Slugs frictional effects

Equations 8.57 and 8.58 are satisfactory except at low liquid rates when the frictional pressure drop is a very small proportion of the total pressure drop. Frictional effects can then even be negative, because the liquid may then flow downwards at the walls, with the gas passing upwards in slugs. 

Pressure drop due to frictional effects Pressure gradient in the slug region, single phase pressure gradient of the continuous phase... 

Excess fluid pressure loss in slugging beds effect of particle-wall and particle-particle frictional interactions... 

In this equation, it is assumed that both the gas and the liquid move in slugs at the same velocity through the orifice. The contribution of the orifice effects to the total pressure drop is small and is of significance only in monolith blocks with high cell density and at high liquid flow rates. The frictional and static pressure drops prevail. The orifice effects may arise if blocks of monoliths stacked on top of each other are used. The contribution of these effects will depend on the extent of obstruction and the length of individual blocks. 

Fotir granular products were employed as test materials. Their particle properties are listed in Table 1. Note that the wall friction angle listed in Table 1 was measured by using Jenike shear tester based on the similarity between the test pipeline internal condition and the shear plate (i.e. a piece of bright mild steel plate). Such similarity was determined manually, not by measuring surface roughness. Since the effect of wall friction on the slug performance is very complicated, further research is needed to address this issue. 

The effect of particle-particle frictional interactions on excess pressure loss was investigated in the same way as described above. Smooth tubes were used, with beds of polished glass spheres and sand particles having essentially the same size distribution and density, but differing in their particle-particle frictional properties. Although the slugging... 

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