Optimization of the factors affecting the drying rate of cassava grates in a rotary drum dryer

Abstract

This study determined the optimum effects of temperature, drum rotation and loading rate on the drying rate of cassava grates using the rotary drum dryer in removing moisture from cassava grates. A Central Composite Design was employed to evaluate a total of 15 fractional treatments derived from the 27 treatment combinations of temperature (75, 944 and 113˚C), drum rotation (15, 20 and 25 RPM) and loading rate (5, 15 and 25 kg/h). The response surface regression obtained optimum conditions of the factors and predicted values on the stationary point on water loss as well as the rate of water removal.

Results from the canonical analysis of response surface on plain water loss show am optimum combination of temperature of 107˚C, drum rotation of 23 RPM and loading rate of 24 kg/h. At 25 kg/h loading rate regardless of any variation of temperature and drum rotation, the rotation of the drum could not be sustained due to heavy load caused by the accumulated weight of the grates inside the drums. The optimum conditions and predicted response values for rate of plain moisture loss were observed to be: temperature of 108˚C, drum rotation of 23 RPM, Loading rate of 26 kg/h. Response surface plots show the opposite effects between loading rates and temperature on the plain water loss as well as the rate of moisture loss. Response surface plots also revealed that RPM has no effect on the plain water loss and rate of moisture removal.