Friction Factors and Shear Stresses

In this section we give expressions for the wall and interfacial friction factors and corresponding shear stresses, starting with the wall friction factor and shear stress. 

Furthermore the mean liquid velocity, vi) can be written rh rh 4rhi 

An alternative method for estimating the wall friction factor is to use a standard pipe friction factor equation, such as the explicit formula of Swamee and Jain, using the equivalent diameter of the film in Rei. Thus, 

Similar to the wall shear stress, the interfacial shear stress is defined as  

For turbulent gas fiow fg i may be computed from some empirical function of the gas Reynolds number, as outlined below. 

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C Method for Estimating Wall Film Thickness and Velocity 13.C.2 Friction Factors and Shear Stresses... 

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