Modelling of moisture and salt transport in gelatine gels during drying at constant temperature

Drying experiments of salted and pure gelatine gels were performed on an original experimental device fitted out with a thermal regulation system in order to keep the temperature of the sample uniform and constant during processing. This system permits to fix different water evaporation fluxes in the range between 10 × 10−6 and 300 × 10−6 kg m−2 s−1. The mean values of moisture and salt contents were measured. The gel samples were cut into slices of 1–5 mm thick and orthogonal to the main direction of migration. A mass transport model based on Fickian formalism was developed in order to predict local moisture and salt contents within the gel during drying. This model takes into account the shrinkage of the material during drying and the influence of gel composition upon values of moisture and salt apparent diffusivities using empirical relationships. The values of the parameters used in these relationships were identified by minimizing the sum of square errors between measured and predicted profiles. In parallel, apparent diffusivities were directly estimated by using a specific treatment of the moisture and salt content profiles which has the advantage of requiring no assumption upon the mathematical relationship between apparent diffusivity and gel composition parameters. Both methods were found in good agreement.