Mathematical modeling for thin layer vacuum belt drying of Panax notoginseng extract

A novel drying method using vacuum belt drying (VBD) technology for drying natural herb extract was proposed. The Panax notoginseng extract was investigated as an example of gentle VBD process. It is a natural herb product widely used in China and other Asia countries. Drying experiments were carried out at drying temperature of (90 °C, 90 °C), (100 °C, 100 °C), (110 °C, 110 °C), feeding speed of 15 ml/min, 20 ml/min, 25 ml/min, and belt speed of 4 cm/min, 7 cm/min, 10 cm/min, respectively. The performance of different mathematical models (Lewis, Page, Henderson and Pabis, Logarithmic, Wang and Singh models) describing the VBD process were then tested and compared. The Logarithmic model gave better prediction than other models, and satisfactorily described the vacuum belt drying process of P. notoginseng extract. The effective diffusivity of P. notoginseng extract varied between 4.86 × 10−7 and 11.0 × 10−7 m2/s over the drying conditions.