Drying Kinetics of Industrial Pineapple Waste: Effective Diffusivity and Thermodynamic Properties Resulting from New Mathematical Models Derived from the Fick Equation

Abstract

This research focuses on the drying kinetics of industrial pineapple processing waste on a flat plate, revealing a two-phase drying process: an initial phase with a constant drying rate followed by a phase with a decreasing drying rate. During the constant rate phase, the convective mass transfer coefficient, influenced by temperature variations from 40 to 70 °C, ranged from 5.69 × 10−7 to 2.79 × 10−7 m s−1. The study introduced a novel approach to modeling the decreasing drying rate phase, applying equations derived from the Fick equation. This process involved determining the activation energy and thermodynamic properties of drying using an experimental forced convection dryer at temperatures of 40, 50, 60, and 70 °C, and an air velocity of 1.5 m/s. Data were fitted to several mathematical models, including Fick’s with four series terms, and versions of the Henderson–Pabis and Page models modified by Cavalcanti-Mata, among others. The Cavalcanti-Mata and modified Page models provided the most accurate fit to the experimental data. Results showed that diffusion coefficients vary per model yet align with literature values. Additionally, enthalpy (ΔH) and entropy (ΔS) values decreased with temperature, while Gibbs free energy (ΔG) increased, indicating that drying is an energy-dependent, non-spontaneous process.