Drying kinetics of turmeric rhizomes and mathematical modeling

Drying kinetics of turmeric rhizomes (finger and mother rhizomes) was investigated by two drying methods namely direct sun drying and solar greenhouse drying with two different drying surfaces (black sheet over mud floor and directly on mud floor). The temperature and RH of ambient air and the air inside the solar greenhouse dryer varied from 31 to 47 ºC and 55 to 16% respectively and 36.5 to 57 ºC and 53 to 14%, respectively during the study period. The moisture content of boiled finger and mother rhizomes was 567 and 257% (db), respectively. Drying rate of turmeric rhizomes was higher (26.15 g of water/h/100 g of bone dry materials) in solar greenhouse dryer than the direct sun drying (23.64 g of water/h/100 g of bone dry materials). Among the drying surfaces, black sheet over mud floor recorded higher drying rate. Drying time of black sheet covered solar greenhouse dried turmeric finger and mother rhizomes were recorded about 52 and 68 h, respectively and reached an equilibrium moisture content of 7.39 and 10.95% (db), respectively. Six thin layer drying models namely Lewis, Page, Modified Page, Henderson-Pabis, Diffusion approximation and Two-term exponential were tested to identify the most appropriate model to describe drying kinetics of turmeric rhizomes. It was found that among the six drying models, Diffusion approximation and Page models are the best models to describe the drying characteristics of turmeric rhizomes.