Experimental Optimization, Drying Kinetics and Energy-Efficiency Assessment of a Developed Refractance Window Dryer for Palmyrah Palm Pulp Drying

Abstract

Refractance Window Drying (RWD) is a promising thin-layer drying technology for reducing drying time and energy consumption while preserving the quality of heat-sensitive food products. This study experimentally evaluated and optimized a developed RWD system for energy-efficient drying of palmyrah palm pulp. A three-factor, three-level Box–Behnken design (BBD) combined with Response Surface Methodology (RSM) was employed to investigate the effects of circulating water temperature, product-layer thickness, and belt speed on drying time, Specific Energy Consumption (SEC), rehydration ratio, and Total Colour Difference (ΔE). Multi-response desirability optimization was performed, followed by thin-layer kinetic modelling using six semi-empirical models and estimation of Effective Moisture Diffusivity () and activation energy. The quadratic models showed excellent agreement with experimental data, with R² values of 0.9982–0.9994. The optimum condition was 75.5 °C, 2.15 mm thickness, and 0.50 m/min belt speed, giving a predicted drying time of 61.4 min, SEC of 12.22 MJ/kg water evaporated, rehydration ratio of 4.45, ΔE of 4.84, and desirability of 0.60. The Page model provided the best kinetic fit (R² up to 0.9996).  increased from 5.69 × 10⁻¹⁰ to 2.26 × 10⁻⁹ m²/s, while activation energy was 71.5 kJ/mol.