Drying Flashcards
(45 cards)
Convective drying
Drying of Wet Solids
Conductive drying
Drying of Wet Solids
Radiation drying
Drying of Wet Solids
Fixed (or static) bed convective drying
Convective drying of wet solids
Dynamic convective driers
Convective drying of wet solids
Factors affecting drying in this manner can be illustrated by reference to the construction and use if a simple form of drier – the tray (shelf or compartment) drier
Fixed (or static) bed convective drying
Fluidized bed drier
Dynamic convective driers
An excellent method of obtaining good contact between the warm drying air and wet particles is found in fluidized bed drier
Dynamic convective driers
General principle of Fluidized bed drier
fluidization
In this process the wet solid is in thermal contact with a hot surface and the bulk of heat transfer occurs by conduction
Conductive Drying of Wet Solids
Vacuum oven and vacuum tumbling drier
Conductive Drying of Wet Solids
Consists of jacketed vessel sufficiently stout in construction to withstand vacuum within the oven and steam pressure in the jacket
Vacuum Oven
Main advantage – is that drying takes place at a low temperature, and as there is little air present there is minimum risk of oxidation. The temperature of the drying solid will rise to the steam or water temperature at the end of the drying, but this is not usually harmful
Vacuum Oven
One design of tumbler drier resembles a large Y cone mixer
Vacuum Tumbling Drier
The vessel is steam jacketed and is connected to a vacuum.
Vacuum Tumbling Drier
It can be used for drying tablet granules, which tumble over the heated surface as the vessel slowly revolves.
Vacuum Tumbling Drier
Heat transfer rates in this equipment are much higher than can be attained in a convectional vacuum oven, where the material is static
Vacuum Tumbling Drier
Radiant heat transmission
Radiation Drying of Wet Solids
use of microwave radiation
Radiation Drying of Wet Solids
Differs from heat transfer by conduction or convection in that no transfer medium (solid, liquid, or gaseous) need be present
Radiant Heat Transmission
Heat energy in the form of radiation can cross empty space or travel through the atmosphere virtually without loss. If it falls on a body capable of absorbing it then it appears as heat, although a proportion maybe reflected or transmitted
Radiant Heat Transmission
________ radiation is seldom used as heat source because it is absorbed very quickly and does not penetrate far into the wet mass. The surface layers dry quickly and the absorption of further energy then raises the temperature of the dry material to a high value, which is often detrimental to the product
Infrared
______ radiation in the wavelength range 10 nm to 1 m penetrates much better than IR radiation
Microwave
Microwaves are produced by an electronic device known as
magnetron
