Effects of drying variables on the characteristic of the hot air drying for gastrodia elata: Experiments and multi-variable model

Energy saving and efficient drying model play important role in the extraction of high quality Chinese medicinal materials. In this work, the gastrodia elata was subjected to hot air drying of revealing the drying characteristics with the medicinal indicator of gastrodin ingredient. The multiple drying variables of drying temperature, air velocity, slice thickness and relative humidity were taken into account. Based on the experimental results, an optimized multi-variable model was established to predict the characteristics of drying the sliced gastrodia elata with hot air. The experimental results show that the optimal model of the Page model enables to predict the water loss process of the sliced gastrodia elata under multiple drying variables. The optimal drying variables were determined based on the maximum gastrodin content, of which the temperature was 60 °C, air velocity was 3.5 m/s, slice thickness was 0.4 cm and relative humidity was 25 %. Meanwhile, the drying quality was improved efficiently. The effective diffusion coefficient of gastrodia elata in the hot air drying ranged from 2.254 × 10−9 m2/s to 3.241 × 10−8 m2/s, and the dry activation energy was 34.16 kJ/mol.