ples were dried in the open sun. For comparison of drying
rate of red and green chillies in the solar tunnel drier with
that of in the open sun, the blanched chilli samples were
dried in solar tunnel drier and in the open sun. Farmers
of Bangladesh dry chilli without applying any pre-treatments
and hence unblanched sample was dried in the open
sun as a control sample. In this study, blanched sample
dried in the solar tunnel drier is termed as ‘solar tunnel drying’
and those dried in the open sun by blanching and
unblanching are termed as ‘improved sun drying’ and ‘conventional
sun drying’, respectively. The drier was loaded
with 80 kg of blanched chilli. The changes of moisture content
with drying time for a typical experimental run for
solar tunnel drying, improved sun drying and conventional
sun drying of red chilli is shown in Fig. 5. Moisture content
of red chilli reached to 0.05 kg kg1
(db) from 2.85 kg kg1
(db) initial moisture content in 20 h of drying in solar tunnel
drier while it took 32 h to bring down the moisture content
of similar samples to 0.09 kg kg1
(db) by improved
sun drying and 0.40 kg kg1 (db) by conventional sun drying
method. This is due to the fact that the chilli in the drier
received energy from the radiation from the sun and more
energy transported from the collector by forced convection,
while the samples dried in the open sun received energy
from only the incident solar radiation and less energy
transported from surrounding environment by natural convec