Ricerc@Sapienza

Abstract: A non-isothermal moving-boundary model for food dehydration, accounting for shrinkage and thermal effects, is proposed and applied to the analysis of intermittent dehydration in which air temperature, relative humidity, and velocity vary cyclically in time. The convection-diffusion heat transport equation, accounting for heat transfer, water evaporation, and shrinkage at the sample surface, is coupled to the convection-diffusion water transport equation. Volume shrinkage is not superimposed but predicted by the model through the introduction of a point-wise shrinkage velocity.

Purpose: Developing a predictive model of the shrinkage of liver tissues in microwave ablation.

‘Annurca’ apple, a southern Italian cultivar, is known for its reddening, taste and flavour among the other types of apples, and also for health promoting effects. The aim of this study is to evaluate the effect of a novel pre-treatment, by dipping in a solution containing trehalose, sodium chloride, sucrose, and of drying process conditions (temperature and time) on drying kinetics and quality attributes of dried apple slabs. Drying experiments were carried out by convective drying at temperatures of 50, 55, 60 and 65 °C at a constant air velocity of 2.3 m/s.

Drying characteristics of persimmon, cv. “Rojo Brillante”, slabs were experimentally determined in a hot air convective drier at drying temperatures of 45, 50, 55, 60, and 65 ◦C at a fixed air velocity of 2.3 m/s. It was observed that the drying temperature affected the drying time, shrinkage, and colour. Four empirical mathematical models namely, Enderson and Pabis, Page, Logarithmic, and Two term, were evaluated in order to deeply understand the drying process (moisture ratio).

We exploit prediction capabilities of the moving-boundary model for food isothermal drying proposed in Adrover et al. (2019). We apply the model to two different sets of literature experimental data resulting from the air-drying process of eggplant cylinders (two-dimensional problem) and potatoes slices (three-dimensional problem). These two food materials, both exhibiting non-ideal shrinkage, are characterized by very different “calibration curves“ i.e. different behaviours of volume reduction V/V0as a function of the rescaled moisture content X/X0.

A moving-boundary model is proposed for describing food isothermal drying. The model takes into account
volume reduction of food materials and it is capable to predict sample shrinkage and surface deformation during
the drying process. It can be applied to any sample geometry (discoid, cylindrical, cubic, parallelepiped) and to
any food material since it can take into account that sample volume can decrease of a quantity that can be
smaller, equal or larger than the corresponding volume of removed water.

We investigate and quantify the error in the estimate of water diffusivity resulting from the adoption of one-dimensional (1-d) models to describe the drying process of thin discoidal or long-thin cylindrical samples. Numerical results obtained with the 1-d and the 2-d moving boundary models recently proposed by Adrover, Brasiello, and Ponso (2019a, 2019b) are compared for different sample aspect ratios.