Effect of viscosity on level swell

The effect of moderately high viscosity ( 100 cP) is to prevent the formation of the churn-turbulent flow regime so that the bubbly flow regime persists at higher superficial gas/vapour velocitiesj(see Annex 3). . , -4 

Considerable work has been. done at JRC Ispra to visualise level swell for viscous fluids17,8,91. This indicates that t moderate viscosity (around. 100 cP) foaming behaviour of the. fluid (if it occurs) dominates viscous effects. Many high viscosity fluids are foamy because they are not pure fluids. At higher viscosities, approaching 1000 cP, there appears to be much less foaming and the flow characteristics are dominated by. viscous effects. 

Experimental work for highly viscous fluids suggests that some disengagement does occur, in that bottomrvented tests results are different from top-vented test results12.1. The flow regime in highly viscous flow ( 1000 cP) is unlikely to be one of those (churn-turbulent or bubbly flow) described in Annex 3. 

Since bubbly flow at high superficial velocity approximates to homogeneous flow, this could lead to the conclusion that the homogeneous vessel assumption is likely to be good for high viscosity systems. 

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