Thermal efficiency and drying Behaviour of Yam slices in a dryer driven by the waste heat of exhaust gases

Abstract

This study investigated the thermal efficiency and thin-layer drying characteristics of yam tuber in a crop dryer driven by the waste heat of exhaust gases. Experiments were conducted at three different progressive levels of drying air temperature (T) of 55 - 75°C; air velocity (va) of 1.0 - 2.0 m/s; and sample slice thickness (X) of 1.0 - 2.0 cm with a batch size of 2200 ± 0.5 g of the blanched yam tubers. Results demonstrate that at varying process conditions, the mean drying time varied between 195 and 705 mins, with the average drying rate, dA in the range of 2.039 - 7.374 gwater/min. The diffusion coefficient of moisture for the tuber samples (De), fluctuated between 7.27 × 10−10 m2/s and 5.60 × 10−9 m2/s, obtained at (55°C, 1 m/s and 1 cm) and (75°C, 2 m/s, and 2 cm) treatment combinations. The thermal efficiency (ηth) of the dryer improved with increasing T, whereas an increase in either va or X caused a reduction in the value of ηth. The range of thermal efficiency values obtained varied in the order: 9.42% ≤ ηth≤ 44.95%. The activation energy for moisture diffusion showed no exact relationship with va. The values ranged from 34.36 to 53.4 kJ/mol. The results obtained in this investigation will come in handy in the design and development of agro-crop commercial dryers that are inexpensive, eco-friendly, energy-efficient and sustainable.

Keywords

• Yam slices
• Thin-layer drying
• Activation energy
• Thermal efficiency
• Drying rate