Mathematical modeling of mixing in a horizontal rotating tubular bioreactor: 'Spiral flow' model

A horizontal rotating tubular bioreactor (HRTB) was designed as a combination of a “thin-layer bioreactor” and a “biodisc” reactor whose interior was divided by O-ring shaped partition walls. For the investigation of mixing in HRTB the temperature step method was applied. Temperature changes in the bioreactor were monitored by six Pt-100 sensors (t 90 response time 0.08 s and resolution 0.002 °C) which were connected with an interface unit and a personal computer. In this work a modified “tank in series” concept was used to establish a mathematical model. The heat balance of the model compartments was established according to the physical model and the “spiral flow” pattern. Numerical integration was done by the Runge-Kutta-Fehlberg method. The mathematical mixing model called “spiral flow” model contained four adjustable parameters (N1, Ni, F cr and F p) and five parameters which characterized the plant and experimental conditions. The “spiral flow” model was capable to describe the mixing in HRTB properly, and its applicability was much better than with the “simple flow” model, presented earlier.