Design and performance evaluation of a Double-pass solar drier for drying of red chilli (Capsicum annum L.)

Performances of a new designed Double-pass solar drier (DPSD) were compared with those of a typical cabinet drier(CD) and a traditional open-air sun drying for drying of red chilli in central Vietnam. The drying times (including nights) to reach the desired moisture content of 10% (on a wet basis) were 32 and 73 h respectively. During open-air sun drying the desired moisture content of 10% (on a wet basis) could not be reached even after 93 h of drying (including nights). The overall drying efficiencies of DSPD and CD to reach the desired moisture content of 10% (on a wet basis) were 24.04% and 11.52% respectively while the overall drying efficiency of open-air sun drying to reach the desired moisture content of 15% (on a wet basis) was 8.03%. Further, ASTA colour value of the solar dried products from the DSPD was higher than those from CD and open-air sun drying. Similar results were obtained for mycotoxins occurrence. Contamination by aflatoxin B1 was significantly lower in dried chilli from DPSD (<0.250 μg kg−1) when compared to traditional open-air drying technique (11.980 μg kg−1). The drying cost per one kilogram of chilli was 39% lower in case of DPSD (0.077 US$/kg) as compared to CD (0.126 US$/kg). The Double-pass solar drier was found to be technically suitable and economically viable for drying of red chillies in central Vietnam.