# Re: [APD] Re: Bubbles? -- or - Some hard topics not adding up!

```Bah yes, I didn't out the Pi in the equation

Pi (2r)^2     Pi 4r^2
--------- ->  -------  take out r^2 and pi (common) = 4
Pi r^2        Pi r^2

Definately need a refresher, or to take my time.  Can't do math like I
used to :-(

On 2/4/2004, "Andrew Mitchell" <andrewm at cse_unsw.edu.au> wrote:

>On Thu, 2004-02-05 at 07:02, David Terrell wrote:
>> You know, I think I just need a refresher geometry class, UGH!  Volume
>> isn't increasing by 2Pi :-(  The circumference does!  I'll do some quick
>> math.  r is the old radius, R is the new radius (R=2r).  So, if
>> v=Pi*r^2, and R=2r, then dv=Pi*4!  HAH, that means a 1.5" pipe has
>> ~12.57 times more volume then a 0.75" pipe of the same length.  Now I'm
>> really starting to think this thing will work ;-)  Man, someone stop me
>> if I'm wrong!
>>
>> -Dave T. (mumbling to himself, 'a^2+b^2=c^2, garblegarblegarble')
>
>um, doubling the diameter should quadruple the area (divide the flow by
>4 in the case of your reactor assuming that your flow rate is limited
>by tubing elsewhere in the system)
>
>Area1=Pi*r^2
>Area2=Pi*(2*r)^2
>     =Pi* 2^2 * r^2
>Area2/Area1=4, not 4*pi
>
>--
>Andrew Mitchell <andrew at andrewmitchell_id.au>
>
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