Describe the use of friction factor chart. [5 Marks]

• It is a logarithmic plot of friction factor as a function of the Reynold’s number over a wide range of the Reynold’s number for a flow in smooth as well as rough pipes.

• The data for the plot are variable such as velocity, density and pipe diameter, etc. using liquids and gases.

• This chart is termed as friction factor chart, Reynold’s number correlation chart and Moody diagram.

• The friction factor is a function of both the Reynold’s number and relative roughness.

• For laminar flow region the friction factor is only the function of Reynold’s number therefore only one line is shown for Reynold’s number upto 2100.

• For laminar flow region equition $ \f = {16}/{\N_{\R}} $ relates the friction factor to Reynold’s number and the above equation is the equation of straight line having slope minus one.

• For turbulent flow the lowest line represents the friction factor for smooth tubes the move convenient empirical equation for this line is $ \f = 0.046\ \N_{\R}^{-0.2} $ . This applies over the Range of Reynold’s numbers from 50,000 to 1 × $ 10^6 $ , another equation applicable over range $ 3 \× 10^6 $ is $ \f = 0.0014 + {0.125}/{\N_{\R}^{0.32}} $ .

• It is clear from the figure that the friction factor is low for smooth pipe as compared to rough pipe and increases as the relative roughness increases for given Reynold’s number.

**The Uses of friction factor chart** > > * Knowledge of volumetric flow rate, density of fluid, viscosity of fluid and pipe diameter. The Reynold's number is calculated. The Reynold's number is used as abscissa and friction factor is read as ordinate. > > * Friction factor is then used in appropriate equation to calculate the head losses due to friction from known pipe size and flow rate. > > * The friction factor is also used to calculate the skin friction which then can be combined with the other forms of friction to get total friction losses in entire flow system. >