Influence of temperature dependence of viscosity on thermal process establishment using CMC-based liquid food model

Abstract

Since determination of the slowest heating zone (SHZ) is a tedious task in thermal process establishment, mathematical simulation has been introduced. In this research, a numerical study on 2-dimensional natural convection in a cylindrical can during sterilization of liquid food (1% Carboxy-methyl cellulose, CMC) was performed to simulate the flow pattern and temperature distribution. SHZ and sterilizing value (F0) were also determined. Temperature dependent viscosity and density were assumed, while heat capacity and thermal conductivity were kept constant. To represent the actual mechanisms of heating in an overpressure retort, nonisothermal boundary condition (B.C.) was applied; the results were compared with isothermal B.C. The non-isothermal B.C. resulted in a slower heating rate and the simulated temperature profiles that agreed well with the experimental data (2.6% RMSE). Simulated SHZ was forced to move downwards from the geometric centre to the bottom of the can and stayed at about 10% of the can height from the bottom. SHZ moved closer to the wall (at r = R/2) as a result of the secondary flow due to natural convection. An increase in viscosity and thermal conductivity and a decrease in specific heat and density of higher than 5% resulted in a significantly lower F0-value.