الفهرس 
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Abstract
The drying process plays a great role in preservation of agricultural products. Solar
energy is one’ of the important economic methods to save energy for air heating in the
drying systems based on the natura] currents. Different modified solar drying systems
have been constructed to investigate the parameters affecting the drying efficiency.
In this study, the developement of direct and indirect drying systems have been
investigated in order to enhance the drying efficiency. For direct drying systems, the
investigation have been carried out to study the effect of tray geometrical position, tray
height ratio, diameter and height of dryer chimney. While for indirect drying systems the
influence of damper strips and guide vanes on drying efficiency have been investigated
at different pattern and the path of air flow.
The present experimental work has been performed for a direct dryer by changing
the distance between the tray and the glass cover for the horizontal and parallel trays to
the glass cover. The removed moisture content of these types have been compared with
the dryer of bottom horizontal tray. The obtained results showed that the drying
efficiency is improved at the same operating conditions. The present investigation shows
that the type of parallel tray has a higher effectiveness compared with the direct dryer
type of the horizontal tray. These results have been compared with the bottom horizontal
tray. For parallel tray at 0.425 height ratio, the maximum removed moisture content
from the product is increased by 13.5 % compared with the bottom horizontal tray. This
maximum moisture content is 10.8 % for the horizontal tray at a height ratio of 0.25.
Experimental work of direct cabinet solar drying system with chimney of different
heights and diameters has been carried out. The removed moisture content of this type
has been compared with the cabinet dryer without chimney having the same absorber
surface area. The results show that the removed moisture content from the product has
been increased within the range of2.2 % to 6.8 % due to the use of chimney with height
/ diameter ratio of 1.33 to 33.33. Maximum increase of moisture content removed from
the product is 6.8 % when using a chimney with height / diameter ratio of 16.67.
Minimum of moisture content removed from the product occurs when using a chimney
of height / diameter ratio of 1.25 . The experimental results show that any increase of
height / diameter ratio than 16.67 leads to decrease the moisture content removed from
the product. At height / diameter ratio less than 1.25 the moisture content removed from
the product decreases than that of the case without chimney.