2.2 Phenomenological Methods
49
Fig. 2.4 Interface between two regions without a and with b guide plates
A central region filled with black pebbles and the side regions entirely consisting of
colorless pebbles were gradually shaped and maintained. The regions were separated
by relatively distinct interfaces. Mixing zones were developed between the central
region and the side regions. The maximum size of the mixing zones was about 4–5
times of the pebble diameter. In addition, a tiny number of black pebbles were found
scattering in the side regions at the spots relatively far from the central region, as
well as a few colorless pebbles scattering in the central region. The scatterings were
mainly caused by pebble bouncing into the opposite regions at the top of the pebble
bed, while the pebbles were being loaded. The regions were horizontally symmetrical
with a bullet-like central area.
Investigation on the mixing zone between differently colored regions is important
to understand the physical mechanism of the pebble flow. To eliminate the mixings
caused by the pebbles’ bouncing on the free surface, the guide plates were installed
at the upper section of the pebble packing, and then the experiments were repeated
[7]. Here, the mixing zone was entirely created by the pebble flow itself without the
contribution of pebble’s bouncing on the free surface. Figure 2.4 display the enlarged
plots of the interface between two regions without and with guide plates installed in
the upper section, respectively. The guide plates have no noticeable influence on the
feature of the two-region arrangement, but an influence on the mixing zone.
The horizontal dispersion of the dense pebble flow leads to the existence of a
mixing zone between the two regions. In the mixing zone, the black and colorless
pebbles are dynamically and stochastically distributed. The pebbles move down
with ceaseless rearranging, but hardly run far away. By installing the guide plates,
the mixing zone was improved and was smaller on a scale of about 2–3 times of the
pebble diameter. Very few pebbles straggled far away into the opposite region. This
means that the originally scattered pebbles were mostly produced by the pebbles’
bouncing on the free surface. Moreover, when the guide plates were installed, the
interface between the regions looked like the waved surface, and any undesired
pebbles hardly appeared. This interesting fact indicates that, for quasi-static pebble
flow, as in pebble-bed reactors, pebbles are restricted or locked by their surrounding
neighbors, and undergo long-lasting frictional contacts with each other [8]. The
pebbles gather in crowds and groups of several pebbles to move down together under
49
Fig. 2.4 Interface between two regions without a and with b guide plates
A central region filled with black pebbles and the side regions entirely consisting of
colorless pebbles were gradually shaped and maintained. The regions were separated
by relatively distinct interfaces. Mixing zones were developed between the central
region and the side regions. The maximum size of the mixing zones was about 4–5
times of the pebble diameter. In addition, a tiny number of black pebbles were found
scattering in the side regions at the spots relatively far from the central region, as
well as a few colorless pebbles scattering in the central region. The scatterings were
mainly caused by pebble bouncing into the opposite regions at the top of the pebble
bed, while the pebbles were being loaded. The regions were horizontally symmetrical
with a bullet-like central area.
Investigation on the mixing zone between differently colored regions is important
to understand the physical mechanism of the pebble flow. To eliminate the mixings
caused by the pebbles’ bouncing on the free surface, the guide plates were installed
at the upper section of the pebble packing, and then the experiments were repeated
[7]. Here, the mixing zone was entirely created by the pebble flow itself without the
contribution of pebble’s bouncing on the free surface. Figure 2.4 display the enlarged
plots of the interface between two regions without and with guide plates installed in
the upper section, respectively. The guide plates have no noticeable influence on the
feature of the two-region arrangement, but an influence on the mixing zone.
The horizontal dispersion of the dense pebble flow leads to the existence of a
mixing zone between the two regions. In the mixing zone, the black and colorless
pebbles are dynamically and stochastically distributed. The pebbles move down
with ceaseless rearranging, but hardly run far away. By installing the guide plates,
the mixing zone was improved and was smaller on a scale of about 2–3 times of the
pebble diameter. Very few pebbles straggled far away into the opposite region. This
means that the originally scattered pebbles were mostly produced by the pebbles’
bouncing on the free surface. Moreover, when the guide plates were installed, the
interface between the regions looked like the waved surface, and any undesired
pebbles hardly appeared. This interesting fact indicates that, for quasi-static pebble
flow, as in pebble-bed reactors, pebbles are restricted or locked by their surrounding
neighbors, and undergo long-lasting frictional contacts with each other [8]. The
pebbles gather in crowds and groups of several pebbles to move down together under