New thin-layer drying models for the design and simulation of cassava root dryers and phenomenological study of interaction water-starch during diffusion

In the present work, drying phenomenology of cassava root slices was studied at 55, 65, 75, 85, 95, 105 and 115 degrees C, and at 5- and 6-mm thicknesses. Chemical analysis, X-ray diffraction (XRD) measurements, and Fourier-Transform Infrared Spectroscopy (FTIR) of samples of cassava, dried at different temperatures, were carried out. Additionally, the performance of three new thin-layer drying kinetics models was analysed. Initial moisture in a wet basis and starch content in a dry basis were 62.4 and 74.8%, respectively. The drying curves showed a monotonic decrease in time and a progressive closeness as the drying temperature increased (with the exception of 115 degrees C), reaching a stage, so-called, dynamic pseudo-equilibrium, located between the typical storage moisture content, and the real equilibrium. Drying rate curves showed a single stage of decreasing drying rate with internal control, while desorption curves showed a sigmoidal characteristic shape of an anomalous diffusion type, confirmed by the potential behaviour of the effective diffusivity with respect to the material moisture content. The 115 degrees C drying curve behaviour was explained by the changes seen in XRD patterns and FTIR spectra. The new Modified-Faneite-Suarez model got an extraordinary performance modelling the cassava drying, while Faneite-Mosquera model got a very good performance and the most recommendable to be used in design and simulation of cassava dryers based on its sound theoretical basis and prediction capabilities in a broad spectrum of temperatures.

Special thanks to the Secretaria de Educación Superior, Ciencia y Tecnología e Innovación (SENESCYT) of the Republic of Ecuador for the financial support of Dr. Angos as Prometeo Researcher.