File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Programming Diversions and the fly likes To PI or not to PI Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Other » Programming Diversions
Bookmark "To PI or not to PI" Watch "To PI or not to PI" New topic

To PI or not to PI

Leslie Chaim
Ranch Hand

Joined: May 22, 2002
Posts: 336
You had a 10" water line that broke down. Unfortunately, there's only 1" pipe available for replacement.

How many 1" pipes is needed (and why/how) to replace the one 10"?



Normal is in the eye of the beholder
Sonny Pondrom
Ranch Hand

Joined: Jun 05, 2001
Posts: 128
Does a 10" line have an inside diameter of 10 inches?
Arjun Shastry
Ranch Hand

Joined: Mar 13, 2003
Posts: 1874

fred rosenberger
lowercase baba

Joined: Oct 02, 2003
Posts: 11480

100. assuming that the flow isn't restricted by surface area of the pipe...

a 10" (i'm assuming this is the inside diameter) pipe has an area of PI * r^2. if our diam. is 10, our radius is 5. so the 10" pipe has a cross-section area of 25PI.

Each 1" pipe has a radius of 1/2", or an area of (1/4)PI. so, we need 100 pipes.

However, the first pipe has a surface area equal to 10PI (times the length, which we can ignore). the 100 pipes have a surface area of 100PI.

I am not a fluids engineer, but i would imagine that more surface area would result in more friction, slowing down the flow, but i have no idea how to calculate that.
[ July 02, 2004: Message edited by: fred rosenberger ]

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Arjun Shastry
Ranch Hand

Joined: Mar 13, 2003
Posts: 1874
Yes, I think so.Factor that determines is I think Reynold's numebr.Ratio of inertial force to viscous force.Bigger pipe will have more intertia.
SJ Adnams
Ranch Hand

Joined: Sep 28, 2001
Posts: 925
I think Poiseuille's Law applies here.

which means that the flow is proportional to r^4

which means 100million 1" tubes!!
SJ Adnams
Ranch Hand

Joined: Sep 28, 2001
Posts: 925
strike that - 10,000 is the answer
I agree. Here's the link:
subject: To PI or not to PI