What Causes the Discrepancy in Calculating Wall Shear Stress in Pipe Flow?

AI Thread Summary
The discussion centers on calculating wall shear stress in a horizontal pipe flow, where the user initially calculated a value of 0.121 Pa but expected 0.968 Pa. The confusion arises from the need to ensure dimensional consistency and the correct application of kinematic viscosity versus dynamic viscosity. Users emphasize the importance of using absolute values for density and the proper units in calculations. Clarification is sought on the necessity of kinematic viscosity in this context, despite having the dynamic viscosity provided. Accurate calculations are crucial for determining wall shear stress in fluid dynamics.
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fully developed flow liquid of dynamic viscosity 2.9x10^-3 Pa.s and relative density 0.9 in horizontal pipe of diameter 12mm, length of pipe=200mm and mean velocity is 0.5m/s

To find the wall shear stress, i used τ=μ.du/dy = (2.9x10^-3)(0.5/0.012) = 0.121Pa

The answer is 0.968Pa, where am i going wrong?

thanks
 
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What are the units of density?
 
Make sure you are dimensionaly consistent and use the kinematic viscosity which is absolute viscosity/density.
 
the density hasnt got any units, it just says the relative density. why should i be using the kinematic viscosity when the shear stress equation requires the dynamic viscosity, which is given
 

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