Question

The Reynolds number for flow of a certain fluid in circular tube is specified as 2500. What will be the Reynolds number when the pipe diameter is increased by 20% and the fluid velocity is decreased by 40% keeping fluid the same?

• A. 200
• B. 1200
• C. 1800
• D. 3600

Answer 1

The correct option is C 1800

$R{e}_1=\frac{V_1{d}_1}{v}=2500$

$R{e}_2=\frac{V_2{d}_2}{v}=\frac{\left(0.6\right)V_1\times \left(1.2d_1\right)}{v}$

$=(0.6\times 1.2)\frac{V_1{d}_1}{v}$

$=0.72\left(2500\right)$

$=1800$