Tray and Gravity Dryers

Convection is the transfer of heat from one point to another within a fluid by the mixing of one portion of the fluid with another. In natural convection, the motion of the fluid is caused by gradients of temperature and gravity. In forced convection, the motion is caused by mechanical means that enhance the rate of heat transfer over natural convection. An example of convection drying would include the use of hot air in tray dryers and fluid bed dryers. 

Gravity flow (usually vertical), e.g., turbo-tray, plate and moving-bed dryers, and rotary dryers (due to the slope)... 

The slurry is applied by direct dip coating of the twin drums in the feed tray at the bottom of the dryer (Figure 11.7) or by splash or spray feeders from a feed reservoir at the bottom of the dryer (Figure 11.8) on to the surface of the two steam-heated drums that are counter-rotating away from each other. - The sheet is formed by adhesion on to the drum surface and is held up against gravity by its surface tension. 

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