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)