Modeling the Drying Kinetics of Saffron Petals Using Different Methods of Fluid and Semi-fluid Substrate Drying

In the process of producing saffron, petals are discarded as waste materials. As a result, in Iran, annually, 7257625 kg saffron petals are obtained as a sub-product. So finding a solution for recycling this huge amounts of waste is very important.This study conducted to find the most appropriate models for saffron petal dehydration with the use of semi-fluidized drier (SFD) and fluidized bed drier (FBD).س For this purpose, a fluidized bed drier was designed to measure the temperature and air flow velocity, and also with the ability of weighing the samples at different intervals with high precision and then. The airflow and temperatures ranges used in SFD and FBD were 0.7-1.7 ms -1 and 45-55 °C, respectively. When the air temperature and airflow respectively increased from 45 to 55°C and 0.7 to 1.7 ms -1 , the dehydration time in SFD or FBD decreased significantly. At air temperature of 45°C and similar conditions, the SFD and BFD could dehydrate saffron petals in airflow and drying times of 0.7 ms -1 for 96 min and 1.7 ms -1 for 30 min, respectively. However, at equal temperature of 55°C and airflow of 0.7 ms -1 , the petal dehydration time of SFD and FBD changed to 36 and 96 min, respectively. The effective moisture diffusivity coefficient in SFD and FBD systems varied from 9.548 × 10-10to 2.455 × 10- 9m 2 s -1 and from 1.114 × 10-9to 1.963 × 10-9m 2 s -1 , respectively. The calculated activation energy in SFD was ranged from 56.83 to 78.78 KJ/mol. Among eleven semi-experimental models tested for the saffron petals dehydration, only two models including logarithmic and modified form of Henderson and Pabis formula were found appropriate to fit the obtained data and show the actual trend of changing moisture ratio versus drying time of saffron petals. Because these models showed highest determination coefficients, lowest root mean squared and minimumsum-squared errors with the actual data.