Smooth ducts better than corrugated

[Sciguyjim]

I know the flexible aluminum drier vent ducting is easy to work with, but if you can use PVC or some other smooth walled ducting you'll have faster airflow due to the smooth inside surface. As an example, I've read that highly corrugated drain pipe has 9 times the flow resistance of smooth walled drain pipe (I'm assuming this is for water since it is drain pipe. Even with air though, a 3" corrugated duct can flow as slowly as a 2" smooth duct.) The pipe in effect flows air, or water, as if it was narrower than it actually is due to the increased resistance due to turbulence. The PVC can also easily be flared at the open end which has a big effect on the ease at which air can enter the tube (see my post on airflow in ducts with different shaped openings.) Here are some articles about making cold air intakes which mention these things:

http://www.autospeed.com/A_0009/article.html

http://zhome.com/Care/airhorns.htm

 

[MolaKule]

In some cases, the corrugated ducts are used to increase turbulence.

 

[Patman]

Quack quack!

Sorry, couldn't resist.

 

[Sciguyjim]

The only place I've heard of where turbulence is wanted is right in front of the MAF, but they say the screen does that. Is there somewhere else one would want it, other than in a carb?

"Quack, quack" ?? Patman, are you implying that the turbulence is not worth considering?

 

[Patman]

No, I was just being silly, because when I hear the work duct, I automatically think of a duck!

Sort of like when someone says duct tape, I think, why do ducks need tape?

 

[Sciguyjim]

Doh! Now I get it.

I guess I was expecting a little flame, though not from you Patman. And I was already getting my comeback arguments ready to post. I've got to learn to chill out a little bit more.

Speaking of duct tape, someone has come out with a brand that is actually called "duck tape". I suppose it had to happen eventually.

 

[Patman]

We also used to call that stuff 200mph tape, cuz Nascar uses it to fix up their bodywork and get back out on the track to run 200 mph.