For steady, fully developed flow inside a straight pipe of diameter $D$, neglecting gravity effects, the pressure drop $\Delta p$ over a length $L$ and the wall shear stress $\tau _\omega$ are related by
- $\tau _\omega =\dfrac{\Delta pD}{4L} \\$
- $\tau _\omega =\dfrac{\Delta pD^2}{4L^2} \\$
- $\tau _\omega =\dfrac{\Delta pD}{2L} \\$
- $\tau _\omega =\dfrac{4\Delta p L}{D}$