This afternoon, I received an email at work from a guy from the Little Rock office. He wanted some help with some tank overflow calcs. He had received some calcs from another group and didn't think they were correct.
Sure enough. They said 5833 gpm would be able to leave through a 6-inch pipe. Really?
5833 gpm is equal to 97 gallons per second ... or about 13 cubic feet per second. That's a lot of flow. A 6-inch pipe has a cross sectional area of about 0.2 sq ft. So, the velocity of the water would be around 65 feet per second. That is flying! Generally, you keep velocities below 10 feet per second to minimize issues, such as high frictional losses.
How did these people come up with 6 inches as being sufficient size? They applied an equation that assumes no losses. Hmmm. How did they compensate? They rounded up to the next available pipe size. The calcs actually said 5 in pipe would be Ok ... they rounded up to 6.
Problem is, at velocities that high, you get an obscene amount of headloss ... like 500 feet over the course of 150 feet of pipe, or something like that (including losses at entrances, exits, etc.).
The things people come up with sometimes!
4 comments:
Good thing they have a REAL engineer - not one of the frictionless kind!
I think people just look air up on the Internet and plug it in.
Oops. Air was supposed to be stuff.
Frightening to think of what other things are getting built on similar sorts of miscalculations.
Post a Comment