Modelling of Nutrient Mist Reactor for ON/OFF Duty Cycle

A mathematical model has been developed to study the ON/OFF mist duty cycle to achieve specified growth of hairy roots. The availability and rate of transport of nutrients to the roots have been taken to be important parameters in design and operation of the reactor. Major mass transfer resis¬tance is provided by the thin liquid film over the root surface which keeps building up during the ON cycle. The same film also acts as a finite reservoir of nutrients in the ab¬sence of any replenishment during the OFF cycle. This reservoir gets depleted as growing roots continue to consume the nutrients. The depletion limits the duration of the OFF cycle as it leads to the lowering of nutrient concentration below the critical value which is required for the specified growth rate. The depleted reservoir is replenished to an extent which depends on feed concentration and duration of next ON cycle. It is found that an increasing feed concentration fed-batch mode of operation leads to a better growth of the roots in the reactor. Interestingly, it also leads to an efficient operation of the reactor whereby the reactor operates at slightly above the required concentration and close to minimum mass transfer resistance.