Friction factor

Friction factor, Moody Diagram, Implicit formulas for friction factor

1. Friction Factor Numerical QUEST CAMPUS LARKANA 17CE

2. Friction Loss in Turbulent Flow 2 For commercially available pipe and tubing, the design value of the average wall roughness has been determined as shown in the following table

3. Problem 3 Statement: Determine the friction factor f if water at 70 o C is flowing at 9.14 m/s in an uncoated ductile iron pipe having an inside diameter of 25 mm. Solution: The Reynolds number must first be evaluated to determine whether the flow is laminar or turbulent:

4. Problem 5 Thus, the flow is turbulent. Now the relative roughness must be evaluated. From previous table we find ε=2.4x10 -4 m. Then , the relative roughness is The final steps in the procedure are as follows: Locate the Reynolds number on the abscissa of the Moody Diagram. Project vertically until the curve for ε /D =0.00961538 is reached. Project horizontally to the left, and read f=0.038

5. Roughness Height (e or ε ) for Certain Common Pipes 6 ε

6. Empirical Solutions for Friction Factor f 7 Colebrook Equation The Colebrook Equation can be used to determine friction factor,f . It describes the curves of Moody Diagram within the range of complete turbulent flow zone. Unfortunately, it is an implicit form equation. Therefore it must be solved using an iterative trial and error procedure.

7. Empirical Solutions for Friction Factor f 8 Benedict suggests the expression proposed by Swamee and Jain , i.e., While for ε /D>10 -4 Haaland recommends

8. Empirical Solutions for Friction Factor f 9 For situations where ε /D is very small, as in natural-gas pipelines, Haaland proposes Where n ~ 3 The use of the Swamee -Jain or Haaland provide an explicit formula of the friction factor in turbulent flow, and is thus the preferred technique.

9. Empirical Solutions for Friction Factor f 10 For laminar flow (Re<2000) the usual Darcy- Weisbach friction factor representation is For turbulent flow in smooth pipes ( ε /D=0) For turbulent flow (Re>4000) the friction factor can be founded from the Moody diagram

10. Empirical Solutions for Friction Factor f 11 Churchill devised a single expression that represents the friction factor for laminar, transition and turbulent flow regimes. This expression, which is explicit for the friction factor given the Reynolds number and relative roughness, is where and