Solar Drying: Fundamentals,Applications and Innovations - National ...

Fadhel - Recent Advancements in Solar Drying
Figure 6.7. Air directing elements installed inside drying chamber (Gülsah and Cengiz,
2009)
A new type of air solar collector, having dimensions 940 x 1850 x 200 mm 3 was
manufactured for supplying hot air necessary for drying. In order to increase collector's
efficiency absorbing surface was manufactured in steps. Also holes of 15mm diameter
were drilled 6 pieces on each step for increasing turbulence effect on the developed expanded
surface collector. In the developed system various drying air velocities were examined
in terms of drying periods. Drying periods of dried grapes in the drying chamber
with air solar collector and over cement ground were compared. Also drying experiments
were made with air directing elements installed inside the dryer and a swirl element
to the entrance of drying chamber was then compared with drying in open air under
natural conditions in terms of drying period. Accordingly 200 h of drying period under
natural conditions decreased to 80 h with the developed dryer having swirl element
with an air velocity of 1.5 m/s. With the increased in the difference of dryer's entrance
and exit temperatures drying period gets shorter (Gülsah and Cengiz,2009).
6.3.4 Solar assisted heat pump dryer system
Heat pump dryers have been known to be energy efficient when used in conjunction
with drying operations. The principal advantages of heat pump dryer is the ability to
recover energy from the exhaust gas as well as their ability to control the drying gas
temperature and humidity. Heat pumps have been extensively used in industry for many
years, although their application to process drying and, in particular, to drying textile
products is relatively lower. The solar assisted heat pump drying system has been operated
successfully. The heat pump recirculation mode and solar mode can be used to
produce the same quality of drying, this allows the drying process to be continues and to
save energy by not burning fossil fuels (Best et al., 1994).
134 Drying of Foods, Vegetables and Fruits