VD

1. VACUUM DRYER

2. PRINCIPLE
• In vacuum dryer material is dried by the
application of vacuum
• When vacuum is applied the pressure is
lowered so that water boils at a low
temperature
• Hence water evaporates faster
• The rate of heat transfer becomes efficient
• So that drying rate substantially enhances

3. CONSTRUCTION
• Heavy jacketed vessel – cast iron
• It can withstand high vacuum within the oven
and steam pressure in the jacket
• The enclosed space is divided in to a number
of portions by means of 20 hollow shelves
which are a part of jacket
• These shelf's provide large larger surface area
– 45-50 metre square

4. • Over the shelfs metal trays are placed
• Oven door is tightly sealed
• Oven is connected to a condenser
• Condenser connected to a vacuum pump

5. WORKING
• The materials to be dried is spread on trays
• The trays are placed on the shelves
• Vacuum is applied so pressure will be
decreases up to 30-60 kilopascals. Because of
that boiling point of the liquid decreases .so
that the liquid will boils at low temperature
than its BP.

6. WORKING
• After applying vacuum ,door is closed firmly
• Steam or hot air is introduced in to the hollow
space of jacket and shelves
• Heat transfer takes place by conduction

7. WORKING
• So that water will be evaporated from the
material at 25-30 °C because of the lowering
of the BP
• Water vapor passes in to the condenser where
condensation takes place.
• At the end of the drying vacuum line is
disconnected
• The dreid material is collected from the trays

8. USES
• Useful for drying heat sensitive materials
which undergo decomposition
• Dusty and hygroscopic materials
• Drugs containing toxic solvents can be
removed and it can be collected in to closed
container

9. ADVANTAGES
• Large surface area for heat transfer
• Handling of the material ,trays and equipment
is eazy
• Electrically heated hollow shelves can also be
used

10. DISADVANTAGES
• Heat transfer coefficient is low
• Limited capacity
• More expensive than tray dryer