Enthalpy-driven optimization of intermittent drying of Mangifera indica L.

Abstract

Intermittent drying is an alternative technology to continuous heat-supply drying that could improve the energy efficiency of the process and the product quality as it reduces both the material enthalpy gain and the heating time. In this study, the application of intermittent drying technology to mango ( Mangifera indica L. cv. Tommy Atkins) drying was analyzed and optimized for different drying temperatures and cycles. The heating and resting times during the intermittent drying were optimized by minimizing an objective function that represents the average enthalpy increment of the material through the process. To quantify the objective function, a model was developed for a cubic shape considering mass and heat transfer and showing non-negligible external resistances, and transport properties as being moisture and temperature dependent. Moreover, specific models for sorption isotherms and heat capacity were identified experimentally for M. indica L. cv. Tommy Atkins that, together with other reported models, were used to complete the overall model formulation. According to intermittent and continuous drying simulations, the average enthalpy gain for the optimized intermittent process decreased between 9% (45 °C, one cycle) and 23% (65 °C, three cycles), and the heating time decreased between 3% (65 °C, three cycles) and 11% (45 °C, one cycle). The optimization results show that there is an advantage of intermittent over continuous drying one as regards material enthalpy and heating time under the operating conditions and constraints that were considered, which indicate a decrease in the energy consumption and an eventual improvement of quality.