For steady, fully developed flow Inside straight pipe of

For steady, fully developed flow Inside straight pipe of diameter D, neglecting gravity effects, the pressure drop ∆p over a length L and the wall shear stress τW are related by

Shear stress on wall,

τW =		-δP	.	R
		δx		2

where		-δP	.	∆
		δx		L

& R =	D
	2

∴ τW =		∆P	×	D	=	∆PD
		L		2 x 2		4L

τW =	∆pD
	4L

τW =	∆pD²
	4L²

τW =	∆pD
	2L

τW =	4∆pD
	D