2. PRINCIPLE
• Hot air continuously circulated through the
substances which is placed in the trays
• Forced convection is the mechanism of
evaporation
• Moisture removed from the solids
• Moist air removed through the outlet
3.
4. CONSTRUCTION
It consists of a rectangular chamber whose
walls are insulated
Trays are placed inside the heating chamber
The number of trays vary with the size of the
dryer
Laboratory scale : minimum 3 trays
Industrial scale: more than 20 trays
5. CONSTRUCTION
• Shape of tray: rectangular, square
• Area: 1.2 -2.4 meter square
• Loading depth of each tray: 10-100 mm
• The distance between the bottom of upper
tray and the surface of the substances loaded
in the subsequent tray: 40 mm
6. CONSTRUCTION
Trays can be loaded in trucks on wheels
Trucks can be easily rolled in to and out of the
chamber
Two trucks can be arranged inside a dryer
Dryer fitted with a fan- to circulate air over
the trays
7. CONSTRUCTION
Electrically heated elements provided inside
the dryer to heat the air
Direction vanes are placed in the corner of the
dryer – to direct the air in the expected path
8. WORKING
1. Wet solid is loaded in to trays
2.Trays are placed in the chamber
3.Fresh air is introduced through the inlet
4.The air passes through the heaters and gets
heated up
5.The hot air circulated by means of fan at 2-5
meter per second
9. WORKING
6.The air picked up water
7. As water evaporates from the surface, the
water from interior diffuses out by capillary
action.
• These events occur in a single pass of air
• the time of contact is short and the amount
of water picked up in a single pass small
10. • So the major fraction 80-90% of the
discharged air is circulated back through fan
• 10-20% of fresh air is introduced in to the next
cycle
11. The moist air discharge through outlet
The constant temperature and uniform air flow
over the material maintained- to achieve uniform
drying
13. ADVANTAGE
• Loading and unloading can be done without
losses
• DISADVANTAGE
• Amount of water picked up in a single pass is
small
• Time consuming
• More labor to load and unload – labor cost high
