Wall-layer disturbance factor

Figure 21 illustrates the ability of the mechanistic model to match complicated suspended solids density profiles from the 152 mm x 152 mm higher temperature pilot plant. Increas suspension densities at the top of the unit are due to considerable internal inertial separation at the exit. The profiles are used to find best fit values of the scale independent "wall-to-core flux coefficient" and "wall-layer disturbance factor". The model effectively predicts the variation of suspension density with height, solids circulation rate and gas velocity using these best fit values. 

Figure 21. Best fit curves of the Senior and Brereton model to density profiles in the UBC CFB pilot combustor. The roof reflection coefficient, wall layer disturbance factor, and core-to-wall flux coefficient were adjusted to obtain the fit. (Gs = solids circulation flux, U = superficial gas velocity), (Senior and Brereton, 1992).

The changing character of the flow in the different regions of the turbulent boundary layer explains certain aspects of the friction factor chart. If the absolute roughness of the pipe wall is smaller than the thickness of the viscous sublayer, flow disturbances caused by the roughness will be damped out by viscosity. The wall is subject to a viscous shear stress. Under these conditions, the line on the friction factor chart... 

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