The effect could also be attributed to that a product with higher
moisture content (most often dried at low temperatures and high
feed flow rates) would tend to have a higher bulking weight caused
by the presence of water, which is considerably denser than the dry
solids (Chegini & Ghobadian, 2007).
Decrease in the bulk density with the increase of the atomization
speed was a result of the particle size and the moisture content of
the samples. Rotary atomization generally produces a larger particle
size in comparison to nozzle atomization. Two-fluid nozzle
atomizers obtain the smallest particles sizes. The atomizer is the
most important feature of a spray dryer. Its selection and operation
are of great importance in achieving cost-efficient production
while maintaining product quality (Masters, 1991).
Other factors such as feed temperature, feed rate, feed concentration,
residual particle size and distribution, as well as powder
temperature, also influence bulk density (Walton & Mumford,
1999).
Statistical analysis revealed the significant linear effects of
atomizer speed and feed flow rate (P < 0.01) on yield (Table 3). Each
drying variable had significant effect on moisture content, as well
as that of the interaction between inlet temperature and atomizer
speed. Outlet temperature had a significant effect on feed flow rate,
and on inlet air temperature.