Design and development of a machine for continuous popping and puffing of grains.

Popping/puffing have been traditionally practiced for enhancing storage life, improving organoleptic
properties and ease of incorporation in ready-to-eat-foods.
Currently, batch type sand and electric popping/puffing
machines involving conduction mode of heat transfer are
employed. The major drawbacks of these methods are
high-energy consumption, scorching of grains, non-uniform product quality, contamination (by sand/ash) and
problems in scale-up. Since fluidization is known to
increase heat and mass transfer, a continuous fluidized
popping/puffing machine (capacity 10–20 kg/h) involving
convective mode of heat transfer is designed/developed.
Hot-flue gas generating from burning of LPG was used as
the eco-friendly fuel. Process parameters such as expansion
ratio, fluidization velocity, terminal velocity, carry over
velocity, bulk density and voidage were estimated for unpopped and popped/puffed rice, maize, jowar (sorghum)
and paddy. Fluidization and carry over velocities for these
grains were in the range of 4.18–5.78 m/s and
2.15–6.18 m/s, respectively. Based on the terminal velocity
of the grains and volumetric air flow rate of the blower,
fluidization chamber diameter was arrived. Chamber
diameter of 0.15 m was found to be sufficient to generate
required air velocity of 6.89 m/s which met the fluidization
and carry over velocities of popped/puffed grains. The
designed fluidization chamber was analyzed for heat and
mass transfer during popping/puffing. Convective heat and
mass transfer coefficients were estimated to be in the range
of 103–187 W/m2 C and 0.124–0.162 m/s, respectively.
Theoretical values for total heat and mass transfer were
similar to the experimental values.