4. Flow characteristics and penetration of gaseous ozone
through stored bulk grain
Initial movement of ozone through the grain was impeded by a
phenomenon described as the ozone demand of the medium
Ozone movement through the grain layer is restricted
by the highly reactive nature of ozone
The
surfaces of many materials act as catalysts for ozone decay. Thus,
the rate of decay of ozone is generally dependent on the surface
characteristics of the materials through which it comes into contact
and temperature. The decay rate of ozone in air is positively
correlated with temperature and has been discussed in the literature
for various containment vessels
reported that gaseous ozone exhibited first-order
decay kinetics as it flowed through glass beads and soil. The increase
of the flow rate of ozone gas through these porous media
decreased the time it took to react with the media and reach a
steady state decay rate. Furthermore, an increase in organic matter
and/or metal oxides on the surface of the particles increased ozone
reaction rate in the media
attributed the high initial rate of ozone consumption in
maize to reactive components on the surface of the grain. As those
reactive components are used up, the primary pathway of ozone
destruction shifts to surface catalyzed decay on the grain kernels
and other objects in the grain bin
found
that ozone was far less effective against insects when the target
individuals were inside the grains, as compared with its efficacy in
empty spaces. Apparently, the presence of grain rapidly increased
the decomposition of ozone. Moreover, there were no differences
between wheat and maize, which clearly suggests that these two
grains have the same effect in ozone decomposition. Still, in field
tests, differences among grains are likely to exist, due to differences
in interstitial spaces among kernels of different size. Thus, it is
postulated that in large-scale applications, ozone flow should be at
rates that are enough to counteract these losses
studied investigated the flow characteristics of ozone
through a less porous grain than maize such as wheat and observed
the flow of ozone through a 3-m column of wheat was similar tothat previously observed for maize, having a Phase 1 in which the
ozone rapidly degraded as the ozone frontmoved through the grain
and a Phase 2 in which the ozone moved freely through the grain
with little degradation. The increasing of the velocity of ozone flow
from 0.02 to 0.04 m/s facilitated deeper penetration of wheat
during Phase 1. Similarly,