ABSTRACT

An active mix-mode solar dryer powered by wind generator and a passive solar dryer both integrated with and without C₃H₈O₃ (glycerol) as thermal storage was designed, fabricated and evaluated with a pre-treated sliced potato. The dryer was designed to operate in a low sunshine belt of the southern Nigerian climate characterized by its low solar radiation intensity, hence the integration of thermal storage material. The study offered the total dryer performance analysis including the exergy, energy, and drying kinetics of the dried product.  The main objective was to develop an active dryer system using only renewable energy (solar and wind energies). The results presented showed that the developed mix-mode solar dryer can save between 9- 16 hrs of drying time compared to ordinary sun drying method when drying 2 mm thick potato slices with the moisture content reduced from 64.2 % to 8.6 11.6 % wet basis.  A shorter drying time of 4h hrs was recorded with solar dryer integrated with wind-powered axial fan and thermal storage while drying with passive solar dryer without thermal storage presented a longer drying time of 25 hrs.  Dipping the potato in a salt solution for 30 seconds before drying quickens the drying rate of the potato compared to dipping it for 60, 90 seconds or blanching for 30 -90 seconds. Additionally, potato pre-treated with salt solution showed very attractive bright colour compared to blanch or none pre-treated potato.  During the experimental periods, the mean radiation intensity ranged from 10 - 626 W/m², the ambient temperature range was 24 ^oC - 50 ^oC and humidity of about 9 - 52 %.  . Under these operating conditions, the average drying efficiency was 28.59% - 29.14 %. In terms of energy utilization for drying purpose, solar dryer, integrated with wind-powered axial fan only, showed higher drying efficiency of 80 % while drying with passive solar dryer with thermal storage presented lower energy efficiency.  The total energy consumption for drying ranged between 435102.2 kJ and 498040.2 kJ while the specific energy consumption was 28.46 to 36.86 kWh/kg. The exergy efficiency ranged from 14.5 – 80.9 % during the sunshine hours.