Mathematical modeling of drying characteristics of chilli in hot air oven and fluidized bed dryers

Abstract

The thin layer drying kinetics of chilli is experimentally investigated in hot air oven and fluidized bed dryers.  Experiments were conducted at inlet air temperatures of 45℃, 50℃, 55℃, 60℃ and 65℃.  The power consumption and quality parameters (color and capsaicin content) were measured in each experiment.  Thirteen different thin layer mathematical drying models were compared by using their regression coefficient, chi square value and RMSE (root mean square error).  The Midilli model was found to be the best mathematical model which could use to satisfactorily predict the moisture ratio of chilli at different drying air temperatures in each type of dryers used.  Surface colour chromaticity parameter a* changed from 32.5 at 45℃ to 25.8 at 65℃ temperature in hot air dryer whereas it was changed from 29.3 at 45℃ to 23.8 at 65℃.  When temperature increases from 50℃ to 65℃, there is a considerable reduction in the colour of chilli in both dryers.  Capsaicin concentration was inversely related with the air temperature and there was a sharp reduction of capsaicin concentration when increasing the temperature from 60℃ to 65℃.  The energy consumption was higher in fluidized bed dryer than the hot air oven dryer when moisture content of chilli reduced from 280% to 9% (d.b) during drying process.  The retention time of the fluidized bed dryer in all operating temperatures was nearly three times less that of hot-air oven dryer due to higher air flow characteristics.  Lowest power consumption occurred at 65℃ temperature setting in both dryers while the fluidized bed dryer consumed nearly 75% more power.

Keywords: mathematical modeling, drying kinetics, capsaicin, fluidized bed, regression