Using chaotic advection to enhance the continuous heat-hold-cool sterilisation process

Abstract

Abstract In a conventional continuous sterilisation process, the food product flows steadily through a heat-hold-cool system, but viscous flow poses a serious challenge as heat transfer is controlled by thermal conduction which leads to a wide radial temperature distribution and slow heating of the core region of the flow. We use a validated Computational Fluid Dynamics (CFD) model to show that the superimposition of transverse mechanical oscillations on the heat-hold-cool sterilisation process of a viscous single-phase Newtonian fluid, creates a strong oscillatory-perturbed or chaotic advection flow which leads to significant improvements in thermal processing uniformity and product quality compared with a conventional process with or without an inline static mixer fitted. Chaotic advection flow produces processing conditions which are more in line with the high temperature for short time (HTST) assumption. Results show that the vibrated process leads to faster nearly-uniform heating and cooling, thus, achieving much higher levels of sterility and product quality in a much shorter process. Industrial Relevance Technological solutions are needed to help solve the long-standing problem of wide variation of product sterility and nutritional quality across the tube in continuous thermal processing of viscous fluids, where much of the product has to be over-processed to ensure sterility throughout, thus, often violating the high temperature for short time (HTST) processing assumption. Superimposing a secondary chaotic flow on the process leads to high levels of sterility, processing uniformity and product quality over relatively short process lengths. This represents an enhanced process which surpasses conventional steady flow sterilisation even when an usually undesirable static mixer is fitted.