Local rate of turbulent energy dissipation in agitated reactors & bioreactors

InvestigatorIng. Bohuš Kysela, Ph.D.
External Investigatorprof. Ing. Pavel Ditl, DrSc.
Duration2012 - 2014

Modeling of dispersion processes, flocculation and the extent of segregation in a turbulent regime is based on the Kolmogorov theory and on the local dissipation rate of turbulent energy e as the basic parameter. The scale up of agitated reactors is nowadays based on the postulate e/N3.d2 const. that was derived on following empirical assumptions: fluctuation velocity u´Nd and integral length scale L d. The assumption L d has been experimentally verified in narrow impeller Re range only, changing of Re by changing the impeller speed N. Experimental results obtained in large vessels are inconsistent with the assumption L d. It seems that L can also depend on Re. Evidence of this hypothesis would change scale up of industrial mixers. The hypothesis can be tested only by experimental measurements in a fully turbulent regime in vessels at least 0,3 to 0,5 m in diameter. A theory explaining the experimental results will be proposed. The results will supplement present-day mixing theory and can be applied for scaling up mechanically agitated vessels and for CFD validation.