abstract

A comprehensive model for the simulation of shrinkage of deformable porous
solid foods. A case study: the convective drying of potato slabs.

Abstract
 
In the context of increased globalcompetition in the food drying business,
staying at the state of the art with respect to research and innovation is proving
crucial.[3,4,8] Lately, following consumer trends, focus has been set ondeveloping mathematical models allowing to model shrinkage of fruits and
vegetables during drying.[1,6,7,9-17]
In this research project, the modelling of potato shrinkage during convective
drying wasconsidered using COMSOL Multiphysics software to implement the
equations. Furthermore, experiments were carried out in a drying tunnel at
different temperatures and air velocities of 1.5m/s withrelative humidity of
25% in order to verify the model output experimentally. During the
experiments, weight and colour were measured at regular intervals. Colour was
measured with a Hunterlab MiniscanEZ colorimeter that uses the CIELAB
colour scale. The geometry used for the potato slabs was of 4.5cm diameter
and 1.5cm height cylinders. This geometry was chosen in order to enable
colourmeasurements throughout shrinkage as the cylinder’s top surface –taken
as reference for colour measurements– diminishes in size.
The mathematical model was developed in 2D, using axial symmetry to extendit to 3D. The GAB isotherm was used to calculate equilibrium moisture content,
while volumetric shrinkage was assumed to be linearly proportional to moisture
content decrease, following results fromresearch conducted by other
authors.[1,7,16] The velocity profile was approximated as constant on top of the
cylinder, with a decrease along the lateral side to zero value at the bottom
edge. Masstransfer coefficients were calculated based on a proportionality
relation with the heat transfer coefficients from Rovedo et al., initially proposed
by Blackwell et al., while the heat transfer...