Heat transfer and residence time distribution in microwave thermal processing of liquid foods

• Grant number: 24/23364-2
• Support Opportunities: Scholarships in Brazil - Master
• Start date: May 01, 2025
• End date: February 28, 2027
• Field of knowledge: Agronomical Sciences - Food Science and Technology - Food Engineering
• Principal Investigator: Jorge Andrey Wilhelms Gut
• Grantee: Maria Luiza Pequeno Cláudio
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The electrification of industrial heating processes, combined with the use of renewable and clean sources of electrical energy, has the potential to reduce emissions and increase energy efficiency. Microwave irradiation is a promising and commercially viable electrotechnology for the food industry. In this context, a microwave applicator for continuous flow heating of liquid foods was developed in a partnership between USP/IMT with financial support from FAPESP and CNPq. A microwave-assisted processing line is being assembled for the thermal treatment of products such as juices and pulps. The product flows in helical or spiral tubes in the microwave applicator, the retention tube and the cooler. In the helical laminar flow, vortices are formed that promote radial mixing and reduce dispersion during residence time, important characteristics for the process. The aim of this project is to develop a mathematical model of the pasteurization process (heating, retention and cooling) considering one-dimensional and two-dimensional product temperature distribution, taking into account characteristics of helical flow, such as the use of a factor to increase radial thermal diffusivity and flatten the velocity profile in the tube (y-laminar model). Experiments on residence time distribution (RTD) and processing using a simulated food for flow rates between 0.5 and 2.0 L/min and temperatures between 50 and 90 °C will allow the adjustment of model parameters, correlated with the experimental conditions. The simulated food consists of water, sucrose, sodium chloride and carboxymethyl cellulose (CMC) with a composition that mimics the dielectric, rheological and thermophysical properties of a juice or pulp. The consolidated models will be tested in validation trials, being analyzed for reliability, ease of use and practical application. Simulation will allow analysis of the process regarding the product's temperature distribution and the consequent effect on the inactivation of enzymes and microorganisms and deleterious effects on quality parameters. Interaction with researchers from the group will allow a case study of simulation of a real food, and adjustments of the microwave cavity model regarding the distribution of the heat generation rate. Results of this research will contribute to the development of this technology that can benefit small and medium producers.