Isothermal Flow in Channels Newtonian Fluids

In the analysis of flow in channels the following assumptions are made  

Fluid viscosity is not affected by pressure changes along the channel. 

The steady isothermal flow of incompresible fluids through straight horizontal tubes is of importance in a number of cases of practical interest. 

Consider the forces acting on an element of fluid as shown in Fig. 5.4. 

Analysis of polymer melt flow High pressure 

In many cases the pressure gradient is uniform, so that for a pressure drop, P, over a length, L, the maximum shear stress will be at the wall where r = R 

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