Question

A circular pipe of 25-mm outside diameter is placed in an airstream at 25C and 1-atm pressure. The air moves in cross flow over the pipe at 15 m/s, while the outer surface of the pipe is maintained at 100C. What is the drag force exerted on the pipe per unit length?

Answer 1

f_D = =3.24 N/m

Step-by-step explanation:

data given

properties of air
`\\u\ of air =19.31*10^(-6) m2/s`

`\rho = 1.048 kg/m3`

k = 0.0288 W/m.K

WE KNOW THAT

Reynold's number is given as

`Re =(VD)/(\\u)`

`= ( 15*0.025)/(19.31*10^(-6))`

= 1.941 *10^4

drag coffecient is given as

`C_D = (f_D)/(A_f(\rho v^2)/(2))`

solving for f_D

`f_D = C_D A_f*(\rho v^2)/(2)`

`=C_D D*(\rho v^2)/(2)`

Drag coffecient for smooth circular cylinder is 1.1

therefore Drag force is

`f_D = 1.1*0.025 *(1.048*15^2)/(2)`

f_D = =3.24 N/m