# Friction factor

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1.
Definition of friction factor

2. Calculation of friction factor

3. Hagen-Poiseuille relation

## 1. Definition of friction factor

The friction factor is representing the loss of pressure of a fluid
in a pipe due to the interactions in between the fluid and the pipe.

f/2=friction factor - **fanning**

D=Pipe diameter in m

u_{m}=mean velocity in m/s

ΔPf=pressure drop due to friction in Pa

L=length of pipe in m

ρ=specific gravity in kg/m3

## 2. Calculation of friction factor

How to find the friction factor of
a pipe ? The different formula below allow you to calculate the
friction factor of a pipe.

In Laminar regime **f/2=8/Re**

In turbulent regime, different
correlations can be used

**Blasius** (only applicable
to smooth pipes) **f/2=0.023.Re**^{-0.20}

**Churchill** (applicable for any Re and ratio e/D)

With e the pipe roughness in m

Another possibility is to use the
Moody Diagram which is actually a friction factor chart where the
friction factor can be read directly.

## 3. Hagen-Poiseuille relation

In Laminar regime, the volumic flowrate can be calculated thanks to
the Hagen-Poiseuille equation

Q=volumic flowrate in m3/s

μ=dynamic viscosity in Pa.s

**Source**

Mecanique et Rheologie des fluides en genie chimique, Midoux,
Lavoisier 1993, page 162, page 274-275