as well as in industrial productions.Their behaviors are of fundamental importance in multiphase systems since the existence of such dispersed particles influences the momentum,mass and heat transport behaviors in these systems.Up to now,a vast body of literature has been published in dealing with the transport phenomena related to a particle surrounded by a fluid under various physical circumstances.In this paper,principal research results for the transport process of a single spherical particle in pure extensional and simple shear flows presented in the literature,including our recent work,are generally reviewed in order to give a comprehensive knowledge in this area.
In our previous work, a low-shear stirred bioreactor was explored. With a pitched blade turbine impeller downflow(PBTD) used, the shear stress generated is high compared with that in some low shear axial flow impellers. KHX impeller is an efficient axial flow impeller, which provides large onflow diffusivity and low shear force. In this work, the KHX impeller was applied in a lower-shear bioreactor and the performance of this reactor was evaluated and compared with that of the PBTD impeller. The experimental results show that the KHX impeller can disperse gas at lower power consumption and gives greater gas–liquid volumetric mass transfer coefficients than PBTD at the same power consumption. An empirical correlation for evaluating the mass transfer coefficient of the KHX impeller in the bioreactor is presented to provide reference for its industrial application.
