Mathematical models to describe the drying process of Moringa oleifera leaves in a convective-air dryer

Abstract

Drying kinetics of Malaysian Moringa oleifera leaves was investigated using a convective-air dryer. The drying parameters were: temperature (40, 50, 60, 70 °C), air velocity (1.3 m s-1, 1.7 m s-1). The drying process took place in the falling rate period and there was an absence of a constant rate period in this experiment. Six mathematical models (Lewis, Henderson and Pabis, Wang and Singh, Peleg, Page, and logarithmic) were selected for the description of drying characteristics of the leaves. The Wang and Singh model was determined as the best model based on the highest overall coefficient determinant (R2) and the lowest overall root mean square error (RMSE). The effective diffusivity (Deff ) was also calculated which was in the range of 3.98 × 10-11 m2 s-1 to 1.74 × 10-10 m2 s-1. An Arrhenius relation was constructed to determine the activation energy for the samples in the convective air dryer. The activation energy for M. oleifera leaves was 39.82 kJ mol-1 and 33.13 kJ mol-1 at drying velocities of 1.3 m s-1 and 1.7 m s-1, respectively.

Keywords

• drying kinetics
• convective-air drying
• mathematical modelling
• effective diffusivity
• activation energy