Study of the Potential for Modifying the Design of a Turbine Stirrer Blade to Reduce the Effect of Shear Stresses on Microorganisms in Cultivation Processes

Abstract

Stirring in bioreactors is an important element for the efficient cultivation of cell cultures in biotechnological production. But high-speed stirrers can create high level of shear stresses that negatively affect microorganisms. Therefore, it is important to develop the design of new stirring devices to minimize the negative impact of shear stresses on cells during cultivation. The purpose of this study is to analyze the effect of the designs of turbine stirring devices, proposed by authors, on the parameters of the stirring process during the cultivation of cell cultures by methods of computer modeling. The computer modeling was performed in ANSYS for the process of liquid stirring in a bioreactor. Two new designs of turbine stirrers have been proposed. The idea of the new design is to divide the working blade into two, i.e. to create a cutout in the blade. In the first case, the cutout is a rectangle, in the second - a parallelogram. To compare the efficiency of the proposed designs, we also modeled the stirring with a classical turbine 6-blade stirrer. Based on the modeling results, were obtained contours of the velocity distribution, turbulent kinetic energy, shear strain rate, velocity vectors, and ISO-surfaces forming the core of the rotation vortex. It was found that the presence of cutouts in the turbine stirrer does not lead to a decrease in the velocity of the main flows and redistribution of motion vectors, but significantly reduces the value of turbulent kinetic energy from and shear strain rate. The maximum value of turbulent kinetic energy for the classical stirrer is 2.489 m2/s2, while for the stirrers with cutouts it barely reaches 1.245 m2/s2. The shear stresses decrease by 10 % from 19.63·10-3 Pa for the classical design to 17.67·10-3 Pa for the stirrer with parallelogram-shaped cutouts. The further development of this study will be to analyze the influence of the geometric parameters of the stirrer with parallelogram-shaped cutouts on the qualitative indicators of stirring. The results obtained in this work can be used by engineers and technologists to design bioreactors with reduced values of shear stresses.