Prediction of Freezing Times in Vegetables Using the Finite Element Method and a Combined Enthalpy and Kirchhoff Formulation

Abstract

Mushrooms are widely commercialized products which are very susceptible to enzymatic browning. Therefore their short shelf-life makes their preservation a crucial task. Freezing of previously blanched mushrooms, either whole or sliced, is a common process to obtain longer durability. A numerical model using the finite element technique was applied to predict freezing times of mushrooms considering the actual shape of the product. The original heat transfer equation was reformulated using a combined enthalpy and Kirchhoff formulation in order to obtain accurate numerical results and enhance the computational speed of the program. A three dimensional geometry was used to describe the sliced mushroom shape. Digital image reconstruction was used to obtain the irregular contour of the food product. The numerical predictions agreed with the experimental timetemperature curves during freezing of mushrooms in a tunnel (maximum absolute error < 3.2ºC). The codes were applied to determine the required processing times for different operating conditions with minimum computational efforts.