Sliding bed flow

One major difference between pneumatic transport and hydraulic transport is that the gas-solid interaction for pneumatic transport is generally much smaller than the particle-particle and particle-wall interaction. There are two primary modes of pneumatic transport dense phase and dilute phase. In the former, the transport occurs below the saltation velocity (which is roughly equivalent to the minimum deposit velocity) in plug flow, dune flow, or sliding bed flow. Dilute phase transport occurs above the saltation velocity in suspended flow. The saltation velocity is not the same as the entrainment or pickup velocity, however, which is approximately 50% greater than the saltation velocity. The pressure gradient-velocity relationship is similar to the one for hydraulic transport, as shown in... 

Babcock, H.A. (1970). The sliding bed flow regime. Proc. P Int. Conf. Transport of solids in pipesYiX 1-16. BHRA Cranfield. 

The situation with regard to dense phase conveying in sliding bed flow is illustrated in Figure 4.45. Since the operating point is likely to be well above the minimum conveying conditions, as with case 3, increasing air supply pressme is unlikely to be a problem, in... 

Sliding Bed Flow This mode of flow is generally nnsatisfactory. Solids slide and roll on the pipe bottom. Excessive corrosion in the pipe bottom occurs quickly. Blockages can occur frequently... 

In the steady-state operation of the OXITOX reactor, pelletized solid of catalytieally aetivated sodium earbonate slides down a Silo type reaetor. Counter-current to the solid flow, the polluted air rises through the sliding bed of solids. At reaction temperature the following reaetion oecurs ... 

Most existing models are suited only to pure dilute-phase or dense-phase (high m ) applications, whereas the possible modes of flow over long distances occur between these two extremes (e.g., dune-flow, sliding beds, irregular slugging, etc.—usually at moderate m ). 

When a body of material moves en bloc it is not flowing in the conventional sense of the word. However, the term bed flow is used here to describe material moving over the whole cross-section of a parallel flow channel while sliding on the boundary container walls, and complements the descriptions of flow regimes for the common types of hopper flow patterns. The cross-section does not necessarily move with uniform velocity this depends to a large extent on the underlying drawdown pattern at the termination of the parallel wall section, as modified in the parallel charmel by the relationship between wall friction and the internal friction of the bulk. 

A concentration gradient occurs in the flow region above a sliding bed. This gradient is due to either turbulent suspension or shearing action of flow at the top of the bed. The shape of the measured concentration profiles gives an indication whether particle dispersion is due to turbulent suspension or due to shearing. 

Fig. 2. Concentration profile in coarse-sand flow. A shear layer above a sliding bed.

Friction on the boundaries of the sliding bed. Inclined flow of the 1.4-2.0-mm-sand mixture at... 

A full analysis of the relation between the shear stress at the top of a sliding bed and the shear layer parameters requires information about the distribution of local solids velocities below and within the shear layer. Since this was not available in our database, the force balance (verified above as being appropriate for en bloc sliding beds) and the measured flow parameters were used to estimate the position of the top of a sliding bed and the value of the interfacial shear stress Xb in flows exhibiting a shear layer (Tab. 2). Processed measurements confirmed a direct relationship between the thickness of a shear layer and the interfacial shear stress (Fig. 6). 

Sand/gravel particles coarser than approximately 0.5 mm were dispersed due to the shearing action of faster flowing carrier above a bed on a top of the sliding bed. The concentration profile may be estimated as being linear within a shear layer. The thickness of the shear layer is related to the shear stress at the top of the sliding bed. 

Abstract. The three modes of glacier flow (ice deformation, sliding, bed deformation) are described. The pattern of flow-lines is deduced from the principle of mass conservation the temperature distribution by considering heat sources and heat transfer by conduction and advection. The mechanisms of surging and of the tidewater-glacier instability are outlined. The interpretation of Heinrich Events as evidence of surges of the Laurentide Ice Sheet is critically reviewed. 

The spent catalyst slide valve is located at the base of the standpipe. It controls the stripper bed level and regulates the flow of spent catalyst into the regenerator. As with the regenerated catalyst slide valve, the catalyst level in the stripper generates pressure as long as it is fluidized. The pressure differential across the slide valve will be at the expense of consuming a pressure differential in the range of 3 psi to 6 psi (20 kp to 40 kp). 

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