Friction Factor of Commercial Pipe

Yoo (1995) has developed two methods for the estimation of friction factor of commercial pipes; one is named as mean zero velocity point method and the other as mean friction factor method, both of which are based on the assumption that smooth surfaces and rough surfaces co-exist inside the same commercial pipe. In the present study the data collected by Colebrook (1938) are re-analyzed using Yoo's methods assumming the smooth surface has no roughness at all so that the Nikuradse equivalent roughness and probability of rough surface are determined for each commercial pipe. It is found that both roughness height and probability have a clear trend in relation with the pipe diameter, and functional relations of both are suggested. The present approach has exellent agreement with most of Colebrook data of friction factor, while Colebrook-White approach has poor agreement with most of his data.