Optimal shape design of bypass holding tubes configuration in asepting processing

Abstract

The concept of aseptic processing originated to solve problems associated with conventional ‘in-container’ sterilization of foods such as low rate of heat penetration to the slowest heating point in the container, the long processing times required to deliver the required lethality, destruction of the nutritional and sensory characteristics of the food, low productivity, and high energy costs. Aseptic processing technique has been successfully applied to liquid foods and acid foods containing discrete particulates. However, the extension of aseptic processing to heterogeneous low-acid liquid foods containing discrete particulates has been difficult due to lack of data on critical factors such as interfacial heat transfer coefficient between the liquid and the particle as well as the residence time distribution (RDT) of particles in the holding tube of the aseptic system. Geometry of holding tube represents a primary parameter in determining the residence time distribution of particulate inside an aseptic processing system. Several configuration had been investigate in the past, including curved geometries in order to minimize spreading of RTD. In the following work an experimental bypass holding tube is optimized numerically and experimentally. Numerical optimization was performed by using the Optimal Shape Design, where the essential element respect to classical numerical simulations in fixed geometrical configurations, is to introduce a certain amount of geometrical degrees of freedom as a part of the unknowns, which means that the geometry is not completely defined, but part of it is allowed to move dynamically in order to minimize or maximize the objective function.