Mathematical modelling and optimization of melon slice drying with response surface methodology in a heat pump drying system

Abstract

The objective of this study was to optimize the process conditions (in terms of air temperature, air velocity and thickness of the slices) using response surface methodology (RSM) to achieve minimum specific energy consumption and maximum moisture diffusivity during drying of melon slices with a closed loop heat pump drying ( HPD) system. An optimum drying temperature of 45 degrees C, air velocity of 1 m/s and slice thickness of 5.04 mm were recommended with following predicted responses close to experimental values: drying time 216.58 min, total energy consumption 2.94 kWh, coefficient of performance heat pump (COPhp) 3.08, coefficient of performance system (COPws) 2.75, specific moisture extraction rate (SMER) 0.22 kg/kWh, drying rate 2.53, L* value 82.53, a* value -1.83 and b* value 25.82. The most suitable models to represent the drying behavior of optimum melon slices was chosen Wang & Sing. Effective moisture diffusivities (D-eff) of the melon slices were ranging from 7.075E-10 - 1.843E-07 m(2)s(-1) and increasing drying air temperature, drying air velocity and slice thickness led to an increment of (Deff).