Experimental research of how the boundary layer lower the pipe drag reduction in transport of dense paste

AbstractA thin boundary layer formed on inner‐pipe wall and brought out wall slip phenomenon when dense pastes were transported in pipe as plug flow. The boundary layer is called slip layer as well, which reduced frictional pressure loss, increased the conveying distance and saved energy consequently. In order to find out the relationship between the properties of boundary layer and the pressure loss, the design of the liquid injection equipment was detailed in this paper. The liquid (such as water, oil or polymer solution) is injected from the pump into the pipe downstream at comparatively small flowrates and formed a lubricating annulus adjacent on the pipe inner wall. By taking coal slime as an example, the test studied pressure loss result from the change of pipeline features and the thickness of boundary layer systematically. Results show that the pressure loss reduced exponentially with the increase of the boundary layer thickness, and the greater the diameter, the smaller the pressure loss. When the shear rate of the boundary layer was getting higher, the lubrication layer played more efficiency on the reduction of the shear stress. Furthermore, these results provide preview for our understanding of the fundamental processes of slime pipe flow and how such flows can be better modelled, optimised and controlled. Copyright © 2017 John Wiley & Sons, Ltd.