Non invasive on-line estimation of temperature distribution in freeze-drying processes

Abstract

Proceedings of the 11th International Congress on Engineering and Food (ICEF11), Athens, Greece, 2011Freeze-drying is a dehydration process often employed in high added-value food and biochemical goods.This technique facilitates the later re-hydration of the resulting product while it helps to maintain its organoleptic and nutritional properties. In order to preserve quality, as well as to reduce the costs of a high demanding energy and time consuming process, the proper handling of the product temperature during the operation course becomes critical. Direct – invasive – measurement methods are potentially dangerous to product integrity what calls for new non-invasive strategies as the one proposed in this work. Our approach combines the mathematical modelling of the leading physical phenomena involved in freeze-drying together with experimental data obtained from pressure rise disturbances in the drying chamber. The data collected from pressure essays are employed to complete the partial differential equation system describing heat transfer mechanism. Numerical issues usually related to solving moving boundary problems, as it is the freeze-drying case, are overcome by applying coordinate transformations which lead to a fixed reference frame. On this new framework, order reduction methods can be used as a tool not only to simplify the system analysis and control but to minimize the computational effort as well, especially when 2D or 3D spatial domains with complex geometries are involvedThe authors acknowledge the financial support received from the 7th Framework Programme of the European Union (CAFE Project – Large Collaborative Project KBBE-2007-2-3-01) and the Spanish Ministry of Science and Innovation (MICINN Project AGL2008-05267-C03-01)N