optimising air flow for printing

Hey guys,
I recently got a sintron Prusa I3 and I've been playing about with different 40mm fan shrouds in order to improve cooling of PLA.
Ive noticed with both Thingverse designs and my own designs is that when the fan is installed, a lot of air seems to be blown away from the duct intake, rather than down to the nozzle.
Ive checked the fan is definitely blowing the right direction. Has anyone had any luck/ experience with increasing air flow/ efficiency to their print beds?

Hi!
Axial fans are not that good in handling back pressure, like when you limit the output in some way. Some of the air will "turn back" and come out the way it came in. This was discussed in another tread on on RepRap forum, can't remember where, sorry. The back flow was enough to lower the temperature on the heat bed causing warping on one half of the print bed.
There are a few things you can do to make it better. Best one is to use a radial fan, they handle back pressure much better. Don't remember the others to well so lets hope someone finds the other thread.

Cheers!

As Slowfoot said, a radial fan (often called a blower) can produce higher static pressures for a more focused stream of air.

Also, I've seen a lot of fan shroud designs that attempt to blow air at the nozzle from all directions. This just results in a net zero air velocity at the nozzle tip, with a lot air ending up blowing up and around the hot end which is not particularly helpful. You really want a high velocity stream blowing across the part at the nozzle tip. There will be some asymmetry in the cooling of the print, but that can't be helped unless you actually rotate the fan as you print.

Thanks for the info guys, I will look into radial fans
I have a bunch of thin clear plastic tubing that was given to me and I was toying with the idea of creating a "chamber" which would house a fan - the outward flow would be (ideally) passed through the tubes where the exhausts would be situated opposite each other near the hot end.
Hopefully this could help increase the radius of the cooling - something for me to experiment with!