ABSTRACT
Safety of thermal processing is the main objective of aseptic processing and packaging. Combined with heat transfer and heat delivery mechanisms, residence time and its distribution dictates the safety and uniformity of delivered thermal sterilization treatments to homogeneous and heterogeneous (particulate) fluid products.
Due to the continuous flow nature and regime of thermal processing for aseptic packaging, flow characteristics of different products are very important. These characteristics determine how the product flows as well as the transfer of heat to the products. Process settings and safety must be calculated based on the worst-case scenario, which includes the fastest-moving fluid element or solid particle that might be processed for which both the residence time distribution (RTD) of particles and the flow profile of liquids are needed.
Scientific knowledge base for flow behavior of homogeneous fluids as well as the methods of residence time distribution measurements and predictions are well established for a broad range of materials and flow regimes, and have been in routine industrial applications for several decades. This is not the case for the heterogeneous or particle-containing products. For such product, theoretical, practical studies and developments of methods for measurements of residence times and their distributions under different flow regimes are still subject to continuous improvement and experimental confirmations.
This chapter presents the current state of scientific knowledge for the theoretical basis for flow and flow distribution for both homogeneous and heterogeneous material, as well as state-of-the-art methodologies for their practical measurement and implementation of obtained results to design and validate process and product safety for a broad range of applications.
