3.13. Drying rate and surface area of potato chips during vacuum
frying
The study of convective heat transfer coefficient was performed
for a control mass of one potato slice, which initially weights 3.5 g.
The change in water content for this control mass was calculated
from the average moisture content data obtained in previous experiments. The change in water mass for one potato chip at different
frying temperatures is depicted in Fig. 3. The curve of water
content for each temperature was fitted to an exponential equation
to obtain the derivative of the curve, which is the drying rate with
respect to frying time, dm/dt (Fig. 8a). The rate constant for water
loss during frying was directly proportional to the frying temperature;
which means that water is evaporated faster at higher
temperatures.
Another important variable in the heat transfer coefficient calculation
is surface area of the material (Fig. 8b), which was calculated
with the diameter data for each frying temperature and, as
expected, it follows the same behavior as the diameter shrinkage.
The final values of surface area were not different between temperatures;
however, the curves have different characteristics during
the frying period.