A pilot ohmic heater was tested for the continuous aseptic processing of strawberry pulp. The
fluid mechanics and the fluid residence time distribution (RTD), in the whole volume of the
vessel and exclusively in the heating zone (between the electrodes), have been numerically
simulated using Computational Fluid Dynamics (Fluent™) for a Newtonian (water) and a
non-Newtonian fluid (strawberry pulp). These simulations were performed at different mass
flow rates (from 0.5 to 2 kg/min.) and different inlet temperatures (from 40 to 90 ºC). RTDs
were determined defining a unit scalar at the inlet and monitoring its value at the outlet. These
results allowed the construction of F-diagrams and the calculation of the hold back (H) and
segregation (S). The simulations showed that for 0.5 kg/min water induces the formation of
more shortcuts (10 % higher H) then pulp. However, for 2 kg/min both fluids display a
similar behaviour (less than 3 % difference between H values). Furthermore, RTD is affected
by the inlet mass flow rate but not so significantly by process temperature. The values of S
calculated for water show that the reactor approaches plug flow behaviour. The RTD
determinations in the heating zone allowed the establishment of an equation for the prediction
of the outlet temperature of the fluid, allowing setting criteria for the aseptic processing of
fluids thus guaranteeing the microbiological safety of the products
