Case1: Velocity unknown for given pressure drop.

C                  Assume velocity of the fluid in the pipe (V).

C                  Calculate Reynolds number (Re)

C                  Read friction factor (f) from Figure 4.3

C                  Calculate frictional loss (hf) using Equation 4.12

C                  Determine pressure drop (ΔP) using Bernoulli equation. 

C                  Compare calculated pressure drop with the given value.

C                  Repeat the steps till an agreement is achieved.

 

We recommend that you use the following steps:

C                  Use Bernoulli equation to obtain frictional head (hf)

C                  Calculate the value of a group ReÖf given as

 

 

Read friction factor (f) from Figure 4.4.

C                  Calculate Reynolds number (Re). 

C                  Calculate velocity of the fluid (V) using Equation 4.12.

 

Example 4.9:  Pressure drop through a galvanized iron pipe is 100 psi.  Inside diameter of the pipe is 1.38 in.  Equivalent length of the pipe is 2000 ft.  Determine the velocity of the fluid if the following information applies:

Viscosity of water = 7.556 ´ 10-4 lb/(ft·s); density of water = 62.36 lb/ft3

Roughness of the pipe = 0.0005 ft.

Assume that pipe is horizontal and entrance and exit losses are negligible                                                                                   

Solution

C                  Pressure drop, ΔP = 1440 lbf/ft2

C                  Frictional losses (hf):

 

C                  Group ReÖf (Equation 4.16):

 

 

C                  Friction factor, f (Figure 4.4) = 0.0078.

C                  Reynold number, Re (Figure 4.3) = 4.98 ´ 104.

C                  Velocity of the fluid, V (Equation 4.12):