ABSTRACT
The most frequently used reactor in biotechnology is a mixing vessel. In this type of reactor the contents are agitated, resulting in an increased surface area in aerated aerobic cultures and an improved temperature transfer (either heating or cooling) at the inner surface of the reactor. Depending on the requirements of agitation, different parameters must be known when designing and scaling-up propellers. To calculate the energy required, a dimensional analysis with the determinant values of the agitation process can be performed. A further important relationship serves to calculate the shear forces created by the propeller in the reactor. A dimensional analysis of the agitation process gives not only several geometrical relationships but also three terms. These terms serve as the dimensionless description of the power characteristics of a propeller. The Newton number, Ne, is a function of: N, the energy transferred to the liquid from the propeller; n, the rotational speed of the propeller; dR, the diameter of the propeller; and ρ the density of the liquid stirred in the fermenter.
