APV Dryer Handbook - Umbc

BOTTOM PLATE
SWIRL CHAMBER
ORIFICE PLATE
Figure 27. Simplex nozzle for spray drying
dryer to produce powder. A more efficient way to reduce viscosity is to increase
the feed temperature. This has the added advantage of further increasing the
spray dryer capacity, since less heat is required inside the dryer to raise the
droplet temperature.
PRESSURE NOZZLE
A pressure nozzle atomizer requires the use of a high pressure pump to feed the
liquid to the dryer. It typically produces a powder with a high bulk density, a
narrow particle size distribution and, in the case of fat containing powders a low
free-fat content.
The principle disadvantage in spray drying is that there is very little adjustment of
possible flow rate without changing the powder properties or shutting down to
change the nozzle set-up. In a nozzle atomizer, the liquid is pumped into a swirl
chamber and passes out through an orifice plate.
CONE ANGLE
To get the best mixing between the liquid spray and the hot air coming into the
dryer, it is important to use the widest spray angle possible. As the nozzle pressure
increases, you will observe that the edge of the spray pattern tends to curve
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