Question

Two pipes are being considered for a pipeline. Pipe A has diameter of 0.8 m with a roughness of 1.20 mm; pipe B has diameter of 0.9m and a roughness of 1.35 mm, it is better to select pipe B because:

None of the answers

The relative roughness is the same so it doesn’t matter

c. The frictional loss in B is larger than A

The frictional loss in A is larger than B

Answer 1

Let the roughness of pipes follow a linear equation.

For pipe A, D= 0.8m and for D= 0.8m the roughness is 1.20 mm

Hence by unitary method, the value of roughness for pipe A for Diameter= 1m is:

$\frac{1.2}{0.8}*1= 1.5 mm/m$

Now,

For pipe B, D= 0.9m and for D= 0.9m the roughness is 1.35 mm

Hence by unitary method, the value of roughness for pipe A for Diameter = 1m is:

$\frac{1.35}{0.9}*1= 1.5 mm/m$

Hence both the pipes has same relative roughness per meter of Diameter. Hence, any of them can be used.