Fluid dynamics continuity equation

[Nanu Nana]

Homework Statement

Through a (cylindrical) heating tube, warm air has to flow with a velocity of 3m/s in order to heat a rectangular spacewhich is 12 m long, 10 m wide and 2.5 m high. How large the radius of the tube should be if the air in the room get refreshed every 15 minutes ? Assume that the air-density in the tube and in the room are equal.

Homework Equations

Continuity equation
A1 x v1 = A2 x v2[/B]

The Attempt at a Solution

Flowrate = Volume/ t V/t = A x v
Flowrate = 12x10x2.5 = 300 m3 / 900 s = 0.33
0.33 = A2 x 3m/s
A2= 0.111 m^2
So to find the radius you have to use area of cilinder
A=pi x 2x (r)^2
0.111= pi x 2x (r)^2
r= 0.132 m why do i get this answer ?? . Its wrong .answer has to be 0.1881 [/B]

 

[Chestermiller]

What is the equation for the area of a circle?

 

[Nanu Nana]

A= pi x (r)^2
Now its correct
Thank you