DRYING CURVES OF SOME TROPICAL AGRICULTURAL CROPS OF SMALL HOLDING FARMS

摘要

Tropical agricultural crops such as coconut, tapioca, sweet potato and chili are typically planted by smallholder farmers for their own use and for sale. These crops are generally preserved by sun drying, whichrnrequires a long drying time and large areas of open space. In order to save space and time, biomass fired andrnsolar dryers have been suggested and their design requires the determination drying curves of the crops. Therndrying of coconut, tapioca, sweet potato and chili is performed in a constant environmental chamber forrnrelative humidities 30, 45 to 60 % and temperature in the range of 40°C, 50°C and 60°C, at an air flow rate ofrn1 m/s. The characteristic drying curve of coconut, tapioca, and sweet potato are found to have no constantrndrying rate period, but there are two falling rate periods, namely an initial rapid drying period and a slowerrndrying period. The first falling rate periods fit the polynomial model, whereas the second falling rate periodsrnfit the power law model. The characteristic drying curves of chilli however are found to have no constant raternperiod and only one falling rate period. The falling rate period curves of chilli fit the power law model.