Chapt06

# Prandtl derived eq 653 in 1935 and then adjusted the

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: lve if Red is known and f is wanted. There are many alternate approximations in the literature from which f can be computed explicitly from Red 1/4 4000 Red 105 H. Blasius (1911) 0.316 Red f (6.55) 2 1.8 log Red Ref. 9 6.9 Blasius, a student of Prandtl, presented his formula in the first correlation ever made of pipe friction versus Reynolds number. Although his formula has a limited range, it illustrates what was happening to Hagen’s 1839 pressure-drop data. For a horizontal pipe, from Eq. (6.55), 1/4 L V2 L V2 p f 0.316 hf d 2g d 2g g Vd or p 0.158 L 3/4 1/4 d 5/4 7/4 V (6.56) at low turbulent Reynolds numbers. This explains why Hagen’s data for pressure drop begin to increase as the 1.75 power of the velocity, in Fig. 6.4. Note that p varies only slightly with viscosity, which is characteristic of turbulent flow. Introducing Q 1 2 4 d V into Eq. (6.56), we obtain the alternate form p 0.241L 3/4 1/4 d 4.75 Q1.75 (6.57) | v v For a given flow rate Q, the turbulent pressure drop decreases with diameter even mo...
View Full Document

## This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

Ask a homework question - tutors are online