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
Post a Comment
Post a Comment