Processi assistiti da sorgenti elettromagnetiche a radiofrequenza e a microonde (RF e MW) per i settori alimentari e dell'essicazione

Nowadays dying process is one of the most energy intensive processes in food industry, plastic industry, textile industry and in many different industrial sectors. The most important and used way to eliminate the water from a material are processes based typical on the forced convection of hot air that can be dehumidified at a certain relative humidity that typically depends from the material that it is necessary to dry. In some special applications, for example in plastic industry it is necessary to use hot and dry air: not high temperature (up to 180[degC]) to guarantee the product integrity and low dew-point (up to -40[degC].) to guarantee extremely low material RH (up to 10[ppm]). In food industry, instead, and for example in coffee-roasting processes, air temperature may reach 300[degC] to guarantee high heating rates and Maillard reactions but they are characterized by high dew-point (also 10[degC]). Because of the request of producers in the last 30 years is to have higher and higher productivity of drying lines, industry and its R&D departments invested great resources (in terms of time and money) to obtain fastest processes. One of the first concept was to modify batch processes to obtain continuos processes with high convection-air temperature. Two of the main problems of modern hot-air processes are the global efficiency of drying and how the hot air is generated. Many drying process are nowadays characterized by process-air temperature as high as possible and that practically increases specific losses to the environment. It is clear that in 2022 it is no longer ecologically acceptable to burn hydrocarbons as methane, ethane or propane, but recent world events caused, for example, a large increase in natural gas (up to about +200[%]) and that questioned the economic convenience of gas compared to electric energy, also for heating. For that reason Radiofrequency and Microwave drying and heating processes are becoming nowadays more and more interesting. But why they are so interesting? It is clear that it is not physically possible to reduce the latent heat of vaporization of water, but because of microwaves and radio-frequency waves directly heat materials, and in many cases directly generate power sources inside the wet-material matrix they make possible in many applications to dry (at a certain drying rate) with lower temperatures: “cold dry”. In home-appliance applications, such as microwave ovens, new technologies: Solid State MW generators are becoming interesting to improve final product quality and to solve some famous problems, such as the non uniformity in food heating. Because of it is necessary to design system with certain field distribution, to guarantee high efficiency and high quality product: metaphysical computer-aided methods (e.g. FEMs) make possible to design with high accuracy processes and devices. For that reason in my work the scientific approach follows, for every problem (and example) proposed the following line-up: a) Process analysis and State Of Art analysis: It is necessary to obtain a benchmark of the actual process (drying, heating, thawing, cooking). It is necessary to define process performances indicators (PPI), b) Material characterization: Because of electromagnetic, temperature, mass flow problem are described by partial differential equations, if properties are not accurate, the design FEM based will not be accurate. c) Pre-design of the device: Analytical approaches, and the solutions of some particular cases make possible to get a preliminary draft of the prototype. d) Virtual deisign by multiphysics analysis: FEM models and numerical optimization of the process. e) Protoype and testing of the system: validation of the model and of the device