True Density Prediction of Garlic Slices Dehydrated by Convection

Physiochemical parameters with constant values are employed for the mass‐heat transfer modeling of the air drying process. However, structural properties are not constant under drying conditions. Empirical, semi‐theoretical, and theoretical models have been proposed to describe true density (ρ p ). These models only consider the ideal behavior and assume a linear relationship between ρ p and moisture content (X); nevertheless, some materials exhibit a nonlinear behavior of ρ p as a function of X with a tendency toward being concave‐down. This comportment, which can be observed in garlic and carrots, has been difficult to model mathematically. This work proposes a semi‐theoretical model for predicting ρ p values, taking into account the concave‐down comportment that occurs at the end of the drying process. The model includes the ρ s dependency on external conditions (air drying temperature ( T a )), the inside temperature of the garlic slices ( T i ), and the moisture content ( X ) obtained from experimental data on the drying process. Calculations show that the dry solid density (ρ s ) is not a linear function of T a , X , and T i . An empirical correlation for ρ s is proposed as a function of T i and X . The adjustment equation for T i is proposed as a function of T a and X . The proposed model for ρ p was validated using experimental data on the sliced garlic and was compared with theoretical and empirical models that are available in the scientific literature. Deviation between the experimental and predicted data was determined. An explanation of the nonlinear behavior of ρ s and ρ p in the function of X , taking into account second‐order phase changes, are then presented.