UNSTEADY NATURAL CONVECTION HEATING OF A CANNED NON-NEWTONIAN LIQUID FOOD

摘要

This paper is concerned with the modeling of complex thermal-fluid phenomena that arises during the process of sterilization of canned food. In the sterilization process, food contained with a typical cylindrical can is subjected to a sudden change in temperature as the can is immersed in a steam bath at saturation temperatures of the order of 120 degrees C. Because of this transient heating event, complex transient buoyant motion is initiated in the can and therefore the heating of the food is as a result of diffusion and buoyant or natural convection processes. A Finite Volume method was used to investigate the unsteady two dimensional (axisymmetric) natural convection of a non-Newtonian liquid food during sterilization. The non-Newtonian liquid food was modeled using carboxy-methyl cellulose. Because its apparent viscosity depends on both temperature and non-linear velocity gradients, the resulting mathematical formulation is highly non-linear, thereby requiring a highly coupled implementation of the Finite Volume Method. Transient two dimensional velocity and temperature fields were obtained for different heating conditions and can aspect ratios. It was found that lower can aspect ratios and lower index n generally lead to shorter sterilization times.