TRANSIENT TEMPERATURE AND VELOCITY PROFILES IN A CANNED NON-NEWTONIAN LIQUID FOOD DURING STERILIZATION IN A STILL-COOK RETORT

Natural convection heating of a canned liquid food during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation for an axisymmetric case, using a finite element code. The model liquid has constant properties except viscosity (temperature dependent and shear thinning) and density (Boussinesq approximation). The velocity field establishes itself much more rapidly than the temperature field. The maximum axial velocity is of the order of 10(-4) m s-1 because of low Grashof number. The coldest point is not fixed but migrates in a region that is 10-12% of the can height from the bottom of the can and at a radial distance approximately one-half of the radius. On the basis of the computed particle path it appears that the liquid initially located just below the top center is exposed to the minimum heat treatment and should be of most concern in the thermal process calculations.