Study of the heat transfer coefficients in a microwave assisted pasteurisation process

Abstract

The heat treatment of foods aims the inactivation of unwanted microorganisms and/or enzymes. However, in this treatment changes affect the acceptability of the product. Pasteurization is a mild heat treatment, widely applied in the food industry to process liquid products medium heat exchangers. Pasteurization can be divided into three stages: heating, retention and cooling. Focused microwave heating is a technology that has been studied for having the potential to replace heat exchangers promoting faster heating and reducing the loss of quality attributes. However, the adoption of this technology requires prior assessments in terms of process design. In this way, the objective of this work is to study the heat transfer coefficients involved in the microwave-assisted thermal processing in a pilot unit Microwave Lab25-UHT/HTST EHVH (Micro Thermics, USA). Different process conditions will be considered: product flow rate (0.4 to 2.0 L/min), process temperature (60 to 120 °C) and type of fluid (water, glycerine, CMC solution). The heat transfer coefficients will be obtained from the experimental data in the preheater, cooler and retention tube (loss of heat to the environment). Results will be correlated with flow rate and fluid properties based on thermal resistance theory. Dimensionless variables compatible with the rheological model of power law will be adopted. This work will contribute to the development of a process simulation model for determination of temperature and residence time distributions of the product in order to evaluate the effects of high temperature on safety and quality attributes.