Calculation of true thickness of the bed

119. In a cooling tower of a power plant, water flows in a pipe of inner diameter 0.2 m with a velocity of 0.1 m/s . Assume water’s coefficient of viscosity and density are $8*10^{-3} N s /m^{2}$ and $1000 kg /m^{3}$ , respectively. The flow will be characterized as

a) Critical /transitional flow

b) laminar flow

c) trubulent flow

D) eddy flow

Solution:

Reynolds number is dimensionless quantity and describes the ratio of inertial forces to viscous forces in a flowing fluid.

$R_e=\frac{\rho v D}{\eta}$

$\eta$ - fluid dynamic viscosity in kg/ m s =$8*10^{-3} N s/m^2$

$\rho$ - fluid density in $kg/m^3$ = 1000 $kg/m^3$

v - fluid velocity in m/s = 0.1 m/s

D - pipe diameter in m = 0.2 m

$R_e=\frac{1000*0.1*0.2}{8*10^{-3}}$

=$\frac{20}{8*10^{-3}}$

=$\frac{20*10^{3}}{8}$

$R_e=2.5*10^{3}$

$R_e=2500$

This flow is Critical / Transition flow.

Some important points regarding Reynolds number:

1. If $R_e$ < 2000 , the flow is called Laminar

2. If $R_e$ > 4000 , the flow is called Turbulent

3. If 2000<$R_e$>4000 , the flow is called Transition