3.1.2 Pinning under different gas superficial velocities
In this paper, the pinning appears firstly in the downstream of Johnson
net among the abnormal phenomena. Fig.6 shows that the pinning thickness
grows with the gas superficial velocity. However, the growing rate
reduces with gas superficial velocity
(u g>0.39 in this paper).
Compared to type RA, the pinning is hardly seen and its thickness
decreases in type RB (Fig 3 and Fig.6). It is because that the gas-solid
baffles breaks the particle force chains, or the force transfer between
the left and right areas in type RB. In other words, the particle-wall
force has positive correlation to its horizontal position: it has large
value in gas downstream while small one in gas upstream9. The force is lower in type RB than that in type RA,
that is because the former has two individual areas divided by the
gas-solid baffles. The particles are more easily to move downward under
smaller particle-wall force (or upward particle-wall friction force) in
type RB.
In the experiment, the pinning is not originate from the bottom of the
gas downstream, the point of (L , 0) 9. The
pinning thickness equation (2) is then modified by addingC 1 in equation (A1) of Appendix . In type
RB, the bed width L becomes L /2 in the left and right
area. However, the pressure distribution uniformity changes in the left
and right beds. To consider these factors, one coefficient a is
introduced in equation (3-4). The calculated results agree well with the
experimental ones in both type RA and RB (Fig.6). According to above
equations, the pinning will be well controlled by the gas-solid baffles
in type RB, especially when the gas-solid baffles are put in the middle
of the bed x /L =0.5.
,, (2)
(3)
, , (4)